Refractive Error Flashcards
What is myopia?
Image projects in front of retina “near sightedness”
Causes of myopia
Image is projected in front of retina because …
a. Refractive myopia: .. refractive system (lens) is too convex (converging) i.e. image converges too quickly
b. Axial myopia: … A-P axis of the eye is too long, therefore the projection point is in front of the retina (even if lens is normal)
c. Acute myopia: … especially in diabetes, where hyperglycaemia leads to the swelling of the lens therefore increasing its convexity
Sx of myopia
Blurry vision (esp far away); eye strain; headache
Rx of myopia
Diverging lens; LASIK
What is hypermetropia?
Image projects behind the retina “far sightedness”
Cause of hypermetropia
Image is projected behind the retina because…
a. Refractive hypermetropia: … lens is too concave (diverging)
b. Axial hypermetropia: A-P axis is too short
Sx of hyperometropia
blurry vision (near); eye strain; headache
Rx of hypermetropia
converging lens; LASIK
What is presbyopia?
Decreased ability to focus on near objects (cannot make lens convex) due to:
1. loss of elasticity of lens and/or,
2. decrease strength of ciliary muscles
that occurs with increasing age
Rx of presbyopia
Converging lens; presbyLASIK
What is astigmatism?
Irregular curvature of refractive system resulting in different image projection points in the vertical and horizontal axis, leading to a distorted image projected onto the retina
i.e. vertical and horizontal axis projecting at different points
What is regular astigmatism?
Vertical and horizontal axis are perpendicular
i.e. two different curves at 90 degrees to each other
(like a football, rather than a soccer ball)
What is irregular astigmatism?
Vertical and horizontal axis are not perpendicular
i.e. cornea has variable degree of curvature along each axis
Are both regular and irregular astigmatism corrected with glasses?
No, only regular astigmatism
