Session 4: Wednesday September 30, 2015: Anatomy of the Eye, Associated Eye Conditions and Functional Implications

 Housekeeping  Questions from last week? ◦ Updates from the AES Conference in Halifax  Anatomy of the Eye, Associated Eye Conditions and Functional Implications ◦ Retina

The Retina

 Functions to convert relevant information from the external environment into a neural impulse which is sent to the brain  Has two primary layers: ◦ Inner neurosensory retina ◦ Retinal pigment epithelium (RPE)  When these layers separate, you get a retinal detachment

 The retina lines the posterior two thirds of the eyeball  The neural retina is firmly attached anteriorly at the ora serrata (near the ciliary body) and at the margins of the optic nerve

 Posterior Pole ◦ 5-6 diameter zone situated between the superior and inferior temporal arteries

 Macula Lutea – Macula ◦ 1.5mm diameter area in the posterior pole, lateral to the optic disc

 Fovea Centralis ◦ 0.35 mm wide zone in the macula ◦ Is a depression, such that light falls directly onto the cones. ◦ Avascular

 Optic Disc ◦ 3mm medial to the centre of the macula ◦ No photoreceptors (Blind Spot)

 Peripheral Retina ◦ The remainder of the retina outside of the posterior pole ◦ Rich in rods

 RPE  Photoreceptors  External limiting membrane  Outer nuclear layer  Outer plexiform layer  Inner nuclear layer  Inner plexiform layer  Ganglion cell layer  Nerve fiber layer  Internal limiting membrane Neurosensory Retina

 Pigment cell layer that nourishes the retinal cells  Located just outside the retina and attached to the choroid

 2 Types ◦ Rods ◦ Cones (3 Types)  Contain molecules called photopigments which absorb light ◦ Rhodopsin in the rods ◦ One in each of the three cone types  Each photopigment absorbs light most effectively at different parts of the visible spectrum

 Within the photoreceptor cells, the photopigments lie in specialized membranes that are arranged in highly ordered stacks parallel to the surface of the retina  Rod cells are not located in the macula, but cones are densely packed there  In extreme peripheral retina there are 10 rods per cone

RodsCones  Long and narrow  One visual pigment ◦ Rhodopsin  No color vision  120 million in number  Multiple rods connect to one nerve fiber  Poor visual resolution  Best in dim light (scotopic)  Detect motion  Short and conical  Three visual pigments ◦ Chlorolabe (green light) ◦ Erythrolabe (red light) ◦ Cyanolabe (blue light)  Color vision  6.5 million in number  One to one cone to nerve fiber in fovea  Excellent visual resolution  Best in bright light (photopic)

 Is a zone that interdigitates around the rods and cones  Composed of the outermost ends of Muller’s cells ◦ Muller’s cells extend vertically from the external to internal limiting membranes ◦ They lend structural and nutritional support to the retina

 Contains cell bodies of the rods and cones

 Location where rod and cone axons synapse with biploar horizontal cells

 Contains nuclei of bipolar horizontal, amacrine and Muller’s cells ◦ Transmit information within the retina

 Bipolar cells axons and ganglion cell dendrites synapse in this layer  Is the location of the second and final intraocular synapse

 Contains second order neurons for vision

 Contains a roughly concentric arrangement of the one million ganglion cell axons  These axons exit the eye at the optic disc and form the optic nerve

 Basement membrane which lies against the vitreous  Covers the entire surface of the retina from the ora serrata up to the optic disc.

 Light entering from the left visual field … ◦ strikes the retina of the left eye on the nasal side ◦ strikes the retina of the right eye on the temporal side  Light entering from the right visual field… ◦ Strikes the retina of the left eye on the temporal side ◦ Strikes the retina of the right eye on the nasal side

 Inherited disorder ◦ Affects males and females alike ◦ Autosomal recessive  Affected individual has received the disease-causing gene from both parents ◦ Incidence is between 1/1660 and 1/15000  Usually diagnosed before age 20, but can start by age 6 ◦ Some may not notice significant vision loss before age ◦ Total loss of sight is rare ◦ Vision is between 20/200-20/400

 Vision loss cannot be corrected with glasses or contact lenses ◦ No treatment is currently available  It affects the macula ◦ Causes a loss of central vision ◦ Limits the person’s ability to see color and details ◦ Vision loss is caused by a loss of cone cells

 Usually diagnosed between Can be difficult to detect.  Because of the late diagnosis and often quick progress of the disease can cause emotional and acceptance issues.  May have other related eye conditions.

