Eye Conditions

This page provides basic information about numerous eye conditions including a description, associated vision loss, accommodations and implications for learning.

Anatomy of the Eye
Description: It is a stationary, inherited genetic condition that the child is born with; it is not progressive so it should not get any worse as the child grows up. The cone photoreceptors in the retina do not work correctly. May be associated with Nystagmus, a fine wobble of the eyes and High Hypermytropia (long sight) Peripheral visual fields usually intact, this is because peripheral vision is mediated by rods and cones whereas central vision and acuity are mediated by cones only. Currently no treatment for retinal dystrophy but the associated refractive error may be corrected.

Effects on Vision: Vision is blurred (reduced visual acuity often around 6/60), no colour vision and Photophobia (an aversion to bright light) Child may notice vision is worse in bright light and better in dim light. (especially central vision)

Educational Implications: Considerations and adaptations for the level of visual acuity and reduced or absent colour vision. LVA or large print recommended, coloured charts or diagrams will need some pattern marking. Environmental factors to consider, dim light, dark glasses or peaked cap. Child may rely on peripheral vision for O&M but will need time to adjust to different lighting conditions. Glare from computer screen or white board can be reduced by reversing polarity or choosing a warmer background shade.

Achromatopsia (Rod Monochromatism) or (Stationary Cone Dystrophy) (PDF)

Description: Albinism is a hereditary condition. There are different types, Oculocutaneous Albinism of that causes a lack of pigmentation in the hair, skin and eyes, Ocular Albinism affects only the eyes. The lack of pigment in the iris allows too much light to fall on the retina causing glare. Abnormalities may also occur in the retina, this in turn affects the formation of the nerve pathways from the eyes to the brain, which results in decreased visual acuity.

Effects on Vision: Albinisim is a non-progressive condition and so as the individual ages it will not. Albinism can cause Photophobia (an aversion to bright light) A student may notice their vision is worse in bright light and better in dim light (especially central vision). Along with light sensitivity the student may also have astigmatism, lowered visual acuity and nystagmus (side to side rhythmic eye movement).

Educational Implications: Environmental concerns such as glare from the windows and lights in a classroom must be addressed since they may cause sensitivity and pain. It is important to consider magnification aids and enhanced print for student such as larger font size and making text bold. Also teachers should consider minimizing visual clutter on maps and other diagrams. The role of the orientation and mobility instructor is important in helping to familiarize the student with new areas particularly those which are subject to changing light.

Albinism (PDF)

Description: In order to develop properly a child's visual system requires well focused images, without them, permanent visual impairment may occur within the brain (visual cortex). This is why the detection and treatment of causes of visual impairment should occur at an early age. The condition in which the brain does not develop the capacity to see well owing to the poor quality of the pictures presented to it during early life is called derivational Amblyopia. Amblyopia is very often associated with strabismus or squints.

Effects on Vision: The image from the amblyopic eye is likely to have a lower visual acuity than the other eye when the eyes are tested separately. The image may be so poor and blurred that the brain will rely on the good eye for sight and the student will have monocular vision.

Educational Implications: Students with one damaged eye and one healthy one may require the good eye to be patched for a number of hours every day to encourage development of the pathways from the weaker eye.

Amblyopia (Lazy Eye) (PDF)

Description: Aniridia is a congenital condition describing the failure of the iris to develop. If the iris partially develops then it is called partial Aniridia. The iris dilates and contracts the pupil controlling the amount of light entering the eye. It is also responsible for the color of the eye. Anaridia usually affects both eyes, although the degree may vary. Other parts of the eye that can be affected are the cornea and lens. As well, the pressure inside the eye can be higher leading to glaucoma. Nystagmus (rapid involuntary eye movement) and strabismus (squinting) are often present with anaridia. Anaridia is not progressive, however it is often associated with syndromes involving other health issues.

Effects on Vision: Eyes are permanently dilated and do not react to light. This reduces the focal ability of the lens causing blurring. It also results in over-sensitivity to light (photophobia) causing glare on sunny days. Glasses can increase focal ability and reduce glare.

Educational Implications: Environmental considerations are important due to oversensitivity to light. In particular, preferential seating, lighting, contrast and magnification should be considered. Concept and skill development may be initially delayed, however, with proper adaptations and accommodations, the student should catch up. Low vision aids may assist the student for near and far point viewing. Students typically do not have difficulties moving around.

Aniridia (PDF)

Description: Absence of one or both eyes which may result from genetic or chromosome abnormalities or unknown factors. Eyes have almost completely failed to grow ñ may affect one or both eyes- where only one eye is absent the other eye may also be smaller than normal which can lead to other associated conditions, glaucoma, cataracts. In some cases other parts of the face have not grown correctly resulting in cleft palate. Learning difficulties can sometimes occur along with Anophthalmia. Prosthetic (artificial) implants may be worn which also help the face grow.

Effects on Vision: In rare cases even though there does not appear to be an eye present a small part may have grown giving the child limited ability to see bright lights or shapes even if skin covers the orbit. Where eyes are completely absent there will be no light perception at all.

Educational Implications: Child will most probably be a tactile learner; and will need considerable support in all areas of the expanded core curriculum. Routine is important to establish good sleeping patterns.

Anophthalmia (PDF)

Description: Aphakia is the absence of the lens of the eye. Aphakia is most often associated with the surgical removal of a cataract but children may be born with congential aphakia.

