Refractive Errors

Question 1

Define Astigmatism?

Answer 1

Refractive error when the eye doesn’t focus light evenly in all directions due to change in the lens shape or cornea curvature.

‘Rugby ball shaped’

Question 2

Define irregular astigmatism?

Answer 2

Principle meridians are not perpendicular to each other.

Occurs in corneal ulcers/keratoconus

Question 3

Define Regular astigmatism?

Answer 3

Principle meridians are 90 deg from each other.

Question 4

What are the 3 types of regular astigmatisms and explain each?

Answer 4

With the rule - Vertical meridian is the steepest.

Oblique - Principle meridians are neither at 90deg or 180deg

Against the rule - Horizontal meridian is the steepest

Question 5

What are the 3 types of regular astigmatisms and explain each?

Answer 5

With the rule - Vertical meridian (90) is the steepest.

Oblique - Principle meridians are neither at 90deg or 180deg

Against the rule - Horizontal meridian (180) is the steepest

Question 6

How do you treat ATR Astigmatism?

Answer 6

Corrected with a PLUS CYLINDER LENS between 150 - 30 degrees

Question 7

How do you treat Oblique Astigmatism?

Answer 7

Corrected with a PLUS CYLINDER LENS between 31-51deg + 121-149deg

Question 8

What lens are used to manage astigmatism?

Answer 8

Regular - Soft toric lenses (Combi of cylindrical and spherical lenses)
Irregular - RGP (Rigid gas permeable) contact lenses