Complications of myopic photorefractive keratectomy with the excimer laser

Clinical and morphological response to UV-B irradiation after excimer laser photorefractive keratectomy

This paper represents an update on a study that has been reported elsewhere (Nagy ZZ et al: Ophthalmology 104:375-380, 1997). The aim of the study was to evaluate the clinical and light- and electron-microscopic effects of ultraviolet-B (UV-B) exposure on the outcome of photorefractive keratectomy (PRK). A total of 42 pigmented rabbits were used in the study. One eye from each of 12 rabbits received a 193 nm 45-microm deep (-5.0 diopters [D]) excimer laser PRK, one eye from each of 12 rabbits received a 135-microm deep (-15.0 D) excimer laser PRK, and one eye from each of 12 rabbits received a 270 microm deep (-30.0 D) excimer laser PRK. Twenty-one days after PRK, six of the laser-treated eyes from each group were exposed to 100 mJ/cm2 UV-B (280-320 nm). The other six rabbits from the PRK groups received no further treatment. One eye from each of six rabbits received only UV-B irradiation, serving as control. Subepithelial haze was evaluated before and after UV-B irradiation. Clinical changes were followed by laser tyndallometry, confocal corneal biomicroscopy, ultrasound biomicroscopy, and endothelial specular microscopy. Corneal morphology was assessed 4, 8, and 12 weeks after UV-B exposure, employing light microscopic and transmission electron-microscopic techniques (TEM). Eyes only exposed to 100 mJ/cm2 UV-B exhibited keratitis for 2 days, but showed no haze and were histologically normal at all time intervals. The PRK-UV-B-irradiated rabbit eyes exhibited a significant increase of stromal haze compared to the eyes receiving PRK alone; this phenomenon correlated with the depth of photoablation. The severity of clinical findings also correlated with the previously attempted photoablation depth; in PRK-UV-B-irradiated eyes the symptoms were much more serious than in eyes treated with PRK alone. Histologically, the main difference between the UV-B-irradiated and nonirradiated-post-PRK eyes was the presence of anterior stromal extracellular vacuolization in the UV-B-exposed eyes. The vacuolated foci were confined to the PRK treatment area, contained increased numbers of keratocytes and showed a disorganization of normal collagen lamellae. Transmission electron microscopy revealed activated keratocytes containing abundant rough endoplasmic reticulum, prominent Golgi zones, and extracellular vacuoles filled with amorphous material. The haze and morphological changes showed a tendency to incomplete resolution over a period of 12 weeks. Ultraviolet-B exposure during post-PRK stromal healing exacerbates and prolongs clinical symptoms and the stromal healing response, which is manifest biomicroscopically by augmentation of subepithelial haze. The findings suggest that excessive ocular UV-B exposure should be avoided during the period of post-PRK stromal repair and that UV-B may modulate the response of tissues to excimer 193 nm, and perhaps, other laser energy in general.

Complications of excimer laser photorefractive keratectomy for myopia

PURPOSE

To evaluate the safety and complication rates of excimer laser photorefractive keratectomy (PRK).

SETTING

Assutah Laser Center, Tel-Aviv, Israel.

METHODS

This retrospective study evaluated the complication rate after PRK in 825 consecutive patients who had PRK for myopia and had a follow-up of at least 12 months.

RESULTS

At 12 months postoperatively, 4.0% of patients suffered from overcorrection and 8.6% from undercorrection. Induced astigmatism developed in 1.4% of all operated eyes. Three percent of the patients had haze, and 3.6% reported glare or halos. Twenty-three eyes (2.7%) lost one line or more of best corrected visual acuity (BCVA). Ptosis developed in 0.4% of the eyes, and 3.5% had a significant increase in intraocular pressure resulting from corticosteroid treatment. There were no complications in 678 eyes (82.5%).

CONCLUSION

Eighty-two percent of eyes having PRK did not develop complications. In 18.0% one or more complication, mainly undercorrection, overcorrection, or loss of BCVA, occurred.

Excimer laser photorefractive keratectomy for high myopia: four-year experience with a multiple zone technique

PURPOSE

The purpose of the study is to evaluate the results of the authors' 4-year experience with excimer laser photorefractive keratectomy (PRK) and multiple optical zone corneal ablation in highly myopic eyes.

METHODS

The authors retrospectively evaluated 56 eyes of 44 patients (mean refraction, -11.3 diopters [D]; range, -5.75 to -24.5 D) who underwent PRK with a Visx Model 20/20 laser (Visx, Santa Clara, CA). Preoperative visual acuity of 20/40 or better was present in 46 eyes. Corneal ablation was divided into concentric optical zones (4, 5, and 6 mm), allowing corrections of up to 18 D, with a refractive goal of within -1 D from emmetropia in 49 eyes. A hand-held fixation system was always used, and a nitrogen-blowing system (NBS) was used in the first 21 eyes only.

RESULTS

Before retreatment, the range of final cycloplegic refraction from emmetropia in eyes treated with NBS versus not was within +/-1 D in 6 (28.6%) and 15 eyes (44.1%), between -1.25 and -3 D in 5 (23.8%) and 14 eyes (41.1%), and more than -3 D in 10 (47.6%) and 5 eyes (14.7%), respectively. No lines of visual acuity were lost in 37 eyes (80.4%) with 20/40 or better visual acuity before surgery. Three eyes showed vision loss due to worsening of myopic maculopathy and one due to corneal haze. Correction stabilized within 9 months, and at a mean time of 25.6 months, the correction attained was of -8.5 +/- 3.6 D, achieving 90.3% of attempted correction. Eyes with preoperative myopia less than -10 D (n = 27) showed regression less than -1 D in 8 eyes (29.6%), between -1.25 and -3.00 D in 5 eyes (18.5%), and greater than -3.00 D in 1 eye (3.7%); eyes with more than -10 D (n = 29) regressed in 3 (10.3%), 6 (20.7%), and 1 eye (3.4%), respectively. Severe haze was observed in 11 eyes (19.6%) 3 months after surgery. Two eyes showed decentration greater than 1.5 mm. At last examination, night driving problems were reported by 12 (41.4%) of 29 patients evaluated who drive.

CONCLUSIONS

After the NBS was eliminated, the multiple-zone technique achieved a long-term, stable 83.1% reduction of preoperative myopia. Patients with severe myopia appreciated reduction of most of the refractive defect, although perception of halos was noted by 16 patients.

Excimer Laser in situ Keratomileusis for Myopia

PURPOSE

To evaluate the efficacy, safety, and predictability of excimer laser in situ keratomileusis (LASIK) for the correction of myopia.

METHODS

Forty-six consecutive eyes that had LASIK with the VISX 20/20B laser and Chiron corneal shaper were evaluated. Mean spherical equivalent of the preoperative manifest refraction was -9.40 +/- 3.78 diopters (D) (range, -3.50 to -19.75 D). The refractive effect (postoperative refraction minus baseline refraction), residual refractive error (refractive effect minus planned correction) and uncorrected and spectacle-corrected visual acuity were examined.

RESULTS

Mean follow-up was 6.1 months (range, 3 to 9 mo). Spectacle-corrected visual acuity was unchanged in 39 eyes (84.78%), significantly improved in five eyes (10.86%), and worse in two eyes (4.34%). Uncorrected visual acuity was 20/20 or better in 15 eyes (32.6%) and 20/40 or better in 39 eyes (84.78%). Thirteen eyes (28.26%) had a postoperative spherical equivalent refraction within +/- 0.50 D and 36 eyes (78.26%) within +/- 1.00 D of attempted correction. No intraoperative complication occurred. Postoperative complications were few and not severe: three eyes (6.52%) developed regular astigmatism, two eyes (4.34%) had interface deposits, and three eyes (6.52%) had small epithelial cysts in the interface.

CONCLUSION

LASIK with the VISX 20/20B laser is safe, moderately effective, and relatively predictable for correcting myopia from -3.50 to -19.50 D. Predictability decreases with increasing myopia.