Effects on Vision: Without the lens, the eye cannot adjust its focus for seeing at different distances. Surgery is required. In cataract surgery, an artificial lens is inserted to replace the lens removed. For very young children a contact or artificial lens implant can be very difficult. If the lens is not implanted, children will need to wear thick glasses to achieve a clear image. On-going surgeries and multiple operations may be necessary.

Educational Implications: Individuals with aphakia should be encouraged to wear their glasses and contact lenses all the time. A Teacher of the Visually impaired will be able to assess and offer educational strategies in the classroom for students. For instance, students will benefit from adequate, but not excessive, lighting and high-contrast reading materials. Individuals should never look directly at light sources and glare may be an issue. An Orientation and Mobility instructor may be required for navigation in new and unfamiliar environments.

Aphakia (PDF)

Description: Astigmatism is a type of refraction error. The human cornea is spherically shaped. When light bounces off the cornea it creates one point at the back of the eye. A refraction error occurs when light bounces off a misshaped cornea and creates two points at the back of the eye resulting in blurred vision. Often astigmatism occurs when other eye conditions are present or as a result of an injury to the eye.

Effects on Vision: A student with astigmatism may have slightly blurry vision and often have to work harder to see. This includes squinting, eyestrain and visual fatigue. Students may also develop Strabismus (lazy eye) when one eye has a more pronounced astigmatism. Astigmatism is one of the most common eye conditions and can be corrected with glasses.

Educational Implications: Students with astigmatism may get headaches from visual strain and fatigue. It is important that students take a break and allow their eyes to relax. Wearing glasses is also very important to prevent eye strain.

Astigmatism (PDF)

Description: Bardet-Biel Syndrome is a genetically inherited combination of conditions that can affect vision, learning difficulties, blood pressure and kidney function. It can also cause the growth of extra fingers and can delay or eliminate puberty. The associated eye condition is retinitis pigmentosa (RP), which is a problem with the rod and cone photoreceptors in the retina. Most commonly the cells controlling the rods are impaired although it can also affect the cells controlling the cones. RP is a degenerative condition. It progresses slowly and may lead to total blindness in adulthood.

Effects on Vision: If the rods are affected then there will be deceased vision in low light or at night. Peripheral vision will also be leading to tunnel vision. If the cones are affected there will be a loss of central vision and most colours will not seem bright. Depending on the severity and progression of the damage to these photoreceptors, vision in students may be slightly or significantly impaired. Nystagmus is often associated with Retinitis Pigmentosa.

Educational Implications: About 50% of persons will have developmental delays ranging from mild to severe. Mobility may be affected due to peripheral vision loss. Environmental considerations regarding lighting and preferential seating may also be considered. If the cones are not affected and acuity is not an issue then magnification and low vision aids may not be required.

Bardet-Biel Syndrome (PDF)

Description: A genetic disorder affecting the cells of the eyes and brain, the enzymes do not work correctly which leads to a build up of fat and protein. The number of cells in the eyes and brain gradually become smaller leading to progressive symptoms. Not every child develops all the symptoms but they include, decreased fine motor ability, clumsiness, changes in mood and personality, shorter attention span, spurred speech, poor memory, onset of epilepsy (between age 7 and 16) and deterioration in vision. Associated condition may include Keratoconus and cataracts.

Effects on Vision: Normally onset between ages 4 to 10, initially affecting the macula and developing to include the whole retina. Slowly progressing blurred vision usually leading to functional blindness within three years of diagnosis.

Educational Implications: Emphasis on the expanded core curriculum, as blindness is associated Braille is an option, however additional challenges presented by progressive learning difficulties and seizures. Anti-Convulsant medication may lead to drowsiness. Prognosis will have effect on family and attitude to education.

Batten's Disease (PDF)

Description: There are a number of factors which can cause cataracts such as long-term exposure to sunlight (ultraviolet light) and complications stemming from other diseases such as diabetes and rubella. Cataracts may also result from an eye injury such as a trauma or drug use during pregnancy. Studies have shown that there is also a genetic propensity where cataracts are concerned. There are three classifications of cataracts, nuclear, cortical and subcapsular. Cataracts can be removed in an operation, performing this early prevents the student developing amblyopia or lazy eye. After surgery the student will require lenses, and may need patching to strengthen the weaker eye.

Effects on Vision: The lens of the eye is affected by cataracts. Often the lens becomes cloudy and prevents light from refracting onto the retina at the back of the eye.

Educational Implications: Cataracts can affect student's visual acuity and cause decreased reading efficiency and problems seeing the board due to a cloudy lens. Student will need time for adaptation to light change (going from the indoors to outside). Also O&M is important for environmental awareness especially at night time.

Cataracts (PDF)

Description: A syndrome is when a number of different conditions are always seen together. CHARGE is sporadic which means it occurs by chance. Each letter of CHARGE stands for the condition or body part affected. Coloboma (A notch like cleft is present in the developing eye) ñ Heart ñ Atresia choanae (parts of the nose don't develop) ñRetarded growth and development ñ Genital abnormalities ñ Ears (hearing impairment). With colobama parts of the eye do not fully develop, depending on how far back it goes this can affect the eye lid, iris, lens, retina or optic nerve. Associated conditions include nystagmus (fine wobble of the eyes), microphthalmia, cataracts' and glaucoma.

