Camus Kar Man Choy

A comparative study of biweekly disposable contact lenses: silicone hydrogel versus hydrogel.

Background:  Our aim was to compare the clinical performance of a biweekly (second generation) silicone hydrogel lens and a biweekly hydrogel lens worn for daily wear modality.

Effect of one overnight wear of orthokeratology lenses on tear composition.

Purpose. To evaluate the effect of one night of orthokeratology lens wear on ocular surface health based on the changes in tear components, including ascorbate, urate, lactate dehydrogenase (LD), lactoferrin, lipocalin, lysozyme, secretory immunoglobulin A (sIgA), and serum albumin. Methods. Changes in tear components in eight healthy young men before and after 7-h overnight ortho-k lens wear were studied. Subjects attended on two separate occasions during a 1-week period, on one occasion wearing lens overnight and on the other wearing no lens. Tears (yawn-induced) were collected by capillary tube before lens fitting and on awakening. Tear ascorbate and urate were measured by high-performance liquid chromatography; LD was measured by a commercial kit method; tear proteins were measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Results. Ascorbate, sIgA, albumin, and LD increased significantly overnight with and without overnight lens wear (p < 0.05); however, no significant increases were found in tear urate, lactoferrin, lipocalin, or lysozyme (p > 0.05). Without lens wear, tear ascorbate, sIgA, albumin, and LD increased by 21%, 34%, 9-fold, and 13-fold, respectively (p < 0.05). With ortho-k lens wear, significant flattening of the apical curvature was observed as expected, and the increases in tear ascorbate, sIgA, albumin, and LD (increases were 56%, 76%, 13-fold, and 14-fold, respectively) were significantly (p < 0.05) greater than with no lens. There was significant correlation seen between changes in albumin and LD with (r = 0.762; p = 0.037) and without (r = 0.738; p = 0.046) ortho-k lens wear. Conclusions. The result of tear ascorbate suggests that corneal cell disturbance is small after one night of ortho-k lens wear. The marked increases in albumin and LD suggest that the ocular surface is under additional hypoxic stress during overnight ortho-k lens wear.

UV‐Mediated DNA Strand Breaks in Corneal Epithelial Cells Assessed Using the Comet Assay Procedure¶

Abstract Ultraviolet (UV)-mediated DNA damage in various tissues has been well documented. However, research on the damaging effect of UV irradiation on the DNA of corneal epithelium is scarce, even though this is of interest because the cornea is directly exposed to damaging solar (UV) radiation. In this study, we developed a corneal epithelium Comet assay model to assess the background DNA damage (as strand breaks) in cells retrieved from different layers of the porcine corneal epithelium, and to investigate the effect of UV irradiation on DNA damage in corneal epithelial cells. Results show that the background DNA strand breaks decreased significantly (P < 0.001) toward deeper layers of the epithelium. Exposure to the same intensity (0.216 J/cm2) of UVA, UVB and UVC caused a significant (P < 0.001) increase in DNA strand breaks of deeper-layer cells: mean ± SD %DNA scores (10 gels per treatment, with 100 irradiated cells scored per gel) were 10.2% ± 1.4% for UVA, 27.4% ± 4.6% for UVB, and 14.7% ± 1.8% for UVC compared with 4.2% ± 0.5% for controls (ambient room light). This study has shown for the first time that the Comet assay for DNA strand breaks can be used successfully with corneal epithelial cells. This report will support future studies investigating environmental influences on corneal health and the assessment of possible protective strategies, and in applying DNA lesion-specific versions of the Comet assay in this corneal epithelial cell model.

Antioxidant Content and Ultraviolet Absorption Characteristics of Human Tears

Purpose. Dry eye syndrome is a common age-related disorder, and decreased antioxidant/ultraviolet (UV) radiation protection in tears may be part of the cause. This study aimed to compare the tear antioxidant content and flow rate in young and older adults. The total antioxidant content and UV absorbing properties of various commercially available ophthalmic solutions used to alleviate dry eye symptoms were also examined. Methods. Minimally stimulated tears were collected from 120 healthy Chinese adults with no ocular pathology. Two age groups were studied: 19 to 29 years (n = 58) and 50 to 75 years (n = 62). Tear samples from each subject and 13 ophthalmic solutions were analyzed for total antioxidant content (as the Ferric Reducing/Antioxidant Power value). Tear flow rates were estimated from time taken to collect a fixed volume of tear fluid. UV absorbance spectra of pooled fresh reflex tear fluid and the ophthalmic solutions were determined. Results. Results showed that the antioxidant content of minimally stimulated tears from older subjects (398 ± 160 &mgr;mol/l) was not significantly lower than that of younger subjects (348 ± 159 &mgr;mol/l; p = 0.0915). However, there was a significant difference in the tear flow rates between the two groups (p < 0.0001), with the younger group having three to four fold higher flow rate. None of the commercial preparations tested had detectable antioxidant content, and none showed the UV absorption characteristics of natural reflex tears. Conclusions. The effect of low flow rate on the dynamic antioxidant supply to the corneal surface indicates that older subjects have poorer overall defense against photooxidative and other oxidative processes. This could predispose older persons to corneal stress and development of dry eye syndrome. The commercially available artificial tears tested lack both the antioxidant content and UV absorbing characteristics of natural tears. Artificial tears formulations that help restore natural antioxidant and UV absorbing properties to the tear film of the aging eye may help prevent or improve dry eye symptoms and promote ocular health.