Laser in situ Keratomileusis for Myopia of -2 to -25 Diopters

PURPOSE

To evaluate excimer laser in situ keratomileusis in the treatment of low, high, and excessively myopic eyes in Taiwan, 77 patients (104 eyes) were treated with Nidek EC-5000 excimer laser and divided into four groups.

METHODS

In situ keratomileusis was performed with a Chiron or SCMD microkeratome. The Nidek EC-5000 excimer laser was used, with multiple passes and a multiple zone ablation technique was performed for myopia higher than -10.00 D.

RESULTS

In eyes with a preoperative spherical power equal to or less than -7.00 D (29 eyes of 18 patients), the preoperative cycloplegic mean spherical equivalent refraction was -5.44 +/- 1.36 D. The mean postoperative subjective spherical equivalent refraction was 0.25 +/- 0.64 D at 1 month, 0.056 +/- 0.55 D at 3 months, -0.069 +/- 0.415 D at 6 months, and 0.022 +/- 0.496 D at 9 months. The predictability of postoperative 9 month results demonstrated that 86.21% of eyes were within +/-0.50 D, 96.55% were within +/-1.00 D, and 100% were within +/-2.00 D of emmetropia. In eyes with a preoperative spherical power equal to or less than -10.00 D and higher than -7.00 D, 26 eyes of 17 patients had a preoperative cycloplegic mean spherical equivalent refraction of -8.41 +/- 0.84 D. The mean postoperative subjective spherical equivalent refraction was -0.043 +/- 1.15 D at 1 month, -0.12 +/- 0.92 D at 3 months, -0.21 +/- 1.05 D at 6 months, and -0.37 +/- 1.04 D at 9 months. The predictability of postoperative 9 month results demonstrated that 76.92% of eyes were within +/-0.50 D, 80.77% were within +/-1.00 D, and 96.5% were within +/-2.00 D of emmetropia. In eyes with a preoperative spherical power equal to or less than -15.00 D and more than than -10.00 D, 40 eyes of 27 patients had a preoperative cycloplegic mean spherical equivalent refraction of -12.65 +/- 1.51 D. The mean postoperative subjective spherical equivalent refraction was 0.275 +/- 1.72 D at 1 month, -0.30 +/- 1.34 D at 3 months, -0.47 +/- 1.23 D at 6 months, and -0.62 +/- 1.23 D at 9 months. The predictability of postoperative 9 month results demonstrated that 62.5% of eyes were within +/-0.50 D, 75% were within +/-1.00 D, and 87.5% were within +/-2.00 D of emmetropia. For 19 eyes of 15 patients with a preoperative spherical power greater than -15.00 D, the preoperative cycloplegic mean spherical equivalent refraction was -19.53 +/- 2.61 D. The mean postoperative subjective spherical equivalent refraction was -0.40 +/- 1.22 D at 1 month, -0.69 +/- 1.34 D at 3 months, -0.83 +/- 1.40 D at 6 months, and -0.65 +/- 2.99 D at 9 months. The predictability of postoperative 9 month results demonstrated that 31.5% of eyes were within +/-0.50 D, 52.63% were within +/-1.00 D, and 63.16% were within +/-2.00 D.

CONCLUSION

LASIK is a safe and effective technique for the treatment of low, high, and excessive myopia.

Astigmatism induced by spherical photorefractive keratectomy corrections

PURPOSE

The purpose of the study is to evaluate the induced astigmatism after spherical photorefractive keratectomy on the Summit Omnimed (Summit Instruments, Waltham, MA) and the Nidek EC-5000 (Nidek Co. Ltd, Aichi, Japan) excimer lasers.

METHODS

A total of 4269 eyes of 3289 patients were treated with a 5-mm optical zone using the Summit Omnimed excimer laser and 1825 eyes of 1303 patients treated with the Nidek EC-5000 excimer laser. The final astigmatic refractive outcome was compared with the initial refraction by vector analysis (Alpin and Jaffe method).

RESULTS

Subjective astigmatic refraction for the Summit laser reduced from a mean of -0.39 diopter (D) +/- standard deviation (SD) 0.33 D (range, 0 to -2.50 D) to -0.33 D +/- SD 0.41 D (range, 0 to -3.00 D). Surgically induced astigmatism (SIA) had a mean of 0.42 +/- SD 0.34 D (range, 0 to 2.89 D). Mean SIA increased with increasing preoperative astigmatism by 0.60 D SIA for every 1.00 D of preoperative cylinder. For the Nidek laser, subjective astigmatic refraction changed from a mean of -0.18 D +/- SD 0.21 D (range, 0 to -1.25 D) to -0.30 D +/- SD 0.33 D (range, 0 to -3.00 D). Surgically induced astigmatism had a mean of -0.32 D +/- SD 0.29 (range, 0 to 3.05 D). Mean SIA increased with increasing preoperative astigmatism by 0.47 D SIA for every 1.00 D of preoperative cylinder.

CONCLUSIONS

The authors show that spherical photorefractive keratectomy corrections can induce significant astigmatic change, particularly if a large amount of preoperative astigmatism is present.

Effect of topical fluoroquinolones on corneal re-epithelialization after excimer laser keratectomy

PURPOSE

To measure the effects of commercially prepared topical fluoroquinolones on the healing rate of epithelial defects in the rabbit cornea after excimer laser keratectomy.

SETTING

The Doheny Eye Institute and the Department of Ophthalmology, University of Southern California School of Medicine, Los Angeles, California, USA.

METHODS

Twenty-four New Zealand white rabbits had unilateral excimer laser superficial keratectomy to create a circular, central corneal epithelial defect. Following keratectomy, each rabbit was randomly assigned to one of three treatment groups, each consisting of eight rabbits. Each rabbit was treated with one drop of the assigned medication, each hour until epithelialization was complete; Group 1 received ciprofloxacin, Group 2, ofloxacin, and Group 3, preservative-free artificial tears as a control. The epithelial defect was stained with fluorescein and photographed every 12 hours with a cobalt blue filtered light. Planimetric measurements of the wound area were made with an image analysis system.

RESULTS

The control group eyes were re-epithelialized within 84 hours. The fluoroquinolone-treated eyes required 144 hours for complete healing. Both ciprofLoxacin and ofloxacin significantly delayed corneal epithelial healing (P = .0055) compared with the control. Two animals treated with topical ciprofloxacin developed a white precipitate in the area of the epithelial defect; however, the precipitate did not prevent closure of the epithelial defect. No such precipitate was seen with ofloxacin.

CONCLUSION

These data suggest that both ofloxacin and ciprofloxacin influence corneal wound healing in rabbits after laser keratectomy and that their healing rates did not differ. A white precipitate that appeared in the epithelial defect area in some rabbits treated with ciprofloxacin did not prevent closure of the defect.

Effect of Transforming Growth Factor β1 on Stromal Haze following Excimer Laser Photorefractive Keratectomy in Rabbits

BACKGROUND

Transforming growth factor beta (TGF-beta) has been shown to affect wound repair. Anti-transforming growth factor beta 1 antibodies have been shown to neutralize its activity.

METHODS

Seventeen New Zealand White rabbits underwent unilateral photorefractive keratectomy followed by corneal staining with dichlorotriazinyl fluorescein. Three groups received topical transforming growth factor beta 1: 1 microgram/ml, 10 micrograms/ml, and 100 micrograms/ml; one group topical anti-transforming growth factor beta antibody (200 micrograms/ml); and a control group vehicle only. Corneal haze was graded from 0 to 4, weekly. Rabbits were sacrificed at 5 weeks and histopathological analysis and fluorescence microscopy performed.

RESULTS

All treated eyes developed haze and had epithelial erosions. No statistically significant differences in haze score were seen among individual treatment groups (Kruskal Wallis p > 0.05). The anti-transforming growth factor beta antibody group had less haze than all other groups at every week after the first. Comparing all transforming growth factor beta 1 treated eyes as one group to the antibody group, significantly less haze was seen at weeks 3 and 4 in the antibody treated group (p = 0.028 and 0.013, respectively). This study is limited by small group size and further studies are needed to confirm these results.

CONCLUSION

TGF-beta may be involved in stromal haze formation, and topical anti-TGF-beta 1 antibody may help reduce the development of stromal haze.