Effects on Vision: Depends if both eyes are affected (colobomata), where one eye has fully formed the student will function well and have monocular vision. Where the coloboma is deep and has reached the retina and optic nerve vision may be poor and there will be visual field loss and reduced acuity. The student will very often be short sighted and require glasses.

Educational Implications: Student may have visual field loss and would need to be positioned in the classroom to take advantage of better eye where one eye is affected. High contrast and adaptations for low vision including low vision aids and large print may be required. It is likely the student will have a dual sensory loss and if this is the case would need advice from a teacher for Deaf blind.

CHARGE syndrome (PDF)

Description: Coats' Disease is a very rare congenital, nonhereditary eye disorder, causing full or partial blindness, characterized by abnormal development of blood vessels behind the retina. Blood leaks from the abnormal vessels into the back of the eye, leaving behind cholesterol deposits and damaging the retina. It usually affects only one eye.

Effects on Vision: Coats' disease results in a gradual loss of vision. At advanced stages, retinal detachment is likely to occur. This will result in total blindness in the afflicted eye. An early warning sign of Coats' disease is yellow-eye in flash photography. It will glow yellow in photographs because light is reflecting off the cholesterol deposits.

Educational Implications: The associated retinal detachment can result in visual field loss, where parts of the visual field are missing. Preferential seating in the classroom should be considered. Since it is unilateral there can be loss of depth perception. Physical and spatial activities should be assessed for potential dangers. Deterioration usually begins in the upper part of the vision field so reading environments (near and far) should be assessed for access and efficiency.

Coats' Disease (Exudative Retinitis) (PDF)

Description: A non-progressive defect in any part of the eye ranging from the eyelid to the optic nerve or retina present at birth. It commonly looks like a notch and can affect one or both eyes. A coloboma is caused by abnormal development of the eyes during pregnancy.

Effects on Vision: A coloboma can affect any structures in the eye. The effect is dependent on the size and position of the coloboma. If a coloboma develops near the back of the eye there is a greater likelihood of a visual impairment. If the retina is affected the student may have difficulties with central vision. Optic disc and retinal colobmas may result in retinal detachment later in life. There is no treatment for coloboma at present.

Educational Implications: Students with coloboma's present in both eyes will be visually impaired but the degree and severity of the visual impairment will vary. It is important to note that students may experience photophobia (which is sensitivity to bright lights). Also increased font, reduced visual clutter and visual aids for magnification may be required by the student.

Coloboma (PDF)

Description: Cone dystrophy refers to a range of disorders characterized by problems with the cone photoreceptors of the retina. If it is congenital it is referred to as stationary and is also known as achromatopsia. If it is acquired it is referred to a progressive, as it may worsen. Most cone dystrophies are genetic. It does not lead to total blindness.

Effects on Vision: Since the cones are responsible for clear, central and colour vision, all of these may be affected. The student's visual acuity will be reduced. Also, the student may have poor central vision, difficulty distinguishing colours and may be photophobic. Nystagmus is often present which may contribute to blurring.

Educational Implications: The student's vision will be affected by bright light which may in turn affect reading. Tinted glasses may make reading more comfortable as would a slant board to reduce glare. The student may benefit from enlarged text to compensate for blurred central vision. Mobility is not greatly affected if the student is aware of, and takes precautions to minimize glare and light sensitivity.

Cone Dystrophy (PDF)

Description: CVI* is a condition where the connections to the visual cortex of the brain are damaged. This most often happens at or before birth. Since it is the brain that interprets what the eye sees and creates cognitive understanding, this impairment does not involve the structures of eyes. Often acuity is fine, however, the student can't interpret what he/she is seeing. This form of visual impairment is not progressive and understanding visual material can improve over time. It is often associated with cerebral palsy so motor and speech functions may also be affected. *This condition was formally known as Cortical Visual Impairment.

Effects on Vision: Difficulty interpreting visual information using either the dorsal stream or the ventral stream. Damage to the dorsal stream affects the interpretation of 3 dimensional information. Damage to the ventral stream affects the recognition of faces and objects. There is great variability in the severity of visual processing depending on the extent of the damage to the brain.

Educational Implications: Students with CVI benefit from instructional materials that are bright, well spaced and uncluttered. Masking may help the student isolate print and graphical information. They also benefit from materials that are stationery, and properly positioned. Simple explanations will assist the student in associating what they are seeing with what it is.

Cerebral Visual Impairment (CVI) (PDF)

Description: This is a very rare condition which affects the collagen of the eyes thus making the eye weaker and more prone to damage.

Effects on Vision: Effects vary and can include Myopia, retinal detachment and Keratoconus. Myopia ñ or short sightedness, typically due to a slightly elongated eye or a cone shaped cornea, this means that the image is not focused correctly on the retina. When the shape of the eye is affected the retina is in danger of becoming thin, splitting or detaching as it will not stretch. Some students get Keratoconus, the cornea or front of the eye becomes cone shaped causing blurred vision.

Educational Implications: This depends on what symptoms the student experiences ñ a functional vision assessment is recommended to determine how vision is affected.

Ehlers-Danlos Syndrome (PDF)

Description: A congenital or secondary condition involving the pressure inside the eye being too high because drainage gap is blocked, causing progressive damage to the cornea (stretch marks) the optic disk and nerve. The cause is not known but hereditary factors may play a part. The pressure inside the eye may cause it to enlarge (buphthalmos) associated conditions include aniridia, rubella, Reiger's anomaly, uveitis and retinopathy of prematurity.

