Download Anatomy of the Eye, Conditions, and Functional Implications

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
Rods


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
Cones


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 30-40
◦ 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 6-20. 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! 