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A. El Maftouhi–Quaranta, M. Puech, R. Amar, D. Lebuisson; Pachymetry of Corneal Flap by OCT 3 . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1332.
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© ARVO (1962-2015); The Authors (2016-present)
Stratus OCT 3 provides high resolution retinal images, but for corneal imaging only OCT 1 has also been employed. This work presents the results and the interest of OCT 3 in corneal imaging after Lasik surgery
The OCT technique (Carl Zeiss, Méditec.) has been initially applied to explore the posterior segment of the eye. By defocusing the laser beam, using an optic system, we could obtain high–resolution images of the cornea. This retrospective study concerns 52 eyes (35 patients) that underwent Lasik surgery. In 40 eyes, the corneal flap has been obtained by a conventional microkeratom and in 12 eyes, by laser Femtosecond (Intralase). For all patients, a corneal OCT 3 imaging was obtains. Measurements of the corneal flap and of the residual stromal bed at the corneal apex have been unregistered. The follow–up after surgery varied from 3 weeks to 8 years. Corneal thickness obtained by OCT 3 has been compared to the ultrasounds–pachymetry that represents the gold standard. Ultrasounds measurements have been realized at the corneal apex, with patient in a prone position, trying to optimize the quality of measurements.
In all eyes, the flap could be visualized, even for the more ancient surgeries. This has been possible thank to the hyper reflectivity of the residual stromal bed interfacing with the mild reflective flap. The thickness of the corneal flap obtained by a microkeratom varied from 76 µ to 315µ with a mean of 180µ against an expected thickness of 160 µ.
Flaps produced by the Femtosecond laser varied from 107µ to 166µ in thickness with a mean value of 134µ, against an expected value of 110µ. A difference of +/– 10µ has been found between the measurements of OCT 3 and the ultrasounds technique ones, at the apex
OCT 3 allows to analyze and to measure the cornea by using a no–contact and easy to perform procedure. Moreover, it provides semi–quantitative, anatomic data on the effects produced by the intra–stromal surgery. Considering the observed variations of thickness of the corneal flap, it is mandatory to perform an OCT 3 analysis of the cornea before any recurrent surgery, to ascertain the thickness of the residual stoma bed (250µ) avoiding corneal impairment due to ectasia.
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