Effects on Vision: Early detection and intervention can control the pressure and reduce the impact on vision. Blindness can occur in a few cases, the combination of eye structures affected with the addition of amblyopia caused by visual deprivation in the formative years contribute to the visual impairment. Peripheral vision often first affected as nerve fibres from the peripheral retina are most susceptible to raised pressure. Some students experience photophobia.

Educational Implications: Adaptations to accommodate reduced visual acuity or field loss. Both factors would need to be considered, the student with reduced VA may need to sit close to the front of the class to see the board, low vision aids and or large print may be recommended. Field loss would require positioning to optimize best visual field. Reduced peripheral vision would have an impact on student's mobility in the classroom. Where photophobia is a feature lighting needs to be considered. Frequent hospital appointments may interfere with schooling.

Glaucoma (PDF)

Description: Is a reduction in vision in one half of the visual field. Hemianopsia, may be caused by various medical conditions, such as a tumor, stroke or trauma which may involve a brain injury. Hemianopsia will vary from patient to patient and may result in absolute loss on one side or partial reduction of vision. Homonymous hemianopsia affects the right halves or the left halves of the visual fields of both eyes. Heteronymous hemianopsia is a loss of vision in either both nasal halves.

Effects on Vision: It may affect either the right or left side of the visual field and it can be permanent. Hemianopsia can produce various effects, from minor to severe. For example, a person may be able to see only to one side when looking ahead, or objects that the person sees may differ in clarity or brightness. Such visual impairment can make it difficult to perform daily tasks, from reading to crossing streets. There is no specific treatment for hemianopsia.

Educational Implications: Students may benefit from the use of magnifiers or special prism lenses. It is recommended that the student work with a teacher of the visually impaired to provide adaptations in the classroom and in Physical Education. It is important to consider preferential seating to allow the student maximum viewing of the classroom. An Orientation and Mobility specialist may help the student navigate unfamiliar environments safely.

Hemianopsia (PDF)

Description: The term 'hydrocephalus' means ëwater on the brain'. Clear fluid is pumped from the blood into the brain and then eventually reabsorbed. If the cavities (called ventricles) of the brain do not drain the fluid adequately, pressure builds up and the ventricals increase. A brain scan will show enlarged ventricles in the brain.

Effects on Vision: The optic nerve is affected as it atrophies or wastes due to the pressure from the fluid. Often this results in the student developing optic atrophy and a cortical visual impairment. This is caused by the damage to the visual cortex by direct pressure or interruption to the blood supply. There is a great variability in the severity of visual processing depending on the degree of brain damage. Another symptom of hydroceophalus is the student may be unable to move their eyes upwards. To compensate they move their entire head to view an object. Often a shunt (or tube) is inserted into the brain to drain the fluid.

Educational Implications: Students with hydrocephalus may experience difficulties with their shunt, so headaches, vomiting and visual or behavioural disturbances must be monitored. The student will benefit from materials that are well spaced, bright and uncluttered. The use of large graphics and particular colors such as red and yellow are quite helpful along with simple information and instructions.

Hydrocephalus (PDF)

Description: Hyperopia is a vision condition in which distant objects are usually seen clearly, but close objects do not come into proper focus. Farsightedness occurs if your eyeball is too short or the cornea has too little curvature, so light entering your eye is focussed behind the retina. Retinitis Pigmentosa and Microphthalmia are associated with Hyperopia.

Effects on Vision: Common effects of farsightedness include difficulty maintaining a clear focus on near objects. As well, students may experience eye strain, fatigue and/or headaches for close work, as well as aching or burning eyes and possible irritability after sustained concentration. Depending on the severity, glasses or contacts may improve vision.

Educational Implications: Student's may squint in order to help focus near point objects. Learning may be impacted by reduced or difficulty with concentration. Interaction with others may be affected by lack of ability to recognize facial expressions and body language. Low vision aids and text enlargement may assist with the reading of curricular and instructional materials.

Hyperopia (Farsightedness) (PDF)

Description: Leber Congenital Amaurosis is a genetically inherited condition in which both parents carry a recessive gene since they do not experience symptoms. Many parents are unaware they are carriers until one of their children is affected. Leber's begins to affect vision from birth to the first few months getting progressively worse. At this time there is no treatment.

Effects on Vision: Leber affects the rods and cones so both the visual field and visual acuity are severely affected. The dystrophy of the retina includes black specking narrowing of the retinal arties and the optic disc becoming pale. This condition often results in blindness.

Educational Implications: Students with Leber Congenital Amaruosis often have a severe visual impairment since both acuity and their fields are impacted. Therefore most students will need to use Braille. They will also require extensive training and support from and Orientation and Mobility Instructor.

Leber Congenital Amaurosis (PDF)

Description: This inherited syndrome affects the connective tissue in the body which can affect the heart, large blood vessels, lungs, joints, bones and eyes. For the eyes connective tissue problems can result in myopia, displaced lens, cataracts, retinal detachment and strabismus.

Effects on Vision: Myopia means distance vision of the student will be blurred. If the lens is displaced the student may have double vision as two images will be focussed on the retina. A displaced lens can also cause astigmatism and cataracts which also blur vision. Students with Marfan syndrome are at higher risk for retinal detachment which can lead to islands of vision which interrupt the normal field of view.

Educational Implications: Depending on the degree of myopia the student may benefit from a slant board for near viewing. Blurred vision may be somewhat corrected by glasses and preferential seating. Retinal detachment may result in eccentric viewing or the need for preferential seating. Low vision aids to enlarge print may assist the student with their schoolwork.

