low vision

Revisit Trial Frame Refracting

The growing aging population is making this classic technology relevant again.

Jean A. Astorino, O.D., Media, Pa.

Trial frame refracting for the primary-care optometrist may seem low tech in today's electronic driven world. Aside from its use by low vision specialists like myself, few still utilize it, as the phoropter, and, more recently, the automated phoropter have pretty much taken its place. That said, you should consider reacquainting yourself with trial frame refracting because the aging population (those age 65 and older) is on the rise, increasing the need for this classic technology.

In fact, the aging population comprised 39.6 million of the U.S. population in 2009, according to the Administration on Aging, (U.S. Department of Health & Human Services). Specifically, they represented 12.9% of the U.S. population — roughly one in every eight Americans. This is a growth of 5% from 2000. Further by 2030, about 19%, or 72.1 million, older persons will comprise our country.

Here, I explain why trial frame refracting is ideal for low vision patients and how employing this tried-and-true technology can grow your practice.

Dr. Astorino makes a point to trial frame refract all her low vision patients, as she finds the results yield the most accurate refractions.

Revoked license

An 85-year-old male was referred to me by his ophthalmologist for a low vision evaluation.

History: The patient's ocular history revealed pseudophakia and Fuchs' dystrophy OU, for which he underwent a corneal transplant OD 11 years prior to this visit. After the transplant, the patient's best visual acuity was 20/200 OD, 20/60 OS and 20/60 OU. Since this patient lived in a state where one must have at minimum 20/50 OU vision to drive, he had to forfeit his driver's license.

Exam findings: As is my usual protocol for a low vision evaluation, I began trial frame refracting the patient with a high contrast low vision chart positioned at 10 feet under evenly dispersed illumination. The patient took one look at the low vision chart and said, "you're the first doctor I've been to who isn't testing me on a hologram." He further explained that the backlit effect of the usual projector charts always made the "black numbers float in a fog."

The patient's entering visual acuities on the low vision chart were 10/60 OD and 10/30 OS with his prescription of −4.25 −4.25 x 160 OD and +1.25 −1.00 x 170 OS. As I proceeded with my trial frame refraction, utilizing my hand-held cross cylinders and the just-noticeable difference formula, the patient continued to accept more … and more … and even more cylinder OD. The left eye refraction, however, remained unchanged.

With a final refraction of −6.00 −9.00 x 170 and acuity of 10/15 OD, the patient was very happy. In order for the patient to get his driver's license back, however, I had to test him with his trial frame refraction on the "hologram," or projector chart. The result: His new prescription yielded an improved acuity of 20/30 OD and 20/25 OU.

Discussion: How many of us have written off a patient's "bad eye" when we are told by the patient that his vision has been 20/200 for eleven years? Low vision cases like this one teach us that it's important to always give each eye the benefit of the doubt and to trial frame refract without bias.

Management: I provided the patient with a pair of glasses that met his final refraction, and I'm thrilled to report that he took his driver's test and passed. But, this patient's story doesn't end here.

His ophthalmologist recently contacted me. He said the patient was experiencing some discomfort due to the anisometropic nature of his refractive error. The ophthalmologist further told me that he thought a secondary lens implant piggybacked on the initial posterior chamber intraocular lens along with peripheral corneal relaxing incisions to decrease the astigmatism would benefit the patient's right eye. As we continued talking, I eventually realized that the reason the surgeon called was that he couldn't wait to tell me that my trial frame refraction was the reason behind his assessment and plan.

The procedure was of benefit. The patient is now 20/20 with a minimal prescription, even on the "hologram chart."

And as I've been working on this article, by a very ironic coincidence, I saw this patient again. This time, when I walked into my exam room, however, he wasn't sitting in my exam chair, his wife was — she'd been referred to me by her husband.

It's all about accuracy

Low vision patients tend to rely on eccentric viewing, as they must move their eyes or heads to look around any scotomas caused by eye disease. A trial frame allows for this, improving testing accuracy.

Also, a trial frame enhances accurate vertex distance, which is very helpful for these high refractive error patients.

Furthermore, this method of refracting allows the presentation of greater increments of lenses. Because phoropter lens increments are +/−0.25, most low vision patients are unable to see any difference between these lenses.