Real-time confocal microscopic observations on human corneal nerves and wound healing after excimer laser photorefractive keratectomy

PURPOSE

Corneal wound healing after excimer laser photorefractive keratectomy (PRK) passes through a series of characteristic stages which have earlier been defined by means of histological, histochemical, and biochemical approaches. We investigated the potential of confocal microscopy to verify morphological changes in human corneas in vivo after PRK.

METHODS

Ten corneas of eight patients that had earlier undergone PRK were examined at different postoperative time points (7 days-34 months). One of the PRK patients was examined sequentially three times. Three additional corneas, which had earlier undergone corneal grafting surgery and then were subjected to excimer laser photoastigmatic keratectomy (PARK), were studied as well. Seven healthy untreated corneas served as controls to define the normal morphology of human cornea. A tandem scanning confocal microscope (TSCM) was used to generate real-time images of the corneas on an S-VHS videotape. The images were either digitized and further processed or the individual video frames were produced with a video printer.

RESULTS

Seven days post-PRK in vivo confocal microscopy revealed the presence of morphologically immature surface epithelial cells. Delicate nerves, activated keratocytes and deposition of extracellular light-reflecting scar tissue were perceived. The epithelium appeared normal one month post-PRK. Ongoing activation of the anterior stromal keratocytes along with extracellular scar tissue were detected. We also observed increasing numbers of regenerating subepithelial nerve leashes with somewhat twisted pattern. Highly reflective, presumably activated keratocytes were no longer detected 6-7 months post-PRK. Hypercellularity with scar tissue could still be found up to 30 months post-PRK. Only one cornea examined 34 months post-PRK showed normal keratocyte morphology and recovery of the anterior stroma. However, the morphology of subepithelial nerves was still somewhat abnormal. The two corneal grafts examined 11 or 32 months post-PARK exhibited a normal-appearing epithelium but considerable stromal hypercellularity and extracellular scar deposition. The subepithelial nerves were poorly regenerated in one eye and fairly well detectable in the other. The third graft examined 15 months post-PARK revealed the presence of enlarged surface epithelial cells and dense stromal scarring but no nerves.

CONCLUSION

TSCM clinically confirms the earlier histological data on healing of excimer laser wounds. It offers a distinct improvement in the assessment of excimer laser-treated corneas, as it enables cellular details and nerves to be perceived in vivo. In addition the thickness of the stromal scar can be be measured for e.g. planning of phototherapeutic keratectomy.

Macular hemorrhage after excimer laser photorefractive keratectomy

We describe three patients with high myopia, 13.0 to 20.0 diopters (D), who had typical myopic macular hemorrhages 1 to 6 months after photorefractive keratectomy (PRK). The hemorrhages eventually resolved, with resultant permanent decrease in vision and pigmentary and atrophic changes in the macula. Highly myopic eyes are predisposed to bleeding in areas of lacquer cracks and to myopic choroidal neovascularization formation. Awareness of potential retinal pathology in patients having PRK and follow-up retinal examinations are warranted.

Photovaporization rate and profile of an erbium-chromium:YAG laser in the fundamental mode

PURPOSE

To evaluate the ablation characteristics of an experimental erbium:YAG (Er:YAG) laser and assess whether it delivers sufficient output for performing photorefractive keratectomy.

SETTING

Department of Ophthalmology, Virchow-Clinics, Humboldt University, Berlin, Germany.

METHODS

An experimental Er:YAG laser, the erbium-chromium:YAG, running in fundamental mode was used to evaluate the energy profile. Measurements obtained using a joulemeter were compared to the ablation profiles of cadaver pig eyes. The pig eyes were treated with different fluences (mean 0.8 to 2.9 J/cm2) and, after histological preparation, were examined using light and scanning electron microscopy.

RESULTS

Measurements with the joulemeter and in the cadaver pig eyes showed a Gaussian-curved profile of energy (ablation). In the current setting, the diameter of ablation was 3.5 mm. Histological examination showed a homogeneous profile of ablation with minor thermal damage.

CONCLUSION

The Er:YAG laser running in the fundamental mode allows homogeneous ablation of corneal tissue. The Er:YAG laser is easier to handle technically than the excimer laser and has none of the potential risks of ultraviolet light.

Five years results of photorefractive keratectomy for myopia

PURPOSE

To evaluate the long-term stability, complications, and causative factors in eyes that had photorefractive keratectomy (PRK) for myopia.

SETTING

Kangnam St. Mary's Hospital, Seoul, Korea.

METHODS

This study evaluated the results of PRK in 201 myopic eyes with a consecutive 5 year follow-up. Preoperative myopia ranged from 2.25 to 12.50 diopters (D), with astigmatism of less than 1.50 D. The Excimer laser was set to a maximum correction of -6.50 D at a 5.0 mm diameter ablation zone. Patients with more than 7.00 D of myopia had double-pass PRK with two different ablation zone sizes (5.0 and 4.5 mm). The data were statistically analyzed using polynomial regression for evaluating long-term stability and myopic regression and Cox's proportional hazard model for evaluating causative factors.

RESULTS

An uncorrected visual acuity better than 20/25 was achieved in 62.4% of eyes. The main complication after PRK was myopic regression. Mean refractive error 5 years after PRK was -2.43 +/- 1.90 D. It was -1.49 +/- 0.60 D in moderately myopic eyes (less than 6.50 D) and -3.55 +/- 2.31 D in highly myopic eyes (over 7.00 D). According to our evaluation, the possible causative factors for myopic regression were pre-PRK refraction (P < .0001) and post-PRK corneal haze (P = .01); their relative risks were 3.33 and 1.93, respectively. Multivariate analysis eliminated the corneal haze factor.

CONCLUSION

Myopic regression occurred as long as 5 years after PRK, with the most important factor for myopic regression being pre-PRK refraction.

Corneal Ablation Profilometry and Steep Central Islands

BACKGROUND

Photorefractive keratectomy with large diameter ablations using a uniform laser beam has produced central undercorrections, or "steep central islands" in patients, as seen with videokeratography.

METHODS

Using a custom optical profilometer to measure corneal ablation profiles and a VISX excimer laser system, we measured the effect of ablation algorithms, diameter, depth, and dioptric correction on enucleated porcine eyes and living rabbit eyes. Our profilometer was verified using a 43.00 diopter (D) spherical surface and a 35.00 and 43.00 D bicurve test surface as a model for the ablated cornea.

RESULTS

The profilometer measured the test surfaces to within 3 microns of predicted values. Photorefractive keratectomies showed over-ablation peripherally and under-ablation centrally which increased with ablation diameter and dioptric correction. Fixed diameter ablations 2 to 6 mm in diameter and 10 to 80 microns deep showed stromal ablation rates vary spatially but not with ablation depth. These spatially variant ablation profiles were used to re-engineer the ablation algorithm and to produce photorefractive keratectomies with improved sphericity.

CONCLUSIONS

Steep central islands are caused by the spatial variance of tissue ablated with a uniform laser beam irradiance. This aberration can be corrected by modifying the laser ablation algorithm to correct for the spatial variance of stromal ablation.

Refractory intraocular pressure increase after photorefractive keratectomy

A patient with developmental angle anomaly developed a corticosteroid-induced refractory increase in intraocular pressure (IOP) after photorefractive keratectomy (PRK). Trabeculectomy was required to reduce the pressure. Although rare, corticosteroid-induced refractory IOP increase is a serious complication of PRK and may necessitate trabeculectomy. More frequent monitoring of IOP in post-PRK patients and a re-evaluation of postoperative treatment are indicated.

Keratitis from corneal anesthetic abuse after photorefractive keratectomy

After having photorefractive keratectomy (PRK), a 29-year-old man suffered from delayed epithelial healing and corneal stromal ring infiltrates. All laboratory results including smear, culture, and biopsy for bacteria, herpes simplex virus, and Acanthamoeba were negative. The suspected cause was patient abuse of anesthetics. Subsequently, it was discovered that for 6 months, since just after the PRK, the patient had intermittently used topical proparacaine drops. After all medication was discontinued and the eye pressure patched, the corneal epithelium healed completely. Practitioners should consider the possibility of topical anesthetic abuse in cases of keratitis after PRK.

