GEPY 6911: Functional Implications of Visual Impairment Session 4: Monday, October 15, 2012: Anatomy of the Eye, Associated Eye Conditions and Functional Implications

Agenda Housekeeping Any questions from last week’s lecture? Discuss quizzes Anatomy Quiz: Date change to October 18th Syndromes Quiz: Date change to November 8th Optics Quiz: Date change to November 15th Anatomy of the Eye, Associated Eye Conditions and Functional Implications Optic Nerve Visual pathway

Optic Nerve and Visual Pathway Anatomy of the Eye, Associated Eye Conditions and Functional Implications Optic Nerve and Visual Pathway

Optic Nerve Composed of nerve fiber layer bundles (retina ganglion cell axons) that exit the eye through the optic disc It is the connection between the eye and the brain It carries the impulses formed by the retina for interpretation by they brain Is the second cranial nerve Is part of the Central Nervous System

Each optic nerve contains both nasal and temporal fibers from the same eye Injury to one optic nerve (before the optic chiasm) affects only fibers to the eye on that side

Associated Eye Conditions and Functional Implications

Optic Atrophy Any condition causing degeneration of the optic nerve Degeneration of ganglion cells Damage to optic nerve Injury to optic chiasm/tract Can be congenital or acquired Congenital: tumor, inflammation, infection, trauma Associated with prematurity, hydrocephalus, hypoxia Acquired: Trauma, tumor, thyroid eye disease, MS

Is sometimes inherited (AD fashion) Degeneration of ganglion cells Vision loss is progressive Vision stabilizes between 20/40 and 20/200 Color vision difficulties Inherited as Leber Hereditary Optic Neuropathy Vision decreases rapidly Loss of color vision and contrast sensitivity Affects males more than females Vision loss occurs in one eye at a time Visual symptoms occur between 15 and 35 years of age In 50% of cases, vision can improve spontaneously

The ophthalmologist will see: Visual field defects Color vision abnormalities Contrast sensitivity reduction Optic disc pallor Pupil reflex abnormalities Abnormal blood vessels

There is no treatment for optic atrophy Treatment of underlying cause is sometimes possible Once atrophy has taken place, vision loss is irreversible

Optic Neuropathy Damage to the optic nerve and its fibers Various causes Heredity Inflammation Trauma Brain tumor Radiation

Vision loss can be sudden or gradual Can affect one or both eyes As damage to the nerve progresses, there will also be impaired color discrimination and loss of contrast sensitivity Can be progressive and can recur Treatment No treatment to optic nerve once damage has occurred Treatment of underlying causes can cause stabilization of vision

Optic Nerve Hypoplasia A congenital condition in which the optic nerve is underdeveloped Is diagnosed by the presence of a small, pale optic nerve, which is confirmed on MRI

Visual impairment ranges from mild to severe Cause Most have no identifiable cause Associated with Maternal diabetes Maternal alcohol and drug abuse Young maternal age (less than 20 years of age) Visual impairment ranges from mild to severe May affect one or both eyes May see nystagmus or strabismus In general, is non-progressive

Treatment None Treat associated eye conditions Strabismus Amblyopia Nystagmus

Functional Implications of Optic Nerve Atrophy, Neuropathy and Hypoplasia ONH, OA and ON are commonly associated with other visual conditions as well as many syndromes, i.e., DeMorsier Syndrome (Septo- Optic Dysplasia) or CVI. Is stable throughout life. Maybe associated with strabismus or nystagmus.

Functional Implications of Optic Nerve Atrophy, Neuropathy and Hypoplasia Low Visual Acuity (No light perception to perfect vision) 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.

Functional Implications of Optic Nerve Atrophy, Neuropathy and Hypoplasia 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).

Functional Implications of Optic Nerve Atrophy, Neuropathy and Hypoplasia 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.

Functional Implications of Optic Nerve Atrophy, Neuropathy and Hypoplasia 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”

Functional Implications of Optic Nerve Atrophy, Neuropathy and Hypoplasia 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.

