Tests done on phoropter Flashcards
Describe the steps in doing the clock chart test
- complete the ret and record the net finding
- remove any cylinder that may have been in the phoropter
- Fog the eye to 20/40 with spherical lenses
- Project the clock chart target
- Ask pt to tell you which time is the darkest and sharpest (if all the lines are the same, there is no cyl and stop the test)
- Take the smaller number and x by 30 and set cylinder axis to this value
- If you get similar darkness and sharpness between diff times x the smaller numbers by 30 and put it somewhere in between the values
- Add -0.25 cylinder to the axis you have set on the phorphter that you got from your findings and keep adding cylinder as long as the pt tells you the original “time” is darker and sharper.
- Stop when all the lines are equally sharp or when a diff time becomes darker
What does the near testing suite (FCC/NRA/PRA/ vergences/phorias) look for?
- Where the eyes are focused when fixating a near target (looks for lag/lead of accommodation)
- How much accommodation the patient has
- How efficiently can the patient use their accommodation
- how the eyes are aligned
- how well do both the eyes work together
What does it mean if you get a really high NRA value?
you have probably overminused the patient
What dose it mean to get a really high FCC result
you have overminused the patient
what does it mean if you get a negative FCC result
the patient has a lead of accommodation which is rare and they may need VT
To accurately predict the refractive error from the VA, you need to know all of the following
- distance VA
- near VA
- patients age & epidemiology
- patient’s habitual rx
When reduced vision is only at near or only at distance what does this mean?
That the reduced vision is to due a refractive error change that is spherical only because an astigmatic refractive error would have adversely affected vision at all viewing distances
what is the net near?
carrier (distance rx) + add
For a patient who is a hyperope and a presbyope you would add more plus power in the ____ only
carrier (distance rx)
what does eggers chart tell us about predicting cylinder?
every line =0.50 D change
Ex:
20/25 = 0.50
20/30 = 1.00
when VA is reduced at both distance and near by the same amount, this means there is a ____change only. So when trying to find the rx, only account for this value using eggers chart.
cylinder
How do you predict an rx for a patient who has reduced vision at distance and near but worse VA at near?
- Look at near VA and figure out how much cylinder change is expected.
- Look at distance VA and figure out lines of reduction
- Subtract lines of reduction at near from distance.
- Total line reduction equals the change in the spherical rx
How do you predict an rx for a patient who is a hyperope, who has astigmatism and is also a presbyope whose vision is more reduced at near than at distance?
- Calculate the lines of reduction at distance and figure out the value
- Calculate the lines of reduction at near and figure out the value
- Take the difference between the lines of reduction at near and at distance
- Total reduction value gets added to whatever the add power is
- The value of lines of reduction at distance gets added to their distance rx.
How do you predict an rx for a patient who is a myopic presbyope?
- Look at near VA and assume you will have to increase the habitual NET NEAR by PLUS sphere using eggers chart
- Look at distance VA and assume you will have to change the carrier by an amount of minus sphere from Eggers chart
- Calculate the add power by taking the difference between the net near and carrier
