eye (visual disorders) Flashcards
what is the definition of myopia?
short-sight
close objects are seen clearly and distant objects remain blurry and out of focus
why does myopia occur?
- the cornea is more curved than normal leading to increased refraction (light rays meet before reaching the retina due to more angle)
- elongated eyeball
- age, ciliary muscles lose tensile strength
how can myopia be corrected?
concave lens in either contact lenses or spectacles, causes rays to diverge before entering eye so it can focus on the retina
what is the definition of hyperopia?
long-sight
a person can easily view distant objects but has difficulty focusing on objects that are nearby
light rays fail to meet at the retina as angle is not sharp enough
why does hyperopia occur?
- short eyeball
- a cornea which is too flat, affects its ability to refract
- poor accomodation ability by the lens
how can hyperopia be corrected?
convex lens in spectacles or contact lenses, causes light rays to converge slightly before entering eye so lens can focus them on the retina
what is the definition for cataracts?
a condition where crystalline protein of the eyes are altered, making regions of cloudiness in the lens resulting in impaired vision and in extreme cases, blindness
why do cataracts occur?
age and UV
how can cataracts be corrected?
day surgery: making an incision in the cornea removing the damaged lens and replacing it with a synthetic intra-ocular lens which replaces the natural lens
laster cataract surgery, breaks the lens to more accurately place artificial lens in lens capsule
what is the definition of astigmatism?
vision is blurred at all distances as a result of a misshaped cornea where curvature is not uniform in all directions
why does astigmatism occur?
present from birth, develops after an eye injury, disease or surgery
how can astigmatism be corrected?
eyeglasses and contact lenses
laser-assisted surgery
