[Surgery in myopic astigmatism: arciform keratotomy and PKR versus PARK]

Two surgical techniques for treatment of myopic astigmatism are compared: One technique is a combined procedure with relaxing incision and photorefractive keratectomy (RI PRK), the other one is photoreactive keratectomy done for correction of myopia and astigmatism (PARK). Fifty-nine eyes (42 patients) were operated by IR PRK. The preoperative myopia was between -1.5 and -14 D and the astigmatism between -0.75 and -6 diopters. Thirty-two eyes (20 patients) were treated with the PARK. The preoperative myopia was between -1 and -15 D and the astigmatism between -0.5 and -4. In 38 cases, relaxing incisions allowed to correct astigmatism entirely. The mean preoperative sphere of -6.8 D before PRK was 1.4 D and the spheres between -1 and -15 D. Twelve months after treatment, 26 eyes on 30 were spherical. The spherical equivalent varied between +0.75 and -1.50 D. Relaxing arciform incision presents the advantage to correct high asymmetric astigmatism without corneal thinning, as well as mixed astigmatism. At the present time, the PARK allows to correct only symmetrical myopic astigmatism.

CONCLUSION

The predictability of the results is high if the cylinder is less than 3 D and the sphere less than 6 D. Beyond this limit, there is a higher risk of regression, and haze related with the depth of photo-ablation and we prefer RI-PRK.

Clinical results of excimer laser photorefractive keratectomy: a multicenter study of 265 eyes

Efficacy, predictability, and safety of excimer laser photorefractive keratectomy were evaluated at centers in Paris and Brest, France. Photoablation was performed with the VISX laser on 265 eyes (151 at the Paris center and 114 at the Brest center). The eyes were clinically and statistically evaluated over a six month follow-up. Initial myopia ranged from -0.7 to -19.4 diopters (D) (mean spherical equivalent [SE] -5.9 D) in the Paris center and from -0.9 to -14.5 D (SE -4.5 D) in the Brest center. At both centers, the mean uncorrected visual acuity was worse than 20/200; over 90% of cases in each center had a best uncorrected visual acuity of 20/100 or worse. Results are reported globally and for subgroups of myopia: Group A, SE better than or equal to -3.0 D; Group B, SE worse than -3.0 D and better than or equal to -7.0 D; Group C, SE worse than -7.0 D. Uncorrected visual acuity was significantly improved in the patients followed for six months; 64% of Paris cases and 62% of Brest cases obtained an uncorrected visual acuity of 20/40 or better. Predictability of the treatment was good; 67% of Paris eyes and 74% of Brest eyes were less than 1.0 D from the intended correction after six months. The data suggest that the initial myopia affected the efficacy and predictability of the treatment; results in the mild to moderate myopia eyes were significantly better than results in the severe myopia eyes. One case of visual acuity regression (less than one line) was observed in the two groups. This was associated with corneal haze of moderate intensity.

Myopic keratomileusis by excimer laser on a lathe

BACKGROUND

We designed an excimer laser keratomileusis delivery system to increase the regularity of the refractive cut surface and allow greater precision in the level and shape of the ablated zone.

METHODS

A parallel faced corneal disc was produced by microkeratectomy from six human eyes and surgical keratectomy in 12 beagle corneas. A 193-nanometer excimer laser that was used to project an oval beam onto the corneal disc was rotated on a flat surface to ensure overlapping of the ovally ablated areas between pulses.

RESULTS

Electron microscopy of eye bank lenticules demonstrated a circular smooth regularly concave ablation zone. Histological examination of nine clear corneas confirmed thinning of the stroma without fibroblastic reaction and no epithelial hypertrophy. Mean preoperative corneal power of 43.15 +/- 2.18 decreased postoperatively to 33.61 +/- 2.34.

CONCLUSIONS

The new technique of excimer laser keratomileusis has the advantage of a cut surface smoother and the clear zone is devoid of the stepwise concavity and irregularity seen in diaphragm based photoablation delivery systems.

Photorefractive keratectomy in 176 eyes: one year follow-up

Beginning in March 1992, 176 eyes from 176 patients underwent photorefractive keratectomy with the Summit Technology Eximed UV200LA. This study was designed to evaluate the efficacy of this method.

Preliminary study of argon fluoride (193 nm) excimer laser trabeculectomy. Scanning electron microscopy at five months

There is an increasing interest in the use of the excimer laser in ophthalmology, particularly in refractive surgery. The argon fluoride (193 nm) excimer laser ablates tissue with a high degree of precision and without any mechanical or thermal damage to surrounding structures. In this study, the argon fluoride excimer laser was experimentally used in the rabbit model to perform a trabeculectomy. Clinical and scanning electron microscopic evaluations showed a successful and patent filtering procedure. At the five-month follow-up the trabeculectomy was smooth and regular and there was no evidence of inflammation or thermal damage on the surrounding structures.

[Epithelial and stromal healing after radial keratotomy. Scanning electron microscopy analysis]

A study of corneal healing after radial keratotomy was conducted under scanning electron microscopy in 28 papio-papio baboons. The appearance of the incisions after follow-ups ranging from one hour to three and a half years postoperatively permits to emit some hypotheses regarding the precise mechanisms of action of radial keratotomy, as well as those governing any functional or anatomical complications susceptible to occur after the operation.

[Endothelial effects of radial keratotomy in a non-human primate]

The study of the endothelial repercussion of radial keratotomy has been done on 33 corneas of 21 non human primates, using Scanning Electronic Microscope. Various lesions has been observed; the relationship between these lesions and the surgery parameters have been studied. One can conclude that the lesions are constant; their severity is related to the number and the depth of the incisions; as for their evolution, they do not seem to worsen with time during the experimental study (1 hour to 18 months).