You can read each article or click on each of these points, and you will be brought to the official Conclusion of each article.

• 1) Loss of corneal sensitivity after PRK
• 2) PRK may induce visual problems
• 3) Corneal damages recovery longer than thought
• 4) PRK consequences may hinder cataract surgery.
• 5) Cornea extremely vulnerable for at least two weeks after PRK
• 6) PRK induced changes reach deeper layers than thought
• 7) Loss of contrast sensitivity after PRK seriously hinder night driving in majority. Lenses give no help
  
  

J Refract Surg 1999 Jan-Feb;15(1):38-45

Loss and recovery of corneal sensitivity following photorefractive keratectomy for myopia.

Murphy PJ, Corbett MC, O'Brart DP, Verma S, Patel S, Marshall J
Department of Vision Sciences, Glasgow Caledonian University, Glasgow, United Kingdom. pmu@gcal.ac.uk

BACKGROUND: Photorefractive keratectomy affects corneal innervation in a new, and drastic, way. This inevitably results in a significant loss of corneal sensitivity. This paper investigates the pattern of sensitivity loss and recovery following PRK for low to moderate myopia. METHODS: Patients were recruited for two separate studies. Longitudinal Study: 10 patients, treated with a -6.00 D/6 mm PRK ablation, were examined over a 1-year period. Transverse Study: A comparison was made between 35 non-contact lens wearers, 80 contact lens wearers, and 60 patients who underwent five different PRK treatments, 1 year previously. Corneal sensitivity was assessed using the Non-Contact Corneal Aesthesiometer at four corneal locations: centrally, temporally, medially, inferiorly, on all patients. RESULTS: Longitudinal Study: Corneal sensitivity was significantly reduced at week 1, with a further significant reduction at week 2. A gradual recovery in sensitivity then followed to reach preoperative levels by 1 year. Transverse Study: There was no significant difference in corneal sensitivity found as a result of different PRK ablation depths. The depth of ablation was not a factor in corneal sensitivity recovery in low to moderate myopic corrections. Corneal sensitivity in the PRK treated eyes was significantly lower than in the control groups.

1) CONCLUSION: The immediate loss of corneal sensitivity after surgery was due to the total removal of the corneal epithelial nerve supply and a substantial portion of the underlying stromal nerves. The further decrease at week 2 was probably due to the new epithelium acting as barrier to stimulation. The gradual recovery of corneal sensitivity was most likely caused by epithelial reinnervation within the ablation zone, but this was still below normal levels at 1 year after surgery. Corneal nerve function demonstrates a biphasic pattern of loss and recovery following the excimer laser correction of low to moderate myopia.

Graefes Arch Clin Exp Ophthalmol 1999 Feb;237(2):161-5

PRK-induced anisometropia in the rabbit as a model of myopia.

Bryant MR, Kampmeier J, Er H, Kasetsuwan N, Sanchez-DiMartino D, Shah SS, McDonnell PJ
University of Southern California School of Medicine, Doheny Eye Institute, Los Angeles 90033, USA. bryant@hsc.usc.edu

BACKGROUND: Current animal models of myopia, such as the chick and the tree shrew, have characteristics that limit their applicability to human myopia and/or their use among researchers. The purpose of this study was to establish a rabbit model of myopia based on photorefractive keratectomy (PRK)-induced anisometropia. METHODS: A group of five pigmented rabbits was treated with a monocular -5 D PRK at 5 weeks of age. At 10 weeks of age, two of the eyes were retreated with a second -5 D PRK procedure to compensate for partial regression of the refractive effect. A second group of six pigmented rabbits was treated with a monocular -6 D PRK at 10 weeks of age. Longitudinal measurements of corneal curvature, refraction, and axial length were performed until the rabbits were 13 and 21 weeks of age in groups 1 and 2, respectively. The rabbits in each group were from the same litter. RESULTS: Keratometry and retinoscopy measurements confirmed the refractive effect of the PRK procedures. At the final measurement point in group 1, the PRK-treated eyes were significantly longer than the untreated eyes (16.01 +/- 0.45 mm vs 15.45 +/- 0.56 mm). In group 2, the PRK-treated eyes were significantly longer by 0.19 mm and 0.20 mm at ages 19 and 21 weeks, respectively.

2) CONCLUSIONS: PRK-induced anisometropia is an effective technique to induce hyperopic error compensation in the rabbit as a model of myopic development. The technique is effective if the PRK procedure is performed at either 5 or 10 weeks of age. However, after PRK at 5 weeks of age, partial retreatment may be necessary due to regression of the PRK effect.