To further ensure you provide these patients with the best prescription via trial frame refractions, you should follow these five tips:

1. Use a low vision chart. Don't use a projector chart. Because low vision patients also have reduced contrast sensitivity, a projector chart doesn't provide enough contrast to properly test these patients' vision. A low vision chart, however, is designed purposely in high contrast for this reason.¹

Also of note: A low vision chart contains many acuities beyond the equivalent of 20/400. Therefore, whereas many low vision patients are used to only being able to read "the big E," on the projector chart, they are able to read many pages of acuities on the low vision chart. I've found that this usually intrigues patients to the point that they're very attentive during my refractions — something else that ensures accurate testing.

2. Place direct illumination evenly on the chart. Do this to further increase contrast while decreasing the chance of glare. Enable each patient to choose his optimal contrast, glare control and overall testing conditions via a brightness control gooseneck exam light.

3. Cater the room illumination for each patient. This also optimizes testing conditions. For example, a patient who has albinism may find better testing conditions with dim light, whereas a retinitis pigmentosa patient may prefer brighter room illumination. Many times, however, choice of illumination may not correlate to the characteristics of the ocular disease. Therefore, as is the case with direct illumination selection, allow the patient to assist in choosing the room illumination.

4. Perform the trial frame refraction at 10 feet. Place the low vision chart at 10 feet instead of at the standard 20 feet used for projection charts. The magnification produced by this closer testing distance increases the likelihood the patient will more easily discern differences in the lenses presented during subjective refraction.

5. Use the just-noticeable difference formula. Thankfully, this formula is helpful in determining the most effective increments of lenses to use for each patient's trial frame refraction. To determine the just-noticeable difference (i.e. the smallest diopter of lens change the patient's vision can appreciate), take the denominator of the visual acuity found at 10 feet during low vision acuity testing on a high contrast low vision chart, and divide it by 100. For example, a patient who sees 10/100 has a just-noticeable difference of +/− 1.00. (100 divided by 100 is 1.00) In this example, you would present +/−1.00 lenses when testing for sphere power. The same rationale holds true for choosing which power of hand-held cross cylinder to use when testing for cylinder power.

As the patient's vision improves, recalculate the just-noticeable difference — meaning the increments would decrease with better vision. Continue to apply the concept in this same manner throughout the refraction. Other than these differences, the subjective refraction is performed as usual.²

Growing your practice

Through my 15 years of providing low vision services, I have seen many cases in which the trial frame refraction made all the difference, and, therefore, garnered me referrals from both patients and fellow eyecare practitioners. With the aging population on the rise, I expect to see even more.

Consider this:

One of my referring doctors — a glaucoma specialist — now sends patients to me for what he likes to call "a glaucoma refraction."

Also, a retina specialist suggested in a letter to a cornea specialist that all mutual patients be referred to me for my "expertise in astigmatic correction."

In addition, a different retina specialist and I shared a special moment when he realized that my trial frame refraction of +10.00 −1.75 x 090 from a −5.25 sphere improved vision from 20/800 to 20/400 in a monocular patient. Although still 20/400, improving vision by 2X for a low vision patient is very significant. The improvement brought this patient and his wife to tears. That was January 2010. The patient passed away in April 2010. That retina doctor now makes sure to refer all his patients to me for low vision, understanding that the first test that the patient undergoes is the trial frame refraction.

Considering the aging population comprises such a large part of our population and it is growing, it's the perfect time to reinstate trial frame refracting into your primary care practice. As illustrated, this classic technology is ideal for low vision patients, as it enhances prescription accuracy for them. And, by providing these patients with the most accurate refraction, you'll amass several referrals from a very large population of both doctors and patients. OM

1. Cummings, Roger W., Muchnick, Bruce G., Whittaker, Stephen G., Special Testing in Low Vision, pg. 47-70. In Essentials of Low Vision Practice, Brilliant, Richard L., Butterworth-Heinemann, Woburn, MA 1999

2. Appel, Sarah Deborah and Brilliant, Richard L., The Low Vision Examination, pgs. 19-46. In Essentials of Low Vision Practice, Brilliant, Richard L., Butterworth-Heinemann, Woburn, MA 1999

Dr. Astorino founded Astorino Vision Rehabilitation, which now has locations in four Pennsylvania counties surrounding Philadelphia and one in Wilmington, Del. E-mail her at lowvision@astorinovisionrehab.com. Or, send comments to optometricmanagement@gmail.com.