The Visual Pathway The optic nerves leave the back of each orbit and further recede where they converge to meet at the optic chiasm Optic chiasm All nasal retinal fibers from both eyes cross over to the opposite side Some inferior nasal fibers loop briefly up into the opposite optic nerve before moving into the optic tract (von Wilebrandt’s knee) Is located near the pituitary

After leaving the chiasm, nasal fibers from the OPPOSITE eye and temporal fibers from the SAME eye join to form the optic tracts Right optic tract Temporal fibers from right eye Nasal fibers from the left eye Come from the right half of each eye’s retina Contain information from the left half of the visual field

These paired halves of each visual field are homonymous Meaning they contain information from the same side of each eye

Each optic tract continues traveling backward around the outside of the midbrain portion of the brain stem to end in the lateral geniculate body (LGN) Nerve fibers from the ganglion cells synapse here This gives rise to the neurons that travel together as the optic radiations

Optic Radiations When the nerve fibers leave the LGN, they fan out Some wing forward and laterally around the lateral ventricle into the temporal lobe Others pass superiorly through the parietal lobe Nerve fibers eventually terminate around the calcarine fissure in the occipital lobe The area responsible for vision at the end of this area is Brodmann area 17 or visual cortex

A large portion of the posterior tip of the occipital cortex contains macular fibers Each area in the in the retina is represented in a corresponding area of the visual cortex Left visual cortex perceives objects in the right visual field of each eye Superior fibers responsible for the inferior visual field terminate along the upper lip of the calcarine fissure Inferior fibers responsible for the superior visual field terminate along the lower lip

After visual information is sent to the visual cortex, it must be sent on for further processing Some areas of the brain are specialized for processing certain aspects of vision Dorsal stream The “where” pathway Detection of motion, spatial orientation, localization Parietal lobe Ventral stream The “what” pathway Recognition of objects (color and form) Temporal lobe

The brain is much more complicated! Messages are then sent on to other parts of the brain that control: Eye movements Pupil reactions Reactions to visual stimuli And so much more…

Associated Eye Conditions and Functional Implications

Visual Field Defects Characteristic patterns of visual field defects are associated with abnormalities in different portions of the sensory visual pathway Three anatomic sections: Prechiasmal – affecting visual field of involved eye Chiasmal – affecting the temporal half of each eye’s field Postchiasmal – defects affect either both right halves or both left halves of each eye’s field

Causes of visual field defects are numerous and include: The more posterior the lesion, the more congruous the visual field defect!!! Causes of visual field defects are numerous and include: Glaucoma Vascular disease (stroke) Tumours Retinal disease (RP) Hereditary disease Optic neuritis Toxins Drugs Trauma Post surgery

Hemianopsia

Hemianopsia is a loss of vision affecting half of the visual field See Figure 6.1 in text! Hemianopsia occurs more frequently in stoke and traumatic brain injuries Some improvement in visual fields may be possible in hemianopsia Is dependent on the cause of the loss and extent of the damage There is no specific treatment for VF loss Rehabilitation is helpful!

Functional Implications of Hemianopsia Difficulty tracking, moving down the lines, rereading.

Functional Implications of Hemianopsia Focusing on the end of the word, not the beginning. Can’t read ahead.

Functional Implications of Hemianopsia Visual Field Loss: Learning reading strategies that can help with field loss, such as, where to focus or using outlines to focus attention. Orientation and Mobility, white cane. Learning to scan the environment, head turns. Preferential seating in class or during presentations.

Cerebral Palsy (CP) A non-progressive condition resulting in damage to the brain before, during or shortly after birth Can cause: Developmental delay Seizures Damage to motor system (movement/posture) Visual impairment

Visual Impairment Multiple injuries throughout the visual system due to inadequate oxygen Can lead to: Optic nerve damage (optic atrophy) Retinal disease (ROP) CVI Can sometimes have poor control of eye movements

Anatomy Quiz to be completed by October 18th! Next 2 Classes: CVI Anatomy Quiz to be completed by October 18th!