Gerard C. de Wit PhD and Arnulf Remole BFA, OD, MS, PhD Clinical

Clinical management of aniseikonia An overview Management linical management of aniseikonia has long been neglected by a The three basic steps of aniseikonia large part of the optometric community. One of the main management are: reasons is the lack of simple and accurate instrumentation for • Objectively measuring the aniseikonia C • Subjectively verifying that the patient diagnosing and measuring aniseikonia. With the knowledge that the number of aniseikonia patients is significant, and that aniseikonia would be helped by prescribing rules of thumb often do not predict the actual situation well, new iseikonic lenses products have recently emerged on the market to manage • Determining a new spectacle aniseikonia clinically. prescription to correct for the aniseikonia

Aniseikonia is a binocular condition in Alternatively, the aniseikonia can also be Measurement which left and right images differ in size or simulated by presenting images of (objective eikonometry) shape. There are two types of aniseikonia – different size to the two eyes. This is There are two methods of measuring static and dynamic aniseikonia1. The first shown in Figure 1, where binocular aniseikonia: space perception eikonometry type is the classical aniseikonia, denoting a separation should be achieved by using and direct comparison eikonometry. The perceived image size difference with a red-green anaglyph glasses (see later). objective in a space perception fixed gaze direction. The second type of eikonometric measurement is to neutralise aniseikonia is also called induced space distortions induced by the anisophoria2 and denotes a perceived Incidence aniseikonia. Although this method can be image size difference due to unequal prism The incidence of aniseikonia is often quite accurate in a laboratory setting, it is effects when looking through different underestimated. The most well known less suited for clinical use. To our parts of the two (anisometropic) spectacle patient group at risk is the knowledge, there are also no commercially lenses. For clinical purposes, the two types anisometropes. The prevalence of available instruments based on this of aniseikonia are often related. The static anisometropia (>1D difference) above the method. aniseikonia is typically (but not always) age of 20 is 5-10%4. A second large group Regarding direct comparison two thirds of the dynamic aniseikonia1. of patients at risk for aniseikonia is the eikonometric tests, there are at least two people who have had cataract or tests commercially available. One is the Symptoms refractive surgery. For example, Kramer et NAT (New Aniseikonia Test, Handaya, Table 1 classifies the symptoms of al5 found that 40% of all pseudophakes Tokyo, Japan). The other is the aniseikonia aniseikonia. Because most of these are had ophthalmic complaints referable to test of the aniseikonia management rather general, it is sometimes difficult for aniseikonia. In England alone, there are software called the Aniseikonia Inspector the optometrist to recognise the condition. approximately 250,000 cataract (Optical Diagnostics, Culemborg, the However, recognising and treating the operations annually6. Because these Netherlands). symptomatic aniseikonia will usually numbers are significant and because The principle of direct comparison result in very grateful patients and may aniseikonia rules of thumb have been eikonometry is that a different size target is also be financially rewarding for the proven unreliable7,8, testing for, and presented to each eye and that those two optometrist. managing, aniseikonia is important. size targets have to be made equal in size

Symptom Percentage of patients Headaches 67% Astenopia (fatigue, burning, tearing, ache, pain, pulling, etc)67% Photophobia 27% Reading difficulty 23% Nausea 15% Motility (diplopia)11% Nervousness 11% Vertigo and dizziness 7% General fatigue 7% Distorted space perception 6%

Table 1 Characteristic symptoms reported by 500 patients referred for aniseikonia examination3

For someone to experience the discomfort of aniseikonia, he/she could put an afocal size lens in front of one eye. Figure 1 This type of lens induces a magnification, When using red-green anaglyph spectacles, this image shows the discomfort produced by but does not have an optical power. 3% of aniseikonia (assuming the viewer does not have inherent aniseikonia)

39 | December 12 | 2003 OT Clinical Gerard C. de Wit PhD and Arnulf Remole BFA, OD, MS, PhD

Figure 2 Layout of the aniseikonia test of the Aniseikonia Inspector. The patient uses red-green spectacles to separate the two half-circle size targets Figure 3 binocularly. The objective of the test is to make the two half-circles Determining an aniseikonia corrected prescription with the Aniseikonia visually equal in size Inspector software is fast and easy

