GEPY 6911: Functional Implications

of Visual ImpairmentSession 2: Wednesday, September 16, 2015:

Anatomy of the Eye, Associated Eye Conditions and Functional Implications

Housekeeping items

Start Anatomy of Eye, Associated Conditions and Functional Implications

Agenda

Any questions from last week?

Textbook

Weekly discussion◦ Any questions?

Housekeeping Items

Anatomy of the Eye, Associated Eye Conditions

and Functional Implications

Protect the eye from injury

Exclude excessive light from the eyes

Cleanse and moisten the cornea

Eyelids

We have an upper and lower eyelid◦ The only difference between the two is the

presence of the levator palpebral superious muscle in the upper lid

When we discuss the size of an eyeball, we are referring to the size of the palpebral fissure◦ Normal is 30mm wide, 15mm high

The lid margin is separated into anterior and posterior portions by the “gray line”

Eyelashes are on the anterior portion of this line◦ They also protect the eye and are innervated by

sensory nerves Modified oil and sweat glands open into the

follicles of the lashes◦ Some of these glands secrete the oily layer of the

tear film The lids are composed of 7 layers

There are three types of lid abnormalities

◦ Ptosis

◦ Ectropion

◦ Entropion

Moistens

Cleans

Lubricates◦ Prevents friction between the eye and the lids

Lacrimal Apparatus

The lacrimal gland contributes secretions to the tear film

Tear film has 3 layers◦ Lipid (fat) layer – from glands connected to lashes◦ Aqueous layer – from lacrimal gland◦ Mucous layer – from cells in conjunctiva

Blinking maintains a continuous tear film layer over the surface of the eye

Tears drain into the lacrimal sac and nasolacrimal duct via the lacrimal puncta

Tears drain out of the eye with blinking

Some infants can have an obstrucion in the nasolacrimal duct

The nasolacrimal duct drains into the nose

The eyes reside in 2 symmetrical bony cavities called the orbits

Serve to protect and maximize the function of the eye

Is pear-shaped with the widest diameter at the front 7 bones contribute to form the orbital walls

◦ Frontal◦ Lacrimal◦ Palentine◦ Zygomatic◦ Maxilla◦ Sphenoid◦ Ethmoid

The Orbit

The orbit contains:◦ Eyeball in the anterior portion (1/5 of the space)◦ Optic nerve◦ The 6 extraocular muscles◦ Nerves which innervate/stimulate the muscles◦ Blood vessels◦ Lacrimal gland◦ Connective tissue◦ Fat

They function to move the eye in different directions◦ Provide us with binocularity◦ Provide us with an expanded visual field

They move and rotate the eye in all directions

There are 6 in each orbit

Extraocular Muscles

Lateral Rectus◦ Moves the eye horizontally (out)◦ Innervated by the 6th CN

Medial Rectus◦ Moves the eye horizontally (in)◦ Innervated by the 3rd CN

Superior Rectus◦ Move eye up (also in and intorts)◦ Innervated by the 3rd CN

Inferior Rectus◦ Moves the eye down (also in and extorts)◦ Innervated by the 3rd CN

Superior Oblique◦ Intorts the eye (also moves down and out)

Inferior Oblique◦ Extorts the eye (also moves up and out)◦ Innervated by the 3rd CN

When there is a problem with the extraocular muscles (length, placement or ability to function) the eyes will not be properly aligned, and the images seen by the two eyes are too dissimilar for the brain to fuse them

This will result in either the brain suppressing one eye, or double vision

Misaligned eyes = Strabismus Brain suppression = Amblyopia

Associated Eye Conditions

Amblyopia will be discussed in a later slide

Strabismus can be:◦ Tropic – cannot be controlled under binocular

viewing conditions◦ Phoric – can be controlled by the brains efforts to

achieve binocular vision

Strabismus occur for many reasons◦ Inherited (common)◦ Paresis◦ Trauma◦ Restriction◦ As the result of another syndrome/disorder

Esotropia◦ An inward turning of the eyes◦ Most common form of strabismus◦ Congenital esotropia can appear in the first 6

months of life◦ Usually impaired depth perception◦ Can be treated with eye muscle surgery◦ Accommodative esotropia can be treated with

glasses for near

Exotropia◦ An outward turning of the eyes◦ Common strabismus of childhood◦ Usually starts of intermittent, and can sometimes

stay that way◦ Can be worse for distance fixation and in bright

light◦ If it becomes constant, eye muscle surgery can

help

There are other conditions that can cause strabismus◦ Thyroid Eye Disease◦ Superior Oblique Palsy◦ Brown’s Syndrome◦ Duane’s Syndrome◦ Orbital Floor Fracture

Strabismus in children will lead to suppression and amblyopia

Strabismus in adults will lead to diplopia (double vision)

A thin, translucent, mucous membrane that helps protect the eyeball

It covers the undersurface of the lid, the curves and covers the sclera (white part of the eye) and ends at the cornea

