Hypertonic Saline-Assisted Laser-Assisted Subepithelial Keratectomy For The Correction Of Moderate And Low Myopia

Objective: To evaluate the effectiveness of hypertonic saline(5%sodium chloride) in execution of corneal epithelial flap in laser-assisted subepithelial keratomileusis (HS-LASEK) for treatment of moderate and low myopia. The results were compared to the cornea treated with 20% alcohol.Methods: 48 patients(96 eyes) with moderate and low myopia were divided into 2 groups. In Group A (A-LASEK, 22 patients 44 eyes) , 20%alcohol was used to create the epithelial flap; in GroupB (HS-LASEK,26 patients 52 eyes) , 5%sodium chloride was used to create the epithelial flap. Postoperative visual acuity, refraction power, time of epithelial healing, and haze were recorded. The patients were followed-up for 6 months.19 New Zealand rabbits (38 eyes) were divided into 3 groups randomly, In saline Group (right eyes of 11 rabbits and left eyes of 7 rabbits ) : treating with 5% sodium chloride for 25 seconds; in alcohol Group (left eyes of 11 rabbits and right eyes of 7 rabbits): treating with 20%alcohol for 25 seconds. Before and after treating, the cornea thickness was measured by A-scan ultrasonography. in control Group (1 rabbits, 2eyes) : normal cornea. All cornea were observed by light microscope.34 patients(right eyes of 19 patients and left eyes of 15 patients were treated with 5% sodium chloride for 25 seconds; left eyes of 19 patients and right eyes of 15 patients were treated with 20% alcohol for 25 seconds) were chosen consecutively, their cornea thickness were measured by A-scan ultrasonography. Some cornea flaps were studied by light microscope and TEM.Results: The mean time of epithelial healing was (4.5±0.2) days in A-LASEK eyes, while (3.8±0.4) days in HS-LASEK eyes, the difference of epithelial healing time between the two groups was statistically significant. Visual acuity in all patients were improved after the surgery, 3 days after operation, visual acuity reached 0.8 or better in 27.3% (12/44) of A-LASEK eyes and 48.1% (25/52) of HS-LASEK eyes, the difference between the two groups was statistically significant(P<0.05). Two weeks after operation corneal haze was found in 13 eyes(29.5%) of A-LASEK group and 15 eyes(28.8%) of HS-LASEK group, but the grade of haze was below 0.5 and had no effect on visual acuity, after 3 months, haze was noted in 10% of eyes in each groups ,the difference of corneal haze between the two groups was no statistically significant ( P >0.05). One day after operation, 12 eyes (27.3%) of A-LASEK and 6 eyes (11.5%) of HS-LASEK had obvious pain, the difference between the two groups was statistically significant(P <0.05).Rabbits' corneas were thicker than before being treated with 20%alcohol and thinner than before being treated with 5% sodium chloride. Then the human's corneas became thicker by both alcohol and hypertonic saline.Pathological results were that epithelial cell's edema was seen in all rabbits, and stroma became thicker with 20% alcohol and thinner with 5% sodium chloride. Cell edema was seen in all human epithelial specimens.In alcohol's group, Microvilli absence, wide gap between cells and discontinuity of basement membrane were observed. In hypertonic saline group, we could observ abundant microvilli and continual basement membrane.Conclusion:1. HS-LASEK is a safe surgery for the correction of moderate and low myopia as A-LASEK, and have a better curative effect than A-LASEK.2. Bowman's membrane ensured LASEK a safe surgery, that is no harm to endothelial cell.3. The basement membrane were observed to attach to the basal cell in results that the basement membrane was the plane of cleavage of the corneal.