Conditions Of The Eye/blindness

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The two most common types of testing for vision are:

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1. Visual acuity testing-used to measure the level of best vision and need for corrective lenses
2. Visual field testing

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Visual acuity is defined as

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the sharpness of the visual image perceived

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A standard test of visual acuity is

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the Snellen test

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Visual field is defined as

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the size of the area that individuals can see without turning the head or moving the eye

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Peripheral vision is measured

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by a curved device called a perimeter

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An individual is considered to have a visual impairment

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when any deviation of normal vision exists

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Categories of visual impairments include

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-refractory errors
-difficulty with coordination of the eyes
-opacities of the eye
-damage of the eye due to injury
-damage to the eye secondary to other conditions
-degenerative changes of the eye

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Visual impairments can occur in the following areas of vision:

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-central field of vision
-peripheral field of vision (e.g. tunnel vision)
-night vision (e.g. night blindness)
-color vision (e.g. color blindness, or achromatopsia)
-binocular vision (e.g. diplopia)

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The term blindness means

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a deviation in vision causing total loss of light perception

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Legal blindness is defined as:

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-visual acuity not exceeding 20/200 or worse in better eye with correcting lenses
-central field of vision limited to an angle of 20 degrees or less
-this definition describes those with total vision loss and those with some remaining vision function but who have significant visual impairments

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The most frequent cause for diminished visual acuity are:

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refractive errors

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Refractive errors:

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-occur when changes in the cornea, aqueous humor, lens, or vitreous humor prevent proper bending of light rays to converge on the retina
-types include: myopia, hyperopia, astigmatism, and presbyopia

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Refractory errors are usually treated:

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with corrective lenses of a surgical procedure called radial keratotomy

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Myopia means

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-nearsightedness
-can occur at any age

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Hyperopia means

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-farsightedness
-can occur at any age

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An astigmatism

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-results from irregularity of shape of the cornea or (at times) the lense so that vision is distorted
-can occur at any age

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Presbyopia

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-is a condition usually associated with aging
-involves gradual loss of accommodation due to loss of elasticity of the lense and weakening of the ciliary muscle
-individuals with this conditions must hold small objects and printed material farther and farther away to see clearly bc the eye can no longer adjust the shape of the lense

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Incoordination of the eyes

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-can be the result of heredity, disease, or damage to the brain
-is when both eyes do not work together to form a single image
-types/conditions include: nystagmus, strabismus

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Nystagmus

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-a.k.a. "dancing eyes"
-is a condition in which the eyes move involuntarily even though the gaze is fixed in one direction
-movement is most often horizontal
-may be congenital or it may develop later in life due to a neurological or other disease/condition

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Strabismus

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-is a condition in which the eyes cannot be directed to the same object or in which the eyes are crossed, turning inward
-is classified according to the type and magnitude of misalignment
-may result from unequal ocular muscle tone or from a neurological condition
-symptoms include double vision and/or eye strain
-it can often be corrected by surgery, corrective lenses, medications, or a combination of the three

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Suppression amblyopia

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-"lazy eye"
-condition in which one eye does not develop good vision, usually bc of strabismus
-usually treated at an early age by placing a patch over the eye

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Opacities of the eyes

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-any condition (including injuries, inflammation, or disease) that causes scarring or clouding of the cornea
-can cause partial or total loss of vision
-most common type=cataracts

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A cataract:

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-is a clouding or opacity of the lens of the eye
-is a common cause of visual impairment in older adults but can also be congenital, inherited, or the result of ocular trauma or inflammation, as well as of a disease or condition (e.g. diabetes)
-usually bilateral but can also form in both eyes at different rates

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Treatment of cataracts involves

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-removal of the lens and it's replacement with an implant
-with glasses
-both

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The most common type of eye injury is

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-an injury to the cornea caused by a foreign body

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Keratoplasty

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-corneal transplant
-a surgical procedure typically performed when the cornea becomes so scarred that vision is severely compromised

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What type of doctor would you see after injuring your eye?

