Complications of myopic photorefractive keratectomy with the excimer laser

Photorefractive Keratectomy for Myopia of 6 to 12 Diopters

To conduct a prospective, nonrandomized clinical trial to assess the efficacy, stability and safety of the use of excimer laser photorefractive keratectomy (PRK) to correct myopia of greater than -6.00 diopters (D) in Singapore. Two hundred thirty-three eyes of 176 patients with a mean preoperative spherical equivalent refraction of -8.70 +/- 2.3 D (range, -5.75 D to -18.13 D) underwent PRK with a 193nm ArF excimer laser (ExciMed, Summit) for myopic corrections of between -6.20 D and -11.90 D. The first 66 of 233 eyes that reached at least 1 year of postoperative follow up are reported. One year postoperatively, the mean manifest spherical equivalent refraction was -1.50 D +/- 1.90 D (range -6.25 D to +3.25 D); 34% of eyes were within +/- 1.00 D of attempted correction; uncorrected visual acuity was 20/40 or better in 75% of eyes. No eyes lost two or more Snellen lines of spectacle corrected visual acuity. Central corneal haze was mild in 20% of eyes and moderate in 3% of eyes. Five eyes developed ocular hypertension that subsequently resolved with treatment. Excimer laser PRK is reasonably effective and safe in the treatment of -6.00 D to -12.00 D of myopia. However, it is less accurate than PRK in eyes with low to moderate myopia and is more likely to result in significant corneal haze.

Treating myopia with the excimer laser: the present position

Images

Corneal endothelial status 12 to 55 months after excimer laser photorefractive keratectomy

PURPOSE

To investigate the long-term effect (range, 12-55 months) of photorefractive keratectomy (PRK) on the human corneal endothelium.

METHODS

Specular microscopy of the central corneal endothelium was performed on 106 patients who underwent PRK to correct myopia. The duration of follow-up varied from 12 to 55 months (mean, 33 months; median, 37 months). Patients were divided in two groups: group 1 included 32 patients (35 treated eyes) with preoperative and postoperative central endothelial images; group 2 included 26 patients from group 1 and 74 additional patients with postoperative central endothelial images of the treated and untreated fellow eyes.

RESULTS

In group 1, preoperative and postoperative values were as follows: mean cell density (+/- standard deviation), 2950 +/- 329 cells/mm2 and 2907 +/- 337 cells/mm2, respectively (P = 0.43); polymegathism index, 0.29 +/- 0.06 and 0.28 +/- 0.05, respectively (P = 0.38); pleomorphism index, 65.8% +/- 5.6% and 64.2% +/- 5.6%, respectively (P = 0.22); figure coefficient index, 0.86 +/- 0.05 and 0.87 +/- 0.02, respectively (P = 0.20). In group 2, postoperative values of the treated and untreated eyes were as follows: mean cell density, 2912 +/- 363 cells/mm2 and 2922 +/- 434 cells/mm2, respectively (P = 0.86); polymegathism index, 0.28 +/- 0.05 and 0.30 +/- 0.08, respectively (P = 0.04); pleomorphism index, 64.93% +/- 7.49% and 64.07% +/- 8.31%, respectively (P = 0.45); figure coefficient index, 0.88 +/- 0.03 and 0.88 +/- 0.03, respectively (P = 0.79).

CONCLUSIONS

Photorefractive keratectomy caused no damage to the central corneal endothelium. Polymegathism differences in treated and untreated eyes could be attributed to modifications in corneal metabolism or to a yet unknown mechanism.

Clinical analysis of excimer laser photorefractive keratectomy using a multiple zone technique for severe myopia

PURPOSE

In an investigational procedure, excimer laser photorefractive keratectomy for severe myopia was performed at three clinical trial centers to determine the effectiveness of the multiple zone technique.

METHODS

A VisX Model Twenty/Twenty excimer laser (VisX, Santa Clara, California) was used to perform photorefractive keratectomy on 14 severely myopic eyes (-10.37 to -24.5 diopters) of 12 patients by using a multiple zone technique. Postoperative follow-up ranged from six months to two years; retreatments were performed on four patients, with a follow-up of at least nine months.

RESULTS

At six months postoperatively, before retreatment, three of the 14 eyes were within 2 diopters and seven of the 14 eyes were within 4 diopters of attempted correction. Regression of effect to more severe myopia was worse in five eyes treated with nitrogen gas blowing. Retreatments also demonstrated considerable myopic regression. Three patients had loss of two or more lines of best-corrected visual acuity, and these patients also had moderate or severe levels of haze.

