Pupil response to tropicamide following laser in situ keratomileusis

The Effect of Corneal Refractive Surgery on Glaucoma

Laser-assisted refractive procedures have become very popular in the last two decades. As a result, a "generation" of patients with altered corneal properties is emerging. These patients will require both cataract extraction and glaucoma follow-up in the future. Since the glaucoma examination largely depends on the corneal properties, the reshaped postrefractive surgery cornea poses a challenge in the diagnosis, follow-up, and management of the glaucomatous patient. In order to overcome this problem, every patient who is planned to undergo corneal refractive surgery must have a thorough glaucoma examination in order for the ophthalmologist to be able to monitor their patients for possible glaucoma development and/or progression. Some examinations such as tonometry are largely affected by the corneal properties, while others such as the evaluation of the structures of the posterior pole remain unaffected. However, the new imaging modalities of the anterior segment in combination with the most recent advances in tonometry can accurately assess the risk for glaucoma and the need for treatment.

Pupil response to tropicamide following corneal crosslinking

PURPOSE

To evaluate the effect of corneal crosslinking (CXL) with ultraviolet A (UVA) irradiation on pupil response to tropicamide 0.5% instillation.

METHODS

This prospective interventional study enrolled 17 patients (19 eyes) with progressive keratoconus who underwent CXL with UVA irradiation. Central corneal thickness (CCT) was evaluated with the use of anterior segment optical coherence tomography (Visante OCT 3.0). Pupil diameter was measured with the use of Colvard infrared pupillometer before the instillation of tropicamide 0.5% and after the instillation of tropicamide every 5 minutes for total duration of 30 minutes. Corneal epithelial integrity was examined with the use of fluorescein dye staining. Measurements were performed 1 day preoperatively and 1 month postoperatively, with emphasis on simulating the same light conditions regarding the pupil measurements.

RESULTS

No intraoperative or postoperative complications were observed in any of the patients. Mean CCT decreased significantly (p<0.001) 1 month postoperatively. Mean postoperative pupil size did not change significantly at any time point compared to the mean preoperative measurements.

CONCLUSIONS

The CXL procedure seems not to impair effectiveness of topical drugs, using pupil size measurements after tropicamide 0.5% instillation.

Effect of Corneal Thickness on the Penetration of Topical Vancomycin

PURPOSE

To study the influence of corneal thickness on intraocular penetration of topical ophthalmic drops, using vancomycin 50 mg/mL drops as a model.

METHODS

The study included 58 eyes of 58 patients undergoing phacoemulsification cataract extraction. The central corneal thickness was measured by ultrasonic pachymetry on the day of surgery. Thirty minutes before the surgery, one drop of topical vancomycin 50 mg/mL was instilled three times with 10-minute intervals: 30 minutes, 20 minutes, and 10 minutes before the surgery. At the beginning of surgery, a small specimen of aqueous humor was aspirated and sent to the laboratory for measurement of drug concentration to determine the effect of corneal thickness on vancomycin concentration in the anterior chamber.

RESULTS

There was insufficient amount of aqueous humor for analysis in 9 samples, leaving a total of 49 samples. The mean central corneal thickness was 539.7 (±39.5) μm (range, 458 to 635 μm). The mean vancomycin concentration in the anterior chamber was 0.220 (±0.209) μg/mL. There was no significant association between vancomycin concentration and corneal thickness (r = -0.07, p = 0.62, Pearson correlation). When patients were divided into three groups based on the mean (±1 SD) central corneal thickness, no significant differences in vancomycin concentrations (in micrograms per milliliter) were encountered: 0.267 (±0.247) (for corneal thickness <500.2 μm), 0.209 (±0.212) (for corneal thickness of 500.2 to 579.2 μm), and 0.200 (±0.160) (for corneal thickness >579.2 μm) (p = 0.73, analysis of variance).

CONCLUSIONS

Corneal thickness does not influence the penetration of topically applied vancomycin into the anterior chamber.

Mitomycin C aqueous humor concentration after photorefractive keratectomy: an experimental study

PURPOSE

To evaluate mitomycin C (MMC) aqueous humor concentration after photorefractive keratectomy (PRK).

METHODS

In this experimental study, twenty-four eyes of 12 male pigmented rabbits were divided into 4 groups and studied at the Institute of Vision and Optics, Department of Medicine, University of Crete, Greece. Eyes in groups 1 and 2 underwent PRK to correct -5 diopters (D) in a 6-mm optical zone, while sponges soaked with 0.02% MMC were applied on the exposed corneal stroma for 60 and 120 seconds, respectively. Similarly, eyes in groups 3 and 4 underwent PRK to correct -10 D in a 6-mm optical zone, while sponges soaked with 0.02% MMC were applied on the exposed corneal stroma for 60 and 120 seconds, respectively. Aqueous humor was extracted from all rabbit eyes 10 minutes after MMC application and high-performance liquid chromatography was performed immediately to detect and quantify MMC levels.

RESULTS

The mean aqueous humor concentration of MMC was 0.23+/-0.03 microg/mL, 0.39+/-0.05 microg/mL, 0.28+/-0.04 microg/mL, and 0.52+/-0.16 microg/mL in groups 1, 2, 3, and 4, respectively. The effect of application time and correction on aqueous humor MMC concentration was significant (p<0.0001 and p=0.019), while the exposure time had a greater impact on aqueous humor MMC concentration when compared with the attempted correction.

CONCLUSIONS

Both exposure time of MMC on the corneal stroma and the attempted correction was correlated with MMC aqueous humor concentrations.