3.1.1 Uses instruments to measure corneal curvature and assess its regularity.

What is a keratometer used for and what does it measure

A keratometer is used to measure the radius of curvature of the cornea (central 3mm). It is

measured in two principal meridians (90 degrees apart)

0.05mm = how much D

0.25DC

What is WTR and ATR

WTR - flattest along H meri

ATR - flattest along V meri

What are the uses of Keratometry

- Establishing power of corneal astigmatism

- Obtaining directions of meridians to determine is against-the-rule (ATR) or with-the-rule

(WTR) astigmatism.

- Radii of curvature for contact lens fitting

- Assessing fit and wetting of soft contact lenses

- Detection of corneal pathology, i.e., keratoconus.

What is the B/L keratometer

o One position keratometer, variable doubling mechanism.

+

Advantages: measures both meridians at the same time, quick and easy

to use.

-

Disadvantages: inaccurate if irregular astigmatism, short working

distance which leads to errors.

What is JS keratometer

o Two position, fixed doubling keratometer.

+

Advantages: good for measuring irregular astigmatism,

longer working distance so more accurate.

-

Disadvantages: requires second adjustment to measure

2nd principal meridian

Possible questions:

o Calculations e.g., calculate the corneal astigmatism for Ks of 7.70@180 and 7.80@90?

Difference between Ks is 0.1mm, then convert to dioptres = 0.50DC.

o Flattest k reading, 7.70@180 or 7.80@90? 7.80@90.

o Be able to calculate corneal astigmatism (CA) and lenticular astigmatism (LA) if given Ks and

spectacle prescription