March 28, 2012
5 min read

Understanding proprioception may be the key to treating visual fatigue

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Patient complaints usually treated with artificial tears, therapeutic medications and pain relievers may be resolved with the proper eye wear.

Headache, dry eye and eye strain are common complaints among eye care patients. One clinician has achieved a high degree of success by treating these patients with base-in prism.

“Our proprioceptive system, known as our ‘sixth sense,’ provides subconscious feedback to our visual system regarding where an object (e.g., words in a book or images on a computer screen) is in space,” Jeffrey P. Krall, OD, co-owner of Krall Eye Clinic in Mitchell, S.D., told Primary Care Optometry News in an interview. “However, our eyes do not mediate conscious eye position. When our eyes have misjudged the distance of an object from us, cortical supervision is required to adjust this retinal disparity. Without correction, many people will develop headaches and associated asthenopia.”

Convergence insufficiency

Conventional wisdom says that symptomatic convergence insufficiency is caused largely by decreased near point of convergence associated with increased exophoric deviation between the two eyes. For example, a person with 10 D of exophoria at near should have more pronounced symptoms of headache, dry eye sensation or eye strain than a person with 5 D of exophoria.

Jeffrey P. Krall, OD
Jeffrey P. Krall

But Dr. Krall believes that the amount of deviation has little meaningful correlation to symptoms.

“If you take a patient that is 1 D exophoric at near, and take another patient that is 10 D exophoric at near, either patient could be symptomatic,” Dr. Krall said. “It has very little to do with the magnitude of the deviation, because that is not the mechanism causing the problem. The ocular muscles are more than capable of converging.”

Extensive research by Dr. Krall revealed that patients who were monocular were basically asymptomatic.

“It is truly a binocular problem, not a monocular problem,” he said. “The eyes are focused in one location but converged to another. By altering this correctly, though, there is a high likelihood that symptoms will resolve.”

Patients with proprioceptive symptoms will describe headaches that start at the front of their head and often migrate to the occipital region, but they do not occur upon waking, Dr. Krall said. Two other symptoms are photophobia and sleepiness after reading for a short period.

Diagnostic testing

The best way to diagnose a patient with proprioception disparity is based on symptoms, according to Dr. Krall. “If patients are asymptomatic, they do not have a problem,” he said.

Devices such as the Titmus Optical Vision Screener (Honeywell, Morris Twp., N.J.) and the Optec Vision Tester (Stereo Optical Co., Chicago) provide “the gross phoria between the two eyes, but that is not the problem,” Dr. Krall said. “However, generally, the greater the exophoria, the more likely the patient will be symptomatic.”

Opt-Align (Stereo Optical Co.) is a new diagnostic instrument that can effectively measure proprioceptive disparity. “Opt-Align addresses the relationship between peripheral and central vision and the disparity between where the eyes are perceived to be converged and where the object is located. It does this by permitting peripheral binocularity while our central vision is monocular,” Dr. Krall said. “Ultimately, you need to test patients both centrally and peripherally to measure proprioceptive disparity, which Opt-Align achieves.”

Opt-Align has some similarity with the Turville infinity binocular balance test, Dr. Krall said.

“Under the right conditions in a 20-foot room, you can probably get similar results with the Turville,” he said.

Treatment for proprioceptive symptoms

Therapy for proprioceptive disparity consists of changing eye alignment with prism. For a patient who is nonpresbyopic, “single-vision lenses will resolve the problem,” Dr. Krall said. “However, you have to place the correct amount of prism in their lenses in order to align their convergence point to where they are focused. This is the key.”

By measuring and correcting proprioceptive disparity in tandem with the patient’s nearsightedness or farsightedness, “symptoms disappear,” Dr. Krall said.

Several new progressive lenses are available. Signet Armorlite (San Marcos, Calif.) offers Kodak lenses with Anti-Fatigue Progressive Technology.

“Shamir Insight [San Diego, Calif.] took their Autograph II and added base-in prism to the reading area and called it Autograph II Relieve,” Dr. Krall said. “They did the same with the Relax lens and called it Relax with Relieve. Relieve is exclusively distributed through Walman Optical.”

Dr. Krall has been treating symptomatic patients for 15 years and estimates a nearly 85% success rate.