Low Visual Acuity (between 20/200 to 20/400)  May appear to change depending on lighting.  May benefit from low vision aids such as magnifiers or monoculars.  May benefit from assistive technology such as CCTV, Zoomtext or Magnifier mouse.  May benefit from large print.  May benefit from descriptions of pictures  Many of these students need to learn Braille and cane skills.

Photophobia:  When completing a FVA, test the student in different types and levels of lighting.  May benefit from wearing sunglass or brimmed hat.  May benefit from sitting with back to windows.  Avoid objects that produce glare such as magazines or shiny toys. (Different lighting and/or positioning can reduce glare).

Poor Contrast sensitivity:  May appear to change depending on lighting.  May benefit from clear and high contrasting materials i.e. black on white.  May benefit from high contrasting pictures or verbal descriptions.  May benefit from high contrasting marking in environment i.e. edges of stairs.

Visual Field Loss  Scotomas (blind spots) in the central visual field can cause difficulty reading and traveling. O&M, cane travel and scanning techniques are all important. A LMA may be needed if there are changes.  Scotomas or Blind spots in the visual field may make reading or recognizing people and places difficult.  Students with blind spots may exhibit eccentric viewing or appear to be looking to the side instead of at you.  “wavy vision” or “blurry spots”

Colour Vision:  Colour vision can be affected.  Label pictures that are colour dependent (i.e. maps or diagrams) with symbols or tactiles.  Use high contrasting colours.

 Is an infection caused by a single-cell parasite, Toxoplasma gondii  Is acquired by ◦ Contact with cats or cat feces ◦ Eating raw or undercooked meats  The disease can be transmitted from mother to child during pregnancy ◦ A small percentage of these infants can be born with retinal scarring ◦ Vision loss is permanent

 Can have localized blind spots  Vision can be better than 20/100 in more than half of affected individuals  Reactivation of infections in old scars can cause further vision loss  Treatments are available in the form of drug therapy, which can ◦ Kill the parasite ◦ Reduce inflammation ◦ Minimize scarring  Treatments cannot ◦ Restore lost vision ◦ Prevent reactivation of disease

Toxoplasmosis is a life long concern that can “pop up” late in life even though there were no initial symptoms.

Although rare, can cause low visual acuity (20/100)  May benefit from low vision aids such as magnifiers or monoculars.  May benefit from assistive technology such as CCTV, Zoomtext or Magnifier mouse.  May benefit from large print.  May benefit from descriptions of pictures

Retinal Scarring may cause “blind spots”  Scotomas (blind spots) in the central visual field can cause difficulty reading and traveling. O&M, cane travel and scanning techniques are all important. A LMA may be needed if there are changes.  Scotomas or Blind spots in the visual field may make reading or recognizing people and places difficult.  Students with blind spots may exhibit eccentric viewing or appear to be looking to the side instead of at you.  “wavy vision” or “blurry spots”

Photophobia:  When completing a FVA, test the student in different types and levels of lighting.  May benefit from wearing sunglass or brimmed hat.  May benefit from sitting with back to windows.  Avoid objects that produce glare such as magazines or shiny toys. (Different lighting and/or positioning can reduce glare).

 In RP, photoreceptors are slowly damaged due to an inherited genetic mutation ◦ Many different mutations can cause RP  It is slowly progressive  1/3500 Canadians has RP  Early symptoms ◦ Difficulty seeing at night and in dim light conditions ◦ Loss of peripheral vision  Diagnosed in childhood or early adolescence

 In RP, rod photoreceptors are lost first ◦ As more rods are lost, the cones also start to die  May be triggered by rod cell death  Clinical findings ◦ Mottled pattern on the retina  Due to the accumulation of dark pigment ◦ Thinning of blood vessels ◦ Waxy appearance of optic nerve

 As RP progresses, peripheral vision is slowly lost  Uncomfortable sensitivity to light and glare is common  Eventually people with RP lose central vision, and some will go on to lose all light perception  No treatment is available

 May be a part of a syndrome i.e. Ushers Syndrome, Bardet – Biedl Syndrome or Leber Congenital Amaurosis.  Genetic  Different forms and may look different for different people  Generally causes the most problems in teenage years

 Emotional Impact and understanding.  Social impact  Can affect learning/ learning media.