by either holding size lenses in front of base curve, centre thickness, index of About the authors one eye, or by physically changing the size refraction, and back vertex distance. Dr Gerard C. de Wit is involved with of one of the size targets. Besides the lack of instrumentation, research at Optical Diagnostics in the Figure 2 shows the half-circle size determining an iseikonic prescription was Netherlands. Dr Arnulf Remole is on the targets of the Aniseikonia Inspector test. too big a hurdle for some optometrists to faculty of the School of Optometry at the The layout of the test, in particular, the actually manage aniseikonia. However, University of Waterloo in Canada. (in)visibility of binocularly fuseable with the advent of computers, objects around the size targets, is determining such a prescription has Special offer important in comparison with become much easier (Figure 3). For viewing Figure 1, Dr de Wit is offering eikonometry9. Due to binocularly visible to send a simple pair of red-green objects around the size targets, the NAT Conclusion spectacles to the first OT readers to email test seems to underestimate aniseikonia10, Clinical management of aniseikonia used him at [email protected]. while the Aniseikonia Inspector test to be done only by a few specialists. The measures aniseikonia more correctly10,11. main reasons for this lack of skill and References knowledge among optometrists are 1. Remole A, Robertson KM (1996) Verification believed to be outdated and insufficient Aniseikonia and Anisophoria: Current Concepts and Clinical Applications. (subjective eikonometry) instruction, the lack of simple and Runestone Publishing, Waterloo, Ontario, The second step in aniseikonia accurate instrumentation, and the Canada. management is often to verify if the relatively complicated or time-consuming 2. Friedenwald JS (1936) Diagnosis and patient would be helped by iseikonic determination of iseikonic spectacles. On treatment of anisophoria. Arch. lenses. The reason is that the sensitivity to the other hand, the number of Ophthalmol. 15: 283-307. aniseikonia can vary a lot from patient to aniseikonia patients is substantial and 3. Bannon RE, Triller W (1944) Aniseikonia patient. Some patients are very grateful if growing, due to the ageing population – a clinical report covering a ten-year 1% of aniseikonia is corrected, while and the increase in cataract and refractive period. Am. J. Optom. 21: 171-182. others might not be bothered by as much surgery operations. 4. Weale RA (2002) On the age-related prevalence of anisometropia. Ophthalmic as 3% of aniseikonia. Subjective Another reason, heard sometimes, for Research 34: 389-392. eikonometry can be done by simulation, not managing aniseikonia, is that 5. Kramer PW, Lubkin V, Pavlica M, Covin R as shown in Figure 3, but a better way may iseikonic prescription spectacles can be (1999) Symptomatic aniseikonia in be to use size lenses. cosmetically unattractive. Of course, this unilateral and bilateral pseudophakia. depends a lot on the amount of A projection space eikonometer study. Correction aniseikonia to be corrected and the frame Binoc. Vis. Strabis. Q. 14: 183-190. Equivalent to a sphere and cylinder size. There might also be a trade-off to 6. NHS Executive (2000) Action on Cataracts: refractive error, there is an overall and a undercorrect aniseikonia to keep the Good practice guidance. Department of meridional aniseikonia. For clinical spectacles attractive. The trade-off between Health, London (www.doh.gov.uk/cataracts). purposes, correcting the overall appearance and correction will depend a 7. Lubkin V, Shippman S, Bennett G. et al aniseikonia is usually most important and lot on the patient and on the severity of (1999) Aniseikonia quantification: error 1 sufficient . That is, overall aniseikonia gives the symptoms. Many aniseikonia patients rate of rule of thumb estimation. rise to headache and asthenopia. would prefer to trade a reduction in good Binoc. Vis. Strabis. Q. 14: 191-196. Meridional aniseikonia, on the other appearance for more visual comfort. Also, 8. Kramer P, Shippman S, Bennett G et al hand, gives rise to distorted space the patient might purchase two pair of (1999) A study of aniseikonia and Knapp’s perception. spectacles – one for optimum visual Law using a projection space eikonometer. The most effective way to reduce or comfort for daily routine and one for Binoc. Vis. Strabis. Q. 14: 197-201. eliminate aniseikonia is to provide an optimum appearance during social events. 9. Ogle KN (1950) Researches in Binocular Vision. WB Saunders, Philadelphia, USA. iseikonic prescription. One cannot change A product like the Aniseikonia 10. McCormack G, Peli E, Stone P (1992) the effective power at the cornea, because Inspector now gives the optometrist the Differences in tests of aniseikonia. Invest. this would reduce the patient’s visual opportunity to manage aniseikonia. Ophthalmol. Vis. Sci. 33: 2063-2067. acuity. However, one can change the Potential rewards will be some very 10. De Wit GC (2003) Evaluation of a new accompanying spectacle magnifications of grateful patients, a larger patient base, and direct-comparison aniseikonia test. the corrective lenses by manipulating the a possible increase in revenue. Binoc. Vis. Strabis. Q. 18: 87-94.

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