Subjective Refracton Flashcards
Where do they focal lines of an image form in a patient with uncorrected astigmatism? (Focal lines) What is in the middle of these lines?
Horizontal rays in front of the retina (image has height with no width)= vertical focal line
Vertical rays behind the retina (image has width with no height)= horizontal focal line
COLC in the dioptric midpoint
What is the purpose of the initial sphere refinement?
COLC on retina
Max plus or min minus that produced best VA
Describe the correlation between VA and spherical error in a myope or non accommodating hyperope. (20/20, 40, 60, 80, 120, 200)
20/20- 0.50D
20/40- 0.75D
20/60- 1.00D
20/80- 1.50D
20/120- 2.00
20/200- 2.50D
What are the possible targets for JCC?
One line above best VA
Two lines above best VA
Verhoeff rings
How do we keep the COLC on the retina during cylinder refinement? Why do we do this?
Everything we change the cyl power by X diopters, we must hinge the sphere by -X/2 diopters
When we change cyl with minus cyl powers the front focal line moves and the back stays constant, sphere moves the entire interval onto the retina
What focal line does the fan chart move?
Back focal line (JCC moves the front)
How do we perform the fan chart?
Start by placing the back focal line on retina
Find BS to place COLC on retina
Estimate uncorrected astigmatism using chart and add PLUS sphere equal to half of estimated astigmatism to place back focal line on retina
Remove the cylinder so only sph in phoropter
Have patient view fan chart (clearest line from their perspective is their axis, indicate focal line closest to retina)
What is the astigmatism uncorrected for each V/A through a BS correction? (20/20, 25, 30, 40, 60, 80, 120, 200)
20/20- 0D
20/25- 0.50D
20/30- 1.00D
20/40- 1.50D
20/60- 2.00D
20/80- 3.00D
20/120- 4.00D
20/200- <4.00D
What is the difference between the doctor perspective and patient perspective?
Doctor- X
Patient- 180-X
What do the patients response on fan chart tell is regarding their meridians?
Tells us the orientation of the emmetropic meridian (or close to it) which must correspond with minus cyl axis
Cyl axis= doctor perspective +/- 90 for meridian
What can we present instead of fan chart for less choices?
Blocks one matching the orientation of clearest line and the other 90 degrees away
How can we ensure that our fan chart/block cyl refinement actually corrected the astigmatism and didn’t just put the COLC on the retina?
Fog by +1.00 sph to move interval, blocks should be equally blurred
What check tests can we perform during 2nd BS refinement?
+0.50 sph (turns patient into .50 myope)
+1.00 sph (turns patient into 1D myope)
Duochrome (blue bends best, hyperope green clear, myope red clear, emmetrope with be equal)
What is the goal of binocular balance?
Ensure that the accommodative stimulus in each eye is equal (equal amount of uncorrected ametropia in each eye)
How we binocular balance a presbyopia patient?
Yes because you want to ensure that they will need the same presbyopia addition in each eye
What is it called when the eyes are in different position under monocular versus binocular viewing?
Phoria
Describe successive alternate occlusion (binocular balance). What is the problem with this method?
Fog by +1.00
Alternatively cover each eye and ask which is clearer
Add more fog to the less blurred eye until each are equally blurry
Reduce fog OU until max plus Lens give best VA
*problem- patient is never binocular
How do we perform vertical prism dissociation? What is the problem with this method?
Fog each eye by +1.00
Add 6 BU and 6BD
Ask patient if top or bottom image is clearer
Add more fog to less blurred eye until 2 images are equally blurred
Remove prisms and reduce fog OU until max plus lens gives best VA
*problem- patient cannot fuse images (patient eyes are essentially in monocular position)
How do we perform Humphriss immediate contrast?
Fog one eye
Test each eye with the other fogged to determine which line they see clearer
Patient is binocular and fusing
Central 2-3 degrees of retina is blurred since one eye is fogged
Best for patient with differences in BCVA since they are testing one eye at a time
Describe the septum (turville infinity balance) method for binocular balance.
Uses a septum to separate the visual fields
Fog each eye by +1.00
Ask patient which side of the line is clearer
Add more fog to less blurred eye until the 2 images appear equally blurred
Remove septum work down to max plus lens that gives best VA
Describe how we can use Polaroid techniques (vectograph) for binocular balance.
Polaroid only allow transmission in a single plane
Letter with transmission axis opposite of the polarization of the eye will be visible by that eye (black on white background)
Fog +1.00
Add more fog to less blurred eye
Reduce fog, max plus to best VA
Describe how we perform the polarized duochrome binocular balance technique.
Right circle seen by left eye, left circle seen by right eye
No fogging
Adjust so that R=G or same endpoint