Br J Ophthalmol 1998 Dec;82(12):1393-400

Confocal microscopy reveals persisting stromal changes after myopic photorefractive keratectomy in zero haze corneas.

Bohnke M, Thaer A, Schipper I
University of Bern, Department of Ophthalmology, Switzerland.

AIMS: Micromorphological examination of the central cornea in myopic patients 8-43 months after excimer laser photorefractive keratectomy (PRK), using the slit scanning confocal microscope. METHODS: Patients were selected from a larger cohort of individuals on the basis of full corneal clarity (haze grading 0 to +1; mean 0.3) and their willingness to participate in the study. 15 eyes of 10 patients with myopic PRK (-4 to -11 D; mean 6.7) and an uneventful postoperative interval of 8-43 months (mean 26) were examined. Contact lenses had been worn by eight of the 10 patients for 4-11 years (mean 6.7) before surgery. Controls included the five untreated fellow eyes of PRK patients, 10 healthy, age matched volunteers without a history of ocular inflammation or contact lens wear, and 20 patients who had worn rigid gas permeable (n = 10) or soft contact lenses (n = 10) for 2-11 years. Subjects were examined with a real time flying slit, scanning confocal microscope using x25 and x50 objectives. RESULTS: In PRK treated patients and contact lens wearers, basal layer epithelial cells sporadically displayed enhanced reflectivity. The subepithelial nerve plexus was observed in all individuals, but was usually less well contrasted in the PRK group, owing to the presence of a very discrete layer of subepithelial scar tissue, which patchily enhanced background reflectivity. Within all layers of the stroma, two distinct types of abnormal reflective bodies were observed in all PRK treated eyes, but in none of the controls. One had the appearance of long (> = 50 microns), slender (2-8 microns in diameter) dimly reflective rods, which sometimes contained bright, punctate, crystal-like inclusions, arranged linearly and at irregular intervals. The other was shorter (< 25 microns), more slender in form (< 1 micron in diameter), and highly reflective; these so called needles were composed of crystal-like granules in linear array, with an individual appearance similar to the bright punctate inclusions seen in rods, but densely packed. Both of these unusual structures were confined, laterally, to the ablated area, but were otherwise distributed throughout all stromal layers, with a clear predominance in the anterior ones. These rods and needles were observed in all PRK treated corneas, irrespective of previous contact lens wear. On the basis of qualitative inspection, the incidence of rods and needles did not appear to correlate with either the volume of tissue ablated or the length of the postoperative interval. In contact lens wearing controls, highly reflective granules, reminiscent of those from which the needles were composed, were found scattered as isolated entities throughout the entire depth and lateral extent of the corneal stroma, but rods and needles were never encountered. The corneal endothelium exhibited no obvious abnormalities.

3) CONCLUSION: Confocal microscopy 8-43 months after PRK revealed belated changes in the corneal stroma. These were manifested as two distinct types of abnormal reflective bodies, which had persisted beyond the stage when acute wound healing would have been expected to be complete. The clinical significance of these findings in the context of contrast visual acuity and long term status of the cornea is, as yet, unknown.

J Cataract Refract Surg 1999 Jan;25(1):140-3

Intraocular lens power calculation after decentered photorefractive keratectomy.

Speicher L, Gottinger W
Department of Ophthalmology, University of Innsbruck, Austria.

4) A 59-year-old patient who had photorefractive keratectomy (PRK) to correct high unilateral myopia developed a progressive nuclear cataract. Phacoemulsification and intraocular lens (IOL) implantation were performed. However, determination of IOL power using automated keratometry and computerized videokeratography was not successful in this case of high axial myopia because of a decentered ablation zone, resulting in too-steep keratometric readings. Postoperative hyperopia could only be corrected by an IOL exchange. Because it may not be possible to determine the exact keratometric values for IOL calculation after PRK, subtracting the change in refraction induced by PRK from the preoperative keratometric readings might have been more accurate in this patient.

J Cataract Refract Surg 1998 Dec;24(12):1571-4

Changes in corneal epithelial barrier function after excimer laser photorefractive keratectomy.

Kim JY, Heo JH, Park SJ, Choi YS, Wee WR, Lee JH
Department of Ophthalmology, Seoul Municipal Boramae, Korea.

