| Summary: | <b>Purpose:</b> To describe symmetry of response in fellow eyes of patients undergoing photorefractive keratectomy (PRK) for myopia, analyse the risk factors leading to asymmetry in response and to determine if delayed treatment of the second eye increases safety and predictability of PRK. <b>Methods:</b> Retrospective review of case records of 133 patients who underwent bilateral myopic PRK and had a minimum follow up of 6 months in both eyes. <b>Results:</b> Postoperative uncorrected visual acuity, spherical equivalent (SE) refraction within ±1D of emmetropia, best-corrected visual acuity (BCVA) and corneal haze were not significantly different in fellow eyes of patients undergoing PRK for myopia. Of 87 eyes in group 1 (myopia &lt;6D), 96.6% had uncorrected visual acuity &#8805;6/ 12, 89.7% were within ±1D of emmetropia, none lost &#8805;1 line BCVA, and none had haze &#8805;grade 3. Similar results for 98 eyes in group II (myopia 6 to 9.9D) were 75.6%, 55.1%, 2.0% and 2.0% respectively. For 81 eyes in group III (myopia &#8805; 10D) the results were 42.7%, 33.3%, 8.6%, and 4.9% respectively. Among 84 patients with similar preoperative myopia in both eyes, 54 (64.3%) patients had a postoperative SE difference &#8804; ID in fellow eyes. Risk factors for asymmetric response among fellow eyes included increasing preoperative myopia (p&lt;0.001) and dissimilar treatment technique in the two eyes (p=0.03). Corneal haze did not increase significantly after the third postoperative month. <b>Conclusion:</b> This study demonstrates that considerable symmetry of response exists in fellow eyes of patients undergoing myopic PRK. Early PRK in the fellow eye of patients with &lt; 6 D myopia is safe and allows quick visual rehabilitation of the patient. In patients with myopia &#8805;6D, a 3-month interval before treating the second eye may improve the safety of the procedure.
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