A transparent barrier covering the contents of the orbit

Conjunctivitis (pinkeye) is an inflammation or infection of the conjunctiva

Conjunctiva

Fibrous layer that provides support to the globe

Helps to maintain the shape of the eye The extraocular muscles attach to the

sclera to move the eye It covers the entire globe except for the

front of the eye (cornea) The boarder between the cornea and the

sclera is called the corneoscleral limbus

Sclera

Is the major refractive surface of the eye (2/3 of eye’s refracting power)

Is the window for the eye, therefore any disease or injury can adversely affect vision

Corneal transparency is due to:◦ The arrangement of cells◦ The avascularity◦ The regularity and smoothness of the epithelium

Cornea

The cornea is composed of 5 layers:◦ Epithelium

Must be kept moist to maintain transparency and nutritional status

Responds rapicly to repair◦ Bownman’s layer

Cannot regenerate if damaged – will scar◦ Stroma

Makes up 90% of the corneal thickness If penetrated is vulnerable to infection and scarring

◦ Descemet’s Membrane◦ Endothelium

Contains a pump which dehydrates and nourishes the cornea

Refracting power

◦ Light rays enter the eye through the cornea and are bent so that they converge at a point of focus on the retina (macula)

◦ Sometimes light rays are not focused on the retina due to The size of the eyeball The shape of the eyeball The curvature of the cornea

Hyperopic (farsighted)◦ Light rays converge behind the retina◦ The eyeball is too short◦ Will need glasses for near◦ Example Rx: +4.00

Plus lens

Myopic (nearsighted)◦ Light rays converge in front of the retina◦ The eyeball is too long◦ Will need glasses for distance◦ Example Rx: -5.75

Minus lens

Astigmatic◦ Light rays converge on more than one axis◦ The eyeball is shaped more like a football with a

short axis and a long axis◦ Will be corrected with glasses with a cylindrical

lens◦ Example Rx: +2.50-1.75x180

Refractive Errors◦ Occur in 52% of the population over three years of

age◦ Can be corrected with

Eye glasses Contact lenses Intraocular lens implants Refractive surgery (in some cases)

◦ In patients with significant myopia, the length of the eye can continue to increase, causing it to become thin and stretched. Can cause the lens of the eye to dislocate Can put the patient at risk for retinal detachments

Associated Eye Conditions

Amblyopia◦ In children, before the age of about 10,

uncorrected refractive errors can cause amblyopia◦ Is defined as the reduction of visual acuity in one

or both eyes due to poor visual input Without this input, the brain fails to develop properly

◦ Most common cause of monocular vision loss◦ Can be caused by

Strabismus Refractive errors Deprivation

If caused by strabismus◦ The misaligned eye is suppressed (ignored) to prevent

double vision◦ Sometimes strabismus surgery will re-align the eyes and

make the brain pay attention to the eyes once again◦ Patching is required!

If caused by refractive errors◦ Unequal refractive errors (anisometropia)◦ The brain will only pay attention to the eye with the

clear vision◦ Glasses will help to level the playing field◦ Patching is required!

If caused by deprivation◦ The brain will only pay attention to the clear image ◦ Surgery to remove a cataract, etc. is necessary◦ Patching is required!

Amblyopia Treatment◦ This is required in most cases of amblyopia◦ The better seeing eye is either patched or blurred to

force the eye to pay attention to the weaker eye Can wear an eye patch Can use Atropine drops

◦ Vision in both eyes must be monitored closely in both eyes

◦ The visual system can respond to amblyopia treatment until about 8-10 years of age

◦ The younger the child, the better the chances of recovering vision

◦ If amblyopia is detected late, or treatment is unsuccessful, the vision loss is irreversible.

While patching, students will be functioning with a lowered visual acuity and temporary accommodations may need to be made.

Depth perception Compliance with patching can be an issue.

Parents, teachers and students will need support.

Functional Implications of Amblyopia

Keratoconus◦ An extreme form of corneal curvature, whereby

the cornea becomes cone shaped◦ The center of the cornea becomes thin and in

extreme cases can rupture◦ Is rare◦ Bilateral◦ Inherited ◦ More common in males◦ Presents as blurry vision in the teenage years

Can be associated with other conditions and diseases◦ Down Syndrome◦ RP◦ Aniridia

Contact lenses are helpful in the early stages◦ Usually rigid lenses

Corneal transplant may be necessary in later stages◦ Is successful in over 85% of cases

Blurred vision – Large print, electronic text or magnification Assistive technology i.e. Zoomtext or

Quicklook Monocular Receiving notes from the board or electronic

notes i.e. through email or a memory stick

Functional ImplicationsKeratoconus and possible accommodations

Sensitivity to light• wearing brimmed hats or sunglasses• Sitting with their back to windows• Closing blind or curtains.• When possible dimming lights or using a • Desk light.

Poor Night Vision• May require assistance at night or the use of a white cane.

Eye Strain or fatigue – • Use large and high contrast print• Take frequent breaks from using visual materials• Use auditory materials for longer reading assignments

Cont.

Questions/Comments?

Next week we move inside the eye….stay tuned!