Remember in elementary school when someone would whisper something to a classmate, and the teacher would ask, Is there something youd like to share with the class?
We posed that question to this years crop of third- and fourth-year optometry students. As in years past, we asked them to share what theyve learned in their clinical experience with their classes in our annual Student Case Report Challenge.
We also asked our three judgesLeonid Skorin, O.D., D.O.; John E. Musick, O.D.; and Robert Walker, O.D.to pick the three winning papers, and then asked Thomas L. Lewis, O.D., Ph.D., Review of Optometrys case reports coordinator, to act as a tie-breaker for the grand prize. We asked them to share their opinions about the quality of care the patient received, the papers value to the profession, authors enterprise and quality of writing. We thank these judges for their dedication to this difficult task.
Thanks also to the faculty advisers, who shared their time and experience mentoring these students:
We share the grand prize-winning paper in the January 2002 issue. All three winning cases are only on Review of Optometry OnLine.
Grand Prize Winner: Carey Aston Patrick, a fourth-year student at University of Houston College of Optometry, wins a Keeler Vantage binocular indirect ophthalmoscope for her paper, Aniseikonia Secondary to Unilateral Pseudophakia and Scleral Buckle Repair Surgery. Mrs. Patrick spent 10 years as a finance and marketing strategies analyst before entering optometry.
The patient had no significant medical history, but he had undergone three surgeries O.S. First, he underwent phacoemulsification with a posterior chamber in-the-bag IOL implant. He developed rhegmatogenous retinal detachment postoperatively and underwent successful reattachment with moderately high scleral buckling in all quadrants and pars plana vitrectomy. He eventually required an IOL exchange due to mislocation of the first IOL. After the second surgery he complained of dizzy spells when wearing his glasses, even though his acuity was 20/20. The dizzy spells and reduced depth perception persisted even after he was fit with soft contact lenses.
The patient insisted that his acuity was not as good as it had been before. His ophthalmologist attributed the symptoms to spherical discomfort and meridional magnification, and planned no treatment. The patient then went to several other eye doctors and obtained two more sets of spectacles (distance and near), including one set with base-in prism, but these failed to relieve his symptoms.
Diagnostic Data Refraction yielded -2.50D for 20/15 O.D. and +0.25 -1.50 x 111 for 20/15 O.S., with a +2.00D add O.U. for near. Topography and keratometry, when compared to the refraction, confirmed the presence of intraocular cylinder.
During cover testing, the patient described the view in his left eye as double and fuzzy. Amsler grid testing was normal O.D., but revealed a speed bump-shaped distortion O.S. that was 2-3 degrees superior to fixation. Randot circles indicated 40 arcsec at 16 inches then suppression O.S. We were unable to obtain a response to global stereo. Sensorimotor testing and biomicroscopy of the external and anterior segments were normal.
Given the significant anisometropia and absence of other binocular causes for his symptoms, we decided to test for aniseikonia. Standard eikonometry was inconclusive. The patient reported that the center of the image in the left eye was stretched vertically but that the nonius lines were not misaligned. Space eikonometry, however, was positive for aniseikonia.
To differentiate the aniseikonia from metamorphopsia, we gave the patient a set of afocal meridional magnifiers (1.3%, 3.4% and 4.75%) to attach over his right spectacle lens to see if any improvement would result. The patient liked the 3.4% magnifier so well that he drove his car while wearing the magnifier, against our advice.
Diagnosis Treatment and Follow-up The contact lenses and eikonic distance spectacles resulted in acuity of 20/15 O.U. Vectographic stereoacuity at distance is 1 arcmin. Near spectacles with the same base curve and center thickness yielded improved stereoacuity of 20 arcsec local and 250 arcsec global.
The metamorphopsia is still present but is no longer troublesome to the patient. He reports that the swim effect has disappeared with the contacts, allowing him to resume playing tennis. He also says that the eyestrain and dizziness are gone with either spectacles or contacts, and that he interchanges freely. The patient is satisfied with the cosmetic appearance of the spectacles and wears them more than he does the contact lenses.
