Eyes 3 Flashcards
strabismus
imbalance of extraocular muscles
Symptoms: amblyopia (poor visual acuity), poor depth perception, double vision, eye strain, headaches, unable read comfortably or fatigue when reading, unstable or jittery vision
Treatments: Should be corrected in childhood with surgery (shortening/lengthening/changing the position of extraocular muscles), glasses/contact lenses, or patch
esotropia vs exotropia
“cross-eyed” vs “wall-eyed”
emmetropia
image focused perfectly on retina
myopia
(nearsightedness) - your eyeball is too long, image focused in front of retina
Can be corrected with concave lens
hyperopia
(farsightedness) - your eyeball is too short, image is focused “behind” retina
Can be corrected with convex lens
presbyopia
(old eye) – hardened lens over time that is not flexible, not able to accommodate near or far.
Can be corrected with bifocal lens, concave top and convex bottom
astigmatism
caused by irregularly shaped cornea so that instead of being round it is football shaped (could be the lens) causing refractive error of multiple focal points in front or behind the retina (or both)
Symptoms: blurred vision or distorted vision to some degree at all distances, eyestrain and headaches especially after reading or prolonged visual task, need to squint frequently
Treatments: eyeglasses or contact lenses, LASIK surgery reshapes the cornea by lifting a thin flap and lasers remove tissue from the inner layer of the cornea, PRK (photorefractive keratectomy) lasers remove tissue from the superficial and inner layers of the cornea, Orthokeratology which uses retainer rigid contact lens to reshape the cornea
cataract
clouding of lens typically after age 40 yrs due to clumping of proteins in the nucleus or cortex of the lens. (risk factors: age, smoking, radiation, diabetes, previous trauma, or congenital)
Symptoms: blurred vision, lights seem too bright or glaring, glare with headlights at night with halo, poor night vision, difficulty reading, or colors seem faded
Treatments: Corrected with surgery – open up capsule, break up nucleus and cortex and suck it out, then replace interior with plastic intraocular lens. Implant can’t change focus, but can be adjusted with glasses.
Prevent with diet high in Vitamin E and antioxidants from fruits and vegetables with carotenoids, selenium, and Vitamin C. Don’t smoke and wear sunglasses to shade from UV radiation.
glaucoma
loss of vision from intraocular pressure that damages the optic nerve
If channels for draining aqueous humor are blocked, then fluid builds up that increases pressure on the optic nerve.
Also due to complications from eye surgery, blunt or chemical injury to the eye, blockage of blood vessels in the eye, inflammatory conditions of the eye.
Risk Factors: Family history, over age 40 yrs, diabetes
Eventually causes blindness from compression of optic nerve
Symptoms: Often no symptoms until late in the disease, loss of peripheral vision, eye pain, headache, blurred vision, halos around lights, narrowing of vision (tunnel vision), over time central vision loss until blindness if untreated.
Treatments: No cure to restore vision. Eye drops to reduce production of aqueous humor or increase drainage, Laser surgery to open up the tubes for fluid to drain or hole in iris for better flow or create a new channel to drain the fluid
Cannot be prevented but early detection and treatment can control the disease because loss of vision is irreversible.
detached retina
part (tears) or all of the retina pulls away from the choroid layer. If not treated can lead to blindness (within few days) because cells die due to lack of blood.
As age, vitreous humor can thicken and form clumps and shrink away from the retina causing the retina to pull away and bleed. Blows to the head (boxing, football, etc) can tear the retina. Then fluid flows under retina and separates it more.
Symptoms: Person sees floaters (spots, specks, or lines that float in field of view) or flashes of light at the edges of the visual field, shadow/curtain across part of your field of view that does not go away, sudden loss of peripheral vision that gets worse over time.
Treatment: Surgery is necessary with lasers that make tiny burns or freezes (cryopexy) around the area to seal the retina to the back wall of the eye.
retinitis pigmentosa
rare hereditary disease that leads to degeneration of photoreceptors (first rods, then cones). Onset in childhood/adolescence and by age 40 usually legally blind.
Symptoms: Progressive vision loss starting with night vision and peripheral vision, loss of color perception, and central (reading) vision, then “tunnel vision”, eventual total blindness, ophthalmoscope see dark deposits in the retina
No Cure
Treatments: Vision aids (cane, guide dogs, lenses), surgical placement of growth factors, transplantation of fetal neural retina or retinal pigment epithelial (RPE) tissue, retinal implants - placement of retinal prosthesis or phototransducing chip, subretinal gene therapy, Vitamin A, Lutein, Zinc, and Omega-3 rich diet, may slow progression.
Age-related Macular Degeneration (AMD) –
gradual loss of central vision due to degeneration of the macula by Dry – metabolic end products (drusen) collecting under the retina and scarring and thinning retina or Wet – abnormal blood vessels growing under the retina and leaking blood
25% of Americans over 65 have this (leading cause vision loss)
Symptoms: center of vision becomes blurry then darkened, straight lines become distorted, colors become less vivid or darker, will not go totally blind just loss of central vision
Treatment: Eat healthy diet, protect eyes from sun, avoid smoking, exercise, laser surgery to destroy blood vessels, medication to slow/stop growth of blood vessels (anti-VEGF therapy), no cure to restore vision
direct vertical pathway
Ganglion cells ↑ Bipolar cells ↑ Photoreceptors
ganglion cells
their axons fire action potentials to the optic nerve which goes to the brain
bipolar cells
connections
