Accommodation. A special word when it comes to the information our visual system takes in at near. Particularly within arm’s length. We say it’s due to a change in the shape of the lens inside the eye, though that’s really an oversimplification. The size of the iris plays a big role too, with its size controlling the amount of light getting through the pupil space in the first place, which controls your depth of focus. For years we measured it with a retinoscope, though I find myself increasingly drawn to our Grand Seiko Open View Autorefractor (OVA) to objectively document what the patient is doing. The OVA give you a real-time pattern that is easy to demonstrate to parents and other professionals.
First I’ll show you a few pictures of the OVA so you get a feel for what I’m referring to.
Here’s the instrument from a side view. Note the open view of the rectangular opening, in this instance having a nearpoint card suspended on a rod at a 33 centimeter viewing distance from the patient’s eyes. The viewing screen tells the examiner when the patient’s eyes are centered.
The patient above has his head on a chin rest, with his forehead positioned against he upper bar. He looks at letters on the nearpoint card and is instructed to keep them clear. For younger children you may use pictures. You can ask the patient questions about the near target if attention is a factor. The examiner can watch the patient’s pupil centered in the viewing screen, and it should constrict as the patient is accommodating.
We typically record distance measures of focus, while the patient is looking through a window across the room. You need enough unobstructed space to make sure the patient isn’t accommodating, but you’ll also be able to judge that by looking at the numbers on the screen as focusing state is being recorded.
So here’s a printout of a representative recording. Right eye <R> is the upper and left eye <L> is the lower. The computer samples five times and then gives its best fit result. We are more interested in the consistency or variability of the five readings than in the best fit data. The printout to the far left has the distance findings. For the R eye, the last four of the five findings are +0.25-0.50cx140-ish, so it’s a good bet that is the “true” distance finding as the best fit singular number under the line shows, and that the accommodative posture was at its resting state. For the L eye, the same holds true except the value is Pl-0.25.
The printout to its right is for near, and it shows accommodative flux for both eyes. No two findings in succession match each other. That flux is more important to us than the best fit singular finding. If you repeat the finding through a tentative nearpoint plus lens addition, and/or yoked prism trial, you can look for increased stability of the accommodative profile. Ultimately the results of vision therapy are aided by progress evaluations showing change in the data from baseline values.
When talking to parents about this, you can demonstrate the data rather than trying to describe what your retinoscope shows which is very valuable and insightful, but relatively abstract to a patient. For the accommodative system, it’s the cardiac analog of stethoscope sounds vs. an EKG printout. One isn’t necessarily a substitute for the other.
A few other applications. When there is pseudomyopia, or accommodative spasm tendencies, the distance findings will show fluctuations in value similar to the near values above, where they will differ from one another by a diopter or more. When the patient has amblyopia, the values between the right and left eyes often differ, because accommodation is usually substandard through the amblyopic eye. Similarly for ABI, or any other condition affecting accommoodation, sequential objective measures that are demonstrable in printout form are very valuable.
Preparing this piece took me back nine years ago to the lovely editorial that Dr. Irwin Suchoff, then editor of the Journal of Behavioral Optometry, wrote about the book from which these concepts are derived, and what a joy it was to work with my co-author, Dr. Werner. The cover graphic was designed to celebrate the intelligent use of auto-refraction as smart retinoscopy.
– Leonard J. Press, O.D., FCOVD, FAAO