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

2. 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

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

4. 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

5. 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

6. Associated Eye Conditions and Functional Implications

7. 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

8. 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

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

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

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

12. 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

13. 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

14. 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

15. Treatment None Treat associated eye conditions Strabismus Amblyopia
Nystagmus

16. 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.

17. 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.

18. 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).

19. 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.

20. 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”

21. 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.

23. 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

26. 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

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

29. 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

31. 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

32. 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

33. 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

35. 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…

36. Associated Eye Conditions and Functional Implications

37. 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

38. 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

39. Hemianopsia

40. 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!

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

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

43. 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.

44. 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

45. 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

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