Corneal stromal wound healing in refractive surgery: the role of myofibroblasts.

8 pages, 8 figures.-- PMID: 11328757 [PubMed].-- Open Access full-text paper available at the publisher's site.

/pdf/ocular-aberrations-before-and-after-myopic-corneal-5aesi8jd9g.pdf

Ocular aberrations before and after myopic corneal refractive surgery: LASIK-induced changes measured with laser ray tracing.

Background The purpose of this research was to study the visual outcome of excimer laser photorefractive keratectomy and laser in situ keratomileusis (LASIK) for the correction of moderate and high myopia. Methods Twenty partially-sighted eyes of 20 patients were divided into two groups, LASIK and photorefractive keratectomy. Ten eyes underwent LASIK and the other 10 photorefractive keratectomy. Follow up was at 1, 3, 6, and 12 months. The LASIK technique included a nasally based, 150 microns thick, 8.0 x 9.0 mm diameter, truncated, disc-shaped corneal flap created with a microkeratome; and the ablation of the stroma with a 193-nanometer ArF excimer laser. The flap was returned to its original position and held in place by apposition. The photorefractive keratectomy technique included mechanical removal of the epithelium and ablation of the stroma with a 193-nanometer ArF excimer laser. Results LASIK series: One eye had a ruptured globe during the second postoperative month and was excluded from the study. The preoperative spherical equivalent refraction ranged from -10.62 to -25.87 diopters (D). The attempted correction ranged from -8.00 to -16.00 D. Postoperative refraction and corneal topography stabilized between 4 and 12 weeks. Spectacle-corrected visual acuity was within 1 Snellen line of preoperative in all eyes. The refraction in six eyes (66.6%) was within +/- 1.00 D of the intended correction, and in eight eyes was within +/- 2.00 D (88.8%) at 12 months. The mean attempted correction (11.40 +/- 2.60 D) was close to the mean achieved correction at 12 months (11.96 +/- 3.10 D). The mean postoperative refractive astigmatism (1.50 +/- 0.97; range, 0.25 to 3.50 D) was close to the preoperative astigmatism (1.70 +/- 1.15; range, 0 to 3.75 D). Endothelial cell density at 12 months showed an average 8.67% of cell loss. All eyes showed a clear interface. Photorefractive keratectomy series: The preoperative spherical equivalent refraction ranged from -10.75 to -23.12 D. The attempted correction ranged from -8.80 to -17.60 D. Postoperative refraction showed regression throughout the follow-up period, and corneal topography did not stabilize. Spectacle-corrected visual acuity was within 1 Snellen line in eight eyes. Two eyes lost 2 and 3 Snellen lines. One eye was within +/- 1.00 D, and three eyes (30%) were within +/- 2.00 D of the intended correction at 12 months. The achieved correction mean (7.17 +/- 5.29 D) was 61% of the attempted mean (11.72 +/- 2.81 D) at 12 months. The postoperative refractive astigmatism (1.80 +/- 0.95; range, 0.50 to 4.00 D) was very close to the preoperative (1.90 +/- 1.33; range, 0 to 5.00 D). Endothelial cell density showed an average of 10.56% cell loss at 12 months. The mean haze at 12 months was 1.2 (0 to 4 scale). Conclusion LASIK, although more complicated because of the use of a microkeratome, was more effective than photorefractive keratectomy in higher myopes. LASIK created less corneal haze. The refraction was more stable with LASIK in the correction of high myopia. Its predictability was three times that of PRK.

Excimer laser in situ keratomileusis and photorefractive keratectomy for correction of high myopia.