PURPOSE: To use fluorophotometry to measure corneal epithelial barrier function after excimer laser photorefractive keratectomy (PRK). SETTING: Seoul National University Hospital, Seoul, Korea. METHODS: Twenty-five eyes of 21 patients (13 women, 8 men) had PRK to correct myopia. Corneal epithelial healing time was measured and corneal epithelial permeability to sodium fluorescein evaluated by fluorophotometry 1, 2, and 3 weeks after surgery. RESULTS: Epithelial permeability showed a statistically significant increase 1 week after surgery and returned to its preoperative level 1 week later. Comparative studies according to epithelial healing day and corrected diopter showed results that were not statistically significant (P > .05).

5) CONCLUSION: These results suggest that PRK delays complete reconstruction of corneal epithelial barrier function. In humans, the corneal epithelium regained its normal barrier function 2 weeks after PRK. Thus, at least during these weeks, care should be taken to minimize further epithelial trauma.

Arch Ophthalmol 1998 Nov;116(11):1425-31

In vivo confocal microscopy after photorefractive keratectomy in humans. A prospective, long-term study.

Frueh BE, Cadez R, Bohnke M
Department of Ophthalmology, Inselspital, University of Berne, Switzerland. beatrice.frueh.epstein@insel.ch

OBJECTIVE: To assess corneal morphological characteristics in vivo after photorefractive keratectomy (PRK) in humans. METHODS: Eighteen eyes were examined before and after PRK by means of in vivo confocal microscopy. Epithelial, stromal, and endothelial morphological characteristics were recorded. Minimum follow-up was 12 months. RESULTS: Immediately after PRK, the anterior stroma showed marked intercellular edema. At 1 month, fine linear structures were noted in the anterior stroma and midstroma, and a thin hyperreflective scar was present. The linear structures and the scar tissue were more marked at 4 months but were still present up to 26 months. Anterior stromal keratocyte density increased significantly 1 and 4 months after PRK, whereas midstromal and posterior keratocytes and endothelial cell densities did not change. Basal epithelial nerves were recognizable as early as 1 month after PRK. Contact lens-related microdots in the stroma remained unaffected.

6) CONCLUSIONS: The stromal linear structures represent a finding that is detectable only by confocal microscopy at high magnification, is not related to previous contact lens wear, and is still visible 26 months after PRK. The extension of these structures as far as the midstroma indicates that the permanent corneal changes caused by PRK affect deeper stromal layers than the immediate subepithelial region.

Ophthalmologe 1998 Jun;95(6):420-6

[Change in twilight vision and glare sensitivity after PRK]. [Article in German]

Katlun T, Wiegand W ALZ Augenklinik Hamburg.

BACKGROUND: Morphological changes in the corneal surface after PRK may result not only in refraction fluctuations and reduction in visual acuity, but also in changes of contrast sensitivity. The aim of this study was to investigate whether PRK has an influence on contrast sensitivity with and without glare with a subsequent effect on the ability to drive cars. PATIENTS AND METHODS: Anonymous inquiries were made by means of a questionnaire sent to 114 patients after bilateral PRK in which the patients were asked to assess subjectly their driving ability. Additionally, in 66 eyes of 66 patients with a mean myopia of -5.3 D, an investigation on contrast sensitivity was performed according to the recommendations of the DOG (German Ophthalmological Society) using a Rodenstock nyctometer. RESULTS: Postoperatively, 55% of the patients felt more comfortable driving a car than preoperatively, 31% did not recognize any change, and 14% felt more uncomfortable driving car. Contrast sensitivity with or without glare 2 weeks postoperatively was so much reduced in 77% or 53%, respectively, of the patients that the criteria for driving a car in Germany were not fulfilled. Within the first 12 months after PRK the number of impaired patients diminished but even 1 year after PRK the number of patients with reduced contrast sensitivity with and without glare was higher than before PRK. Surprisingly, however, the criteria for driving a car with respect to contrast sensitivity with and without glare were not fulfilled even before PRK by as much as 44% and 24% of the patients, respectively.

7) CONCLUSIONS: All patients must be informed about the possible impairment for driving a car before PRK is performed.

Useful links

Refractive Surgery. If you haven't done it yet, read it!

There is an interesting article from BBC : people who regained 20/20 through laser are NOT any more accepted in German police, due to poor night vision

http://home.satx.rr.com/rksa/eyeknowwhy/index.htm
This WAS the address of "Eye see why refractive surgeons wear lenses". It is again not available

http://www.eyenet.org/public/ref_surg/ref-surg.html
belonging to American Academy of Ophtalmology, refractive surgery.

http://www.surgicaleyes.org/ A good site, devoted to promote a better understanding of operations.

First hand reports: check the http://www.americaneye.com message board.

Refractive Surgery   article from BBC   The birth of Buena Vista   Summer holiday courses in Italy  English links
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