Retinoscopy, trial frame exam key to low vision refraction

Issue: June 1998

BySusan E. Marren, OD FAAO

A good refraction is essential to effectively prescribing low vision aids. The primary care physician most likely has all the necessary tools to refract these special patients. Our low vision experts shared their favorite refracting methods, addressing eccentric fixation, contrast and cylindrical errors.

Kathleen Fraser Freeman, OD, FAAO, of the Santa Rosa Low Vision Clinic in San Antonio, relies more on retinoscopy than any other technique to determine a patient's refractive error before moving on to prescribe low vision devices. Although many practitioners use autorefractors, Dr. Fraser Freeman likes the information she obtains from the reflex about the media. She added that coloboma patients can be tough to retinoscope because of the associated staphyloma, causing a more minus reflex.

Another objective method Dr. Fraser Freeman uses for the patient who cannot cooperate (because of dementia, young age, etc.) is to look in the back of the eye with a direct ophthalmoscope and determine the approximate error from the diopters needed to see clearly. For instance, if the patient has a "fair amount of nystagmus, you may get close enough with the ophthalmoscope reading" to begin the refraction with a trial frame, she said.

Roger Cummings, OD, FAAO, of the Eye Institute of the Pennsylvania College of Optometry, Philadelphia, also likes retinoscopy, but unlike Dr. Fraser Freeman he will also use an autorefractor for a baseline. "The objective baseline is critical," he said.

Paul Freeman, OD, FAAO, FCOVD, of the Department of Ophthalmology at Allegheny General Hospital, Pittsburgh, reports that variable distance retinoscopy can be helpful for complicated cases. "You can move in and out, or you can use handheld lenses to get a starting point. The accuracy depends on the person doing it, but it's a great starting point for the patient who is difficult to work with," he said.

He uses a ruler or estimates his working distance. "If I get a dark reflex, then I'll get really close to see if I've got a high myope, or I might put ±10 or ±20 D in a flipper and scope over that."

Richard Brilliant, OD, FAAO, said that in the past month he has found an autorefractor to be a tremendous help to him at the Moore Eye Foundation, Springfield, Pa., enabling him to quickly reach an accurate prescription. "The patients have been overwhelmingly positive about it," he said. "I feel very comfortable with the results I'm getting with the autorefractor."

Dr. Cummings suggested a careful keratometry reading for phakic patients as a starting point for cylinder power and axis. Dr. Fraser Freeman added that K readings are especially helpful for the nystagmus patient.

Louis Frank, OD, FAAO, uses his corneal topographer on his low vision patients at North Shore Eye Specialists in Danvers, Mass. He initially purchased the instrument for laser patients but has discovered its value for low vision patients, even beyond that of a keratometer.

Using eye charts

Maintaining fixation during retinoscopy requires a visible target for the partially sighted patient. Dr. Cummings likes the ETDRS acuity chart, available from The Lighthouse in New York. The chart can be used at any distance and will still be accurate. He also uses the reduced ETDRS for near acuities.

Dr. Fraser Freeman uses the Feinbloom chart in her practice, and Dr. Brilliant utilizes the same chart because he feels that it is easier for the patient to respond to. It has very large optotype and less optotype per page; some pages have only one optotype. The optotype is numbers which are generally easier to read than letters. It allows the patients to read many more numbers than they typically can read from the charts commonly used for non-low vision patients.

"It can motivate them because they think they are doing better than they have been able to do anywhere else," Dr. Brilliant said. "It motivates them to continue to work hard and to be positive about what can be done."

"The key to all of this is not the equipment, but the person conducting the tests," Dr. Freeman pointed out. That said, he likes a reading/training card that Wayne Hoeft, OD, developed, which measures acuity, identifies the type of print each line trains the patient to read, gives instructions such as where to have the light and how to hold the card, and ends with encouraging words for the patient. Both he and Dr. Brilliant report that it is not unusual for patients to cry when they are able to see something for the first time.

Dr. Hoeft has also developed a near point training card for the patient to take home, which instructs the patient in the same manner in which he or she is taught in the office. These are available through Mattingly International Inc. [Escondido, Calif., (800) 826-4200].

Trial lenses for subjective exam

All perform the subjective refraction through trial lenses in a trial frame. Most clinicians use handheld ±0.50 Jackson crossed cylinders for the astigmatic check. Although some use the higher-powered lenses, Dr. Fraser Freeman reports that recent research shows that a cross cylinder lens larger than ±0.50 D does not give any advantage and causes more distortion of the image.

"With high cylinder axis patients, such as albinos, I'll let them select the cylinder axis in the trial frame by turning the knob. I have them set it three or four times to give me an idea of how sensitive they are and what the approximate axis is," she said.

All also use the "just noticeable difference" technique. This is based on the patient's acuity converted to the 10/10 fraction. For example, for a patient who sees the 100-foot letter at 10 feet (10/100), use the dioptic power created by putting a decimal in the denominator: ±1.00 D.

Dr. Brilliant suggested that when you see a low vision patient for the first time, assume that whatever is in the old glasses is wrong. This is especially true if he or she lives in a nursing home where there is a greater chance of the patient having someone else's glasses. It other cases, patients may have had cataract surgery but continue to wear their old glasses. Or, assume the last refractionist was not as good as you are.

Dr. Fraser Freeman will sometimes blur the nonrefracted eye rather than occluding it. She uses about a +10 D lens, for example, while refracting a patient with a large amplitude latent nystagmus.

Dr. Frank likes to use the Halberg or Janelli clips for the refraction. He said that when he rarely finds a change in cylinder power or axis, he simply puts the whole thing in the lensmeter to determine the new prescription.

