Benzalkonium chloride and gentamicin cause a leak in corneal epithelial cell membrane

Keratoconus

Keratoconus is a progressive eye disorder primarily affecting individuals in adolescence and early adulthood. The ectatic changes in the cornea cause thinning and cone-like steepening leading to irregular astigmatism and reduced vision. Keratoconus is a complex disorder with a multifaceted aetiology and pathogenesis, including genetic, environmental, biomechanical and cellular factors. Environmental factors, such as eye rubbing, UV light exposure and contact lens wearing, are associated with disease progression. On the cellular level, a complex interplay of hormonal changes, alterations in enzymatic activity that modify extracellular membrane stiffness, and changes in biochemical and biomechanical signalling pathways disrupt collagen cross-linking within the stroma, contributing to structural integrity loss and distortion of normal corneal anatomy. Clinically, keratoconus is diagnosed through clinical examination and corneal imaging. Advanced imaging platforms have improved the detection of keratoconus, facilitating early diagnosis and monitoring of disease progression. Treatment strategies for keratoconus are tailored to disease severity and progression. In early stages, vision correction with glasses or soft contact lenses may suffice. As the condition advances, rigid gas-permeable contact lenses or scleral lenses are prescribed. Corneal cross-linking has emerged as a pivotal treatment aimed at halting the progression of corneal ectasia. In patients with keratoconus with scarring or contact lens intolerance, surgical interventions are performed.

Role of Mesenchymal Stem Cell-Derived Conditioned Medium in Modulating the Benzalkonium Chloride-Induced Cytotoxic Effects in Cultured Corneal Epithelial Cells In Vitro

PURPOSE

Benzalkonium chloride (BAK) is a common preservative in ophthalmic formulations that causes cytotoxic damage to the corneal epithelial cells. This study aims to explore the role of mesenchymal stem cell (MSC)-derived conditioned medium in modulating the BAK-induced cytotoxic effects in cultured human corneal epithelial cells (HCECs) as a cell-free therapeutic agent.

METHODS

The in vitro cultured HCECs derived from a HCE cell line were treated with BAK (0.001% and 0.005%, diluted in DMEM/F12, v/v) for 15 min, washed with 1xPBS, and allowed to recover for 24 h in human bone marrow MSC-derived conditioned medium (MSC-CM: undiluted (100%) and diluted (50%, v/v)). On the other hand, HCECs were co-incubated with BAK (0.005%, v/v) and MSC-CM (100% and 50%, v/v) for 24 h. The HCEC-derived conditioned medium (HCE-CM) was used as an optimal control for MSC-CM, whereas HCECs cultured in DMEM/F12 were used as a control. The DMEM/F12 was used as the base medium for the culture of HCECs and preparation of HCE- and MSC-CM. The role of MSC-CM in modulating the metabolic activity, cell death, epithelial repair, and proliferation, in BAK-treated HCECs was evaluated using MTT assay, Propidium iodide staining, scratch assay, and Ki-67 staining, respectively.

RESULTS

Compared to the control, recovery of BAK-treated (0.001% and 0.005%, for 15 min) HCECs in MSC-CM showed significantly reduced cell death with enhanced metabolic activity, epithelial repair, and proliferation. However, in comparison with HCE-CM, the beneficial effects of MSC-CM were predominantly observed at lower BAK concentration (0.001%, for 15 min). Whereas the co-incubation of BAK (0.005%) and MSC-CM for a longer duration (24 h) was marginally beneficial.

CONCLUSIONS

Our results suggest that the MSC-CM is effective in modulating the BAK-induced cell death, retardation of metabolic activity and proliferation in cultured HCECs, particularly at lower concentration (0.001%) and shorter exposure (15 min) of BAK.

Management of keratoconus: an updated review

Keratoconus is the most common corneal ectatic disorder. It is characterized by progressive corneal thinning with resultant irregular astigmatism and myopia. Its prevalence has been estimated at 1:375 to 1:2,000 people globally, with a considerably higher rate in the younger populations. Over the past two decades, there was a paradigm shift in the management of keratoconus. The treatment has expanded significantly from conservative management (e.g., spectacles and contact lenses wear) and penetrating keratoplasty to many other therapeutic and refractive modalities, including corneal cross-linking (with various protocols/techniques), combined CXL-keratorefractive surgeries, intracorneal ring segments, anterior lamellar keratoplasty, and more recently, Bowman's layer transplantation, stromal keratophakia, and stromal regeneration. Several recent large genome-wide association studies (GWAS) have identified important genetic mutations relevant to keratoconus, facilitating the development of potential gene therapy targeting keratoconus and halting the disease progression. In addition, attempts have been made to leverage the power of artificial intelligence-assisted algorithms in enabling earlier detection and progression prediction in keratoconus. In this review, we provide a comprehensive overview of the current and emerging treatment of keratoconus and propose a treatment algorithm for systematically guiding the management of this common clinical entity.

