Additional Refraction Methods

What are the additional Astigmatic Tests (besides JCC)?

1. Extending the range of the phoropter

2. Direct Cylinder

3. Line Astigmatism (axis only)

4. Clock Dial

5. Keratometry + Predicting Refractive Astigmatism

6. Dot pattern chart

7. Stenopaeic Slit

When is extending the cyl range of the phoropter, where do you add the additional lens?

into the eyehole with the arrows parallel to axis arrow

When is extending the cyl range of the phoropter, what lens do you add?

-2.00 DC

Why do some patients not respond well to JCC?

can't look over the blur present

How do you test cylinder directly?

1. remove JCC and start with cyl power found objectively

2. Refine axis by rotating wheel until patient sees the most clear (approach from both sides to bracket)

3. refine power by showing 2 choices in -0.25 DC steps

4. Maintain SE

What does the line astigmatism test give us?

axis of astigmatism correction

In what patients would you do a line astigmatism test?

in patients who are not good candidates for objective starting measurements like retinoscopy or autorefraction

What is a line astigmatism test?

subjective test that estimates the axis of astigmatism correction

What would the line astigmatism look like to someone with uncorrected astigmatism??

lines parallel to axis of astigmatism will be most out of focus

If someone has with the rule astigmatism, what lines on the line astigmatism test will look out of focus?

horizontal lines

If someone has against the rule astigmatism, what lines on the line astigmatism test will look out of focus?

vertical lines

What do you instruct the patient to do during the line astigmatism test and what does it mean?

have the patient identify the line that is clearest

axis is 90º away

How do you perform the clock dial test?

1. Start with only sphere power in the phoropter

2. Present clock dial target and add sphere until all lines are blurry

3. decrease plus one click at a time until ONE set of lines become clear

4. The smallest number on the set of clear lines x 30 is the axis

5. Set the cyl wheel to their axis and add cyl power until the line that was most blurred matches the appearance of the line that was most clear

What does it mean if your patient reports that all the lines on the clock dial test became clear at the same time?

patient is a sphere

If your patient reports the 12/6 line is clearest, what is their axis?

6 x 30 = 180º

What do you NOT do during clock dial test?

adjust sphere for SE

Why do you not want to adjust there sphere for SE during clock dial test?

If the circle of least confusion was on the retina, the two principal meridians would look the same and the test would not work

During the clock dial test which meridian are we trying to keep on the retina?

the most plus meridian

What is manual keratometry?

objective measurement of the anterior curvatures of the cornea

What astigmatism does keratometry give us?

corneal astigmatism only

How do we adjust keratometry astigmatism numbers to get refractive astigmatism?

add -0.50 x 090 to account for the lens

How do you get the magnitude of astigmatism with manual keratometry?

difference in power between the two meridians

What is an advantage to manual keratometry (+topography)?

allows us to asses the quality of the corneal refracting surface

What is refractive astigmatism?

total astigmatism, combining the corneal and lenticular astigmatisms

Which surface has the greatest variability across eyes for astigmatism?

cornea

If you get a corneal astigmatism at an axis that is not 180 or 90, how do you factor in lenticular astigmatism?

hard without mathematical aid, just ignore and use their corneal astigmatism

What is the stenoapeic slit used for?

to determine the axis of astigmatism

What are alternatives to binocular prism balance?

Vectographic balance

Dissociated Bichrome Balance

Monocular Bichrome Balance

In what patients would you do the vectographic balance?

patients with large phorias

patents who can see 20/20 with both eyes

patients with no strabismus

patients who suppress and eye and cannot see double with prisms

When is dissociated bichrome balance used?

for patients with unequal acuity between their eyes

How do you perform vectographic balance?

1. display the target (with polarization)

2. dial in +0.50 and the polaroid filter over both eyes r

3. Ask patient to compare left and right images and add +0.25 to whichever side looks clearer

4. Stop when patient reports both sides look equally blurred

5. Patient is balanced, do not adjust sphere of just one eye

How do you perform the dissociated bichrome balance?

1. have both eyes open and isolate a row of letters

2. Add red/green filter and add plus

3. Add prism (3BD OD, 3BU OS) to dissociate patient

4. Have patient look at top chart (right eye) and compare the red/green side, adding lenses until they look equal.

5. Repeat step 4 for bottom chart (left eye)

What step do you not do if you use the dissociated bichrome balance? Why?

do not do binocular subjective sphere because you already know the patient isn't overminused from the balance

How will the patients acuity change after dissociate bichrome balance?

it won't change

When would you use monocular bichrome balance?

when patient supresses an eye and cannot see double

How do you perform monocular bichrome balance?

1. cover one eye and isolate a row of letters

2. add red/green filter

3. add plus until red side looks better

4. ask patient to compare charts, adding +/-0.25 to get both sides to look equal

5. Repeat step 4 for the other eye

What is the best strategy to control accommodation with monocular bichrome balance?

the initial plus you dial in

What step do you not do if you performed monocular bichrome balance?

you do not do binocular subjective sphere because you have already guaranteed you did not over minus the patient

How do yo avoid accommodation during refraction?

1. use the most-plus refractive strategy

2. Use cycloplegic drops

3. Binocular refraction

How does the process of refraction differ if using cycloplegic drops?

same steps as manifest refraction minus binocular balance

When is damp/wet refraction performed?

pediatric patients

latent hyperopes

amblyopes

accommodative spasm, esotropia or high esophoria

before refractive surgery

What part of the prescription is damp/wet refraction usually used for?

sphere only

When would we use binocular refraction?

patients with:

cyclophoria

nystagmus

fluctuations on accommodation

What is cyclophoria?

patients have a 10º or more shift in axis under monocular vs binocular conditions

What is a latent nystagmus?

nystagmus that is apparent on increases under monocular viewing conditions

What are the options of binocular refraction?

Humphriss technique

polarization

septum

What is the Humphriss technique for binocular refraction?

fog the eye not being tested with +0.75-+1.50DS

What patients are the Humphriss technique for binocular refraction used for?

patients with latent nystagmus

What is the polarization slide technique for binocular refraction?

use vectographic slide or borish card to project some letters to one eye and not the other

What is the septum (turville infinity balance) technique for binocular refraction?

physically block a portion of the target for each eye by placing septum in the middle

How much do you want to blur the eye not being tested with Humphriss technique?

20/30-20/40

What binocular balance should you use if you are performing humphriss technique?

one that maintains binocular fusion (like vectographic balance)

What patients would benefit from using a borish card?

latent nystagmus

cyclophoria

How does the septum turville infinity balance work?

septum with two mirrors is placed in front of the patient with acuity charts behind the patient, reflected in the mirror

Why is binocular refraction not the norm?

1. conventional refractive techniques work for majority of patients

2. requires special instruments

3. not pushed in the educational system