Chris P. Lohmann

The Effects of Topical Corticosteroids and Plasmin Inhibitors on Refractive Outcome, Haze, and Visual Performance after Photorefractive Keratectomy: A Prospective, Randomized, Observer-masked Study

BACKGROUNDnThis study of 86 patients with 12 months of follow-up was designed to determine whether topical corticosteroids or plasmin inhibitors have an effect on the outcome of photorefractive keratectomy.nnnMETHODSnPatients were allocated randomly to either steroid (0.1% fluorometholone for 6 months), plasmin-inhibitor (aprotinin 40 IU/ml for 3 weeks), or control (no treatment) groups and underwent either -3.00- or -6.00-diopter (D) corrections.nnnRESULTSnWith -3.00-D corrections, the mean refractive change was significantly greater at 3 and 6 months (P < 0.05) in the steroid group compared with the control group. When steroids were discontinued, the difference became insignificant within 3 months. Similarly, with -6.00-D procedures the mean refractive change was greater at 6 weeks and 3 and 6 months (P < 0.01), but the refractive change again became insignificant 3 months after stopping steroid treatment. Four patients treated with steroids had a hyperopic shift greater than +2.00 D of that intended at 12 months. Similar overcorrections were not noted in the other treatment groups. There were no differences in refractive outcome between the aprotinin and control groups at any stage. With -6.00-D procedures, objective measurements of haze were significantly greater in the aprotinin group compared with the control group at 9 and 12 months (P < 0.05). With this exception, there were no differences in haze, forward or backward scatter of light, best-corrected visual acuity, or halo measurements between the groups.nnnCONCLUSIONSnCorticosteroids can maintain a hyperopic shift during their administration, but this effect is reversed on cessation of treatment. Objective tests have shown that steroids have no effect on corneal haze or visual performance after PRK. There is no justification for routinely submitting all patients to long-term steroid regimens and their associated side effects. Treatment with aprotinin produced no beneficial effect on refractive outcome, and haze was greater in the -6.00-D procedures. The concept of modulating the plasminogen activator/plasmin system to regulate wound healing after PRK is discussed.

Night vision after excimer laser photorefractive keratectomy: haze and halos

A series of 85 patients with myopia, up to −6.00D, was treated by photorefractive keratectomy (PRK), using a 5 mm diameter ablation zone. At six months, 38 patients (45%) reported slight disturbances of night vision, nine (11%) of whom had significant problems. Perturbations of night vision after PRK are seen as starbursts and halos around lights. Corneal haze produces the starbursts, which are usually transient. In contrast, halos are myopic blur circles and may be persistent. Using a computer program, halos after PRK were found to be significantly larger than those in emmetropes and myopes corrected with spectacles (p < 0.01). The halos were diminished by using either artificial pupils or negative lens over-correction. In patients with identical bilateral PRK corrections, except for the ablation zone size, the magnitude of the halo was less with 5 mm than 4 mm zones (p < 0.01). Patients treated with 5 mm reported fewer problems attributable to halo than with the 4 mm ablation diameters (p < 0.01). Halos and pupil diameters were measured in nine patients with significant impairment of night vision haze. Those with starbursts had small hyperopic shifts, minimal halos and high haze and light scatter measurements, whilst patients with halos had large hyperopic shifts, little haze and large pupil diameters. Patients with persistent halo problems benefited from either negative lens over-correction or miotics at night.

DISTURBANCES IN NIGHT VISION AFTER EXCIMER LASER PHOTOREFRACTIVE KERATECTOMY

Eighty-four patients with up to -6.00 dioptres of myopia underwent photorefractive keratectomy (PRK), using 5.00 mm ablation zones. Three months post-operatively 38 (45%) complained of disturbances in night vision, compared with 21 (25%) pre-operatively. In the majority, these disturbances were regarded as negligible. However, 9 (11%) reported significant problems, defined as an inability to drive safely at night with the treated eye. At 12 months, 32 patients (38%) complained of impaired night vision, 4 (5%) of whom had significant problems. A series of measurements were performed to investigate the origins of these disturbances, especially in patients reporting significant problems. Visual impairment from forward scattered light was investigated using a computerised technique. Back scattered light was measured with a charge coupled device–camera system and a computer program was used to assess the degree of halation around a bright light source on a high-resolution monitor. Pupillary diameters were measured by infrared television pupillometry. At 6 months, those reporting a starburst effect around lights at night had small hyperopic shifts, minimal halos and high forward and back light scatter measurements. Patients who reported halo phenomena had large hyperopic shifts, little light scatter and large pupillary diameters. Of the 4 patients who reported significant disturbances at 12 months, all had persistent halo problems. Those with starburst effects in the early postoperative period noticed an improvement with time as their corneal haze gradually improved. Perturbations of night vision after PRK manifest as starbursts and halos around lights. Disturbances in corneal transparency appear to be responsible for starburst effects and are usually transient. Halos are myopic blur circles and may be persistent in a small number of individuals. All patients should be informed pre-operatively of the possible consequences of disturbances in night vision.