Marfan Syndrome (PDF)

Description: The eye does not grow to its full size and may result from genetic or chromosome abnormalities or unknown factors. May affect one or both eyes, glaucoma is an associated condition.

Effects on Vision: The degree of vision loss depends on the severity of the abnormality in each eye. Where the eye has almost completely failed to grow properly visual impairment can be severe. As the eyes are small it is very likely the student will be long sighted, corrective glasses will have the side effect of making the eyes appear larger as long sighted spectacles have a magnifying effect. In severe cases contact lenses or shells may be appropriate; they have a cosmetic effect but can also let some light through to allow the student to benefit from light perception.

Educational Implications: Student will most probably be a tactile learner; and will need considerable support in all areas of the expanded core curriculum.

Microphthalmia or Microphthalmos (PDF)

Description: Myopia is also known as ìshort-sightednessî or nearsightedness. An individual with this condition can see object more clearly up close than objects far away. The most common cause of Myopia is genetic. Additional source may include a student being born prematurely or another eye condition such as a cataract.

Effects on Vision: A student who is considered myopic can usually see objects well such as a book but cannot see the blackboard. In cases of high myopia, near vision can deteriorate to where very close objects are hard to focus on.

Educational Implications: The use of eye glasses, contact lenses or low vision aids (LVA's) has proven particularly helpful in viewing distant objects. Student's may squint in order to help focus on distance objects. Learning may be impacted by reduced or difficulty with concentration. Students may experience visual fatigue when asked to do a lot of reading. Also certain activities may be difficult such as baseball which requires tracking a small, distant and fast moving ball. Consider functional vision and possible learning media assessment.

Myopia (Nearsightedness) (PDF)

Description: There are two forms of neurofibromatosis. The most common is peripheral neurofibromatosis (NF1). The other is central neurofibromatosis (NF2). It is a genetic condition. NF1 is characterized by optic nerve or chiasm glioma which is a benign tumor on these nerve tissues and glaucoma, which is an increase in the pressure inside the eye. NF2 is characterized by optic nerve or chiasm meningioma, which is a benign tumor of the protective layer covering the nerve tissue and cataracts.

Effects on Vision: In both NF1 and NF2 the tumors may press against the nerve and stop the transfer of signals from the eye to the brain. This will cause blurred vision and perhaps pain in the eye. Glaucoma also causes pain. Due to the pressure on the optic nerve glaucoma will cause blurred vision starting on the periphery and progressing to the center. Cataracts cause blurred vision as the lenses become cloudy.

Educational Implications: For glaucoma, visual acuity may not be affected until the advanced stages however visual fields will be affected. Reduced peripheral vision may affect mobility. For cataracts, blurred and hazy vision reduces acuity which affects both near and far point viewing. Text enlargement may assist with reading. Students may have difficulty with mobility due to the visual impairments caused by neurofibromatosis.

Neurofibromatosis (PDF)

Description: A rare genetic disorder where the vitreous jelly and the retina have not grown properly in the unborn child. It only affects boys. Associated conditions include nystagmus (fine wobble of the eyes) learning difficulties, hearing impairment and epilepsy.

Effects on Vision: Depending on the degree to which the eyes are affected. From only mild where the student will have low vision to severe where the student will be blind from birth and only be able to see bright lights and large shapes.

Educational Implications: Emphasis will need to be on the expanded core curriculum, the student may require a learning media assessment to determine if they require large print, Braille or a combination. Considerations will also have to be included if the student has associated learning difficulties or hearing impairment.

Norrie Disease (PDF)

Description: Nystagmus is the involuntary rhythmic movement of the eyes from side to side or up and down. Nystagmus can occur independently or in conjunction with another eye condition or disease. It is often caused by abnormal function in the areas of the brain that control eye movements. Nystagmus is often present at birth but can occur later in life do to disease or injury.

Effects on Vision: The severity of Nystagmus on vision will vary from student to student. The cause of the Nystagmus will be investigated to rule out any other serious conditions. At this time, Nystagmus cannot be cured. Students will often tilt their head in a certain way to find a spot in which the involuntary movement of the eyes lessens. This is known as a ìnull spotî and it often means the students vision will improve. The effects of the Nystagmus is worse for distance than near.

Educational Implications: Students with Nystagmus will often require environment support with lighting. Also color contrast, text and other magnification tools will often be quite helpful. It is important to be aware that a student with Nystagmus will often suffer from visual fatigue especially when expected to do a lot of reading. Stress also affects the student and has been seen to increase the involuntary movement of the eyes. Tasks such as copying from the board will be difficult as it involves frequent changes of focus, providing student with own copy of work to be copied would be preferable.

Nystagmus (PDF)

Description: Ocular Motor Apraxia is characterized by a failure of the eyes to initiate fast eye movements. It is also called Cogan's Ocular Motor Apraxia or Saccadic Initiation Failure (SIF). It is often associated with other learning, language and motor difficulties. It is caused by lack of development of a specific part of the brain.

Effects on Vision: The student may move their head from side to side to change the direction they are looking and compensate for the difficulty moving their eyes. Students may also blink to help initiate fast eye movements.