Late onset corneal haze after photorefractive keratectomy for moderate and high myopia

BACKGROUND

Corneal haze after photorefractive keratectomy (PRK) usually appears within 4 weeks after the procedure. A new type of corneal haze, starting relatively late after PRK, is reported.

METHODS

The authors reviewed the files of their first 1000 consecutive patients who completed a follow-up of 12 months or more and identified all those who had clear corneas for at least 4 months, after which corneal haze appeared. The clinical course in these patients was evaluated.

RESULTS

Late onset corneal haze (LOCH) had occurred in 18 eyes of 17 patients (incidence, 1.8%), appearing 4 to 12 months after PRK and resulting in decreased visual acuity and regression. Treatment with topical steroids or reoperation resulted in partial reversibility of haze and regression.

CONCLUSIONS

A new entity of LOCH is described. The appearance of LOCH suggests that corneal healing and remodeling continue for at least 1 year after PRK.

Ultraviolet-B enhances corneal stromal response to 193-nm excimer laser treatment

PURPOSE

The purpose of the study was to evaluate the biomicroscopic, light microscopic, and electron microscopic effects of ultraviolet-B (UV-B) exposure on the outcome of photorefractive keratectomy (PRK).

METHODS

A total of 24 pigmented rabbits were used in the study. One eye of 16 rabbits received a 193-nm, 45-micron deep (-5.0 diopter) excimer laser PRK. Twenty-one days after PRK, eight of the laser-treated eyes were exposed to 100 mJ/cm2 UV-B (280-315 nm) UV radiation by placing the rabbits in a standard clinically used dermatologic chamber for 7 minutes. Eight PRK-treated rabbits received no further treatment. The remaining eight non-PRK-treated rabbits received 100 mJ/cm2 UV-B only to one eye. Subepithelial haze was assessed before and after UV irradiation. Corneal morphology was assessed 4, 8, 12, and 16 weeks after UV-B exposure, using light microscopic and transmission electron microscopic (TEM) techniques.

RESULTS

Untreated eyes exposed to 100 mJ/cm2 UV-B only exhibited photokeratitis for 2 days, but showed no haze and were normal histologically at all intervals. The PRK-treated UV-B irradiated eyes exhibited a significant increase of stromal haze compared to eyes receiving PRK alone. Histologically, the main difference between the UV-B irradiated and nonirradiated post-PRK eyes was the presence of anterior stromal extracellular vacuolization in the UV-B-exposed eyes. The vacuolated foci were confined to the PRK treatment area and showed increased keratocyte density and disorganization of normal collagen lamellae. TEM showed activated keratocytes containing abundant rough endoplasmic reticulum, prominent Golgi zones, and extracellular vacuoles filled with amorphous material. The haze and morphologic changes showed a tendency to incomplete resolution over the period of 16 weeks.

CONCLUSIONS

The UV-B exposure during post-PRK stromal healing exacerbates and prolongs the stromal healing response and is manifest biomicroscopically by augmentation of subepithelial haze. The findings suggest that excessive ocular UV-B exposure should be avoided during the period of post-PRK stromal repair and that UV-B may modulate the response of tissues to 193-nm excimer laser and perhaps other laser energy in general.

Effect of Variations in Surgical Technique and Patient Management on Outcomes of Photorefractive Keratectomy

PURPOSE

To describe variation in surgical and patient management and to assess their effect on 12-month outcomes of photorefractive keratectomy (PRK).

METHODS

The following variations in surgical/patient management related to PRK were observed and assessed: treatment based on cycloplegic refraction, administration of anesthesia, marking of visual axis, diameter of zone marker, method of epithelial removal, use of intraoperative artificial tears, type of fixation during surgery, replacement of epithelium after surgery, use of a bandage contact lens or two pressure patches, and use of topical nonsteroidal antiinflammatory drugs after surgery. The outcomes assessed were spherical equivalent manifest refraction, spectacle-corrected visual acuity and uncorrected visual acuity.

RESULTS

One year clinical outcomes were assessed prospectively for a group of 645 eyes that underwent PRK or photoastigmatic keratectomy. Spherical equivalent refraction and uncorrected visual acuity were better with decreasing amounts of preoperative myopia (both F > 30.0, both p = 0.0001). Although some surgical variations produced statistically significantly better uncorrected visual acuity on univariate analyses, none of the variations in the techniques assessed were found to be statistically significantly related to clinical outcomes after controlling for preoperative spherical equivalent refraction (all F < 2.5, all p > 0.10). None of the surgical variations were associated with loss of spectacle-corrected visual acuity (all p > 0.10).

CONCLUSION

Clinical outcomes of PRK were not significantly affected by minor variations in clinical and surgical practice.

Undercorrection after excimer laser refractive surgery. Excimer Laser Group

PURPOSE

The incidence and correlations of undercorrection were studied for 1 year after excimer laser surgery for myopia or myuopic astigmatism.

METHODS

A consecutive series of 645 eyes of 440 patients were studied. Eyes were examined preoperatively and at 1, 3, 6, and 12 months after surgery. The parameters evaluated were visual acuity, refraction, and corneal clarity.

RESULTS

Following excimer laser surgery, undercorrection of > or = -1.00 diopters gradually increased from 10% at 1 month to 40% at 12 months. Increasing degree of preoperative myopia was significantly associated with increasing occurrence of undercorrection at 3 months (chi 2 = 17.3, P < .001), 6 months (chi 2 = 53.6, P < .001), and 12 months (chi 2 = 64.8, P < .001). Undercorrection was more common in eyes that had had photorefractive keratectomy than in those that had had photoastigmatic refractive keratectomy (odds ratio, 0.40; 95% confidence interval, 0.25 to 0.60). At 1 year, a loss of 2 or more lines of best-corrected visual acuity was recorded in 38% of undercorrected patients. Loss of 2 or more lines of best-corrected visual acuity was more common in patients undercorrected by -1.00 diopter or more (odds ratio, 8.8; 95% confidence interval, 5.4 to 14.6). No relationship was seen between corneal haze and loss of best-corrected visual acuity. Undercorrection was not associated with age, gender, use of nonsteroidal anti-inflammatory drugs, bandage contact lens wear, or corneal haze. Patients with lower degrees of myopia reached a stable refraction more quickly. At 6 months, 71% were within +/- 0.5 diopter of 1-year refraction. Of 17 patients with undercorrection who were treated with topical corticosteroids, only one patient showed a permanent beneficial change.

CONCLUSION

Occurrence of undercorrection is more common in patients with severe myopia and when simultaneous astigmatic corrections are undertaken.

Photorefractive keratectomy retreatments for regression. One-year follow-up

PURPOSE

Ninety eyes were retreated to correct myopic regression, with or without corneal haze, after primary photorefractive keratectomy (PRK); astigmatism ranging from -0.50 to -3 diopters (D) was present in 43 eyes.

RESULTS

The sphere (mean +/- standard deviation) was -2.82 +/- 1.74 D before repeat surgery. At 6 months, the mean was +0.30 D; at 1 year, it was -0.17 D. Patients were divided into two groups: group 1 included 56 eyes with little or no haze (< or = 1). The mean sphere value for this group was -2.13 D before retreatment; at 1 year, it was -0.20 +/- 0.76 D. At 6 months, 84% of sphere values were within +/- 1 D of the intended correction, with a mean haze value of less than 0.5, similar to that before repeat surgery; there was a mean gain of 0.25 Snellen line of best-corrected visual acuity. Astigmatism equal or greater than -0.5 D was present in 34 eyes (mean, -1.17 +/- 0.55 D). At 6 months, astigmatism was reduced to -0.45 +/- 0.48 D. The second group included 34 eyes with corneal haze greater than 1 (mean, 2.7). The mean sphere value was -3.95 D before photorefractive keratectomy and -0.12 +/- 1.48 D 1 year after treatment. Fifty percent of the mean sphere values were within +/- 1 D at 6 months, with a mean haze value of 1. The gain in mean best-corrected visual acuity was 1.3 Snellen lines. The mean astigmatism in nine eyes was -1.75 +/- 0.75 D before photorefractive keratectomy and -0.72 +/- 0.78 D 6 months after treatment.

