Assigned Readings:
Griffin; pp 34-44
Richman (Bernell Guide); pp. 8-14
I. Introduction: Today's laboratory will reinforce some key elements of accommodative testing and introduce a few new techniques to aid in the diagnosis of accommodative function.
II. Tests utilized to measure accommodative ability. Some of these tests are included in a standard complete primary care evaluation (already covered in pre-clinic courses).
-Amplitude of accommodation: may be monocular or binocular
Monocular Accommodative Amplitudes: the dioptric limit to which the patient can maintain clarity of a small target (20/20)
1. Donder's push up method : the accommodative demand of the small (at acuity threshold) nearpoint target is changed in a ramp fashion as the target is moved toward the patient, who views the target monocularly
- closer target: increased accommodation
2. minus lens method : the accommodative demand of the small nearpoint target is changed in a stepwise fashion as minus lenses are introduced to the patient monocularly
-minus lenses: increased accommodation
Binocular Accommodative Amplitudes: the dioptric limit to which the patient can maintain clarity AND FUSION of small print as the accommodative demand is changed in a stepwise fashion.
1. Donder's push up method : the accommodative demand of the small nearpoint target is changed as the target is moved toward the patient. The net vergence demand also changes as the target is moved.
-increased accommodation binocularly WITHOUT SUPPRESSION -increased accommodative convergence
-increased proximal vergence
-increased fusional vergence (to maintain fusion)
2. Minus lens method : the accommodative demand of the small nearpoint target is changed as minus lenses are introduced to the patient binocularly. The total vergence response, however, must remain at a steady state (to maintain fusion of the stationary target).
AS MINUS LENSES ARE APPLIED:
-increased accommodation binocularly WITHOUT SUPPRESSION
-increased accommodative convergence
-increased fusional divergence to maintain fusion of the stationary target
- PRA/NRA : a small step change in binocular accommodative demand (by - or + lenses) to a stationary accommodative target. While the accommodation demand increases, the net vergence output must remain in a steady state.
1. PRA (minus lens): stepwise increase accommodation demand binocularly WITHOUT SUPPRESSION
- increased accommodative convergence
-increased fusional divergence to maintain fusion of the stationary target
2. NRA (plus lens): stepwise decrease accommodation demand binocularly WITHOUT SUPPRESSION
- decreased accommodative convergence
-increased fusional convergence to maintain fusion of the stationary target
-Accommodative Facility: the ability to repeatedly shift accommodative response rapidly and in a jump-step.
Monocular Accommodative Facility:
1. Near/far accommodative "rock": a jump accommodative stimulus is created as the patient is asked to read small print at distance and then rapidly clear small print held at near point. This test is completed over a one minute time interval
- under MONOCULAR testing conditions; accommodative skills are isolated.
-shift to near target: rapid jump step increase in accommodation
-shift to distance target: rapid jump step decrease in accommodation
2. Plus/minus lens method: plus and minus lenses (usually +/- 2.00D) are introduced to the patient as they attempt to read a sequence of small (20/20-20/25) letters at 40 cm. This test is usually completed in a minute time interval
- under MONOCULAR testing conditions; accommodative skills isolated. The lenses force a jump change in accommodative response
-plus lenses: decreased accommodation in a jump step
-minus lenses: increased accommodation in a jump step
Binocular Accommodative Facility: under BINOCULAR testing conditions; both the accommodation and vergence mechanisms are at play.
1. Near/far accommodative "rock": a congruous jump step demand change to accommodation and vergence
- shift to near target: increased accommodation binocularly WITHOUT SUPPRESSION
-increased accommodative convergence
-fusional vergence adjustment as needed to maintain fusion)
- shift to distance target: decreased accommodation binocularly WITHOUT SUPPRESSION
-decreased accommodative convergence
-fusional vergence adjustment as needed to maintain fusion
2. Binocular plus/minus lens facilities: a rapid change in accommodation and vergence demands
AS -2.00 LENSES ARE APPLIED:
-increased accommodation binocularly in a jump step WITHOUT SUPPRESSION
-increased accommodative convergence
-increased fusional divergence to stationary target
AS +2.00 LENSES ARE APPLIED:
-decreased accommodation binocularly in a jump step WITHOUT SUPPRESSION
-decreased accommodative convergence
-increased fusional convergence to stationary target
III: Alternative Methods Of Dynamic Retinoscopy: An additional group of procedures (besides MEM) conducted at near point to:
-assesses the dynamic relationship between vergence and accommodation
-assesses the suitability of a tentative add
-assesses the balance and accuracy of static retinoscopy
- Book Retinoscopy
1. METHOD:
- working distance should be habitual reading distance
- age appropriate words or pictures are suitable near targets. It is best to have a graded series of reading passages.
- the direction and color of the red reflex are observed as the patient reads passages at their reading level.
- some practitioners will also use reading passages below and above the patient’s grade level
Motion (+0.50 to +0.75 (+0.25 to -0.25) (-0.75 to +2.50 Color Brightness
Below Level At Level Above Level
Reflex Direction increased with Near neutral varies from
motion (+.5 to +.75) (-.5 to +.25) against motion to high with motion (-.75 to +2.50)
Reflex Color white to pink pink to pink brick red
Reflex Brightness bright medium to bright bright to dull
- reflex color is bright and white when the words are understood.
