Choroidal thickness of children's eyes with anisometropic and strabismic amblyopia

Letters to the Editor CHOROIDAL THICKNESS OF CHILDREN’S EYES WITH ANISOMETROPIC AND STRABISMIC AMBLYOPIA To the Editor: Aygit and colleagues1 have reported that “the subfoveal choroid of eyes with anisometropic and strabismic amblyopia is significantly thicker than that of the fellow eye and the age-matched controls.”1 It is likely that this statement was based on an erroneous interpretation of the optical coherence tomography (OCT) measurements. The axial lengths of the anisometropic amblyopic eyes were reported to be appreciably smaller (21.46  1.40 mm [20.05-24.70]) than the strabismic amblyopic eyes (22.22  1.21 mm [20.53-25.42]) and the control eyes (22.02  1.26 mm [20.24-24.94]).1 The refractive errors of the amblyopic eyes in both groups were more hyperopic than the fellow and control eyes. In conventional photography as well as in retinal imaging the size of the image on the film plane or electronic receptor surface is increased when the objective lens is closer to the object. Formulas for the magnification factor based on axial length and refractive error were developed by Bengtsson and Krakau.2,3 A method for performing these calculations on personal computers has been demonstrated.4 The magnification correction factors were calculated using the Bengtsson-Krakau formulas and the mean axial lengths and refractive errors provided in this report.1 The magnification factors were found to 3.17 for the amblyopic anisometropic eyes and 3.07 for the fellow eyes. The magnification factors for the amblyopic

Journal of AAPOS

strabismic eyes were 3.05 and 2.93 for the fellow eyes. The value for the control eyes was 3.01. The percentage difference between the magnification correction factors for the amblyopic and fellow eyes in the anisometropic group was 5.3% and 5.9% for the subfoveal choroidal thickness measurement. The corresponding values for the strabismic group were 8.3% and 3.1% for the choroidal thickness. Application of the magnification correction to the OCT values, therefore, shows that there is very little difference in the subfoveal choroidal thickness measurements. Failure to apply the magnification factor may lead to false impressions of choroidal and retinal thickness. Philip Lempert, MD Ithaca, NY

References 1. Aygit ED, Yilmaz I, Ozkaya A, et al. Choroidal thickness of children’s eyes with anisometropic and strabismic amblyopia. J AAPOS 2015;19: 237-41. 2. Bengtsson B, Krakau CET. Correction of optic disc measurements on fundus photographs. Graefe’s Arch Clin Exp Ophthalmol 1992;230: 24-8. 3. Bengtsson B, Krakau CET. Some essential optical features of the Zeiss fundus camera. ACTA Ophthalmologica 1977;55:123-31. 4. Lempert P. Imaging in Glaucoma. Thorofare, NJ: SLACK; 1996. 35-43. http://dx.doi.org/10.1016/j.jaapos.2015.07.289 J AAPOS 2015;-:1. Copyright Ó 2015 by the American Association for Pediatric Ophthalmology and Strabismus. 1091-8531/$36.00

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