CONCLUSION

There is a significant difference in the outcome predictability between the two groups. A second photorefractive keratectomy can be done 6 months after the primary treatment in patients with regression with or without trace haze. This group has a High predictability in achieving a good correction, with a low complication rate. When haze is present, retreatments are less predictable with 40% of patients overcorrected. Generally, however, these eyes have a statistically significant decrease in haze (Student's t test; P < 0.01) and an improvement in best-corrected visual acuity.

Direct objective quantification of corneal haze after excimer laser photorefractive keratectomy for high myopia

PURPOSE

The purpose of the study is to measure regional distribution differences in corneal haze after excimer laser photorefractive keratectomy for high myopia.

METHODS

The authors developed computerized gradient edge detectors with which were analyzed digitized anterior slit-lamp photographs of 40 eyes, an average of 21.0 plus or minus 14.5 weeks after photorefractive keratectomy for high myopia (-6 to -22 diopters). A treated area an adjacent untreated area on the anterior corneal surface, each containing six regions, were quantified, and the difference was correlated with various parameters.

RESULTS

Mean differences between scarred and clear areas for haze grade 0.5, 1.0, 2.0, 3.0, and 4.0 were 16.9, 26.6, 42.6, 60.4, and 76.4 gray levels, respectively (rs = 0.96; P = 0.0001). A low but statistically significant correlation between the intended correction and postoperative corneal haze was found (r = 0.33; P = 0.037). The mean coefficient of variation of the amount of opacification within each treated area was 9.4%. This coefficient of variation increased with a longer follow-up time (r = 0.88; P = 0.0001). The difference in the intensity of haze between the center and more peripheral regions over the entrance pupil did not correlate with the attempted correction. However, a strong association between a relatively less severe central corneal haze with respect to more peripheral haze and longer follow-up time was found (r = -0.96; P = 0.0001).

CONCLUSION

The amount of corneal haze showed a weak positive association with the attempted correction in excimer laser photorefractive keratectomy for high myopia. Corneal haze appeared fairly uniformly distributed within the ablation zone, but a more heterogeneous distribution was found with a longer follow-up time. Furthermore, later postoperative examinations disclosed a clear trend toward diminishing central opacification relative to peripheral regions over the entrance pupil.

Corneal Wound Healing and Nerve Morphology after Excimer Laser In Situ Keratomileusis in Human Eyes

BACKGROUND

Our aim was to describe wound healing and nerve regeneration in the human cornea after excimer laser in situ keratomileusis.

METHODS

Excimer laser in situ keratomileusis was done in three human eyes 8 days, 54 days, and 4 months prior to enucleation. Acetylcholinesterase reaction was used to histochemically demonstrate the corneal nerves. Immunohistochemical methods were used to demonstrate the following wound healing proteins: cellular fibronectin, tenascin, transforming growth factor-beta 1, and alpha-smooth muscle actin.

RESULTS

All corneas healed without complication. No epithelial hyperplasia appeared and the Bowman's layer was smooth and acellular. An epithelial plug extending up to 100-300 microns under the flap margins was seen in all specimens. Regenerative nerve fiber bundles emerging from sharply cut anterior stromal nerves were observed, but the deeper nerves were normal. Restricted expression of fibronectin and tenascin was found at the wound area. All corneal cell types were positive for transforming growth factor-beta 1 antibody. Cells lining the limbal vessels were positive for alpha-smooth muscle actin antibody whereas the corneal cells were negative.

CONCLUSIONS

The nerve morphology showed only a few abnormalities, especially in deep stromal nerves. Epithelial plugs at the flap margins may maintain a delayed wound healing process for several months but otherwise the process remained active for a relatively short time.

Management and Treatment of Central Steep Islands after Excimer Laser Photorefractive Keratectomy

BACKGROUND

Permanent central steep islands are an undesirable phenomenon that cause distorted images and a significant reduction in visual acuity. We describe treatment of central steep islands with repeat excimer laser photoablation in the central cornea.

METHODS

Three patients with preoperative refractions of -7.50 -2.50 x 170 degrees D (right eye), -8.00 -2.25 x 10 degrees D (right eye) and -6.00 -1.50 x 90 degrees (right eye) developed central steep islands which persisted more than 12 months. All patients lost more than two lines of spectacle-corrected visual acuity and complained of visual disturbances. We retreated the central steep islands with a VISX 20/20 excimer laser PRK ablation that matched the size of the central island measured on videokeratography.

RESULTS

Symptomatic glare and distortion were significantly reduced and the central steep islands were resolved. Several weeks after reablation, spectacle-corrected visual acuity improved to the preoperative level.

CONCLUSION

Central steep island, an infrequent complication of excimer laser photorefractive keratectomy, can be safely removed with a repeat laser ablation that matches the central circular steep area.

Multiple excimer laser retreatments for scarring and myopic regression following photorefractive keratectomy

Excimer laser retreatment for scarring with myopic regression following photorefractive keratectomy (PRK) has been reported. We present the 38 month course of a patient who had PRK followed by two retreatments. The patient experienced scarring with myopic regression after an initial PRK with a 5.00 mm ablation zone. These complications recurred 13 months after retreatment with a 5.00 mm ablation zone. Refractive effect, computer-assisted videokeratography measurements, and corneal clarity remained stable 12 months after a second retreatment with a 6.00 mm ablation zone, indicating that retreatment with a larger ablation zone diameter appeared to be an appropriate method for handling this complication.

Failure of Mechanical Epithelial Removal to Reverse Persistent Hyperopia After Photorefractive Keratectomy

BACKGROUND

Residual hyperopic overcorrection after photorefractive keratectomy (PRK) using early algorithms is a rare but serious complication. Anecdotal evidence suggests that epithelial removal can stimulate epithelial hyperplasia, thereby reducing overcorrection. The aim of this study was to determine if epithelial removal effectively reduced hyperopia after PRK for myopia and, concurrently, to correlate the healing response with the refractive outcome.

METHODS

Enrolled were seven eyes of seven patients (mean age, 44 +/- 13 years) who had undergone PRK with a mean manifest refractive error of +2.21 +/- 0.74 diopters (D). All had undergone PRK an average of 24 +/- 9 months previously. Epithelial removal was performed over the excimer-treated zone with a surgical blade. Subjective refraction, epithelial thickness, corneal topography, and subepithelial haze were measured up to 1 year postoperatively.

RESULTS

Reduction in hyperopia between the baseline and 1-year visit was not statistically significant (mean difference, 0.55 D reduction; p = .102). That epithelial removal did not stimulate a wound-healing response is further supported by the absence of change in epithelial thickness over the first month and the small amounts of subepithelial haze. Central corneal power was reduced by a mean of 0.64 D after 1 month (p < .05).

CONCLUSIONS

Epithelial removal alone did not reduce the hyperopic overcorrection present after PRK, nor did it stimulate epithelial hyperplasia in the majority of these eyes. However, a trend toward improvement was noted with time was noted.

Contact lens fitting after photorefractive keratectomy

AIMS/BACKGROUND

This study evaluated contact lens fitting and the longer term response of the photorefractive keratectomy (PRK) cornea to lens wear. In PRK for myopia problems such as regression, anterior stromal haze, irregular astigmatism, halo aberration, and anisometropia have been reported. Certain patients therefore require contact lens correction to obtain best corrected visual acuity (BCVA).

METHOD

From an original cohort of 80 patients, 15 were dissatisfied with their visual outcome 6 months after PRK. Ten of these were fitted with lenses and monitored regularly.

RESULTS

The best fit rigid gas permeable lens of diameter 9.20-10.00 mm was generally 0.10 mm steeper than mean keratometry readings. Because of lid discomfort five patients were refitted with daily wear soft lenses. All 10 achieved satisfactory lens wear of 10 hours per day. Central corneal steepening of 0.75 D (0.15 mm) occurred in one patient. Two patients had slight central corneal flattening. Three patients discontinued lens wear as they found lens care a nuisance. Four finally opted for retreatment by PRK.