Educational Implications: The student read slowly as his/her eyes won't be able to quickly track a line of print or move quickly to the next line. The student will have difficulty shifting gaze so copying will be slower either from a text or from the board. The student will benefit from as much material as possible being presented on the same viewing plane. The student may exhibit eccentric viewing patterns which should not be interpreted as inattention. The student may experience mobility problems, or travel slower to allow for decreased eye movement.

Ocular Motor Apraxia (PDF)

Description: A group of diseases involving damage to the optic nerve fibres which carry information from the retina to the brain. There are many different suspected causes, including genetic, pressure to the optic nerve or problems during pregnancy. Some students will develop nystagmus.

Effects on Vision: Depending on the severity the effects can range from near normal vision to light perception only. Most students will have reduced visual acuity, and often the central and colour vision will be more affected. In some cases glasses are prescribed, patching may also be indicated when vision is worse in one eye. Student may also have some field defects, though peripheral vision is usually good.

Educational Implications: A functional vision assessment would normally be appropriate to determine visual acuity, font size, crowding and contrast sensitivity. Consider visual acuity and visual fields for placement in the classroom. Where there is colour confusion then resources will need additional references, especially where colour is used as a key. Good task lighting and high contrast materials (black on white) may improve reading speed.

Optic Nerve Atrophy (PDF)

Description: Optic Nerve Hypoplasia is a congenital condition in which the optic nerve does not fully develop. The optic nerve is the cable that relays messages from the eye to the visual brain to be interpreted. When the optic nerve is damaged, vision is disturbed. If a student has Optic Nerve Hypoplasia (ONH) when the eye is viewed by an ophthalmologist the optic nerve head appears unusually small. Individuals with ONH may only have damage to the optic nerve; in other cases it may include neurological difficulties and endocrine abnormalities. ONH is considered one of the leading causes of blindness in North America and can occur in children of all ethnic groups.

Effects on Vision: Restricted fields of vision, Nystagmus and decreased visual acuity. It can occur in one (unilateral) or both eyes (bilateral) and can range from mild to severe; it is not a progressive condition. Students that are born with ONH can have low vision or may be blind.

Educational Implications: Considerations and adaptations important in the classroom environment include reducing a lot of visual clutter. Images should be presented in a clear and simple format. Enlarged print with high contrast such as black on white may be recommended. O&M training is recommended.

Optic Nerve Hypoplasia (PDF)

Description: This is the name given when the student has a cornea that is white or hazy. It is an inherited, congenital condition. If there are issues or problems associated with learning, physical health and physical appearance then it may be referred to as Peter's Plus Syndrome.

Effects on Vision: A hazy cornea will block or diffuse light entering the eye, thus affecting the focus on the retina. As a result vision will be blurred. Vision can be worse in bright light because of glare. Depending on the amount and area of the cornea that is affected, visual acuity will be greatly or minimally affected. A lazy eye can develop when the brain does not receive a clear signal visual signal. This is referred to as amblyopia. If not treated amblyopia can permanently reduce the brain's ability to interpret visual information.

Educational Implications: Due to reduced acuity regular print may be difficult to read without enlargement. Preferential seating or tinted glasses may assist with glare issues. Mobility is not greatly affected if the student is aware of his or her visual limitations.

Peters Anomaly (PDF)

Description: The curvature of the cornea and the lens determine their power, for normal sight the power of the cornea and lens are matched exactly with the length of the eye ball. It is a mismatch between these two factors, the optical power and the length of the eye which cause Myopia (short sight / nearsightedness) and Hypermetropia (long sight / farsightedness). If the eye is too long or too short then the image is not focused properly on the retina and appears blurred. Other refractive errors include Astigmatism where the eyeball curvature is irregular, more the shape of a rugby ball. *** The curvature of the cornea and the lens determine their power, for normal sight the power of the cornea and lens are matched exactly with the length of the eye ball. It is a mismatch between these two factors, the optical power and the length of the eye which cause Myopia (short sight / nearsightedness) and Hypermetropia (long sight / farsightedness). If the eye is too long or too short then the image is not focused properly on the retina and appears blurred. Other refractive errors include Astigmatism where the eyeball curvature is irregular, more the shape of a rugby ball. *** See Snippet for Myopia or Hyperopia or Astigmatism

Effects on Vision: A person with short sight sees things better close up, and with long sight the focusing power is weak as the eyeball is relatively short so objects father away can be seen more clearly. Refractive errors can usually be corrected with prescription glasses.

Educational Implications: Early diagnosis and correction of refractive errors is very important in young children as a blurred image on the developing retina causes ambliopia (lazy eye). Encourage the child to wear their glasses, and give them a variety of tasks to do, very often when the child is engaged in a favoured activity then they will forget about the glasses.

Refractive Error (PDF)

Description: The very fine light sensitive film known as the retina peels away from the back of the eye. This can occur when fluid leaks or collects behind the retina, sometimes as a result of a tear or hole in the retina. There are many conditions which may cause retinal detachment including myopia (because the eye is bigger, and the retina is stretched), an injury to the eye (such as a blow to the head), ROP, Coat's disease, Marfan's syndrome, Stickler's syndrome, Cataract operation, Coloboma - or it may run in families. Effects on Vision: Can result in visual field loss, may have parts of the vision missing while the rest is normal, flashes of light and / or floaters. As long as a Macular area is attached, results of surgery or laser therapy are usually good.

Educational Implications: Where student has field loss it is important to recognize what part of their vision is missing and avoid placing objects in these areas. Students with tendency to develop retinal detachment should avoid blows to the head in physical activity; if this occurs then parents should be notified immediately.