Excimer laser photorefractive keratectomy. 18-month follow-up

Complications of Myopic Photorefractive Keratectomy with the Excimer Laser

The results of excimer laser photorefractive keratectomy (PRK) in 16 blind and 120 sighted eyes (136 patients) are presented. Follow up for the blind eyes was 22 months and for the sighted eyes 8 to 18 months (mean, 1 year). A Summit Technology UV200 excimer laser with fluence fixed at 180 mJ/cm2, beam diameter 4 mm, a frequency of 10 Hz, and ablation rate of 0.22 mu per pulse was used. The range of preoperative myopia was - 1.50 diopters to - 17.50 D (spherical equivalent). Ninety percent of patients undergoing a -2.00 D correction and 75% of patients undergoing a -3.00-diopter correction were within +/- 1.00 D of intended refraction at 6 months. This figure fell to 40% and 20% for the groups undergoing -6.00 D and -7.00 D corrections, respectively. While the trend is toward undercorrection, around 70% of patients in all groups have benefited from a reduction of their myopia by at least half that intended. A variable degree of anterior stromal "haze" was detected in 110 patients (92%) despite a rigid high dose topical corticosteroid regime over 3 months. Best spectacle corrected visual acuity, however, was greater than or equal to preoperative levels in 111 patients (93%). Six patients experienced a reduction of one line of Snellen acuity at 6 months and three of the high myopes lost two lines. No patients lost more than two lines of Snellen acuity. Ninety-four patients (78%) noticed a "halo" around lights at night, more marked in the early postoperative period, which we attribute to the 4-millimeter diameter ablation zone. With a large pupil, both central and paracentral cornea can contribute simultaneously to the retinal image. We have demonstrated considerable individual variation in response to this surgery, which is more marked in high myopia. Although follow up at the present time is limited, to date PRK appears to be a safe procedure that holds considerable promise for refractive surgery in the future.

Photorefractive keratectomy with an argon fluoride excimer laser: a clinical study.

In this study, we report the results of a prospective, double-blind trial to determine whether high-dose topical corticosteroids have an effect on refractive outcome or anterior stromal haze after photorefractive keratectomy. A total of 113 patients were allocated randomly to either placebo- or steroid-treated groups (0.1% dexamethasone metasulphobenzoate for 3 months) and underwent either -3.00-diopter (D) or -6.00-D procedures. At 6 weeks, the mean change in refraction was significantly greater in the steroid-treated group than in the placebo-treated group (-3.00-D group, P = .0015; -6.00-D group, P = .0011). However, when corticosteroids were discontinued at 3 months, this difference became statistically insignificant. There was no statistically significant effect on anterior stromal haze at any stage. Since long-term use of corticosteroids to maintain the initial beneficial effect on refraction would be unacceptable, we conclude that these agents should not be used after photorefractive keratectomy.

The effect of topical corticosteroids on refractive outcome and corneal haze after photorefractive keratectomy. A prospective, randomized, double-blind trial.

A marginal loss of corneal transparency or 'haze' is a phenomenon experienced after photorefractive keratectomy using excimer lasers (193 nm). In this study, the authors present a review of the current literature relating to this phenomenon and illustrate this with an example of pathology from a two-week postoperative human eye. They also report the functional implications of postoperative changes in corneal transparency using psychophysical tests measuring visual acuity at different contrast levels (100, 20 and 5%). The data were collected from 103 patients at various postoperative intervals with a maximum follow-up time of one year. At 100% contrast, the authors found only slight disturbances in the first six to eight weeks postoperatively. At 20% contrast most patients had a decrease of visual acuity in the first six weeks but all returned to the normal range by 14 weeks postoperatively. At the 5% level, all patients showed significant disturbances in the first 12 to 14 postoperative weeks, but again most were back in the normal range after this period. However, some patients showed a second wave of decrease of visual performance at the low contrast level commencing at four months, peaking at nine months, and thereafter again regressing to the normal preoperative level. This second wave of visual disturbance may correlate with cellular responses subsequent to cessation of steroid therapy at three months.

'Haze' in photorefractive keratectomy : Its origins and consequences

The argon fluoride excimer laser emits radiation in the far ultraviolet part of the electromagnetic spectrum (193 nm). Each photon has high individual energy. Exposure of materials or tissues with peak absorption around 193 nm results in removal of surface layers (photoablation) with extremely high precision and minimal damage to non-irradiated areas. This precision is confirmed in a series of experiments on cadaver eyes and the treatment of 25 eyes with anterior corneal disease (follow-up 6 to 30 months). Multiple zone excimer laser superficial keratectomy is considered the treatment of choice for rough, painful corneal surfaces. All patients in this group were pain-free postoperatively. Where good visual potential exists, ablation of a single axial zone is recommended and results in improved visual acuity and reduction of glare. A hyperopic shift was noted in this group.

https://bjo.bmj.com/content/bjophthalmol/75/5/258.full.pdf

D S Gartry

Papers

Excimer laser photorefractive keratectomy. 18-month follow-up

Photorefractive keratectomy with an argon fluoride excimer laser: a clinical study.

The effect of topical corticosteroids on refractive outcome and corneal haze after photorefractive keratectomy. A prospective, randomized, double-blind trial.

'Haze' in photorefractive keratectomy : Its origins and consequences

Excimer laser treatment of corneal surface pathology: a laboratory and clinical study.