By: Thomas I. Porter, OD, FAAO
Telescopes, whether spectacle mounted or hand held are very valuable tools that are often overlooked by the new low vision clinician. If the visual goals include distance tasks, telescopes are certainly one of the best options.
Here are a few clinical tips that you might want to consider. Determine the dominate eye by a means you are comfortable and familiar with. Is this also the better seeing eye? If not the patient may have to be reminded to use the telescope before the better seeing eye. If the patient has problems “winking” or disregarding the image of the other eye then you might try what I call the “cross-over” technique. Have the patient hold the telescope in the hand on the opposite side of the body from the eye they will be using. This means, if the right eye is the sighting eye, hold the telescope in the left hand. This forces the patient to have their hand crossover in front of the left eye, effectively occluding that eye.
Many years ago I noted that many patients seem to have a fairly well established pattern of eccentric viewing until I handed them a telescope. I often saw patients “aiming” the telescope at the wall, ceiling and every direction but at the chart. It seemed that the natural eye/hand position was more in line with the anatomical macula. You can help a patient overcome this tendency with a simple “toilet paper tube”. Have the patient fixate on the eye chart and identify the chart characters. Then have them then introduce the tube before the eye (like holding the telescope). After a few attempts they can often continue to use the eccentric viewing point and sight down the tube. When they reach this level of performance introduce a telescope and determine if they can then more accurately localize on the chart while using the scope. Finally, I like to start with a low power/ large field telescope regardless of magnification needs and “work” my way up to the enlargement power I plan on prescribing.
My final trick is in using a hand-held telescope for shopping. Over the years I’ve had many patients report that the telescope required too much focusing effort to make it a very effective tool in grocery shopping. Here is a quick suggestion. Have the patient stop at a grocery shelf. Extend their arm straight out and touch a product on the shelf. Drop the arm down and focus the telescope on an item on the shelf. Now the telescope is “pre-focused” for a focal distance equal to their arms length. If they “stick” their arm straight out and hold the telescope before the eye, the object will be in focus. Also localization on the object is improved due to propreoceptive feedback.
By incorporating these simple tips into your exam and training routine you can improve your prescribing success rate with this valuable category of low vision aid.