“There are so many people with this problem. It is amazing,” he said. “We are changing the visual system so the eyes converge to the same location where they are focused.”

Study results

Dr. Krall is co-author of a study that appeared in Optometry & Vision Science in 2009 that assessed the effectiveness of base-in prism for adult presbyopes with convergence insufficiency.

All 29 subjects filled out the Convergence Insufficiency Symptom Survey V-15 (CISS) and scored at least 16 points. They were then given two pairs of Kodak progressive-addition glasses in a randomized sequence: one with a base-in prism, the other placebo (the same lens prescription but no prism). Each pair of glasses was worn for 3 weeks consecutively, and at the end of both 3-week cycles the subjects again completed the CISS.

The mean (standard deviation) CISS score decreased from 30.21 at baseline to 13.38 for the base-in prism glasses, compared to a reduction to only 23.62 with the placebo glasses.

Another practitioner’s experience

“Some patients we’ve treated with therapeutics and artificial tears see no resolution to their symptoms,” Paul M. Karpecki, OD, FAAO, director of corneal services and research at Koffler Vision Group in Lexington, Ky., and a PCON Editorial Board member, said in an interview.

Paul M. Karpecki, OD, FAAO
Paul M. Karpecki

Eye alignment “has an incredible place, both from what we understand and know in optometry, as well as being a differential diagnosis for patients who have been suffering for years, without anyone quite finding the reason for it,” he said.

Dr. Karpecki employs Opt-Align to diagnose these problems.

“Instead of taking 5 to 10 minutes to measure eye alignment and phorias on a phoropter, Opt-Align takes only about 60 seconds and gives you the exact numbers for correcting with prism and spectacles,” he said.

Since acquiring Opt-Align last summer, Dr. Karpecki used the device on more than 100 patients in 2011.

“It is amazing how many patients suffer from headaches caused by eye strain but they have been told they are migraines or neurological,” Dr. Karpecki said. “But these symptoms completely resolve with the appropriate correction and diagnosis of the proprioceptive disparity.”

Within days of eyeglass wear, “most patients notice a decrease in frequency, if not complete resolution, of their symptoms,” he said. Glasses are worn indefinitely.

Ophthalmology referrals

Vance M. Thompson, MD, FACS, director of refractive surgery at Vance Thompson Vision in Sioux Falls, S.D., said some of his patients complain of dry eye and eye strain after refractive or cataract surgery.

Vance M. Thompson, MD, FACS
Vance M. Thompson

“It was frustrating doing maximum dry eye therapy with plugs, lubricants and eyelid treatment without patients improving,” Dr. Thompson told PCON.

After being fitted with the proper glasses, his patients with proprioceptive disparity have greatly improved.

“It just blew me away how the small amount of prism in the glasses brought patients such relief,” Dr. Thompson said. He has been referring patients with this condition to optometrists, including Dr. Krall, for the past 5 years.

“We’ve worked really hard on improving the clarity of vision. But there has been this missing component of the comfort of vision,” Dr. Krall said. “The future of eye care will address both issues.”– by Bob Kronemyer


  • Teitelbaum B, Pang Y, Krall J. Effectiveness of base-in prism for presbyopes with convergence insufficiency. Optom Vis Sci. 2009;86(2):153-156.

  • Paul M. Karpecki, OD, FAAO, can be reached at Koffler Vision Group, Eagle Creek Medical Plaza, 120 N. Eagle Creek Dr., Suite 431, Lexington, KY 40509; (859) 263-4631;
  • Jeffrey P. Krall, OD, can be reached at Krall Eye Clinic, 1415 N. Sanborn Blvd., Mitchell, SD 57301; (605) 996-2020;
  • Vance M. Thompson, MD, FACS, can be reached at Vance Thompson Vision, The Talley Building, 1310 W. 22nd St., Sioux Falls, SD 57105; (605) 328-3937;
  • Disclosures: Dr. Karpecki has no relevant financial disclosures. Dr. Krall is a paid consultant to Signet Amorlite Inc., Stereo Optical Company, Dakota Laboratories LLC, Shamir Optical Industry Ltd. and Bausch + Lomb. Dr. Thompson has no relevant financial disclosures.