Relation between corneal haze and transforming growth factor-β1 after photorefractive keratectomy and laser in situ keratomileusis

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Abstract
Purpose: To investigate the relation between corneal haze formation and transforming growth factor-β (TGF-β) after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Setting: Department of Ophthalmology, University of Tokyo Graduate School of Medicine, Tokyo, Japan. Methods: White rabbits were divided into 4 groups, with each group receiving 1 of the following surgeries: manual epithelial abrasion, PRK, lamellar keratotomy, or LASIK. The degree of corneal haze was quantitatively analyzed by measuring the light scattering intensity of corneas before and 4 and 12 weeks after surgery. The expression of type IV collagen and TGF-β1 in the corneas at baseline and at 4 weeks was examined immunohistochemically. Results: The light scattering intensity was significantly greater 4 and 10 weeks after PRK. In contrast, epithelial abrasion, lamellar keratotomy, and LASIK did not influence the light scattering intensity of the corneas. Type IV collagen was detected in the basal lamina of the corneal epithelium and in Descement's membrane in the normal cornea. After epithelial abrasion, there was no change in the distribution of type IV collagen. Four weeks after PRK, the expression of type IV collagen was detected in the subepithelial layer of the laser-ablated area. Four weeks after lamellar keratotomy, type IV collagen was linearly and fragmentarily detected in the corneal stroma. Four weeks after LASIK, type IV collagen was linearly and continuously detected in the corneal stroma and was detected slightly in the subepithelial region of the laser-ablated area. In the normal corneas, the expression of TGF-β1 was not detected in the keratocytes. Four weeks after PRK, the expression of TGF-β1 increased in the keratocytes that proliferated in the subepithelial fibrous layer. In contrast, epithelial abrasion, lamellar keratotomy, and LASIK did not change the expression pattern of TGF-β1 in the keratocytes. Conclusion: The multiplier effect of epithelial abrasion and excimer laser ablation in PRK may increase the expression of TGF-β1 in keratocytes and induce corneal haze.

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