Change in the Phoria state of the eye after refractive surgery for myopia Dr Umang Mathur, Dr Archana Gupta, Dr Suma Ganesh Dr Shroff’s Charity Eye Hospital, Daryaganj, New Delhi The authors do not have any proprietary or financial interest in a product, method or material used in this study. There are no competing interests in this study

Aim To study the change in the phoria state of the eye after refractive surgery for myopia Design: Prospective non comparative study All patients interested in refractive surgery were screened

Methods Inclusion criteria Exclusion criteria Bilateral myopia Age>18 yrs Willingness for refractive surgery Eligibility for refractive surgery Anisometropia < 1D Exclusion criteria Unilateral Amblyopia Presence of any other ocular disease Any previous intraocular surgery Patient not willing for refractive surgery Patients unsuitable for refractive surgery Planned monovision

Methods Pre operative work up Routine LASIK work up including The spectacles worn were evaluated for the power, presence of a bifocal segment and any prism if incorporated For correction, the manifest refraction was aimed for in all cases - no deliberate over or under-corrections attempted. Orthoptic evaluation Head posture evaluation Hirschberg test Cover test Prism bar cover test for distance and near (and in all positions of gaze) both with and without glasses wherever possible Extra ocular movements Near point of convergence, near point of accommodation Fusional amplitudes Worth 4 dot test for fusion/suppression Ran dot E for stereopsis. Patients with a deviation of greater than or equal to three prism diopters* were included in the study

Methods Standard LASIK technique LASIK flap created with a Hansatome at 160 or 180 microns depth and the stromal bed was ablated using a Visx star S4 excimer laser Postoperative evaluations one week six weeks three months six months post Orthoptic evaluation at each visit Any symptoms/ complaints in near work activities Statistical Analysis: The paired t test was used in analyzing the results

Results Of the 87 screened subjects, only 70 were found eligible; these were screened and 11(15%) were enrolled Parameters Results Female: Male 10:1 Average age 26.46 yrs (SD: 7.29; range: 19 to 45 yrs Average MRSE RE -4.81 D (SD: 3.22) Average MRSE LE - 4.76 D (SD: 2.93) Mean Anisometropia 0.71 D (SD: 0.76) All the deviations were exodeviations

Change in the deviation post operatively Pre op Post op Distance 5.36 pd (SD: 9.69) 4.45 pd (SD: 7.84) Near 7.45 pd (SD: 6.59) 4.90 pd (SD: 3.2) P= 0.464 P = 0.261

Discussion Approximately 1.5 million LASIK being done every year - myopia - most common diagnosis… it is important to anticipate and predict postoperative complications In our study… phorias present in 15% of the patients who underwent refractive surgery Although not statistically significant, there was a general trend towards an overall improvement in the degree of deviation post operatively

Review of Literature But, there are multiple case reports of diplopia/decompensation post refractive surgery !!! On detailed review, all had risk factors: Targeted monovision Unilateral refractive surgery Anisometropia Amblyopia Kushner B J, Lionel Kowal. Diplopia after Refractive Surgery: Occurrence and Prevention. Arch Ophthalmol 2003; 12:315-321. Schuler E, Silverberg M, Beade P, Moadal K. Decompensated strabismus after laser in situ keratomilleusis. J Cataract Refract Surg 2000; 26: 1552-4.

Discussion Deviations preoperatively controlled with deliberate myopic overcorrection or prisms in glasses - missed in the pre operative evaluation* There was no such case in our series … ours was a controlled study with strict inclusion and exclusion criteria *Kushner B J, Lionel K. Diplopia after Refractive Surgery: Occurrence and Prevention. Arch Ophthalmol 2003; 12:315-321.

Discussion Strengths Among the first prospective, controlled studies for myopes in the general population presenting for refractive surgery Most reports to date have been isolated case reports that have been retrospectively reviewed once the decompensation settled in Drawbacks Cases with risk factors excluded Larger prospective study needs to be planned

Conclusion Refractive surgery for myopia does not significantly alter the phoria state of the eye Considering the increasing number of refractive surgeries being done, and the implications of missing a well controlled deviation pre operatively, orthoptics should be a part of pre operative work ups