Visual Field Loss  Constriction of peripheral fields may cause poor night vision, difficulty reading and traveling. O&M, cane travel and scanning techniques are all important.  Scotomas or Blind spots in the visual field may make reading or recognizing people and places difficult.  Most students with RP will begin learning Braille in preparation for vision loss.

Photophobia:  When completing a FVA, test the student in different types and levels of lighting.  May benefit from wearing sunglass or brimmed hat.  May benefit from sitting with back to windows.  Avoid objects that produce glare such as magazines or shiny toys. (Different lighting and/or positioning can reduce glare).

Low Visual Acuity (Depends on the progress of RP in individual person)  May appear to change depending on lighting.  May benefit from low vision aids such as magnifiers or monoculars.  May benefit from assistive technology such as CCTV, Zoomtext or Magnifier mouse.  May benefit from large print.  May benefit from descriptions of pictures  Most of these students need to learn Braille and cane skills.

Colour Vision:  Colour vision can be affected.  Label pictures that are colour dependent (i.e. maps or diagrams) with symbols or tactiles.  Use high contrasting colours.

 A rare form of eye cancer affecting the retina of infants and young children  Occurs in every 1/20000 births  Can be unilateral (60%) or bilateral (40%)  Caused by a genetic defect in the retinoblastoma gene  Presents as a white pupil

 Is treatable!!! ◦ Surgery ◦ Chemotherapy ◦ Radiation ◦ Laser  Children must be re-examined regularly for the development of new tumors during the first 3 years of life ◦ Survival rate is 96% ◦ Are prone to other cancers throughout their life  Visual outcome depends on the location of the tumor ◦ Close to optic nerve and macula can cause decreased acuity ◦ Toward the edge of the retina may not have an effect on vision

 If the eye is removed, it is replaced by a prosthesis to protect the orbit of the eye.

Low Visual Acuity (Depending of placement of tumour, may cause loss of visual acuity)  May benefit from low vision aids such as magnifiers or monoculars.  May benefit from assistive technology such as CCTV, Zoomtext or Magnifier mouse.  May benefit from large print.  May benefit from descriptions of pictures

 Retinopathy of prematurity (ROP) is a potentially blinding disease caused by abnormal development of retina blood vessels in premature infants  When a baby is born prematurely, the retinal blood vessels can grow abnormally  When ROP is severe, it can cause the retina to pull away or detach from the wall of the eye  Babies 1250 grams or less and are born before 31 weeks gestation are at highest risk

 When the eye develops, the blood vessels of the retina grow from the optic nerve toward the peripheral retina  When an infant is premature, this growth is incomplete, especially at the outer edges of the retina  Abnormal new blood vessels form at the edge of the developed retina ◦ This area can become scarred leading to retinal detachments  Risk factors ◦ Too much/too little oxygen at birth ◦ Birth weight ◦ Genetic predisposition ◦ Blood transfusions

 Stage 1 ◦ Presence of a line between developed and undeveloped retina  Stage 2 ◦ The line becomes a ridge  Stage 3 ◦ New, abnormal blood vessels grow on and around the ridge  Stage 4 ◦ Leakage from new vessels and scar formation result in retinal detachment  Stage 5 ◦ Detachment of entire retina

 Plus Disease ◦ Rapidly worsening ROP

 Zone I ◦ Area around optic nerve and macula ◦ Poor visual outcome  Zone II ◦ Area between zones I and II ◦ Intermediate prognosis  Zone III ◦ Farthest edge of the retina ◦ Good prognosis

 May hear it described in “clock hours” ◦ A way of indicating how much of a zone has the disease  The need for treatment is determined by ◦ Location ◦ Extent ◦ Stage of ROP  Most cases do not require treatment  Treatment may involve ◦ Laser (peripheral field defects) ◦ Cryotherapy (freezing retina) ◦ Treatment of retinal detachments ◦ Treament of cataracts, glaucoma

 Fewer than 20% of infants have final VA of 20/40 or better  Vision problems can include ◦ Nystagmus ◦ Strabismus ◦ High myopia  Require optical correction

 RoP can be diagnosed in 5 stages. The level of damage is determined by the stage. Some students will have no vision and receive Braille and Cane instruction, while others will not qualify for services.  May be paired with other eye conditions.

