Changes in corneal epithelial barrier function after excimer laser photorefractive keratectomy

Contact lens wearing and chronic cigarette smoking positively correlate with TGF-β1 and VEGF tear levels and impaired corneal wound healing after photorefractive keratectomy

PURPOSE

To study the correlation of gender, contact lens (CL) wearing, chronic drinking and chronic smoking with wound healing cytokine levels and corneal recovery after photorefractive keratectomy (PRK).

MATERIALS AND METHODS

One hundred and twenty-eight age-matched patients (180 eyes) undergoing PRK were enrolled. PDGF, EGF, VEGF, HGF and TGF-β(1) protein levels were measured in tears by enzyme-linked immunosorbent assay either preoperatively or 2, 7 and 15 days after PRK. Patients were seen between one day and five days postoperatively for the evaluation of epithelial healing. Delayed re-epithelialization was defined as healing after day 5. All patients were followed for haze formation for a minimum of three months.

RESULTS

All cytokines increased significantly during the first two postoperative days (p < 0.001). PDGF, EGF, HGF decreased to the preoperative levels by day 7, whereas TGF-β1 and VEGF remained elevated over the entire period of observation of 15 days, although to a lesser extent than the second day after surgery, in CL-wearers and smokers, respectively (p < 0.01). The Pearson correlation analysis showed that: (i) CL-wearing positively correlated with TGF-β1 amounts, while chronic smoking positively correlated with VEGF production; (ii) CL-wearing and TGF-β1 amount were found to be associated with early haze formation, whereas chronic smoking and VEGF level with delayed re-epithelialization. No association was found between gender or alcohol consumption and cytokine levels or wound healing.

CONCLUSIONS

Our findings highlight for the first time the important role that cigarette smoking and CL wearing may have in altering the tear cytokine network and impairing corneal epithelial wound repair after surgical injury.

Examination of the restoration of epithelial barrier function following superficial keratectomy

The goal of the present study was to determine the rate of restoration of the corneal epithelial barrier following a superficial keratectomy using a functional assay of tight junction integrity. Adult Sprague-Dawley rats were anesthetized and a 3-mm superficial keratectomy was performed. The eyes were allowed to heal from 4 h to 8 weeks and the rate of epithelial wound closure was determined. To examine the restoration of the barrier function, EZ-Link Sulfo-NHS-LC-Biotin (LC-Biotin) was applied to all eyes, experimental and control, for 15 min at the time of sacrifice. This compound does not penetrate through intact tight junctions. Indirect immunofluorescence was performed with anti-laminin, a marker of basement membrane; fluorescein-conjugated streptavidin to detect the biotinylated marker; and anti-occludin and anti-ZO-1, markers of tight junctions. Epithelial wound closure was observed at 36-42 h after wounding. LC-Biotin did not penetrate the intact epithelium. Upon wounding, LC-Biotin penetrated into the stroma subjacent and slightly peripheral to the wound area. This pattern was present from 4-48 h post-wounding. The area of LC-Biotin localization decreased with time and the functional barrier was restored by 72 h. Occludin and ZO-1 were present at all time points. The number of cell layers expressing these proteins appeared to increase at 48 and 72 h. Continuous laminin localization was not observed until at least 7 days after wounding. Barrier function is restored within 1-1.5 days after epithelial wound closure. The loss of barrier function does not extend beyond the edge of the original wound. The restoration of barrier function does not appear to correlate with reassembly of the basement membrane in this model.

Pupil response to tropicamide following laser in situ keratomileusis

PURPOSE

To investigate the effect of corneal thinning after laser in situ keratomileusis (LASIK) on the corneal penetration of topical eye medication.

SETTING

Department of Ophthalmology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.

METHODS

Laser in situ keratomileusis surgery was performed in 19 eyes of 10 patients enrolled in this prospective study. Measurements were made before surgery and 3 months postoperatively. After instillation of tropicamide 1%, the change in pupil size over time was measured with a Colvard pupillometer. Central corneal thickness (CCT) was measured with ultrasonic pachymetry before and 3 months after LASIK. The corneal epithelial condition was also examined by fluorescein dye staining.

RESULTS

The mean CCT decreased significantly from 564 microm +/- 33 (SD) before LASIK surgery to 514 +/- 48 microm 3 months postoperatively (P<.0001). Pupil diameter 10, 15, and 20 minutes after tropicamide 1% instillation was significantly larger 3 months after surgery than preoperatively (P=.0083, P=.0043, and P=.0144, respectively). The mean time to reach a pupil diameter of 6.0 mm decreased significantly from 14.4 +/- 4.3 minutes in preoperative eyes to 11.5 +/- 2.3 minutes in postoperative eyes (P=.0281). Mild punctate corneal epithelial staining (fewer than 5 spots) were observed in 4 eyes at the 3-month postoperative examination.

CONCLUSIONS

Pupil dilation after tropicamide 1% instillation was significantly faster after LASIK surgery. Corneal thinning that resulted from LASIK enhanced corneal penetration of tropicamide 1%.

