eye Flashcards
how does sight work
Light passes through cornea, pupil, lens, and vitreous body to stimulate sensory receptors (rods and cones) on the retina.
emmetropia
normal
normal
emmetropia
orbit
Cavity lined with fatty tissue that contains and cushions the eyeball.
Has several openings through which blood vessels and nerves pass.
muscles
Six short muscles provide support and rotary movement of the eyeball.
Connect the eyeball to the orbital cavity.
Four muscles are straight (rectus) muscles and two are slanted (oblique) muscles.
eyelids
Protect the eyeballs from intense light, foreign particles, and impact.
Edges have eyelashes and sebaceous glands, which secrete sebum into the eyelids.
conjunctivia
Mucous membrane that lines the underside of the eyelid and anterior surface of the eyeball.
Protective covering for the exposed surface of the eyeball.
lacrimal apparatus
Includes structures that produce, store, and remove the tears that cleanse and lubricate the eye.
Structures include: Lacrimal gland, ducts and canals.
eyeball
organ of vision
composed of 3 sections
eyeball- outer layer
Composed of the sclera and the cornea.
Posterior portion is the sclera (white)
Anterior portion is the cornea (transparent)
sclera
White” of the eye
cornea
Anterior transparent portion of the eye’s fibrous outer surface.
Surface is curved, allowing it to bend light rays to focus them on the retinal surface.
eyeball- middle layer
Lies below the sclera.
Consists of: Choroid, Ciliary Body and Iris.
choroid
Pigmented, vascular membrane.
Prevents internal reflection of light.
ciliary body
Thickened part of the vascular membrane.
Iris is attached.
Part of the ciliary body governs the convexity (curve) of the lens.
Secretes the aqueous humor (nutrient fluids) that nourish the cornea, the lens and surrounding tissues.
iris
Coloured membrane attached to the ciliary body.
Suspended between the lens and the cornea in the aqueous humor.
Circular opening in centre called the pupil.
Has 2 muscles which dilate or contract to regulate the amount of light admitted by the pupil
eyeball- inner layer
Contains: Lens and Retina.
lens
Colourless crystalline body.
Biconvex in shape
Enclosed in transparent capsule.
Suspended by ligaments just behind the iris.
Functions to sharpen the focus of light on the retina (called accommodation) by changing its shape.
retina
Contains photoreceptive cells.
Translates light waves focused on its surface into nerve impulses.
Photosensitive cells are called rods and cones.
Absence of any rods or cones leads to blind spots in the field of vision.
Contains: Macula lutea and fovea centralis.
mucula lutea
Small, yellow area of the retina.
Site where more than 6 million cone cells are grouped.
fovea centralis
Tiny depression in the retina near the optic nerve.
Contains only cone cells.
Central focusing point within the eye.
Point of greatest visual acuity.
rods
Function in dim light.
Provide low visual acuity (sharpness).
Do not respond to colour.
cones
Active in bright light.
Have high visual acuity.
Respond to colour.
errors of refraction (ametropia)
When light rays fail to focus sharply on the retina.
Due to: Defect in the lens, cornea, or the shape of the eyeball.
Includes: Myopia, astigmatism, hyperopia/hypermetropia and presbyopia.
Tx: Corrective lenses or LASIK surgery.
myopia
nearsightedness
Can see objects up close, but objects at a distance are not in proper focus.
Image falls in front of the retina.
Hyperopia/Hypermetropia
Farsightedness.
Can see objects at a distance, but objects up close are not in proper focus.
Image falls behind the retina.
presbyopia
Form of farsightedness.
Can see objects at a distance, but objects up close are not in proper focus.
Caused by inability of the lens to accommodate because of loss of elasticity.
Occurs between ages 40-45-years (aging process).
Image falls behind the retina.
astigmatism
Cornea or lens has a defective curve.
This curvature causes light rays to diffuse over a large area of the retina, rather than being sharply focused.
LASIK Surgery
Laser-assisted in situ keratomileusis surgery.
Procedure permanently changes the shape of the cornea.
procedure: Small incision is made to the cornea to produce a flap.
Flap is lifted while a laser reshapes the underlying corneal tissue.
Flap is replaced.
Surgery lasts about 15 minutes.
cataracts
Opacities that form on the lens and impair vision.
Opacities produced by protein that slowly builds up over time until vision is lost.
Types: Age-related and congenital.
Tx: Removal of the clouded lens and replacement with an artificial, bendable intraocular lens (IOL).
glaucoma
Characterized by increased intraocular pressure caused by:
Overproduction of the aqueous humor.
Failure of aqueous humor to drain from
the eye due to blockage.
Leads to atrophy of the optic nerve.
Most easily prevented cause of blindness.
acute vs chronic glaucoma
Acute Glaucoma:
Rapid onset of symptoms.
Includes: Pain, redness of the eye, feeling of pressure, blurred vision, decreased visual acuity, moderately dilated and nonreactive pupil.
Without tx, blindness in 3-5 days.
Chronic Glaucoma:
Insidious (gradual) and usually not recognized until too late.
Includes: Mild aching, loss of peripheral visions, seeing halos around lights, and difficulty with night vision.
prevention and treatment of glaucoma
Prevention:
Regular eye examinations.
Easily diagnosis.
treatment
Drugs to reduce the production of aqueous humor.
Eye drops to aid in the outflow.
Surgery to create an opening for circulation of fluid.
strabismus (Heterotropia or tropia)
One eye is misaligned with the other
Eyes do not focus simultaneously when viewing an object.
Misalignment can be in any direction:
Esotropia (inward).
Exotropia (outward).
Up, down, or any combination of these.
Amblyopia (lazy eye) – Vision is suppressed in the “lazy” eye and child only uses “good” eye. Left untreated, blindness in the “lazy” eye results.
treatment of strabismus
Early detection. Must be treated by the age of 6 years. Eye patches. Eye exercises. Corrective lenses. Surgery.
muscular degeneration
Deterioration of the macula (the most sensitive portion of the retina).
Leads to loss of central visual field.
Leading cause of vision loss in North America.
Rarely leads to total blindness.
Causes: Toxic effects of some drugs, and age-related.
Two types: Wet and dry.
Wet: Small blood vessels form under the macula and leak destroying visual cells.
Dry: Small, yellowish deposits develop on the macula and interfere with central vision.
treatment of macular degeneration
Depends on type and severity.
Laser surgery
conjunctivitis (pink eye)
Inflammation of the conjunctiva.
Produces a red or pink eye; pain, swelling, and discharge.
Causes: Secondary to viral, Chlamydial, bacterial, or fungal infections; or allergy.
Tx: Depends on the cause. Antibiotics, antifungals, antihistamines.
blepharitis
Inflammation of the eyelids.
Caused by excess secretions of the sebaceous glands.
Produces greasy scales and sticky, crusted eyelids; leads to itching and burning sensations.
Tx: Daily cleansing of the eyelids.
retinal detachment
Characterized by the separation of the retina from the choroid layer of the eyeball.
Due to: Aging, hypertension, diabetes, trauma, and other systemic diseases.
Symptoms: Seeing floating spots, flashes of light, and gradual vision loss.
Tx:
Limiting eye movements with a patch, bed rest, sedation, appropriate positioning of head.
Laser beam can repair simple tears.
Surgery.
surgical removal of the eye ball
enucleation
nystagmus
condition of rapid, involuntary, rhythmic movements of the eyeball
structure that prevents internal reflection of light
choriod
function of retina
translate light waves into nerve impulses