CONCLUSION

Excimer laser photorefractive keratectomy for severe myopia using a multiple zone technique is associated with considerable regression, haze, and loss of best-corrected visual actuity, especially when performed in association with nitrogen gas blowing.

Diving and hyperbaric ophthalmology

Exposure of the human body to ambient pressures greater than that at sea level may result in various disorders, some of which have ocular manifestations. Additionally, some eye disorders and postoperative states may be adversely affected by the underwater environment or other hyperbaric exposures. The prevalence of recreational, military, and commercial diving, as well as the medical use of hyperbaric oxygen therapy, requires that ophthalmologists be familiar with the effects of the hyperbaric environment on the normal and diseased eye. The ophthalmology and diving medical literatures were surveyed for publications relating to the ophthalmic aspects of diving and hyperbaric exposures. Underwater optics, underwater refractive correction, and ophthalmic aspects of a fitness-to-dive evaluation are summarized. The evaluation and management of ocular manifestations of decompression sickness and arterial gas embolism are reviewed and guidelines for diving after ocular surgery are proposed.

Lasers in ophthalmology

This article reviews the principle uses of ophthalmic lasers, providing historical background with an emphasis on new applications and areas of investigation. Ophthalmic photocoagulation was the first medical laser application and has restored or maintained vision in millions of people. More recently, photodisruption and, increasingly, ablation have gained prominence for treating a wide range of ocular pathology. The unique properties of lasers have also been harnessed for diagnostic purposes, with optical coherence tomography representing a significant improvement over existing imaging methods. Many ophthalmic applications of lasers have been developed, but the field is a dynamic one which continues to evolve along with laser technology itself.

Correction of High Myopia With the Worst Myopia Claw Intraocular Lens

BACKGROUND

Phakic anterior chamber lenses is one of the modalities used to correct high myopia. We report the initial results of our prospective study on the Worst myopia claw intraocular lens (IOL) that is fixated to the anterior iris.

METHODS

We studied 35 eyes in 18 patients with a preoperative myopia ranging from -6.00 to -28.00 diopters (D). The follow up ranged from 6 months (n = 15) to 12 months (n = 20).

RESULTS

In 26 (74.3%) eyes, the postoperative spherical equivalent refractive error was within 1.00 D of emmetropia. The mean refraction was stable between 1 to 2 months and 12 months. The mean spectacle-corrected visual acuity improved from 20/50 to 20/40. The straylight measurements did not show a significant increase postoperatively (p = .64). The mean endothelial cell loss was 5.6% (range, +6.3% to -22.6%) at 6 months, and 8.9% (range, +0.77% to -23.5%) at 12 months. We did not encounter major complications.

CONCLUSION

Implanting a Worst myopia claw IOL in high myopic eyes resulted in a stable, reasonably accurate refractive outcome. This group of patients will be followed longer because of concern over ocular complications with this technique.

Phototherapeutic keratectomy for recurrent corneal erosions

Recurrent corneal erosion may be a difficult disorder to treat, with a number of patients suffering persistent symptoms despite conventional therapy. We present a series of 15 patients (17 eyes) who underwent excimer laser phototherapeutic keratectomy (PTK) for recurrent corneal erosion. In 9 patients a previous episode of corneal trauma could be identified, while in 6 (8 eyes) the problem had occurred spontaneously. The mean duration of symptoms prior to PTK was 13 months (range 6-60 months). All patients had received lubricant ointments, 7 had tried bandage contact lenses and 4 had undergone epithelial debridement with no amelioration of their symptoms. The affect area of epithelium was removed and a 20-30 pulse (5-7 microns) ablation was performed to Bowman's membrane. Great care was taken to avoid the edges of treatment zones from encroaching on the axial cornea. In 11 patients (13 eyes) there was a marked improvement in symptoms post-operatively with no recurrences. The mean follow-up was 11 months (range 6-24 months). Four patients experienced recurrent episodes 3-6 months after PTK and 2 have subsequently been retreated, 1 of whom has been symptom-free for 12 months. Post-operative best corrected visual acuity was unaltered in 9 eyes and improved by at least one Snellen line in 8 eyes. Excimer laser PTK appears to be a safe and promising procedure for recurrent corneal erosion in cases refractory to medical treatment. Further studies are indicated to compare its effectiveness with established surgical procedures.