Due to the interest in P.D.s on this forum, I've been looking a little closer at P.D.s in my office.
I've been collecting some data using various methods:
1. mm ruler measuring near p.d. from inner limbus of one eye to outer of the other at 17 inches, adding 2 mm for near pds smaller than 55, 3 mm for near pds between 56 and 62, or 4 mm for near pds over 62 to arrive at a distance p.d. (my traditional method)
2. mm ruler measuring as above except using a transilluminator fixation light at 17 inches and measuring from corneal reflex to corneal reflex.
3. measuring monocular p.d.s using essilor pupillometer set at optical infinity , subtracting for near p.d.s based on #1 above assumptions, and noting any visible decentration of the corneal reflex from the center of the pupil.
4. recording the binocular p.d. measurement my autorefractor (topcon krp 8000 pA) gives me and noting the decentration of the fixation point from the center of the cornea.
I've recorded 10 of these sets so far and will tabulate them when I get enough to be statistically viable, but #10 just now presented me with a quandary.
This gentleman had the following, referring to the numbers above:
1. 73/69
2. 72/68
3. R 37.5, L 34.5 (far p.d.) with nasal displacement of fixation reflex 1.0 on R, 1.5 on L
4. 69 (!) with same nasal displacment of fixation target as above (I believe this should be a distance p.d. the way the instrument is used)
I tend to think that the autorefractor is off, because most of the time it pretty much agrees with my ruler/pupillometer. Maybe he shifted his head position without my noticing, or maybe it has to do with the apparent displacement of the visual axes noted. I didn't notice the discrepancy until after he departed, or I would have re-run the autorefractor making sure he kept his head position unmoved.
His new rx is approx +1.25 with a 2.25 add and he likes his old PALs.
His Rx from last year was slightly less + and the p.d.s used for his PAL then were R 36 L 34
My inclination is to use the pupillometer measurement of today, but I'm open for suggestions that might arrive here before I finalize the order this evening.
P.D. problem/question
I've been collecting some data using various methods:
1. mm ruler measuring near p.d. from inner limbus of one eye to outer of the other at 17 inches, adding 2 mm for near pds smaller than 55, 3 mm for near pds between 56 and 62, or 4 mm for near pds over 62 to arrive at a distance p.d. (my traditional method)
2. mm ruler measuring as above except using a transilluminator fixation light at 17 inches and measuring from corneal reflex to corneal reflex.
3. measuring monocular p.d.s using essilor pupillometer set at optical infinity , subtracting for near p.d.s based on #1 above assumptions, and noting any visible decentration of the corneal reflex from the center of the pupil.
4. recording the binocular p.d. measurement my autorefractor (topcon krp 8000 pA) gives me and noting the decentration of the fixation point from the center of the cornea.
I've recorded 10 of these sets so far and will tabulate them when I get enough to be statistically viable, but #10 just now presented me with a quandary.
This gentleman had the following, referring to the numbers above:
1. 73/69
2. 72/68
3. R 37.5, L 34.5 (far p.d.) with nasal displacement of fixation reflex 1.0 on R, 1.5 on L
4. 69 (!) with same nasal displacment of fixation target as above (I believe this should be a distance p.d. the way the instrument is used)
I tend to think that the autorefractor is off, because most of the time it pretty much agrees with my ruler/pupillometer. Maybe he shifted his head position without my noticing, or maybe it has to do with the apparent displacement of the visual axes noted. I didn't notice the discrepancy until after he departed, or I would have re-run the autorefractor making sure he kept his head position unmoved.
His new rx is approx +1.25 with a 2.25 add and he likes his old PALs.
His Rx from last year was slightly less + and the p.d.s used for his PAL then were R 36 L 34
My inclination is to use the pupillometer measurement of today, but I'm open for suggestions that might arrive here before I finalize the order this evening.
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