Corneal forward shift after excimer laser keratorefractive surgery.

Area of Science:

• Ophthalmology
• Corneal Surgery
• Refractive Surgery

Background:

• Excimer laser surgery, including photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK), compromises corneal structural integrity.
• Surgical tissue subtraction and disruption of Bowman's membrane are inherent to these procedures.
• A forward shift of the cornea is a common observation post-surgery.

Purpose of the Study:

• To evaluate the antero-posterior movement of the cornea after excimer laser refractive surgery.
• To identify factors predisposing to corneal forward shift.
• To differentiate corneal forward shift from true ectasia.

Main Methods:

• Corneal topography using scanning-slit technology (Orbscan) was employed.
• Posterior corneal elevation was measured to assess antero-posterior movement.
• Patient data including corneal thickness, intraocular pressure, and refractive error were analyzed.

Main Results:

• Eyes with thinner corneas, higher intraocular pressure, and higher myopia requiring greater ablation showed increased predisposition to forward shift.
• A progressive trend of corneal forward shift was observed after PRK, stabilizing by 6 months.
• No progressive thinning or expansion of the cornea was noted during the one-year follow-up, suggesting the shift is not true ectasia.

Conclusions:

• Corneal forward shift after PRK and LASIK is a distinct phenomenon, not indicative of true ectasia.
• This forward shift, affecting both corneal surfaces, may contribute to myopic regression following refractive surgery.
• Understanding this shift is crucial for managing refractive outcomes and patient expectations.