Retinal Detachment (PDF)

Description: A broad range of eye conditions are referred to as Rrtinal dystrophy. Often the cause of retinal dysptrophy is genetic in origin.

Effects on Vision: Retinal dystrophy affects the rod and cone photoreceptors of the eyes and either do not work at birth or begin to worsen over time. Where the rods are affected vision is blurred around the edges and it is difficult to see in areas with decreased light. Where the cones are predominantly affected this will reduce central vision used for seeing fine detail and colours will not be so bright. The student may experience photophobia (discomfort in bright light). Some students with retinal dystrophy will be able to see very little. There are currently no treatments for Retinal Dystrophy although many things can be done to help students in other ways. Associated conditions include nystagmus.

Educational Implications: Students may benefit from text enlargement and low vision aids. A functional vision assessment is recommended. Lighting will need to be considered as the student will not function well in very low light, they may also have an aversion to very bright light. The student may benefit from tinted glasses. Mobility may be affected due to the loss of visual acuity and the changing lighting conditions that may occur outdoors.

Retinal Dystrophy (PDF)

Description: Retinitis Pigmentosa is the general name given to a wide range of genetic eye conditions predominantly characterized by problems with the rod photoreceptors, however in advanced cases the cones may also be compromised. Specific eye conditions associated with Retinitis Pigmentosa are Rod Cone Dystrophy, Leber's Amaurosis and Usher's Syndrome. RP usually progresses slowly. Cataracts and retinal swelling are also associated with retinitis pigmentosa.

Effects on Vision: Usually the rods are more affected than the cones meaning night vision and movement of things are compromised. There will also be a loss of peripheral vision. If the cones are affected then there will be central and colour vision loss.

Educational Implications: Due to reduced vision in low light the student will benefit from good, even lighting. The student will also benefit from preferential seating and may exhibit eccentric viewing or frequent head turning to compensate for the reduced visual field. Mobility may also be affected due to reduced visual fields.

Retinitis Pigmentosa (RP) (PDF)

Description: A very rare tumour of the retina which is normally caused by genetic misprints. Usually develops in the second year of life, or even earlier, sometimes at birth. It usually occurs in both eyes, can also be associated by a rare form of brain tumour. The most common way it is detected is when the normally black pupil of the eye looks paler or white. It may also present as a strabismus (where both eyes don't point in the same direction), red eye or blurred vision.

Effects on Vision: When one eye only is affected it will have very poor vision and may even need to be removed, however the student may be able to see well from the other eye. Where both eyes are affected then the student will have blurred vision. The tumour may be treated conservatively which is as non invasive as possible which the aim to preserve as much vision as possible, this also depends on where the tumour is located.

Educational Implications: This very much depends on the degree of visual impairment and will have to be assessed on a case by case basis, it the student is monocular (only sees from one eye) it will have an impact on speed, depth and distance perception and consideration will have to be made to placement in the class to utilize the better visual field. Where there is loss of visual acuity, the student will require a functional vision assessment to determine placement in the classroom and the appropriate accommodations and resources.

Retinoblastoma (PDF)

Description: Retinopathy of prematurity is characterized by the abnormal growth of blood vessels in the retina of some premature infants. The use of oxygen administered to premature babies in incubators was suspected as a possible cause of the abnormal growth of the blood vessels. Other factors include low birth weight, premature birth 32 weeks or younger and the baby being severely ill at birth.

Effects on Vision: The retina is affected because blood vessels do not reach the edges so blood flow is disrupted. If there is normal growth of the blood vessels, the area is well supplied with nutrients and oxygen. The optic nerve and macula are affected as well as the mid and far periphery. Retinopathy of prematurity can range from a mild reduction in visual acuity to complete retinal detachment and blindness.

Educational Implications: Depending on the severity of the visual impairment which may vary from low vision to blindness the student will require either large print or braille. If the student is not a braille user, they will likely need low vision aids such as magnifiers or a monocular. It is important to be aware of proper illumination for the student while trying to avoid glare. Also, reducing visual clutter is very imperative on maps and diagrams. Instruction and training from an Orientation and Mobility instructor is essential.

Retinopathy of Prematurity (ROP) (PDF)

Description: This is the general name given to a wide range of conditions characterized by problems with the rod and cone photoreceptors. It is congenital and hereditary. It is related to Retinitis Pigmentosa, Leber's Amaurosis and Usher's Syndrome in its effects on vision.

Effects on Vision: If the rods are most affected the student will have blurring around the periphery as well as difficulty seeing in low light. If the cones are most affected the student will have blurred central vision as well as decreased colour vision. They may also be photophobic. Visual acuity is affected depending on the degree and areas affected. However, since both rods and cone are involved, most students will have greatly reduced eyesight.

Educational Implications: Students will benefit from text enlargement and low vision aids. Lighting will need to be considered as the student will not function well in very low light, nor will they function well in very bright light. The student may benefit from tinted glasses. Mobility may be affected due to the loss of visual acuity and the changing lighting conditions that may occur outdoors.

Rod-Cone Dystrophy (PDF)

Description: A congenital underdevelopment of one or both optic nerves (the wiring which carries information to the visual brain) and the septum (the thin wall which connects both halves of the brain). This occurs when there is a disturbance of the developing optic nerve or brain, it may be genetic or caused by other factors. Associated conditions include nystagmus (fine wobble of the eyes) and possible pituitary and hormone disturbances. Patching of the better eye may be indicated to encourage visual development in the affected eye.

