Subjective Refraction Flashcards
Why perform a subjective refracton?
- To determine a Rx through which the patient can see comfortably
- Assess the patient’s blur discrimination
- Because you are not refracting an eyeball. They’re a real person
- When you can’t perform objective testing due to: Media opacities or pinhole pupils
What happens where the vertical rays focus? And what is it called?
The image has no height and infinite width
- Horizontal Focal Line
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What happens where the horizontal rays focus? And what is it called?
The image has no width and infinite height
- Vertical Focal Line
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What is the dioptric midpoint between the two focal lines called?
Circle of Least Confusion (COLC)
What does the progression from where the horizontal rays focus to where the vertical rays focus look like?
Where would a 60 degree focal line be produced?
Where the 150 degree rays focus
How do plus lenses move the focal line?
Plus lenses move the focal lines anteriorly where the rays focus
How do minus lenses move the focal line?
Minus lenses move the focal lines posteriorly where the rays focus
What is the spherical refractive error for a myopic or non accommodating hyperope that sees at 20/30?
0.50D
What is the spherical refractive error for a myopic or non accommodating hyperope that sees at 20/40?
0.75
What is the spherical refractive error for a myopic or non accommodating hyperope that sees at 20/60?
1.00
What is the spherical refractive error for a myopic or non accommodating hyperope that sees at 20/80?
1.50
What is the spherical refractive error for a myopic or non accommodating hyperope that sees at 20/120?
2.00
What is the spherical refractive error for a myopic or non accommodating hyperope that sees at 20/200?
2.50
What are the two common ways to perform cylinder refinement?
- Jackson Cross Cylinder JCC
- Fan Chart
If minus cyl axis (red dots) like at 180 on a JCC where is the power?
The power is VERTICAL
What is the target during JCC?
One or two lines above the best VA or Verhoeff Rings
How is the JCC placed if you during retinoscopy you determined the axis to be 90 degrees?
The JCC wheels will be at 90 with the red and white dots being +/- 45 degrees
How do you move the JCC when the pt tells you that they look position one or two on their first response on axis refinement?
Turn the cyl axis by 20 degrees towards the RED dot
How do you move the JCC when doing cyl refinement?
You place the “P” on the axis you just found
What do you do if the pt prefers the red dots for cyl refinement?
Add more minus
What do you do if the pt prefers the white dots for cyl refinement?
Add more plus
If you correct the cyl by -0.50D what do you do to the sphere?
You add +0.25D of power to the sphere
If you correct the cyl by +0.50D what do you do to the sphere?
You add -0.25D of power to the sphere
What happens to the focal lines when you change cyl with minus cyl?
You are moving the position of the FRONT focal line while keeping the back focal line stationary
What does sphere power do to the interval of strum?
It moves the ENTIRE interval of strum
Where does the fan chart do to focal lines?
The fan chart places the back focal line on the retina
What does the JCC do with the focal lines?
The JCC keeps the COLC on the retina
How much uncorrected astigmatism is found on a patient with a VA of 20/25?
0.50D
How much uncorrected astigmatism is found on a patient with a VA of 20/30?
1.00D
How much uncorrected astigmatism is found on a patient with a VA of 20/40?
1.50D
How much uncorrected astigmatism is found on a patient with a VA of 20/60?
2.00D
How much uncorrected astigmatism is found on a patient with a VA of 20/80?
3.00D
How much uncorrected astigmatism is found on a patient with a VA of 20/120?
4.00D
How much uncorrected astigmatism is found on a patient with a VA of 20/200?
<4.00D
Before performing fan chart you have the following findings:
After finding best sphere the VA of the pt is 20/30 how much uncorrected astigmatism do they have?
How should you adjust the sphere?
What do you do before putting up the fan chart?
Ie: +3.50-1.50x060
They most likely have 1.00D of uncorrected astigmatism
Add +0.50D to the sphere
+4.00-1.50x060
Take out the cyl so now in the phoropteris +4.00sph then you can put up the fan chart
If the pt says the lines on the fan chart all look equally dark what does this mean?
It means the pt has no astigmatism or the COLC is on the retina
Which focal line is nearest the retina if the Rx= -0.50-2.00x030?
0.50D along the 30 meridian and 2.50D alone the 120 meridian
Least ametropic meridian is 30 degree
120 focal line is closest to the retina
If the Dr. sees an angle of 120 what angle does the pt see?
