Corneal Haze Following Refractive Surgery

Abstract

Corneal transparency is essential to visual clarity. The anatomy of the cornea is specifically designed to neither scatter nor absorb light. The spacing and parallel nature of collagen fibers, relative lack of cellularity, and transparent extracellular matrix all contribute to corneal clarity. Surface ablative forms of refractive surgery have been well known to be associated with postoperative corneal haze formation, which is initiated by the complex corneal healing response. 1,2 Haze formation can prolong time to optimal visual outcomes, coincide with refractive regression, and in rare circumstances, lead to corneal scaring.We will review the pathophysiology of corneal wound healing as it relates to refractive surgery, the types of postsurgical corneal haze formation and its association with various techniques of refractive surgery, and discuss preventative measures and treatment modalities for postrefractive surgery corneal haze formation. Corneal Wound HealingThe transparency of the cornea is determined by a variety of anatomic and biomechanical factors. Contributing factors include the uniform diameter, regular spacing, and parallel nature of collagen fibers, and the composition of the paracrystalline extracellular matrix. This extracellular matrix is made of keratin sulfate proteoglycan and is important for collagen polymerization and contributes to the precise organization of fibrils so that visible light is neither scattered nor absorbed. 3,4

Targeted AAV5-Smad7 gene therapy inhibits corneal scarring in vivo

“…Fibrosis is the leading cause of corneal blindness and can potentially be treated by targeted gene therapy [4,7,10]. Following corneal injury, TGFβ drives pro-fibrotic responses by enhancing ECM gene expression, and is responsible for the conversion of fibroblasts into myofibroblasts [34].…”

“…Corneal scarring is the third leading cause of blindness globally, affecting 1.3 million Americans each year [2,3]. Currently, no effective topical treatments exist that cure corneal scarring and the use of intra-operative drugs such as MMC (Mitomycin C) for prevention of corneal haze can be problematic [4]. Hence, corneal transplantation remains the gold standard for treatment of corneal blindness.…”

“…TGFβ signaling plays a crucial role in transdifferentiation of keratocytes into myofibroblasts, the abnormal proliferation of which leads to aberrant collagen deposition causing fibrosis and ultimately loss of visual acuity [4, 14, 21]. Smad (Suppressor of mothers against decapentaplegic) proteins have been shown to be specifically activated by TGFβ superfamily members [22] and they regulate cell growth, proliferation, migration, and differentiation.…”

Efficacy and safety of a 3-month loteprednol etabonate 0.5% gel taper for routine prophylaxis after photorefractive keratectomy compared to a 3-month prednisolone acetate 1% and fluorometholone 0.1% taper

“…Myofibroblasts produce disorganized collagen, causing the appearance of corneal haze and leading to increased light scattering and decreased visual acuity 1. The mainstay in prevention of visually significant corneal haze involves decreasing the corneal inflammatory response with anti-inflammatory medications such as topical corticosteroids or other immunomodulatory medications 2. Previous studies have demonstrated topical corticosteroids to be beneficial in modulating post-PRK corneal inflammatory response, as well as reducing regression 3,4.…”

Comparison of single-step transepithelial photorefractive keratectomy and conventional photorefractive keratectomy in low to high myopic eyes

“…The procedure causes more postoperative pain, delayed epithelial healing, and stromal haze, when compared to Laser in situ keratomileusis (LASIK). [ 1 2 3 ] However, because of the flap-related complications of LASIK, surface ablation techniques are preferred by many surgeons. [ 4 ] Previously, in surface ablation, the epithelium was removed manually (PRK), before the excimer laser application.…”