Regression and epithelial hyperplasia after myopic photorefractive keratectomy in a human cornea

We present the histology of a cornea of a woman who had excimer laser photorefractive keratectomy (PRK) for myopia 6 months before she died in an accident. Preoperative spherical refraction was -6.00 diopters (D) with an astigmatism of -0.50 D. Six months postoperatively, refraction was -4.50 D. Slight corneal haze was noted at 1 and 3 months. The corneal histology showed marked epithelial hyperplasia in the center of the ablation zone without subepithelial deposition of newly synthesized collagen, proteoglycans, or both. The epithelial thickness was 38 microns in the untreated area and 93 microns in the center of the ablation. In conclusion, postoperative epithelial hyperplasia was responsible for regression after PRK in this eye.

Vitality of epithelial cells after alcohol exposure during laser-assisted subepithelial keratectomy flap preparation

Purpose: To evaluate the vitality of epithelial cells after various exposure times to 20% ethanol and epithelial flap preparation in laser‐assisted subepithelial keratectomy (LASEK) using the trypan blue dye test Setting: University Eye Clinic Regensburg, Regensburg, Germany, and the Rayne Institute, Department of Ophthalmology, St. Thomas Hospital, London, United Kingdom. Methods: Five human cadaver eyes were exposed to 20% ethanol for 15, 30, 45, 60, and 120 seconds, respectively. After an epithelial flap (as in LASEK) was prepared, the flap was deliberately cut off. The flaps were soaked in a trypan blue 0.1% solution at 37°C. After 3 washes with phosphate‐buffered saline (PBS), the specimens were reincubated for 30 minutes in culture medium containing 10% fetal calf serum at 37°C. After an additional wash with PBS, the cells were observed with a standard inverted light microscope. Results: After 15‐ and 30‐second exposure to 20% ethanol, most epithelial cells were vital. This changed substantially after 45 seconds, when vital and dead cells were approximately equal. Longer exposure times (60 seconds and 120 seconds) showed predominantly dead epithelial cells. Conclusions: Exposure to 20% ethanol should be 20 to 30 seconds as the number of vital epithelial cells rapidly decreased after that. Vitality of the epithelial flap is probably a crucial factor in the dampened wound response in LASEK compared to that in photorefractive keratectomy.

Regression and wound healing after excimer laser PRK: a histopathological study on human corneas.

Background. The results of excimer laser PRK are promising as more than 80% of eyes with up to −6.0 diopters of attempted correction have refractive results within 1.0 diopter of emmetropia. However, throughout the dioptric range some unexpected results have been observed with individual patients showing an aggressive wound healing response with excessive myopic regression and severe corneal haze. Unfortunately, only limited data are available about the cellular and extracellular responses in human corneas after PRK and this information is important to establish adequate postoperative pharmaceutical treatment. Methods. We made a histopathological and immunohistochemical study on 20 human corneal samples from patients with severe corneal haze and myopic regression. The indirect immunofluorescence method was used for demonstration of collagen types I, III, IV laminin, chondroitin sulphate, dermatan sulphate, and keratin. Results. All corneal specimens showed a hyperplastic epithelium. Histologically, most samples (16/20) showed mainly a loose lamination of extracellular material which could be identified as collagen type IV. The remaining four samples had newly synthesised collagen type III. Conclusions Our histopathological results indicate that corneal wound healing after excimer laser PRK varies among individuals. In some people epithelial basement proteins, such as collagen type IV, are the main wound healing products, whereas in others mainly collagen type III is found postoperatively, which does not effect the synthesis of collagen type IV. This suggests the need for individually-tailored postoperative pharmaceutical treatment regimens.

The role of light scatter in the degradation of visual performance before and after Nd:YAG capsulotomy

The aim of this study was to determine whether capsulotomy size influences visual performance. Snellen visual acuity and forward light scatter (light scattered towards the patients retina, but out of the focussed retinal image) measurements using simple computer graphics based on van den Bergs technique were used to measure visual performance. Twelve patients were studied: 4 had small central capsulotomies through undilated pupils and 8 had wide capsulotomies through dilated pupils. The two groups were matched for age and pre-laser Snellen acuity. Following treatment, both groups had equal improvements in Snellen acuity. There was only a significant(p < 0.001) improvement in forward light scatter readings in the group who received wide capsulotomies. Measurements of forward light scatter are more sensitive than Snellen acuity testing in demonstrating loss of visual performance in patients with media opacities. It is recommended that pupils are dilated prior to Nd: YAG capsulotomy if forward light scatter from capsule remnants and the consequent glare disability are to be minimised.