Prac Exam Theory - Wk 9

Question 1

In fan and block (F&B): When Fogging, how much do we fog by?

Answer 1

If estimated astig -1.00DC or less: just fog by +0.50

If estimated astig -1.00DC or more: fog by +0.50 + 1/2 estimated astig

• this is so we can keep the posterior focal line on or in front of the retina

Question 2

(F&B): If VA with BVS is 6/9 for a 20 year old, what is the expected amount of astig., and how much fog is required?

Answer 2

3 line difference from 6/4.8. 0.50DC per line

0.50 x 3 = 1.50 (above 1)

Fog = 0.50 + 1/2(1.50) = +1.25DS fog

Question 3

(F&B): If VA with BVS is 6/15 for a 20 year old, what is the expected amount of astig., and how much fog is required?

Answer 3

5 line difference from 6/4.8. 0.50DC per line

0.50 x 5 = 2.50 (above 1)

Fog = 0.50 + 1/2(2.50) = +1.75DS fog

Question 4

(F&B): If VA with BVS is 6/7.5 for a 20 year old, what is the expected amount of astig., and how much fog is required?

Answer 4

2 line difference from 6/4.8. 0.50DC per line

0.50 x 2 = 1.00 (NOT above 1)

Fog = +0.50 only

Question 5

(F&B): Advantage and Disadvantage of Fan and Block?

Answer 5

Adv.: accomm. is well control as px fogging places COLC and focal lines in front of retina

Disadv.: less accurate at determining small cylinders than JCC. Also only available on wall charts

Question 6

(F&B): Where does the image focus for myopia and hyperopia?

Answer 6

Myopia: in front of the retina
Hyperopia: behind the retina

Question 7

(F&B): What is ‘with the rule’ (WTR) astigmatism?

Answer 7

If you look at a cross target, vertical lines appear clearer, meaning the horizontal meridian is closer to the retina

Question 8

What is the flow of events from the beginning of subjective refraction until the correction of Astig?

Answer 8

1. Get aided and unaided vision (for rough guide)
2. Use ret to determine correction
3. BVS refinement to place COLC on retina
4. Use JCC or Fan and Block to shrink interval of sturn

Question 9

What do the colours mean on duochrome?

Answer 9

If green target clearer: add more positive

if red target clearer: add more negative

Question 10

Why does duochrome not work well on older patients?

Answer 10

Because of yellowing of the lens with age

Question 11

What are the 2 main techniques for determining Astig?

Answer 11

1. Fogging method (Fan and Block)

2. Jackson X-cyl method (JCC)

Question 12

(F&B): With V-chevron, what do you do if px sees multiple lines clearer?

Answer 12

If 2: choose between

if 3: choose middle

Question 13

What is the aim of Binocular Balancing?

Answer 13

To balance/equalise the accommodation of the 2 eyes. Also to relax accommodation (humphriss)

Question 14

What if VA is 6/9 or worse in subjective refraction? (assuming you ret’d right etc)

Answer 14

Try pinhole
If improvement: could be uncorrected refractive error (likely) or could be paracentral medial opacity (e.g. congenital cataract)

If no improvement: could be STRAB, amblyopia, pathology

[But really though what you’d actually do is IF worse than 6/9.5 chuck out ret and do BVS or return to ret but that may take too long.] update: Chuck out cyl component if ret worse than 6/9.5 but keep sphere for BVS adjust. Then do JCC for cyl

Question 15

When is Binocular Balancing not effective?

Answer 15

• when px has no functional binocularity

- when px older therefere no active accommodation

Question 16

What do you do if Binocular Balancing is not effective?

Answer 16

Use monocular findings

Question 17

List the 5 basic techniques of Binocular Balancing in the order of increasing sensitivity

Answer 17

1. Successive Alternate Occlusion
2. Vertical prism dissociation
3. Blurring or Fogging techniques (humphriss)
4. Septum techniques
5. Polaroid techniques

Question 18

How does SAO (successive alternate occlusion) work?

Answer 18

compare 2 views monocularly with alternating occluder. Use lenses to equalise vision. Add +0.25 to clear eye until reversal obtained

Question 19

How does VPD (vertical prism dissociation) work?

Answer 19

dissociate image with ~2-3 opposite direction vertical base prisms. Px views 6/9 line. Add +0.25 to clearer line

Question 20

What is the advantage of Humphriss fogging?

Answer 20

• not only does it equalise/balance accommodation, but it also fully relaxes accommodation. This means that there is usually little need to do binocular addition afterwards [BUT STILL DO IT IN EXAM]
• Also its simple + accurate

Question 21

Can we perform Binoc. Balance in px with R 6/6 L 6/12? What if STRAB with one eye suppressed?

Answer 21

Yes we can, but you’d need to fog right eye a lot (this is my answer, could be wrong)

If STRAB with suppress than definitely not because they have no functional binocularity in the first place

Question 22

Do we perform binocular balancing on older patients?

Answer 22

No! because they have no active accommodation