Subject And Objective Refraction II

Question 1

Photo-refraction

Answer 1

The refractive state of the eye is assessed by simply photographing the pattern of light returned from the pupil of the eye. Photo is quantitative related to the magnitude of the refractive error

Question 2

Advantages of photo-refraction

Answer 2

• refracting both eyes simultaneously

- requiring only an instant of the subjects attention

Question 3

Application of photo refraction

Answer 3

• refraction of infants/children
• study of anisometropia
• Dx astigmatism

Question 4

What is the equation for photorefraction

Answer 4

PRE=d/(2xpxa)

PRE=magnitude of the refractive error relative to the postion of the camera
A=distance from camera to subject pupil
d=diameters of double-pass point spread image
P=pupil diameter

Question 5

Photorefraction for hyperopic

Answer 5

Red rays will appear in the periphery and blue in the central of the point srepad (far point lies beyond the camera lens)

Question 6

Photo refraction for myopic eyes

Answer 6

Blue rays will appear in the periphery and red in the central of the point spread (far point of the subjects eyes lies between the camera lens and the subjects eye)

Question 7

Objective autorefractors

Answer 7

-good starting point

Question 8

What is the gold standard of refraction

Answer 8

Phoropter

• poor repeatability
• not comprehensive

Question 9

Gives the comprehensive description of the eyes optical aberrations, from which the retinal image can be computed using the theory of physical or geometrical optics

Answer 9

Shack Hartmann aberrometer

Question 10

What are 80% of the eyes defects that can be corrected with glasses

Answer 10

Lower order aberrations

Question 11

What is 20% of defects of the eye what can fixed with LASIK

Answer 11

Higher order aberrations

Question 12

What does an aberrometer/ autorefractor not take into consideration

Answer 12

Neural factors

Question 13

Problems we run into with objective and subjective refractions

Answer 13

• chromatic aberrations
• stiles-crawford affect
• instrument myopia
• maximum plus technique
• measurement plane of the instrument

Question 14

How do we avoid confounding factors when we are trying to compare objective and subjective techniques

Answer 14

Compare WF, and VA refractions when both are measured with the same wavelength, same pupil size, and without accommodation

Question 15

What should we examine when comparing WF and VA refractors

Answer 15

Accuracy and precisions

Question 16

Subjective acuity refraction and different pupil size

Answer 16

Refractive error for subjective method does not change appreciably with the pupil dilates

Question 17

Objective refractions for different size pupils

Answer 17

For 3mm pupil
-hyperopic

For 6mm pupil
-myopic

Question 18

Why does pupil size matter in objective refractions for aberrometer?

Answer 18

Because it catches aberrations and subjective does not

Question 19

Accuracy of WF for a 6mm pupil

Answer 19

• all metrics are the same when the HOA is small

- different metrics give different refractions when HOA are large

Question 20

Accuracy of autorefractor/aberrometer

Answer 20

+/- 1/8 accuracy

Question 21

What is the precision of autorefractor/aberrometer

Answer 21

0.3D