Effects on Vision: Depending on the severity of the condition and if one or both eyes are affected. Sometimes the effects can be small, but were more of the nerves have not developed then less information is transferred and the student will have poor vision. If only the top of bottom half of the optic nerve is affected then the student will have blurred vision in the opposite visual field.

Educational Implications: This very much depends on the degree of visual impairment and will have to be assessed on a case by case basis, where there is visual field loss consideration will have to be made to placement in the class to utilize the better field. Loss of visual acuity will require a functional vision assessment to determine appropriate accommodations and resources. If impairment is severe a learning media assessment and O & M would be recommended.

Septo-Optic Dysplasia (PDF)

Description: Sixth Nerve Palsy is associated with a dysfunction of the sixth cranial nerve which is responsible for allowing the eye to turn out. This causes esotropia, where the eye turns in. The result is double vision (diplopia) in adults. Children are not as affected with diplopia because their brains can turn off the double image. The eye is still turned in however, so amblyopia (reduced vision in one eye) is possible, as the brain shuts down the signal from the affected eye. The condition commonly occurs in one eye only, but it can also occur in both.

Effects on Vision: The main effect is double vision. It is more noticeable at far point fixation, than at near point. It is often reported to improve with time (maximum improvement occurs in the first 6 months). Often patching is prescribed to strengthen the affected eye. Patching will result in monocular vision (one eye only) and it will negatively affect depth perception.

Educational Implications: Preferential seating is recommended so that the student's straight eye provides visual access to a maximum amount of the classroom. Students will often exhibit eccentric viewing habits (head tilt or turning slightly away from the speaker) in order to maximize binocular vision and reduce the double vision. This should be accepted and not be associated with inattention.

Sixth Nerve Palsy (PDF)

Description: An inherited Juvenile type of macular degeneration that causes progressive vision loss usually to the point of legal blindness over the first two decades of life.

Effects on Vision: The macular is the most sensitive part of the retina and responsible for seeing fine detail. Vision may only be mildly reduced at onset. Colour vision usually becomes progressively abnormal. Peripheral visual fields are usually well maintained since it is mostly the central vision affected. Other effects are blind spots, blurriness, photophobia and difficulty adapting to dim light.

Educational Implications: Students with macular damage may benefit from the use of low vision aids. They may need extra time to complete work and possibly given less to do, while still covering the main learning objectives.

Stargardt Disease (PDF)

Description: Strabismus is a condition in which the eyes are not properly aligned with each other. As a result one eye turns in (esotropia), turns out (exotropia), turns up (hypertropia) or turns down (hypotropia). It is usually caused by a lack of coordination between the muscles that control eye movement thereby preventing binocular vision where both eyes focus on the same point in space. It is also known as ìlazy eyeî. Treatment may involve patching the straight eye, glasses or surgery.

Effects on Vision: Strabismus can cause amblyopia (reduced vision) if left untreated, because the brain will shut down the vision from the affected eye. To prevent this, strabismus should be treated as soon as it is noticed. Strabismus can also affect depth perception and may initially result in double vision before amblyopia sets in.

Educational Implications: If student is patched, preferential seating is recommended to maximize visual access to the classroom. Depth perception will also be reduced which may affect physical activity. Strabismus should be reported for treatment as soon as it is noticed.

Strabismus - Esotropia, Exotropia or Hypertropia (PDF)

Toxoplasmosis is caused by an infection from a microscopic parasite that can live inside the cells of humans and animals. It is transmitted through eating raw or undercooked meat and vegetables, coming into contact with cat feces and transfer from mother to infant while pregnant. Often, infected adults do not show any signs or symptoms. Toxoplasmosis is the most common infective cause of childhood visual impairment in developed countries.

Effects on Vision: If a student is born with toxoplasmosis, it may have affected the student's development. Toxoplasmosis can cause inflammation of the retina, cataracts, optic atrophy and Micophthalmos (small eyes). These conditions are all associated with vision difficulties since they cause a loss of visual acuity and visual fields. Antibiotics and surgery may be performed to help correct a number of symptoms, but each case is unique and the outcomes will vary.

Educational Implications: A student infected by toxoplasmosis may need a variety of vision supports and services, but it is dependent upon the area and severity of the affected vision.

Toxoplasmosis (PDF)

This is the general name given when any part of the student's overall field of vision is impaired or non-functioning. It can affect one or both eyes. Field loss can occur because of damage to the eye(s), the visual pathways to the brain, or to the specific parts of the brain that receive visual information.

Effects on Vision: If the affected area is impaired the student will have blurred vision in that part of their visual field. If the affected area is completely damaged, there will be no vision in that part of the visual field. If the macula is damaged the student will have blurred central vision. If the damage occurs at the optic chiasm the student will experience hemianopia. This is a corresponding field loss in both eyes. For example, both eyes lack vision in any of the right, left, upper or lower half of their visual field.

Educational Implications: Students with visual field loss may experience early difficulties with part- whole relationships as concepts are developed. They may benefit from enlargement or low vision aids if acuity is affected. Students will also benefit from preferential seating to maximize the functional benefit of their working visual field. Students may also exhibit eccentric viewing in order to see. This should not be interpreted as inattention. Mobility may be affected, especially when drop offs or dangers from the side may be encountered.

Visual Field Loss (PDF)