CONCLUSIONS

In most cases, contact lenses gave good visual acuity and, in cases of mild irregular astigmatism, a significant improvement over spectacle BCVA. No significant adverse reaction to contact lens wear was found. Although ocular tolerance of lenses was satisfactory, several patients discontinued lens wear or sought improved unaided vision.

Excimer laser photorefractive keratectomy for patients with contact lens intolerance caused by dry eye

AIMS/BACKGROUND

To evaluate epithelial wound healing and visual outcome of excimer laser photorefractive keratectomy (PRK) performed on high myopic eyes with contact lens intolerance due to dry eye.

METHODS

PRK was performed on two groups of patients with non-Sjogren's dry eye: group A (-6 D to -9.5 D, 11 patients, 17 eyes) and group B (-11.5 D to -19.5 D, 11 patients, 16 eyes) in an attempt to eliminate the use of contact lenses (CL). The intended correction was full in group A and 10 D in group B.

RESULTS

Uncorrected visual acuity in group A was better than 20/40 in 12 (80.0%) of 15 eyes at 6 months and in 10 (90.9%) of 11 eyes at 1 year. Fourteen (92.8%) of 17 eyes in group A and four (25.0%) of 16 eyes in group B achieved refraction within plus or minus 1 D of the intended correction at 6 months. Re-epithelialisation was complete in 4 days, and epithelial cell area and permeability returned to the preoperative level within 1 month in all cases. All patients in group A were able to eliminate CL, whereas in group B, one patient needed spectacles for residual myopia and two patients resumed CL use because of regression. One eye with severe subepithelial scar formation and one eye with macular haemorrhage were observed in group B.

CONCLUSION

Our results suggest that PRK is effective for patients with high myopia (-6 D to approximately -10 D) and CL intolerance due to dry eye. Further studies are required to improve predictability and to prevent complications in PRK for very high myopia (> -10 D).

Laser In Situ Keratomileusis to Correct Myopia of -6.00 to -29.00 Diopters

BACKGROUND

Photorefractive keratectomy can cause corneal scarring and visual loss in highly myopic eyes. We evaluated laser in situ keratomileusis (LASIK) because it has the theoretical advantage of preserving both the corneal epithelium and Bowman's layer.

METHODS

In a prospective study, LASIK was performed in 62 myopic eyes (42 patients) using the Automatic Corneal Shaper (Chiron Vision) and the Keracor 116 excimer laser (Chiron Technolas). We measured refraction and visual acuity, and evaluated corneal topography (TMS 1) and corneal clarity after 4 to 8 weeks and 4 to 6 months.

RESULTS

Four- to 6-month follow up was completed in 51 eyes. The mean preoperative spherical equivalent refraction was -14.80 diopters (D) (range, -6.00 to -29.00 D). Postoperatively, the mean deviation from the target refraction was -1.70 D (range, -9.00 to +2.50 D) at 4 to 8 weeks and -1.90 D (range, -9.50 to +2.25 D) at 4 to 6 months. At 4 to 6 months, 19 eyes (37%) were within +/- 0.50 D of the target refraction, 24 (47%) within +/- 1.00 D, 33 (65%) within +/- 2.00 D, and 40 (78%) within +/- 3.00 D. From 4 to 8 weeks to 4 to 6 months, the mean regression of myopia was -0.20 D (0.50 D or less in 24 eyes [47%], 1.00 D or less in 32 [63%], and 2.00 D or less in 42 [82%]). In six eyes (12%), the stromal interface was not visible, in 38 (74%) it was barely visible, and in seven (14%) it was clearly visible. Corneal topography revealed only small variations in clear-zone size and dioptric value, demonstrating a very stable correction 4 to 6 months postoperatively.

CONCLUSIONS

LASIK may be a safe and effective procedure to correct high myopia. Further research is required to develop satisfactory microkeratome technology, effective laser algorithms, and to determine long-term stability of refraction.

Refractive outcome and corneal topographic studies after photorefractive keratectomy with different-sized ablation zones

BACKGROUND

Discrepancies may still occur between planned and actual refractive correction in eyes undergoing photorefractive keratectomy (PRK). The authors have evaluated the use of an enlarged ablation zone.

METHOD

A computerized corneal analysis system has been used to compare the changes of the anterior surface of the cornea and the refractive changes before and 1, 6, and 12 months after PRK in 113 patients (119 eyes) treated with an excimer laser. The patients were divided into two groups: those treated with a mask with a 5-mm window (59 eyes), and those with a new mask with different window openings according to the degree of refraction at the corneal apex, starting from 5 mm in diameter for treatments less than 6.5 diopters (D) and from 7 mm in diameter for higher treatments (60 eyes). In the first group, treatment ranged from -2.5 to -16 D (mean +/- standard deviation. -8.5 +/- 3.24 D); in the second group, it ranged from -1 to -14 D (-7.8 +/- 3.06 D). Treatments were evaluated with a chi-square test.

RESULTS

In the first group of eyes, 46% were within +/-1 D at 1 month, 37% at 6 months, and 39% at 12 months. In the second group of eyes, 73% were within +/-1 D at 1 month, 60% at 6 months, and 58% at 12 months. The comparison between these data and corneal topographic changes shows that both are more stable and predictable with the new mask compared with the 5-mm mask (P = 0.002, 0.02, 0.04, at 1, 6, and 12 months, respectively).

CONCLUSIONS

The use of larger ablation zones improves the predictability and stability of refractive changes.

Corneal haze after mechanical debridement for overcorrection after myopic photorefractive keratectomy

A 47-year-old man had photorefractive keratectomy (PRK) to correct myopia. Three months after surgery he was slightly overcorrected with +1.25-0.5/170 degrees. He then suffered a gout attack and showed a refraction of +2.5-0.5/4 degrees which decreased to +1.75-0.5 degrees. To reduce this permanent overcorrection we performed mechanical debridement of the corneal epithelium. the patient had haze grade 2-3 after 2 weeks and haze grade 0-1 some 4 months later. The refraction was +1-0.5/25 degrees. This case report indicates that mechanical debridement is able to reduce overcorrection after PRK and bears a risk of haze formation comparable to that associated with PRK.

Inflammatory Cells, Refractive Regression, and Haze After Excimer Laser PRK

OBJECTIVE

To examine the role of inflammatory cell invasion and aspects of tissue reaction on refractive regression and corneal haze after myopic PRK in rabbits.

METHODS

Measurements were made for 12 weeks postoperatively of haze intensity, corneal topography, tear cytology, inflammatory cell invasion, subepithelial fibroblast density, and the thickness of the newly laid down connective tissue and of the regrown epithelium.

RESULTS

Inflammatory cell invasion could be prevented by fitting a soft contact lens, but this had no effect on the haze or the regression. Haze intensity correlated with subepithelial fibroblast proliferation but not with new connective tissue formation or epithelial hyperplasia. Neither connective tissue nor epithelium regrew in the form of a lens and thus they could not account for regression. Intensive treatment with corticosteroids resulted in a marked reduction in postoperative haze and a slight lessening of long-term regression. Correspondingly, it reduced fibroblast proliferation.

CONCLUSIONS

Haze appears, at least in part, to be a result of fibroblast proliferation. Regression is possibly caused by slow distortion of existing tissue rather than the growth of new.

Retreatment after excimer laser photorefractive keratectomy. The Melbourne Excimer Laser Group

PURPOSE

To determine the risk factors for undercorrection of myopia after photorefractive keratectomy and to evaluate the efficacy and safety of retreatment.

METHODS

A VISX Twenty/Twenty excimer laser was used to treat myopia and myopic astigmatism of up to -15.00 diopters (spherical equivalent) at the corneal plane. Retreatments were performed primarily for undercorrection with or without coexistent corneal haze or abnormalities on videokeratoscopy. Not every patient who was undercorrected requested retreatment.

