1.During A-scan biometry, a one diopter IOL power error could 

result from an axial length error of:

a. 0.04 m

b. 0.4 mm

c. 1 mm

d. 4 mm

e. 8mm

AnswerAnswer:b

A 0.4mm compression error can result in a 1 diopter 

error in the calculated IOL power.

..

2. During A-scan biometry, corneal compression from excessive 

pressure from the probe will:

a. have no affect on the measurement

b. cause an artificial shortening of the axial length

c. cause an artificial lengthening of the axial length

d. distort the lens

e. damage the probe 

AnswerAnswer: b

..

3. Corneal compression can be suspected by comparing  the 

following readings between scans:

a. anterior chamber depth

b. corneal thickness

c. iris thickness

d. lens thickness

e. posterior chamber depth

AnswerAnswer: a

The A-scan gives a read-out for anterior chamber depth(ACD), 

lens thickness, and total eye length. The normal ACD reading 

is between 2.5 and 4 mm.  Therefore, if the ACD reads 3.2, 3.3, 

3.2 on three measurements, and then reads 2.6 on the fourth, 

the 2.6 may result from a compressed cornea and deviate from 

the measurement.

.

4. Which formula is considered to be most accurate for eyes 

between 22 and 26 mm long?

a. Holladay

b. Hoffer Q

c. SRK/T

d. SRK

e. regression

AnswerAnswer: a

.

5. During a cataract operation, there was posterior capsule rupture 

and an intraocular lens has to be implanted in the sulcus (assuming

the power was not changed). This will result in:

a. no change in the post-operative power

b. myopic shift

c. with-the-rule astigmatism

d. hypermetropic shift

e. irregular astigmatism

AnswerAnswer: b

The lens is placed more anteriorly and therefore 

results in myopic shift.