- reflex color is more pink and dims slightly if the patient is struggling to comprehend a word or passage
- reflex color is dull and brick colored when the patient has given up on comprehending a word or reading passage
- lag of accommodation is neutral to a lead when a patient is making a cognitive effort to understand the reading
- lag of accommodation is greater when a patient is able to understand the reading without much cognitive effort or has given up on the task
- plus probe lenses may be used to assess plus acceptance. these lenses should be placed over both eyes before conducting the test. some practitioners allow the
-patient to read with probe lenses for a few minutes before re-measuring the lag of accommodation
- Stress point retinoscopy: (best used with a spot retinoscope).
1. METHOD:
- The doctor performs retinoscopy (@ X 090 and X 180) while moving a small target (sphere) towards a patient. The magnitude, color and brightness of the reflex is noted
- The inward movement continues to a point where a "flash" in the red reflex is seen
- The flash should occur at about 4 inches in front of the patient
- A remote position of the stress point indicates near point dysfunction
- A variety of plus probe lenses are then used to see what lens combination restores the expected 4 inch "flash point"
2. RECORD:
- the stress point distance
- the color and brightness of the red reflex
- any differences between the 2 eyes
- any differences @ 180 and 090
- the effect of plus lenses stress point distance
IV. A Word About Suppression Checks: A few of many methods to monitor the presence of significant central suppression
1. Physiological diplopia: because Panum's fusional area is quite small in primary gaze, a small target introduced at a 20 cm. working distance while the patient reads letters at 40 cm. should be diplopic, if suppression is NOT taking place. This is the simplest way to monitor suppression and may be used when the patient is behind the phoropter.
2. Polaroid cancellation: polarized filters may be placed over letters so that one set will turn black if suppression takes place in either eye (Polaroid glasses must be worn). Cross polarization will result in some letters turning black with suppression of one eye.
3. Color cancellation: red and green filters may be placed over letters so that color cancellation will blacken certain letters if suppression of either eye takes place(red/green glasses must be worn here!).
USE SUPPRESSION CHECKS WHENEVER COMPLETING BINOCULAR TESTING OR THERAPY!!!
V. A Word (Or Two) About Color Cancellation
1. if the background and figure are seen as the same color through a particular filter, then it will not be visible to that eye (like a polar bear in a snow storm).
2. if the background and figure are seen as different colors through a particular filter, then it will be visible to that eye (like a red polar bear in green snow).
- An example: a red target is printed on a white background. The patient wears a red lens over O.D. and a green lens over O.S. What does the patient see?
Background Figure Figure Seen/Not Seen
O.D. RED RED Not Seen
O.S. GREEN BLACK Seen
VI. Normal and abnormal findings:
A. Accommodative facility
- plus/minus lenses: Several studies, reviewed in Griffin, pg 40-43, indicate the following:
EXPECTEDS
monocular: 10-12 cycles /min.
binocular (with suppression checks): 7-8 cycles/min.
B. Dynamic retinoscopy EXPECTED
1. Nott retinoscopy/MEM +0.25 to +0.50 lag (lags at or above +0.75 or any lead of accommodation is not acceptable)
2. Book Retinoscopy At reading level:
Color: pink to white
Brightness: med.to bright
Lag: near neutral
3. Stress point Retinoscopy "flashpoint" @ 4 inches
C. Kinetic cover test an "eso shift" of less than 5 prism diopters
1. What sort of questions should you ask in a case history to help discriminate between the various accommodative dysfunctions?
2. Would you expect any difference between results of binocular accommodative facility without suppression checks and binocular accommodative facility through suppression checks? Would you expect even results between the two tests in a person with severe convergence or accommodative dysfunction? WHY?????
3. A patient is reading small black print on white paper through a red/green bar reader (a clear acetate sheet that has alternating stripes of red and green. The patient is wearing r/g glasses with the red lens over the right eye.
a. the patient only sees letters through the green bars; the red bar has turned black. Which eye is currently being suppressed?
b. another patient has no suppression as you introduce +2.00 lenses binocularly, but the green bar turns black if -2.00 lenses are introduced binocularly. This patient has no trouble on monocular accommodative testing. What do these results say about this patient's binocular vision skills (accommodation AND vergence)?
4. An accommodative insufficiency pt. has a lag of accommodation of +1.00. With a +1.25 probe lens, the lag is now +0.50. What can be said about plus acceptance? Is an add appropriate?
5. An accommodative excess pt. has a lag of accommodation of +0.50. With a +1.00 probe lens, the lag is now -0.25. What can be said about plus acceptance?
6. A patient has a lag of accommodation of +1.50. With a +1.00 probe lens, the lag is now +1.50. What can be said about plus acceptance?
7. A patient in the fourth grade has a lag of accommodation of +1.50 and a brick red reflex when reading grade appropriate material on book retinoscopy. Interpret the possible implications of this result.