An investigation into corneal enzymatic resistance following epithelium-off and epithelium-on corneal cross-linking protocols.

The aim of this study was to investigate corneal enzymatic resistance following epithelium off and on riboflavin/UVA cross-linking (CXL). One hundred and fourteen porcine eyes were divided into four non-irradiated control groups and seven CXL groups. The latter comprised; (i) epithelium-off, 0.1% iso-osmolar riboflavin, 9 mW UVA irradiation for 10 min, (ii) disrupted epithelium, 0.1% hypo-osmolar riboflavin, 9 mW UVA for 10 min, (iii) epithelium-on, 0.25% hypo-osmolar riboflavin with 0.01% benzylalkonium chloride (BACS), 9 mW UVA for 10 min, (iv) epithelium-on, 5 min iontophoresis at 0.1 mA for 5 min with 0.1% riboflavin solution, 9 mW UVA for 10 min or (v) 12.5 min, (vi) epithelium-on, prolonged iontophoresis protocol of 25 min with 1.0 mA for 5 min and 0.5 mA for 5 min with 0.25% riboflavin with 0.01% BACS, 9 mW UVA for 10 min or (vii) 12.5 min. Enzymatic resistance was assessed by daily measurement of a corneal button placed in pepsin solution and measurement of corneal button dry weight after 11 days of digestion. This study revealed that the enzymatic resistance was greater in CXL corneas than non-irradiated corneas (p < 0.0001). Epithelium-off CXL showed the greatest enzymatic resistance (p < 0.0001). The prolonged iontophoresis protocol was found to be superior to all other trans-epithelial protocols (p < 0.0001). A 25% increase in UVA radiance significantly increased corneal enzymatic resistance (p < 0.0001). In conclusion, although epithelium-on CXL appears to be inferior to epithelium-off CXL in terms of enzymatic resistance to pepsin digestion, the outcome of epithelium-on CXL may be significantly improved through the use of higher concentrations of riboflavin solution, a longer duration of iontophoresis and an increase in UVA radiance.

Effect of Muslim Prayer (Salat) positions on the intra-ocular pressure in healthy young individuals.

Purpose: There is a lack of research examining the effects of Muslim prayer (Salat) positions on the intra-ocular pressure (IOP). Considering its involvement with postural changes, this study aimed to investigate the changes in the IOP upon assuming Salat positions before, immediately after, and after 2 minutes of prayer in healthy young adults. Methods: This prospective, observational study recruited healthy young individuals aged between 18 and 30 years. The IOP measurements were obtained in one eye using Auto Kerato-Refracto-Tonometer TRK-1P, Topcon at baseline before assuming prayer positions, immediately after, and after 2 minutes of the prayer. Results: Forty female participants were recruited, with a mean age of 21 ± 2.9 years, a mean weight of 59.7 ± 14.8 (kg), and a mean body mass index (BMI) of 23.8 ± 5.7 (kg/m2). Only 16% had a BMI ≥25 kg/m2 (n = 15). All participants started with a mean IOP at baseline of 19.35 ± 1.65 mmHg, which increased to 20 ± 2.38 mmHg and declined to 19.85 ± 2.67 mmHg after 2 minutes of Salat. The difference between the mean IOPs at baseline, immediately after, and after 2 minutes of Salat was not significant (p = 0.06). However, there was a significant difference between the baseline IOP measurements and those immediately after Salat (p = 0.02). Conclusion: A significant difference was found between the IOP measurements at baseline and immediately after Salat; however, this was not clinically significant. Further investigation is warranted to confirm these findings and explore the effect of a longer duration of Salat in glaucoma and glaucoma suspect patients.

An Investigation of the Effects of Riboflavin Concentration on the Efficacy of Corneal Cross-Linking Using an Enzymatic Resistance Model in Porcine Corneas.