RESULTS

Of 645 eyes (440 patients) followed up for more than 12 months, 58 eyes (9%) required retreatment. The retreatment rate increased with increasing myopia: 17 (5%) eyes with myopia of less than -5.00 diopters, 30 (13%) eyes with myopia of -5.01 to -10.00 diopters, and 11 (19%) eyes with myopia of greater than -10.00 diopters required a second procedure. A higher retreatment rate was observed after astigmatic corrections than after spherical corrections. Corneal haze after retreatment was no greater than that observed after initial procedures. Twelve months after primary procedures, 378 (75%) of 504 eyes were within 1.00 diopter of emmetropia, whereas 27 (69%) of 39 eyes attained this result after retreatment. A total of 383 (76%) of 504 eyes attained uncorrected visual acuity of 20/40 or better after primary procedures, compared with 25 (64%) of 39 eyes after retreatment.

CONCLUSIONS

The risk of undercorrection requiring retreatment after photorefractive keratectomy increases with the magnitude of the primary treatment. Although less successful than initial procedures, retreatment appears to enhance the results of photorefractive keratectomy.

Comparison of 5-mm and 6-mm Ablation Zones in Photorefractive Keratectomy for Myopia

BACKGROUND

Variation in ablation zone diameter may alter visual acuity and/or refractive effect in photorefractive keratectomy. Despite theoretical benefits of using a smaller diameter ablation zone, clinical studies suggest that a larger ablation zone may decrease problems associated with photorefractive keratectomy.

METHODS

The results of our initial 34 consecutive eyes treated with a 5-mm diameter ablation zone using a Summit Technology ExciMed UV200LA excimer laser were compared retrospectively to our initial 34 consecutive eyes treated with a 6-mm diameter ablation zone using a Summit OmniMed excimer laser. Eyes had a spherical equivalent refraction between -1.00 and -6.00 diopters (D) and astigmatism less than 1.00 D. Patients were followed for a minimum of 6 months.

RESULTS

Eyes treated with a 6-mm ablation zone had less hyperopia and a spherical equivalent refraction closer to emmetropia at 1, 2, and 3 months (P = 0.001). Eyes treated with a 6-mm ablation zone had better uncorrected visual acuity at 1 and 2 months (P = 0.001). Less subepithelial haze was noted at 2 months (P = 0.01) and 3 months (P = 0.002) in the 6-mm group. At 6 months postoperatively, 30 of 32 eyes (94%) treated with a 6-mm ablation zone had a spherical equivalent refraction within 0.50 D of emmetropia, and all 32 eyes (100%) were within 1.00 D of emmetropia; in the 5-mm ablation zone group, 28 of 34 eyes (80%) were within 0.50 D and 29 (85%) were within 1.00 D of emmetropia. Patients treated with a 6-mm ablation zone complained less of night halos and had fewer differences between night and day vision.

CONCLUSIONS

In this study of myopia of -1.00 D to -6.00 D, eyes treated with a 6-mm ablation zone achieve a more rapid visual recovery with less variation in refractive outcome and less adverse effects than those treated with a 5-mm ablation zone.

Radial Keratotomy for Myopia From 5.00 to 13.00 Diopters Two Years After Surgery

BACKGROUND

Radial keratotomy for low myopia can produce good results with few side effects. For higher myopia, predictability becomes less accurate and side effects more common.

METHODS

A retrospective study of 111 eyes of 76 patients were divided into two groups. Group I had 79 eyes with myopia of -5.00 to -8.00 diopters (D); group II had 32 eyes with myopia -8.25 D to -13.00 D. One hundred eleven eyes were followed for 1 year and 90 eyes were followed for 2 years.

RESULTS

Sixty-seven (84.8%) eyes in group I and 12 (37.5%) eyes in group II achieved a refraction within the range of -1.00 D and +1.00 D. Ninety-two percent of group I and 44% of group II achieved an uncorrected visual acuity of 20/40 or better. Three percent lost spectacle-corrected visual acuity. Four eyes developed a hyperopic shift of 1.00 D or more between 2 months and 2 years. Seven other eyes developed a hyperopic shift of 1.00 D or more between 2 months and 5 years.

CONCLUSIONS

Eight-incision radial keratotomy is an attractive option for treatment of myopia up to -8.00 D. For levels above -8.00 D, the results are poorer; there may be a variable period before refraction stabilizes.

Photorefractive Keratectomy for Myopia of -8.00 to -24.00 Diopters

BACKGROUND

Sixty-eight highly myopic eyes (mean refraction, -11.17 diopters [D]; range, -8.00 D to -24.00 D) were treated with excimer laser photorefractive keratectomy and followed 1 year.

METHODS

A 193 nm Meditec excimer laser was used with a 5.0-mm ablation zone without peripheral taper. All patients were followed during a period of at least 1 year. All patients had a complete ophthalmological examination including videokeratography and documentation of haze.

RESULTS

After 1 year, uncorrected visual acuity was 20/20 or better in eight (13%) and 20/40 or better in 48% of eyes; 42% of eyes had a refraction within +0.50 D, 74% within +/-1.00 D, and 90% within +/-2.00 D of the planned correction. The eyes that needed only a single treatment obtained the best results. In 30% of eyes, two treatments were necessary in order to obtain acceptable results. A decrease of spectacle-corrected visual acuity, caused by the laser treatment, was exceptional, probably transient, and increased when a second treatment was necessary. Subjective complaints were present in four of 68 eyes. Eyes with clinically significant regression had more and longer lasting haze.

CONCLUSION

Excimer laser photorefractive keratectomy for myopia of -8.00 D and more give less predictable results than those achieved for less than -8.00 D. Two treatments improve the outcome but cause more loss of spectacle-corrected visual acuity.

Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel

PURPOSE

To evaluate the safety, efficacy, and quality of vision after photorefractive keratectomy (PRK) in active-duty military personnel.

METHODS

Photorefractive keratectomy (6.0-mm ablation zone) was performed on 30 navy/marine personnel(-2.00 to -5.50 diopters [D]; mean, -3.35 D). Glare disability was assessed with a patient questionnaire and measurements of intraocular light scatter and near contrast acuity with glare.

RESULTS

At 1 year, all 30 patients had 20/20 or better uncorrected visual acuity with no loss of best-corrected vision. By cycloplegic refraction, 53% (16/30) of patients were within +/- 0.50 D of emmetropia and 87% (26/30) were within +/- 1.00 D. The refraction (mean +/- standard deviation) was +0.45 +/- 0.56 D (range, -1.00 to 1.63 D). Four patients (13%) had an overcorrection of more than 1 D. Glare testing in the early (1 month) postoperative period demonstrated increased intraocular light scatter (P<0.01) and reduced contrast acuity (with and without glare, (P<0.01). These glare measurements statistically returned to preoperative levels by 3 months (undilated) and 12 months (dilated) postoperatively. Two patients reported moderate to severe visual symptoms (glare, halo, night vision) worsened by PRK. One patient had a decrease in the quality of night vision severe enough to decline treatment in the fellow eye. Intraocular light scatter was increased significantly (>2S D) in this patient after the procedure.

CONCLUSIONS

Photorefractive keratectomy reduced myopia and improved the uncorrected vision acuity of all patients in this study. Refinement of the ablation algorithm is needed to decrease the incidence of hyperopia. Glare disability appears to be a transient event after PRK. However, a prolonged reduction in the quality of vision at night was observed in one patient and requires further study.

Retrospective Comparison of Photorefractive Keratectomy and Radial Keratotomy

BACKGROUND

The efficacy and predictability of photorefractive keratectomy and radial keratotomy become increasingly relevant. This retrospective study compares one surgeon's experience with photorefractive keratectomy and radial keratotomy over a 3-year period from 1990 to 1993.

METHODS

Photorefractive keratectomy was performed on 103 eyes of 76 patients that met the inclusion criteria for the phase IIb, phase III, and phototherapeutic keratectomy studies as delineated by the United States Food and Drug Administration. Radial keratotomy was performed on 117 eyes of 81 patients with up to 9.00 diopters (D) of myopia.

RESULTS

In the photorefractive keratectomy group, 83% of the eyes achieved uncorrected visual acuity of at least 20/40; 37% saw 20/20; 88% had a refraction within 1.00 D of emmetropia, and 63% within 0.50 D of emmetropia. For the radial keratotomy group, 85% of the eyes achieved an uncorrected visual acuity of 20/40 or better; 27% saw 20/20; 88% had a refraction within 1.00 D of emmetropia; and 55% within 0.50 D of emmetropia. There were no serious complications, and only one single eye in each of the photorefractive keratectomy and radial keratotomy groups lost two lines or more of spectacle-corrected visual acuity.

