Evaluation of LASIK Treatment With the Femto LDV in Patients With Corneal Opacity

Since the introduction of LASIK by Pallakaris,^1,2 it has become the most commonly used procedure for the correction of refractive errors. Initially, microkeratomes were used to create flaps in the LASIK procedure, but with the introduction of the IntraLase femtosecond laser (Abbott Medical Optics Inc, Santa Ana, California) in 2001 ³ and subsequent generations of femtosecond lasers used to generate flaps, this technology has become widely accepted. Many studies have compared femtosecond lasers and mechanical microkeratomes.^4--9 These studies have not shown significant differences in visual acuity outcomes,^4,8 but the femtosecond laser is beneficial for flap creation due to the increased accuracy of ablation depth^6,7,9,10 and faster patient recovery.^4,5,10

In addition to the IntraLase FS 60 (Abbott Medical Optics Inc), our clinic utilizes a second-generation of the Femto LDV (Ziemer Ophthalmic Systems AG, Port, Switzerland), which has a top view camera that surgeons can access using a microscope or on screen (Table 1). The IntraLase laser generates adjacent spots with individual spot raster energy of approximately 1 μJ. ¹¹ Between the spots, spaces are present, which result in tissue bridges. In contrast, the Femto LDV irradiates the cornea with small overlapping spots and uses low energy (in the nJ range).¹¹ The Femto LDV also appears to have a lower incidence of opaque bubble layer.^11,12

Corneal opacity or scars can affect femtosecond laser operation.^9,13 For patients with corneal opacity, flaps typically are created using higher energy¹⁴ and are thicker than normal based on the residual corneal bed thickness. This is to prevent the occurrence of gas breakthrough. Gas breakthrough is one of the most common intraoperative complications with femtosecond lasers. Breakthrough occurs when the laser irradiates an area of corneal opacity and bubbles or gas enter the subepithelial tissue, which can result in imperfect flaps. If vertical gas breakthrough occurs and the surgeon fails to recognize this immediately after flap creation, it could result in a torn flap. Undiagnosed vertical gas breakthrough can result in difficult flap lift or possible pseudo buttonholes. ^15--17

In this study, we compare two femtosecond lasers, the Femto LDV and IntraLase FS 60, to evaluate their effectiveness in treating eyes with various levels of corneal opacity.

Patients and Methods

Patient Population

This...