Discussion Some 20-30% of the general spectacle-wearing population may exhibit measurable aniseikonia, yet only 5-6% of cases are clinically significant. There is no preponderance for gender, ethnicity or age. 3
Aniseikonia often results from one of these factors:
Symptoms of aniseikonia typically include non-specific asthenopia and headache-type complaints. Some 25% of patients report photophobia, 23% difficulty reading, 15% nausea and 10% mobility problems.2,7 Another 6% report spatial distortions or perception degradation, as this patient did.2,7 Patients who had well-developed stereopsis before becoming aniseikonic may complain of reduced depth perception, while those with little or no stereopsis to begin with probably will not notice or complain of the reduction or loss. Researchers at the Dartmouth Eye Institute confirmed and described the relationship between apparent image size differences and incorrect spatial localization.3 Reduced stereopsis or depth perception in the absence of another binocular anomaly is often suggestive of aniseikonia, especially when accompanied with non-specific asthenopic complaints.
Complaints are more common among patients whose aniseikonia involves differences in meridional magnification, especially when these differences first onset.7
Diagnosis of Exclusion Space eikonometery, considered the gold standard for definitive diagnosis of aniseikonia, measures the full image size difference between the two eyes, including oblique meridians.1,3 Standard eikonometry measures, by linear comparison, the same quantity as space eikonometry. The Dartmouth Eye Institute showed this to correlate findings with the space eikonometer.3 In the clinic, fit-over magnifiers, both overall and meridional, are most useful to determine if the patients symptoms are relieved, or you can use A-scan to determine differences in axial length.
Alternative tests for aniseikonia include subjective comparison, Maddox rod or double light technique, keratometry and S. Awayas aniseikonia test. Another possibility: empirical calculation based upon refractive status. The rule of thumb is 1% per diopter of anisometropia, but only if the difference is refractive, not axial, in nature.9
Managing Aniseikonia Less accurate correction of aniseikonia is needed for infants and children than for adults, due to their sensory adaptability and tolerance.10
Aniseikonia should clearly be among the preoperative calculations for intraocular implants, refractive surgery, and procedures that modify the shape of the posterior globe (e.g., scleral buckle) and/or distribution of the retinal elements (e.g., macular pucker).11 If there is a significant time lapse between cataract surgeries, consider the likelihood of induced postoperative aniseikonia.
We play an important role in diagnosing and managing aniseikonia. Employ confirmed diagnosis, careful review of symptoms and patient counseling in every case. When standard correction fails, consider designing an eikonic lens. Your patient will achieve better visual results and no doubt will be very satisfied with the quality of your care.
A 56-year-old white male presented complaining that images in his left eye were 20-30% larger than those in his right. He said he noticed this difference since he underwent surgery to repair a retinal detachment. This difference, he said, altered his depth perception and ruined his tennis game. He also complained that a sense of wearing a telescope over one eye made him dizzy, and that he was even more aware of the problem under low light conditions.
At this visit, visual acuity was 20/20 O.D. and 20/15 O.S. with habitual spectacle correction. The patient typically preferred wearing glasses to contact lenses for general use, although he wore his soft lenses for playing tennis.
We confirmed our diagnosis of aniseikonia after a three-week trial with the afocal meridional fit-over magnifiers.
We fit the patient with daily wear RGP contact lenses (spherical O.D., front-surface toric design O.S.). We also ordered eikonic spectacles based upon the subjective results of testing with the meridional magnifiers. For the right eye, we ordered a -2.50D lens and base curves of +10.25D at 111 meridian and +3.00D at 021 meridian, with a 6mm center thickness. For the left eye, we prescribed +0.25 -1.50 x 111, with a +6.00D overall base curve and a 3mm center thickness. The right lens is a bitoric design that provides 4.2% magnification in the 111 meridian. The left lens offers 1.2% magnification overall. The net result is a 3% relative magnification in the right eye in the 111 meridian.
The image size each eye perceives may differ slightly, depending on several factors: dioptric power, distribution of retinal receptors, and the physiological and cortical processes.1 However, aniseikonia generally becomes clinically significant when the relative difference in magnification is 0.75% or more between the two eyes. This size difference exceeds the patients ability to compensate and causes symptoms.1-3 Five percent aniseikonia may be the largest limit that can be tolerated.4 A difference in size perception may be overall, meridional or the result of visual field distortions such as metamorphopsia.
Diagnosing aniseikonia is based upon subjective tolerances for differences in magnification and stereoacuity. Aniseikonia is a diagnosis of exclusion, typically considered only after you rule out other binocular anomalies. A patient with a dramatic decrease in stereoacuity following refractive or other ocular surgery likely has aniseikonia. You may estimate optically induced aniseikonia by comparing the refractive errors between the two eyes, though not every patient with refractive imbalance will be symptomatic.
Treatment options for aniseikonia include:
