Safe Lasik on Thin Cornea with Moderate Myopia Dr. Hardik A. Shroff MD, Dr. Ashok P. Shroff MD Dr. Dishita H. Shroff MD, Dr. V. D. Vaishnav MD Shroff Eye Hospital Near Railway Station, Navsari 396 445. India. Ph. +91-2637-250565 / 250695 Email: sehnavsari@yahoo.co.in We do not have any financial interest in this presentation

-4D to -7D (Spherical equivalent) Demography Cases Eyes Ref. Error Pachymetry Sex Age M F 29 52 -4D to -7D (Spherical equivalent) 473 µm to 500 µm 8 21 19 to 33 years (mean 22.6 yrs)

Residual Refractive Error Ref. Error (Spherical Equivalent) Observations There were no intraoperative complications. Corneal flaps were regular and of adequate thickness. Postoperative period was uneventful. All patients were comfortable. At the end of one year… 34 eyes were emmetropic. 18 eyes had +0.50 D residual error. There was no corneal ectasia. Patients had no complaints like glare, haloes etc. 18 (34.61%) 34 (65.39%) 19 (36.53%) 33 (63.47%) 52 29 Total 8 (15.38%) 2 (3.85%) 7 (13.46%) 3 (5.77%) 10 7 >-6 to -7 D 9 (17.30%) 12 >-5 to -6 D 1 (1.93%) 29 (55.77%) 27 (51.93%) 30 15 -4 to -5 D + 0.5D Plano Better than Pre Op. (1 line) No Change (Pre Op.) Residual Refractive Error B.V.A. (Eyes) No. of Eyes No. of Patients Ref. Error (Spherical Equivalent) Patients: 29, Eyes: 52

Discussion Before some years, when microkeratome heads of only 160µ and above were available and treatment zone options were less, residual stromal thickness > 250 µ was not available with older generation machines in cases of moderate myopia with thin cornea. Now, newer excimer laser machines are available with many variants / options for treatment. Moreover, thinner flaps of 80µ, 100µ of 130µ thickness with good quality are possible. Lately, Femtosecond laser is available for customized flap thickness. By adjusting treatment zone (not less than the size of pupil in scotopic conditions), required ablation can be reduced. Therefore more stroma is available even after ablation. Hence residual thickness can safely be kept over 250µ in many cases of moderate myopia.

Imp. equation We have two areas where we can play: Corneal flap making Pachymetry – Corneal flap thickness – Ablation depth = Residual stromal bed We have two areas where we can play: Corneal flap making Thickness can be reduced by using 100 or 130 µm head (Fig. 1) and Treatment zone Where required ablation can be reduced by decreasing the treatment zone size (not less than 5mm) (Fig. 1)

Discussion (cont…) By taking all possible and acceptable parameters into consideration, if residual stromal thickness achieved is ≥ 250µ then one can go ahead with the procedure. Otherwise one should avoid Lasik and can consider for other option. Those excimer which do not have such facility, but if ablation depth data is available then residual stromal depth can be mathematically calculated. In case of doubt, flap thickness can be evaluated by carefully done intraoperative pachymetry.

Discussion (cont…) However, strict planning and thorough counseling considering patient’s occupation and life style should be done before hand. Patients should also be counseled about very remote or no possibility of retreatment Patients, at times, are ready to accept some residual error in cases of high myopia (e.g. -1 to -2 D refractive error in eyes with -10 D or so). It is important to understand that this procedure is recommended to help needy patients on social ground or job related requirement and just NOT FOR THE MONEY.

Summary In this series, 52 eyes of 29 patients having moderate myopia with thin cornea (pachymetry < 500µ) were successfully treated with Lasik by making thinner flaps and reducing the amount of ablation required by adjusting different parameters, so as to have residual stromal thickness ≥ 250 µ. Thanks……