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-an ophthalmologist

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Other injuries to the eye can include:

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-chemical burns from chemical agents such as those with an alkaline base (cleansing agents, fertilizers, plaster, and refrigerants) or from chemical agents with an acidic base
-corneal laceration
-puncture of the eye
-bleeding into the anterior chamber (hyphema)
-blows to the head

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Conjunctivitis

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-is an inflammation of the membrane that lines the eye, the conjunctiva
-may be caused by infectious organisms (such as viruses or bacteria), allergy, or chemicals
-is easily treated in most cases, is self-limiting, and has no permanent effects

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Two types of infectious conjunctivitis that can cause ulceration of the cornea and subsequent blindness are:

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-gonococcal conjunctivitis
-trachoma

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Uveitis

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-is an inflammation of the uveal tract (iris, ciliary body, choroid)
-may be associated with autoimmune diseases such as ankylosing spondylitis or IBS, or by local/systemic infections such as HIV
-manifestations include sensitivity to light (photophobia) and decreased vision
-is treated with topical medication

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Keratitis

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-is an inflammation of the cornea
-can be associated with herpes simplex (herpetic keratitis) or a complication of HIV, or withi use of contacts (microbial keratitis) due to improper handling of contact-lens equipment and solutions

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Glaucoma

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-comprises a group of conditiosn that result in visual field loss
-is the leading cause of irreversible blindness
-can occur as a primary condition or secondary to other conditions such as diabetes, trauma, infection, prolonged use of medications (steroids)
-develops when the amount of aqueous humor produced exceeds the amount being drained from the eye resulting in increased pressure in the eye

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There are 4 types of glaucoma:

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1. primary open-angle glaucoma
2. secondary open-angle glaucoma
3. primary angle-closure glaucoma
4. secondary angle-closure glaucoma

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Primary Open-Angle Glaucoma:

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-is the most common type
-occurs when the outflow of aqueous humor from the eye is reduced, causing it to build up and increase pressure in the eye
-progresses slowly, over many years
-it produces no symptoms until the optic nerve is sufficiently damaged to reduce visual acuity and visual field, at which point the damage is irreversible
-there is no cure but early detection can control it for many years

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Secondary Open-Angle Glaucoma:

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-also due to reduced outflow of aqeuous humor but is caused by a preexisting or underlying condition such as trauma or steroid use

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Primary Angle-Closure Glaucoma:

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-results from the forward displacement of the iris, which narrows/obstructs the path for aqueous humor outflow
-is a medical emergency-must be treated immediately to prevent blindness
-manifestations include sudden severe pain, sharply decreased vision, nausea and vomiting, and rapid damage to the optic nerve with associated vision loss
-results from abrupt blockage and obstruction of the canal of Schlemm so that aqueous humor rapidly accumulates ni the anterior chamber of the eye

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Secondary Angle-Closure Glaucoma:

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-can result from scarring that blocks the flow of the aqueous humor
-conditions such as diabetes, uncontolled hypertension, and inflmamation of the uveal tract bc of other conditions can cause it
-usually involves surgery

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Treatment/management of Open-Angle Glaucoma includes:

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-medication (eye drops, oral) to reduce pressure in the eye by decreasing amount of aqueous humor produced
-trabeculectomy: a surgery to relieve pressure by creating a passageway through which the humor can drain

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Treatment/management of Angle-Closure Glaucoma

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-use of miotics, eye drops that constrict the pupil, and/or other oral/topical medications immediately to increase outflow of aqueous humor
-a surgical procedure called iridotomy in which a small section of the iris is removed so that flow of humor is increased; is often done by laser
-trabeculectomy

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Retinopathy

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-is any disease or condition that affects the retina
-often are named for their cause, e.g. arteriosclerotic retinopathy (produced by changes that occur in blood vessels in the retina due to arteriosclerosis) or hypertensive retinopathy (from changes that occur in blood vessels in the retina due to high blood pressure)

