Refraction

Question 1

Subjective Refraction

Answer 1

An attempt to determine, by trial and error using the patient’s cooperation, the combination of lenses that will provide the best-corrected visual acuity.

Question 2

What conditions are required for Subjective Refraction?

Answer 2

Conditions that mimic the patients natural viewing experience.

Question 3

What is the Best Vision Sphere?

Answer 3

This can be defined as the highest plus sphere that gives the best VA.

Question 4

What techniques do we have available for subjectively finding BVS?

Answer 4

1. Can give a lot i.e. fog vision to 6/12 then reduce.
2. Ducochrome
3. Presentation Technique.

Question 5

What order should Cyl Power and Cyl Axis be corrected and Why?

Answer 5

Axis before Power

Because you can find the axis without the right power, but you cannot find the right power without the right axis.

Question 6

What is the relationship between Cyl Power and Sph Power?

Answer 6

For every -0.50DC increase in Cyl Power, increase Sphere power by +0.25DS.

Question 7

What are some advantages of Binocular Subjective Refraction over Monocular?

Answer 7

1. It is faster than Monocular Refraction
2. It does not cause Spherical Aberrations from pupil dilation.
3. It does not cause Latent Nystagmus
4. It does not stimulate Cylophorias leasing to Cyl Axis errors.

Question 8

What is 1 disadvantage of Binocular SR?

Answer 8

It is not good for patients with highly dominant eyes.

Question 9

What is the purpose of Binocular Balancing?

Answer 9

During Monocular Refraction Occlusion of the eye not being refracted Proximal Accommodation is stimulated.

If Accommodation is not controlled, an imbalance in Accommodation can be created between the 2 eyes causing the patient to experience Asthenopia when wearing their final Rx.

Question 10

What factors may cause you to alter a Cycloplegic Refraction before prescribing and how would you alter the Rx?

Answer 10

1. If Px is ESO and HyperP =
   Prescribe Minimum Plus for Compensation
2. If Binocular Instability =
   Prescribe Full
3. Esotropia under 4yrs =
   Prescribe Full
4. If Px is Older than 4 and First Time Rx =
   Prescribe closer to Manifest Refraction
5. As a minimum for Px less than 4 =
   Reduced Rx by +0.50 for Tonus

Question 11

How do children’ss eyes develop refractively?

Answer 11

1st Yr = Hyperopia +2.00D
3-5 Yr = Length of globe increases leading to Emmetropisation.
6+ Yr = Mostly Emmetropic
Myopic > Hyperopic