Abstract
To evaluate differences in the subjective aniseikonia and stereoacuity in patients with axial anisometropia after full correction of the refractive error with spectacles, contact lenses, and refractive surgery. A prospective study was performed in Cairo University Hospitals on 20 patients with axial anisometropia caused by unilateral myopia > 5 D with > 4 D inter-ocular difference in spherical equivalent who were suitable candidates for excimer laser ablation (LASIK) or implantable collamer lens implantation (ICL). All patients had measurement of best-corrected visual acuity (BCVA), fusion, stereoacuity, and magnitude of aniseikonia with spectacles, contact lenses, and after surgery. The mean age at time of surgery was 25.7 ± 3.1years. There were no statistically significant differences in the BCVA or stereoacuity with spectacles, contact lenses, or after refractive surgery. Microkonia < 5%) was perceived with spectacles in 8 patients (40%) and remained unchanged in 7 of these 8 patients with contact lenses. Following LASIK (n = 11), there was an induced macrokonia < 2% in 4 patients (36%), persistent microkonia of 3% in 1 patient (9%), and no change in image size in 6 (55%) patients. Following ICL implantation (n = 9), there was a perceived macrokonia of 2% in 4 patients (44%), disappearance of microkonia in 1 patient (11%) and no change in 4 patients (44%). Differences in BCVA, stereoacuity, and aniseikonia after correction of anisometropia by glasses, contact lens and surgery are both clinically and statistically insignificant. Retinal or neural adaptation might have a role in correction for differences in image size.
Highlights
Anisometropia is a condition in which there is a difference in refractive power between the 2 eyes of a patient
Anisometropia is usually divided into axial anisometropia which is caused by a difference in the axial lengths of both eyes, and refractive type which is caused by a difference in dioptric power of the lens or cornea, or a difference in the lens position. [2,3]
According to Knapp’s law, if spectacles were placed at the anterior focal plane of the eye, the theoretical retinal image sizes will be equal in axial anisometropia [5]
Summary
Anisometropia is a condition in which there is a difference in refractive power between the 2 eyes of a patient. According to Knapp’s law, if spectacles were placed at the anterior focal plane of the eye, the theoretical retinal image sizes will be equal in axial anisometropia [5]. Knapp postulated that in axial anisometropia, correction of the refractive error by contact lenses might induce an aniseikonia [5]. With the increasing trend of refractive surgery, studies reported an improvement of best-corrected visual acuity and stereoacuity after different refractive procedures that can be explained by a reduction in aniseikonia after refractive surgery [7,8,9,10]
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