1. 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 India.
Ph /
We do not have any financial interest in this presentation

3. -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)

5. 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 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

6. 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.

7. 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)

10. 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.

11. 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.

12. 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……