Corneal degeneration after silicone oil tamponade in a photorefractive keratectomy treated eye

Three years after uneventful excimer laser photorefractive keratectomy in both eyes, a 34-year-old man sustained a perforating injury in the left eye. The severe injury, followed by endophthalmitis and retinal detachment, necessitated vitrectomy, lensectomy, and an internal tamponade with silicone oil. One month after the accident and operations, disk-shaped corneal edema corresponding to the laser treatment zone appeared. The edematous region showed a circular, ring-like epithelial thickening at the borders and central corneal epithelial erosion. The anterior stroma developed a central opacity that was separated by a clear rim from the developing silicone-oil keratopathy with the typical band shape.

Ocular drug permeation following experimental excimer laser treatment on the isolated pig eye

Excimer laser photorefractive keratectomy (PRK) is a well-established procedure which is frequently applied to correct myopia. Since structural alterations of the corneal epithelium occur after the treatment, a different drug permeation can be assumed. To investigate the effects of PRK on drug permeation, excimer laser ablations with varying depths were performed on isolated pig eyes. The permeation of lipophilic (diclofenac-sodium; D-Na) and hydrophilic (pilocarpine-hydrochloride; P-HCl model drugs were studied in vitro. Under these experimental conditions, P-HCl demonstrated a significant (p < 0.05) enhancement of permeation in relation to the ablation depth. In contrast, corneal epithelial thickness scarcely influenced the permeation rate of D-Na. Not until removing the entire epithelium did a significantly increased permeability occur, when compared to untreated cornea. These results suggest that PRK may significantly reduce the corneal barrier function and alter pharmacokinetics of topical medication.

Effect of Laser in situ Keratomileusis for Hyperopia on Tear Film and Ocular Surface

PURPOSE

To examine the effects of laser in situ keratomileusis (LASIK) for hyperopia on the tear film and ocular surface.

METHODS

A retrospective 12-month analysis of 88 eyes (88 participants) who had LASIK for hyperopia was performed. Participants were evaluated before and after (2 weeks, 1, 3, 6, and 12 months) surgery for dry eye symptoms (McMonnies Dry Eye Survey primary symptoms), tear film stability (fluorescein break-up time), tear volume (phenol red thread test), ocular surface staining (fluorescein), and conjunctival goblet cell density.

RESULTS

Chronic dry eye was experienced by 32% of participants; symptoms were significantly associated with female gender, preoperative dry eye symptoms, lower tear film stability after surgery, greater ocular surface staining after surgery, lower tear volume before and after surgery, and lower goblet cell densities after surgery. Regression rate 12 months after surgery was 32% and significantly associated with female gender, chronic dry eye symptoms, lower tear film stability after surgery, greater ocular surface staining before and after surgery, and lower tear volume before and after surgery.

CONCLUSIONS

Dry eye, particularly in females, is problematic after LASIK for hyperopia and is associated with refractive regression. Current methods for managing the tear film and ocular surface may not control LASIK-induced dry eye, particularly in some females during the first 6 months after surgery.

Relative Mydriasis After Photorefractive Keratectomy

PURPOSE

To report the incidence of anisocoria after unilateral excimer laser photorefractive keratectomy (PRK) for myopia and subsequent corticosteroid therapy in a retrospective and prospective study and to explore possible etiologies.

METHODS

The horizontal pupil diameter was determined in 6 patients (6 eyes) at 21.8 +/- 12.6 months after unilateral wide-field excimer laser PRK (retrospective group) as well as in 8 consecutive patients (8 eyes) before and 3.4 +/- 2.9 months after unilateral PRK (prospective group). The Schwind-Keratom wide-field excimer laser was used. Measurements were done in an examination room using Rosenbaum card comparison pupillometry and with a Goldmann perimeter at 31.5 asb. In the prospective group, the effect of fitting a hard contact lens of zero diopter power and the application of 0.1% pilocarpine were evaluated.

RESULTS

Relative mydriasis was present in all treated eyes and the difference in pupil diameter between the two eyes measured 0.25 to 1.75 mm (retrospective group: +0.56 +/- 0.82 mm; prospective group: +0.72 +/- 0.29 mm). At the time of pupil measurement, the retrospective group had a significantly longer mean postoperative follow-up (21 mo) than the prospective group (3.4 mo) and significantly more eyes still received topical corticosteroid treatment (retrospective group, 1 of 6 eyes; prospective group, 7 of 8 eyes). The amount of anisocoria did not correlate with the applied laser energy, ablation depth, or refractive change, but showed a negative correlation with increasing time after PRK. Neither hard contact lens fitting nor pilocarpine 0.1% reduced the amount of anisocoria significantly.

CONCLUSION

Unilateral PRK with wide-field excimer laser ablation and subsequent application of topical corticosteroids regularly resulted in a relative pupillary mydriasis. Neither an altered corneal profile nor parasympathetic denervation is responsible for this. Weakening of the pupillary sphincter of the treated eye may cause this phenomenon.