Do Multipurpose Solutions Damage Porcine Corneal Epithelial Cells

Purpose. To determine and compare the cytotoxic effects on porcine corneal epithelial cells of commercially available multipurpose solutions (MPS) using fluorescein staining and flow cytometry (FCM). Methods. Effects of exposure time of 10 s to 10 min of MPS containing polyquaternium-1 (MPS-A), polyaminopropyl biguanide (MPS-B), and polyhexanide (MPS-C), on porcine corneal epithelial cells were determined. Cell viability and membrane integrity were assessed by Annexin V-FITC/7-AAD staining and FCM. In further trials, whole corneas were immersed in MPS and control (buffered saline), and corneal fluorescein staining assessed before FCM analysis. Results. Significantly higher percentages of 7-AAD-stained cells (early necrosis) were observed at all exposure times for MPS-A than for other solutions and control (p < 0.05). Exposure time in MPS-A and 7-AAD-stained cell proportions showed significant correlation (r = 0.9957; p < 0.0001). Significantly more cells dual-stained with Annexin V-FITC/7-AAD (late necrosis) after 5 min MPS-A exposure (11.8 ± 1.1%), compared with 1.2 ± 0.9% (MPS-B), 0.9 ± 0.5% (MPS-C), and 1.8 ± 0.2% (control). However, only 10 min exposure resulted in significant increases in fluorescein grades (p < 0.001), with median grade 0.75 for MPS-A, and 0.50 for the other MPS. Conclusions. MPS exposure, especially MPS-A, affected the viability and integrity of porcine corneal epithelial cells. Furthermore, our results confirmed that fluorescein staining correlates poorly with cytotoxicity. As fluorescein staining lacks sensitivity to determine cytotoxic effects of ophthalmic solutions, more objective and sensitive assessment methods such as differential staining and FCM should be developed.

Investigation of corneal effect of different types of artificial tears in a simulated dry eye condition using a novel porcine dry eye model (pDEM).

Purpose: To use a novel porcine dry eye model (pDEM) to study the effect of various artificial tears on corneal abrasion and epithelial cell death under severe “dry eye” conditions. Methods: A 60-second lacrimation-blink interval, which simulates a severe dry eye condition, was set up with our novel pDEM. The corneal protective effect of lubricating the eye for 4 hours with Dulbecco phosphate-buffered saline (DPBS, as control; n = 20) and with 3 types of commercially available artificial tears (n = 17 for each) that contained different lubricating agents was studied. Effect was determined in terms of the change in fluorescein staining grade (on a 0-4 point scale with 0.5 increments) of the cornea and the number of dead cells (by trypan blue staining) on the corneal surface. Results: Median increase in fluorescein grading (median) in corneas treated for 4 hours with artificial tears containing sodium hyaluronate or hydroxypropyl methylcellulose was significantly (P < 0.002) smaller than with artificial tears containing balanced saline with an unknown demulcent or the DPBS control. The numbers of dead epithelial cells in the central corneas lubricated with artificial tears containing sodium hyaluronate or hydroxypropyl methylcellulose (229 ± 71 and 221 ± 65 [SD], respectively) were also significantly (P < 0.005) smaller than those in the corneas of eyes lubricated with artificial tears containing balanced saline with an unknown demulcent or DPBS alone (328 ± 106 and 341 ± 113, respectively). Conclusion: Results show that artificial tears containing sodium hyaluronate or hydroxypropyl methylcellulose as lubricating agents give enhanced corneal protection against desiccation and show the use of this novel pDEM model in evaluating corneal protection from desiccation.

Is ascorbate in human tears from corneal leakage or from lacrimal secretion

Background: This study investigated whether fresh main lacrimal gland secretion contains ascorbate, with a view to providing indirect evidence of an immediate source of this antioxidant in tears. Our hypothesis was that, if the source is corneal leakage, continuous tearing or rinsing of the eye will result in a marked decrease, by dilution, in ascorbate concentration in the reflex tears collected. Alternatively, the ascorbate concentration will be relatively constant if the main lacrimal gland secretion is the main immediate source.

Antioxidants in tears and plasma: Inter-relationships and effect of vitamin C supplementation.