Purpose: To investigate riboflavin concentration on enzymatic resistance following corneal cross-linking (CXL). Methods: Ninety-six porcine eyes were divided into five groups in two treatment runs. Group 1 remained untreated. Group 2 received riboflavin 0.05%, group 3 riboflavin 0.1%, group 4 riboflavin 0.2%, and group 5 riboflavin 0.3%. Treated eyes underwent CXL with ultraviolet A at 9 mW/cm2 for 10 minutes. Eight-millimeter discs from each cornea were submerged in pepsin digest solution. In the first run, disc diameters were measured daily. After 10 days, dry weights were recorded from five samples in each group. In the second run, dry weights were recorded in five samples in each group at 10 and 20 days. Results: CXL-treated corneas took longer to digest than untreated (P < 0.001). Although eyes treated with higher riboflavin concentrations generally took longer to digest, there were no significant differences between groups (P = 0.3). Dry weights at 10 days demonstrated, with each increase in concentration, an increase in weight of residual undigested tissue (P < 0.001). In the second run, with each increase in riboflavin concentration there was an increase in weight of residual tissue (P < 0.001) at 10 days. At 20 days, the dry weight was lower with 0.05% riboflavin compared to 0.3% (P < 0.001) and 0.2% and 0.1% solutions (P < 0.05), with no other difference between groups. Conclusions: There is a consistent dose-response curve with higher concentrations of riboflavin achieving greater CXL efficacy, suggesting that manipulation of riboflavin dosage as well as the UVA protocol can be used to optimize CXL.

Enzymatic Resistance of Corneas Crosslinked Using Riboflavin in Conjunction With Low Energy, High Energy, and Pulsed UVA Irradiation Modes.

PURPOSE: To investigate the effect of various riboflavin/ultraviolet light (UVA) crosslinking (CXL) protocols on corneal enzymatic resistance. METHODS: A total of 66 enucleated porcine eyes, with the corneal epithelium removed, were divided into 6 groups. Group 1 remained untreated. Groups 2 to 6 received riboflavin/dextran for 30 minutes. Group 3 underwent standard CXL (SCXL) with 3 mW/cm(2) UVA for 30 minutes (total energy dose 5.4 J/cm(2)). Groups 4 and 5 underwent high intensity CXL (HCXL) using 30 mW/cm(2) UVA for 3 minutes (5.4 J/cm(2)) and 30 mW/cm(2) for 4 minutes (7.2 J/cm(2)), respectively. Group 6 was exposed to 8 minutes of 30 mW/cm(2) UVA in a 10-second on/10-second off pulsed-radiation mode (p-HCXL; 7.2 J/cm(2)). A central 8-mm disk from each cornea was submerged in pepsin digest solution at 23°C and measured daily. After 13 days, the dry weight was recorded from 5 samples in each group. RESULTS: The CXL-treated corneas took longer to digest than nonirradiated corneas (P < 0.0001). Differences in digestion time also were observed between CXL groups, such that, HCXL (5.4 J/cm(2)) < SCXL (5.4 J/cm(2)) < HCXL (7.2 J/cm(2)) < p-HCXL (7.2 J/cm(2); P < 0.0001). The dry weight of the SCXL (5.4 J/cm(2)) group was higher than the HCXL (5.4 and 7.2 J/cm(2); P < 0.001) and p-HCXL 7.2 J/cm(2) (P <0.05) groups. No difference was detected between the HCXL and p-HCXL 7.2 J/cm(2) groups. CONCLUSIONS: The intensity and distribution of the crosslinks formed within the cornea vary with different UVA protocols. The precise location and amount of crosslinking needed to prevent disease progression is unknown.

Standard versus accelerated riboflavin-ultraviolet corneal collagen crosslinking: Resistance against enzymatic digestion.

PURPOSE: To examine the effect of standard and accelerated corneal collagen crosslinking (CXL) on corneal enzymatic resistance. SETTING: School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom. DESIGN: Experimental study. METHODS: Sixty-six enucleated porcine eyes (with corneal epithelium removed) were assigned to 6 groups. Group 1 remained untreated, group 2 received dextran eyedrops, and groups 3 to 6 received riboflavin/dextran eyedrops. Group 4 had standard CXL (3 mW/cm(2) ultraviolet-A for 30 minutes), whereas groups 5 and 6 received accelerated CXL (9 mW/cm(2) for 10 minutes and 18 mW/cm(2) for 5 minutes, respectively). Trephined central 8.0 mm buttons from each cornea underwent pepsin digestion. Corneal diameter was measured daily, and the dry weight of 5 samples from each group was recorded after 12 days of digestion. RESULTS: All CXL groups (4 to 6) took longer to digest and had a greater dry weight at 12 days (P < .0001) than the nonirradiated groups (1 to 3) (P < .0001). The time taken for complete digestion to occur did not differ between the standard and accelerated CXL groups, but the dry weights at 12 days showed significant differences between treatments: standard CXL 3 mW > accelerated CXL 9 mW > accelerated CXL 18 mW (P < .0001). CONCLUSIONS: Standard and accelerated CXL both increased corneal enzymatic resistance; however, the amount of CXL might be less when accelerated CXL is used. The precise amount of CXL needed to prevent disease progression is not yet known. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.