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Diabetic retinopathy

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-is the most common type of retinopathy and of blindness
-is the result of damage to the retina and is a complication of diabetes mellitus

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Two categories of diabetic retinopathy include:

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1. nonproliferative diabetic retinopathy: caused by changes in blood vessel walls, allowing fluids to leak into retinal tissue and blood vessels to become occluded, causing retinal tissue death
2. Proliferative diabetic retinopathy: results from extensive areas of closure of the small blood vessels in the retina, causing too little oxygen stimulating growth of new vessels that are prone to bleeding and hemorrhaging

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A vitrectomy

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-is a surgery performed to remove hemorrhaging in the case of proliferative diabetic retinopathy

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Retinal detachment

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-when the sensory layer of the retina becomes segmented from the pigmented (choroid) layer, depriving the sensory layer of its blood supply
-may result from a blow to the head, a tumor in the choroid layer, or retinal degeneration caused by medical conditions
-manifestations include loss of vision in different areas of visual field or complete loss of vision
-sugery called scleral buckling is sometimes used as treatment

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Retinitis Pigmentosa

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-is a hereditary degenerative condition of the retina that causes slowly progressive loss of periphreal vision and blindness (in many cases)
-manifestations include difficulty with night vision in late youth/early adulthood and loss of bilateral vision by age 50
-there is no cure or treatment

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Macular degeneration

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-loss of central field of vision while peripheral vision remains intact
-from degenerative changes in the macula (the part of the eye needed for seeing fine detail and central vision)
-occurs after age 50 with no apparent cause
-usually slow, starting with visual distortion or blurring of vision followed by a blind spot occuring in center of field of vision that increases as the condition progresses
-two types: dry or wet form

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Dry versus wet forms of macular degeneration:

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-Dry Form=most common, caused by shrinkage (atrophy) and thinning of macula, causing mild to moderate vision loss
-Wet Form=characterized by significant vision loss due to abnormal blood vessel formation and hemorrhage

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A comprehensive eye examination includes:

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-an external eye exam
-testing of visual acuity and visual field
-viewing a chart through a refractor
-tonometry (used to measure pressure in the eye to detect glaucoma)
-slit-lamp exam (evaluates eyes' structures and screens for cataracts)
-retinal examination (to check for retinal disease)

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An optometrist

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-is a non-physician who specializes in correcting refractive errors
-performs tests of visual acuity and visual field

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An opthalmologist:

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-is a physician who specializes in evaluation and treatment of conditions of the eye

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Treatment and management of eye conditions include:

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-eyeglasses
-contact lenses
-refractive surgery
-prosthetic devices/eye replacement
-assistive devices and low-vision aids
-orientation and mobility training and aids

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Eyeglasses and contact lenses

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-are prescribed by either an optometrist or an opthalmologist

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Refractive surgery

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-is an alternative to wearing glasses or contact lenses
-for myopia, hyperopia, and astigmatism
-includes photorefractive keratectomy (PRK), Laser-assisted in situ keratomileusis (LASIK), and laster epithelial keratomileusis (LASEK)

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Examples of assistive devices and low-vision aids include:

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-optical devices (high-powered lenses and telescopic spectacles)
-non-optical devices (large-print reading material or large-button telephones)
-low technology devices (talking watches, raised-dot markings for oven dials, templates for check signing, talking clocks/timers, writing guides, talking books/audiocassettes)
-high technology devices (video magnifiers and computer systems)
-Braille (including refreshable Braille displays)

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Professionals involved in provision of assistive devices and low-vision aids include:

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-OTs
-low-vision specialists
-orientation and mobility instructors (O&M)
-rehab teachers
-adaptive technology specialists

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Examples of mobility aids include:

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-sighted guides
-guide dogs
-canes
-electronic devices

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The degree of vocational impact for individuals with conditions of the eye or blindness

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depends on the nature of the employment, the type and extent of visual loss, and the life stage at which visual loss occurred