Purpose. To investigate inter-relationships between total antioxidant capacity and ascorbate concentration in plasma and tears, and the effect of antioxidant supplementation with reference to these variables. Methods. Twenty-one subjects were studied in this placebo-controlled, cross-over intervention trial. Fasting plasma and tear ascorbate concentrations and total antioxidant capacity (as Ferric Reducing/Antioxidant Power (FRAP)) were measured pre- and post-supplementation with vitamin C (1 g/day). Results. Mean ± SD ascorbate in tears and plasma at entry were 17 ± 6 and 52 ± 13µM, respectively; FRAP values were, respectively, 273 ± 94 and 1101 ± 168µM. There was no significant correlation between tear and plasma levels (r = -0.068; P = 0.771 for ascorbate; r = 0.418; P = 0.059 for FRAP). Neither was significant correlation seen between the two variables in plasma (r = 0.162; P = 0.483) or tears (r = 0.353; P = 0.117). Acute responses (up to 3 hours) showed a similar pattern of increase in both fluids, however, peak response in tears (33 ± 4µM) was much smaller and slightly later than in plasma (125 ± 13µM). After 4 weeks’ supplementation, ascorbate increased (P < 0.001) in both fluids, however, the increase in tear ascorbate was small (5µM), compared to plasma (38µM). The increase in tear ascorbate appeared to plateau after 2 days’ supplementation; plasma levels were still increasing. Higher tear ascorbate at entry was associated (P < 0.05) with smaller supplementation-related response. No significant changes in FRAP were seen in either fluid (P > 0.05). Conclusions. Ascorbate concentration in both plasma and tears increased with vitamin C supplementation, but the total antioxidant capacity of these fluids did not. Furthermore, the increase in tear ascorbate was modest in comparison to that in plasma, and is suggestive of a “ceiling” for tear ascorbate of under 40µM. Results support the concept of a control mechanism for an integrated antioxidant defense system, and suggest that the amount of ascorbate in tears is both actively controlled and purposefully limited.

Viability of porcine corneal epithelium ex vivo and effect of exposure to air: a pilot study for a dry eye model.

Purpose To explore the use of an ex vivo, in situ porcine cornea as a model for dry eye (exposure keratitis). Methods Twenty-seven porcine eyes were obtained from freshly killed animals at the local abattoir. The viability of 9 corneas (control-baseline group) was assessed within 5 minutes after enucleation on site. A further 18 eyes were transported to the laboratory, where they were exposed to ambient conditions for 4 hours (experimental group A, 6 eyes), for 6 hours (experimental group B, 6 eyes), and for 4 hours with wetting with Dulbecco Phosphate-Buffered Saline every 5 minutes (exposure control group, 6 eyes). All corneas were assessed by trypan blue exclusion for cell viability. Results The number of dead cells in the central region was significantly greater than those in the peripheral region (P < 0.05) in all groups. The number of dead cells in both corneal areas increased significantly (P < 0.05) in the experimental groups with time of exposure, but there was no significant increase in the exposure control group. Conclusion Preliminary data on the number of dead cells in porcine corneal epithelium after enucleation and the effect of exposure were obtained. It was found that after exposure to air, the corneal cells were maintained well by regular wetting, but there was progressively greater cell damage with exposure without wetting. These baseline data will be useful for the further development of the porcine dry eye model to investigate exposure keratitis.

Dry eye and blink rate simulation with a pig eye model

Purpose. To simulate medium level “dry eye” and investigate the effect of “blink” rates in “dry eye” condition using a novel porcine dry eye model (pDEM). Methods. In the first experiment, a 40 s “lacrimation/blink” interval (lacrimation occurring in conjunction with blink) was set in the pDEM to simulate a medium level of “dry eye” condition. In the second experiment, “lacrimation” interval was set at 60 s and three different “inter-blink” intervals of 6, 12, and 20 s were set in groups A, B, and C, respectively. The integrity of each cornea was assessed before and after experiments by slit-lamp microscopy with sodium fluorescein solution. The viability of corneal epithelial cells was assessed by the Trypan blue exclusion test after the experiment. Results. The amount of sodium fluorescein staining was significantly (p < 0.05) lower at the end of the experiment, when the “inter-blink” interval was set at 12 s. The medians of the final fluorescein grades of corneas in the pDEM were grade 1.5, 1.0, and 2.0 when the “inter-blink” intervals were set at 6, 12, and 20 s, respectively. There was no significant difference in the number of damaged cells between the central and peripheral corneas with different “inter-blink” intervals. Although in each case the peripheral area had a lower number of non-viable cells than the central area of the cornea, there was no significant change in the number of Trypan blue stained cells in either area with different “inter-blink” intervals. Conclusion. Different severity levels of “dry eye” can be simulated using the newly developed pDEM. Increased blink rate may protect the cornea against desiccation-induced damage; however, increased blink rate may also increase shear force between the cornea and conjunctiva and result in mechanical damage because of increased frictional force.