Low Visual Acuity (Depending on stage of RoP and the affect to the retina)  May appear to change depending on lighting.  May benefit from low vision aids such as magnifiers or monoculars.  May benefit from assistive technology such as CCTV, Zoomtext or Magnifier mouse.  May benefit from large print.  May benefit from descriptions of pictures  May benefit from Braille

Photophobia:  When completing a FVA, test the student in different types and levels of lighting.  May benefit from wearing sunglass or brimmed hat.  May benefit from sitting with back to windows.  Avoid objects that produce glare such as magazines or shiny toys. (Different lighting and/or positioning can reduce glare).

Visual Field Loss  Constriction of peripheral fields may cause poor night vision, difficulty reading and traveling. O&M, cane travel and scanning techniques are all important.  Scotomas or Blind spots in the visual field may make reading or recognizing people and places difficult.

Colour Vision:  Colour vision can be affected.  Label pictures that are colour dependent (i.e. maps or diagrams) with symbols or tactiles.  Use high contrasting colours.

Low Contrast:  May appear to change depending on lighting.  May benefit from clear and high contrasting materials i.e. black on white.  May benefit from high contrasting pictures or verbal descriptions.  May benefit from high contrasting marking in environment i.e. edges of stairs.

Possible poor depth perception: May benefit from high contrasting outlines on environment i.e. stairs or playground equipment.  May benefit from having time to explore new areas and being warned of changes in ground level.

 Inherited disorder of pigment development  Affects ◦ Eyes ◦ Skin ◦ Hair  Melanin is reduced or absent ◦ Causes fair skin, blue eyes  Pigment is required for the development of the retina, especially the fovea

 Two main types of Albinism (according to phenotype) ◦ Oculocutaneous Albinism  Reduction or absence of melanin in the skin, hair, and optic system  Pale skin appearance ◦ Ocular Albinism  Changes in the optic system only with no clinical difference in skin and hair color ◦ Each category can be further divided into specific genetic mutations

 When melanin is absent: ◦ Abnormal decussation of optic nerve fibers (more next week)  This leads to a predominance of monocular vision and decreased binocular depth perception. ◦ Foveal hypoplasia ◦ Congenital nystagmus  Clinically can see iris transillumination

 The presentation of Albinism can be emotionally or socially difficult  Commonly associated with strabismus and nystagmus.  Sensitivity to the sun and light.

Photophobia:  When completing a FVA, test the student in different types and levels of lighting.  May benefit from wearing sunglass or brimmed hat.  May benefit from sitting with back to windows.  Avoid objects that produce glare such as magazines or shiny toys. (Different lighting and/or positioning can reduce glare).  Spot lighting, such as using a lamp or lighting only the necessary area may help a student with Albinism see.

Low Visual Acuity (20/100 – 20/400)  May appear to change depending on lighting.  May benefit from low vision aids such as magnifiers or monoculars.  May benefit from assistive technology such as CCTV, Zoomtext or Magnifier mouse.  May benefit from large print.  May benefit from descriptions of pictures

Poor Contrast sensitivity:  May appear to change depending on lighting.  May benefit from clear and high contrasting materials i.e. black on white.  May benefit from high contrasting pictures or verbal descriptions.  May benefit from high contrasting marking in environment i.e. edges of stairs

Colour Vision:  Colour vision can be affected.  Label pictures that are colour dependent (i.e. maps or diagrams) with symbols or tactiles.  Use high contrasting colours.

Poor depth perception (if there is strabismus): May benefit from high contrasting outlines on environment i.e. stairs or playground equipment.  May benefit from having time to explore new areas and being warned of changes in ground level.

Continue with anatomy…the visual pathway BRING COFFEE!