Refractive errors

Question 1

What is astigmatism?

Answer 1

Irregularly shaped cornea / lens resulting in inability to focus on things at any distance

Question 2

What is with-the-rule astigmatism and what is against-the-rule astigmatism?

Answer 2

With the rule = steepest curve is in vertical axis - vertical beams of light focus in front of horizontal beams / converges vertical beams more powerfully
Against the rule = steepest curve is in horizontal axis - horizontal beams focus in front of vertical

Question 3

What are the different problems with focusing in astigmatism?

Answer 3

Simple hyperopic = first focal line is on retina, 2nd is behind
Simple myopic = first focal line is in front of retina, 2nd is on
Compound hyperopic = both focal lines are behind
Compound myopic = both focal lines are in front

Question 4

What causes presbyopia?

Answer 4

A progressive decrease in the accommodative capacity of the lens

Question 5

What is the pathophysiology of presbyopia?

Answer 5

Increased stiffness of the crystalline lens

Manifests clinically as a progressive difficulty in reading at the usual distance

Question 6

How is presbyopia treated?

Answer 6

Spectacles - often bifocals

Surgery - corneal ablation, keratoplasty