180-X
180-120= 60 degree angle
If Rx= -0.50-2.00x030? Which focal line will be nearest the retina for the patient’s perspective?
120 focal line is closest to the retina for the Dr thus the focal line nearest the retina for the pt will be 180-120= 60 Focal line
This would be the line they report as seeing on the fan chart
What is the meridian of the Rx if the patient reports that the clearest focal line is 30 degrees?
Focal line nearest the retina for the Dr is at 180-30= 150 Focal line for the Dr
Meridian= 150+/- 90= 60 Meridian
Their Rx will be ___-____x060
What can you also do with fan chart if all the lines is too much for the pt?
You can introduce blocks with the block lines at the axis the pt wants and you keep adding minus cyl till both blocks look equal in darkness
What do you do if during the block test you placed the COLC on the retina rather than correcting the astimatism?
When you perform +1.00sph check one block will appear more clear so you have to re check the cyl power
What are the check tests you can peform?
+0.50sph
+1.00sph
Duochrome (Biochrome test)
If you add +1.00 what VA should the be reading?
~20/50 in between 20/40-20/60
What will a hyperope report for the duochrome test?
Green appears clearer/darker
What will a myope report for the duochrome test?
Red appears clearer/darker
What is the goal of binocular balancing?
To ensure that accommodative stimulus in each eye is equal.
How would you binocular balance a pt who needs OD: +3.50 OS: +2.50
OD: +2.50 OS +2.00
- Now both eyes are both 0.50 hyperopic
Should you balance a presbyope?
Yes! Need to make sure they need the same add in each eye
What’s the difference between monocular/ binocular viewing?
The eyes are in different position in monocular vs binocular viewing= phoria
What is it called if the eye are underconverged in monocular viewing? How does this affect binocular viewing?
Monocular they are exophoric thus under binocular they have to converge more
If the pt is exophoric what happens when you occlude an eye? What happens when you uncover the eye to make them binocular again?
The eye turns out
The eye turns back in when the occluder is being removed
What type of accommodation reaction does an exophoric patient have?
The eyes have to converge more -> more accommodation when binocular
What are binocular balancing techniques?
- Successive alternate occlusion
- Vertical prism dissociation
- Humphriss contrast
- Septum Technique “Turville’s infinity balance”
- Polaroid techniques “Vectograph”
What is the best technique for ambylopes?
Humphriss Immediate Contrast
What is the problem with Successive Alternate Occlusion (SAO)?
What is the general protocol for this test?
- Fog each eye by +1.00
- Alternatively cover each eye and ask with eye is less blurred
- Add fog till equally blurry
- Reduce fog to get best VA
Problem: Pt is MONOCULAR
What is the problem with Vertical Prism Dissociation (VPD)?
What is the general protocol for this test?
- Fog each eye by +1.00
- 6 BU in one eye and 6 BD in other eye
- Add fog until equally blurry
- Remove prisms and reduce fox for best VA
Problem: Pt is NONFUSED
What is the problem with Humphriss?
What is the general protocol for this test?
- Fog one eye
- Pt views duochrome and responds for unfogged eye
- Test the next eye
Problem: Blurred vision so central 2-3 of retina is blurred
- Parafoveal and outer retina in each eye is unaffected
Pt is fused and binocular :)
What is the general protocol for Septum (Turville Infinity Balance)
- Fog each eye by +1.00
- Which side of line is less blurred (OD or OS letters
- Add fog till equally blurry
- Remove septum and reduce fog for BVA
How does vectograph work?
Filters at different transmission axis only allow the transmission of light in that direction thus if the letter is polarized at an opposite direction they will only reflect light at that direction so when viewed with opposite transmission axis filters the letter will appear black
The rectangles are seen by both eye which allows the pt to be FUSED & BINCOLUAR
How will these letters look? What is happening here?
F is only allowing in/ reflecting light at 45 and the filter is only transmitting light at 135 thus the F will appear black on a right background for the right eye
The L is only allowing in/ reflecting light at 135 and the filter is only transmitting light at 135 thus the L will appear white on a white background
What is the polaroid/ vectograph protocol?
- Introduce polarized target/ filters
- Fog each eye by +1.00
- Which letter is less blurred?
- Add fog to less blurred
- Reduce fog until BVA
How is polarized duochrome performed?
The left two circles are seen by the right eye and the right two circles seen by the left eye
- Adjust the power for each eye till the red and green are equal
No fogging lenses needed here