CONCLUSION

Photorefractive keratectomy and radial keratotomy are both effective procedures, and result in similar refractive outcomes for myopia of -1.00 to -9.00 D.

Excimer laser photorefractive keratectomy

Excimer laser photorefractive keratectomy has been used for the correction of myopia, hyperopia and astigmatism. This laser removes tissue through a process termed photoablative decomposition, in which incident photon energy is sufficient to break molecular bonds. Selective removal of tissue across the anterior corneal surface results in a change in anterior corneal curvature. The surgical outcome may be influenced also by interindividual variability in wound healing and pharmacologic interventions. The nature of the excimer laser-tissue interaction, and clinical outcomes of predictability, stability and complications of surgery for myopia are discussed in detail.

Excimer retreatment for scarring and regression after photorefractive keratectomy for myopia

AIMS/BACKGROUND

Scarring associated with regression of refractive effect can occur after photorefractive keratectomy (PRK) for myopia. The experience of treating these complications is reported.

METHODS

Eighteen of 285 eyes (6.3%) were retreated with the excimer laser. Age, sex, preoperative primary treatment keratometry, pre-primary treatment, pre-retreatment and post-retreatment spherical equivalents, best corrected and uncorrected visual acuities were recorded and analysed.

RESULTS

At 6 months post-retreatment, the mean spherical equivalent was -2.07 dioptres (D) (SD 4.60 D). This spherical equivalent persisted in eyes followed for 12 months (-2.85D, SD 4.09 D). Nine of 18 eyes (50%) had uncorrected visual acuity of 6/12 (20/40) or better. If retreatment was undertaken within 6.5 months of the initial PRK, then scarring was likely to recur (p = 0.035). Nine of 10 eyes (90%) which had a retreatment spherical equivalent less than two thirds of their primary treatment spherical equivalent were within plus or minus 1.25D from emmetropia after retreatment. Four of 11 eyes (36%) followed for 12 months after retreatment rescarred with further regression.

CONCLUSION

The data showed that eyes with scarring and regression of myopia should not be treated with PRK within 6 months of the initial procedure. Eyes with the highest percentage of regression towards their initial myopia tend to have a poor response to retreatment.

A multicenter trial of photorefractive keratectomy for residual myopia after previous ocular surgery. Summit Therapeutic Refractive Study Group

PURPOSE

The Summit Therapeutic Refractive Clinical Trial is a nine-center prospective, nonrandomized, self-controlled trial to assess the efficacy, stability, and safety of using a standardized technique of excimer laser photorefractive keratectomy (PRK) to correct residual myopia in eyes with previous refractive surgery or cataract surgery.

PATIENTS AND METHODS

Eligible eyes with a mean residual myopia of -3.7 +/- 1.8 diopters (D) (range, -0.63 to -11.00 D) underwent PRK with a 193-nm excimer laser for myopic corrections between -1.50 and -7.50 D. Standardized settings were used for the ablation zone, ablation rate, repetition rate, and fluence. One hundred seven of the first 114 treated eyes were examined 1 year after PRK, with 98% of eyes having had refractive keratotomy and 2% having had cataract surgery.

RESULTS

One year postoperatively, the mean manifest spherical equivalent refraction was -0.6 +/- 1.4 D (range, -6.50 to 2.50 D); 63% of eyes were within +/-1.00 D of the attempted correction; and uncorrected visual acuity was 20/40 or better in 74% of eyes. Twenty-nine percent of eyes lost two or more Snellen lines of best-corrected visual acuity, and central corneal haze was moderate or severe in 8% of eyes.

CONCLUSIONS

Excimer laser PRK is effective in reducing residual myopia after previous refractive and cataract surgery. However, it is less accurate than PRK in eyes that did not undergo surgery and is more likely to cause a loss of best-corrected visual acuity 1 year after treatment.

Two-zone excimer photorefractive keratectomy for moderate myopia. Six- to 18-month follow-up

PURPOSE

To study the results of the two-zone photorefractive keratectomy (PRK) in 35 eyes of 27 patients with moderate myopia of 6 to 8 diopters (D) over 6 to 18 months.

METHODS

An excimer laser was used with a fluence of 160 mJ/cm2 at a frequency of 5 Hz. The ablation was performed with two zones (6 and 5 mm). All patients received topical steroid (0.1 fluorometholone) tapered over 4 months.

RESULTS

There were no significant untoward effects in any patient. There were minimal changes in contrast sensitivity, brightness acuity, and astigmatism. Uncorrected visual acuity of 20/40 or better was obtained in 77% of patients at 6 months, in 73% at 12 months, and in 71% at 18 months. A refraction of +/-1.0 diopter was obtained in 69% at 6 months, in 65% at 12 months, and in 71% at 18 months. There is no statistically significant difference at 6, 12, and 18 months in both visual acuity and refraction.

CONCLUSIONS

Two-zone PRK in moderate myopia is safe and reasonably effective. The results are stable from 6 to 18 months.

Increased release of immunoreactive calcitonin gene-related peptide (CGRP) in tears after excimer laser keratectomy

The purpose of the study was to quantify the neuropeptide calcitonin gene-related peptide (CGRP) in normal human tear fluid and to determine the effect of photorefractive excimer laser keratectomy (PRK) on its release in tears. CGRP was assayed in tear fluid samples using an enzyme immunoassay (detection limit 0.2 micrograms ml-1). Tear-fluid samples were collected preoperatively, 1, 2 and 7 days after PRK and analysed for CGRP. The changes in tear-fluid secretion were also monitored. The intra-assay variation was 3.0-7.0%. Despite the marked hypersecretion of tears, the concentration of CGRP did not decrease following PRK indicating a concomitant increase in CGRP release by sensory nerves and/or lacrimal gland(s). Consequently, the release of CGRP in tears increased from 197.9 +/- 36.6 ng min-1 (mean +/- S.E.M.) to 1723.0 +/- 402.4 ng min-1 (P < 0.01) on day 1, and to 2304.2 +/- 561.1 ng min-1 (P < 0.01) on day 2. On day 7, only minor elevation (377.02 +/- 83.24 ng min-1) was observed. It is concluded that CGRP is a component of normal human tear fluid. The ocular irritation response related to the photoablation induces an enhanced release of CGRP in tears. As a compound present in corneal sensory nerves CGRP may have a role in wound-healing.

Corticosteroids for Reversal of Myopic Regression After Photorefractive Keratectomy

With the aim of reversing myopic regression laser photorefractive keratectomy (PRK) after excimer, the effect of high-dose topical corticosteroids in modulating changes in refraction and corneal transparency was assessed prospectively. Twenty-four eyes of 23 patients (mean preoperative spherical equivalent refraction -7.36 diopters (D); range, -4.12 D to -19.25 D), demonstrating myopic regression ranging between 1.00 D and 6.88 D (mean: 2.64 D), were treated according to the same therapeutic protocol. Changes in corneal haze, corneal topography, and refraction were evaluated over 6 months. Eighteen eyes (78.26%) showed 1.00 D or more reversal of myopic regression. Sixteen eyes (69.56%) regained the attempted correction present when corticosteroids were first stopped (+/- 1.00 D). The difference between mean refraction before reintroducing corticosteroids (-2.64 D; range, -1.00 D to -6.88 D) and when stabilization occurred (-0.60; range, +1.50 D to -4.50 D) was statistically significant (P < 0.01). The improvements in corneal haze and spectacle corrected visual acuity were also significant (both P < 0.01). Stabilization occurred between 1 to 4 months after surgery (mean, 2.22). In five eyes (21.74%) increased intraocular pressure of more than 20 mm Hg were reduced with beta-blockers. Topical corticosteroid therapy can modulate refractive changes after PRK, appearing to reduce myopic regression. However, a longer follow up will be necessary to determine the final refractive outcome of these eyes.