A new prescription or a change in prescription must be compared to the old glasses, preferably with the proposed change held over the old glasses.

Dr. Fraser Freeman finds that many patients will reject proposed changes once they are back in their habitual eye and head posture with their old glasses in place.

Dr. Brilliant always uses a trial frame and lenses for any proposed changes and has the patient walk around or watch television in the waiting area with them.

Refracting with telescopes?

Dr. Fraser Freeman says that she and her colleagues refracted patients behind telescopes before the evolution of adjustable telescopes. Refracting behind telescopes is no longer necessary, she said. Current thinking is that accommodation is too difficult to control with the telescope in place. So in nearly all cases today, the refraction is finalized first.

Dr. Freeman does not routinely refract with a telescope. If it is necessary, however, the clinician should place a lens between the eye and the telescope for the working distance before attempting any refraction to avoid stimulating accommodation.

Refracting eccentric fixation patients

When autorefracting a patient who has eccentric fixation and is not yet aware of how to aim his or her eyes, Dr. Brilliant tells the patient what the target is. Then he says: "Now move your eyes around, pretending to look at a clock dial. Start at 12:00 and go around the dial to see if it is clearer or easier in any position to see the target."

When trying to refract a patient with eccentric fixation, Dr. Fraser Freeman uses a target quite a bit larger than threshold and instructs the patient to do the best he or she can to "hold it with the part of the eye that sees the best."

Because eccentric fixators can confuse changes in eye position with the lens change, she explains in this way: "Be careful. Sometimes when you shift your eye, you'll lose the number. Make sure the lens is actually making the change." With these patients it is especially important to double-check any change over their own glasses.

Filters for depth perception

Dr. Brilliant also suggested checking the patient's contrast sensitivity as a part of the trial frame refraction. He tries different filters to see if contrast is enhanced because this may, in turn, help with mobility. He asks if patients have trouble walking up unfamiliar stairs or seeing curbs where there might be poor contrast.

Dr. Brilliant uses Corning CPF lenses - photochromic lenses made by Corning (Corning, N.Y.) especially for low vision patients. They reduce glare, enhance contrast and eliminate haze. He tries the filter during the subjective refraction and, if they notice a difference, he takes them outside to try it.

Dr. Frank likes to check the effects of filters for the nearpoint correction, as well as checking for binocular or monocular preference. "There are times when the patient prefers to use the eye with a lesser acuity because of an improved contrast sensitivity," he said.

He uses the contrast sensitivity chart from Visitec (Sarasota, Fla.) [available through Lighthouse Enterprise, (800) 453-4923] and the spectacle prescription with the filters to assess which eye is preferred or if binocular conditions are preferred. Patients with optic nerve disease may respond unexpectedly to contrast-enhancing filters.

Dr. Fraser Freeman added that she likes to do morning and evening checks on refractions for those in conventional lenses (8 D adds and similar prescriptions) at the first visit. "This way, if a shift in vision occurs, the patient knows to expect it," she said.

Considering cylindrical errors

Dr. Cummings makes a special effort to assess the importance of the cylindrical component of the refractive error before working on the addition the patient will use. If the cylinder makes no difference, there is a larger range of devices available. "You never know how the patient will respond," he said.

Dr. Frank reminds practitioners to "look for unusual refractive errors when patients have conditions often associated with refractive error such as Marfan's syndrome and retinopathy of prematurity," he said. "For instance, a patient with albinism will come in with a well-intended spherical prescription from a practitioner, and with careful retinoscopy we find that a lot of these patients have significant cylindrical errors."

For Your Information:

Roger Cummings, OD, FAAO, may be reached at the Eye Institute of the Pennsylvania College of Optometry, 1202 Spencer, Philadelphia, PA 19141; (215) 276-6163 or (215) 276-6060; fax: (215) 276-1329; e-mail: RCummings@PCO.edu.

Kathleen Fraser Freeman, OD, FAAO, may be reached at Santa Rosa Low Vision Clinic, 315 N. San Saba, Suite 900, San Antonio, TX 78207; (210) 228-0030; fax: (210) 228-0277; e-mail:FreemanKP@aol.com.

Paul Freeman, OD, FAAO, COVD, may be reached at Allegheny General Hospital, Department of Ophthalmology, 320 E. North Ave., Pittsburgh, PA 15212; (412) 359-6300; fax: (412) 262-9448; e-mail:FreemanKP@aol.com. Neither Dr. Cummings, Dr. Fraser Freeman or Dr. Freeman has a direct financial interest in any products mentioned in this article, nor is either a paid consultant for any companies mentioned.

Richard Brilliant, OD, FAAO, may be reached at Moore Eye Foundation, Healthtex Pavillion II, Springfield Hospital, 100 W. Sproul Road, Suite 100, Springfield, PA 19064; (610) 690-4900; fax: (610) 690-4910. Dr. Brilliant has no direct financial interest in any of the products mentioned in the article, nor is he a paid consultant for any companies mentioned.

Louis Frank, OD, FAAO, may be reached at North Shore Eye Specialists, 85 Constitution Lane, Ste. 100C, Danvers, MA 01923; (978) 774-7033; fax: (978) 774-0341; e-mail:NSEye@aol.com. Dr. Frank owns stock in a company which sells corneal topographers. He is not a paid consultant for any companies mentioned in this article.

Susan E. Marren, OD, FAAO, may be reached at (609) 829-4229; e-mail: SMarren@aol.com. Dr. Marren has no direct financial interest in the products mentioned in the article, nor is she a paid consultant for any companies mentioned.