Disinfectant dodecyl dimethyl benzyl ammonium chloride (DDBAC) disrupts gut microbiota, phospholipids, and calcium signaling in honeybees (Apis mellifera) at an environmentally relevant level

One of the impacts of the Coronavirus disease 2019 (COVID-19) pandemic has been a profound increase in the application amounts of disinfectants. Dodecyl dimethyl benzyl ammonium chloride (DDBAC) is a widely used disinfectant, yet its hazards to non-target species remain largely unknown. We are unaware of any studies assessing DDBAC's impacts on honeybee, a pollinator species that is a useful indicator of environmental pollution essential for many forms of agricultural production. Here, we assessed the potentially negative effects of DDBAC on honeybees. After conducting a formal toxicity evaluation of DDBAC on honeybee mortality, we detected an accumulation of DDBAC in the honeybee midgut. We subsequently studied the midgut tissues of honeybees exposed to sub-lethal concentrations of DDBAC: histopathological examination revealed damage to midgut tissue upon DDBAC exposure, microbiome analysis showed a decreased abundance of beneficial midgut microbiota, lipidomics analysis revealed a significant reduction in cell membrane phospholipids with known functions in signal transduction, and a transcriptome analysis detected altered expression of genes involved in calcium signaling pathways (that variously function in calcium absorption, muscle contraction, and neurotransmission). Thus, our study establishes that DDBAC impacts honeybee midgut functions at multiple levels. Our study represents an early warning about the hazards of DDBAC and appeals for the proper stewardship of DDBAC to ensure the protection of our ecological environment.

Tear dynamics testing and quantitative proteomics analysis in patients with chronic renal failure

Ocular surface changes may develop in patients with chronic renal failure (CRF) undergoing hemodialysis. In recent years, an association of CRF with dry eye syndrome has been emphasized. However, tear proteomics of CRF patients has not been analyzed. Here, we performed systematic profiling of the tear film proteins in CRF patients through use of isobaric tags for relative and absolute quantitative (iTRAQ) MS/MS, aiming to identify associations between dry eye symptoms and expression of tear proteomic changes in patients with CRF undergoing hemodialysis. Twenty CRF patients and ten healthy subjects underwent a series of ophthalmic examinations. Tear samples from the participants were analyzed by iTRAQ approach. A total of 1139 tear proteins were screened, and 212 differentially expressed proteins were identified. The pattern changes included 77 whose expression levels were upregulated (fold increase >1.2) whereas 135 others that were downregulated (fold decrease <1/1.2). Bioinformatics analysis showed that these proteins were significantly enriched in lipid metabolism, inflammatory, and immune response pathways. Furthermore, APOA1, APOA4, APOB, APOE, S100A8, S100A9, S100A4, HSP90B and other molecules were significantly changed. Our study elucidated the characteristics of tear dynamics and protein markers in CRF patients undergoing hemodialysis. Significance: Despite the association of chronic renal failure (CRF) with dry eye disease, there are no reports describing potentially important differentially expressed tear proteins in CRF patients undergoing hemodialysis. It is still a challenge to obtain a comprehensive description of the pathogenesis of dry eye in CRF patients which hinders establishing a patient specific therapeutic scheme. Our study is the first iTRAQ proteomics analysis of the tears of patients with CRF, which reveals the changes in the protein expression profile in CRF patients afflicted with dry eye disease. The identity was verified of some relevant differentially expressed proteins, and they may be candidate diagnostic markers of dry eye disease in patients with CRF. These tear film protein constituents found in hemodialysis patients can be of important clinical significance in treating this condition. SIGNIFICANCE: Despite the association of chronic renal failure (CRF) with dry eye disease, there are no reports describing potentially important differentially expressed tear proteins in CRF patients undergoing hemodialysis. It is still a challenge to obtain a comprehensive description of the pathogenesis of dry eye in CRF patients which hinders establishing a patient specific therapeutic scheme. Our study is the first iTRAQ proteomics analysis of the tears of patients with CRF, which reveals the changes in the protein expression profile in CRF patients afflicted with dry eye disease. The identity was verified of some relevant differentially expressed proteins, and they may be candidate diagnostic markers of dry eye disease in patients with CRF. These tear film protein constituents found in hemodialysis patients can be of important clinical significance in treating this condition.

Ocular toxicology: synergism of UV radiation and benzalkonium chloride

PURPOSE

To investigate the combined toxic effect of ultraviolet (UV) radiation and benzalkonium chloride (BAK), a common preservative in ophthalmic eye drops, on human corneal epithelial cells (HCEC).

METHODS

Cultured HCEC were exposed to different combined and separate UV (280-400 nm) and BAK solutions at relevant human exposure levels. Human exposure to UV can occur before, during, or after eye drop installation, therefore, three different orders of ocular exposures were investigated: UV and BAK at the same time, UV first followed by BAK, and BAK first followed by UV. Control treatments included testing HCEC exposed to BAK alone and also HCEC exposed to UV alone. In addition, phosphate-buffered saline (PBS) was used as a negative control. After exposure, cell metabolic activity of the cultures was measured with PrestoBlue, and cell viability was determined using confocal microscopy with viability dyes.

RESULTS

BAK alone reduced the metabolic activity and cell viability of HCEC in a dose- and time-dependent manner. UV alone at a low dose (0.17 J/cm²) had little toxicity on HCEC and was not significantly different from PBS control. However, UV plus BAK showed combined effects that were either greater than (synergistic) or equal to (additive) the sum of their individual effects. The synergistic effects occurred between low dose UV radiation (0.17 J/cm²) and low concentrations of BAK (0.001%, 0.002%, 0.003%, and 0.004%).

CONCLUSIONS

This investigation determined that at relevant human exposure levels, the combination of UV radiation (280-400 nm) and BAK can cause synergistic and additive toxic effects on human corneal epithelial cells. This finding highlights the importance of considering the combined ocular toxicity of BAK and solar radiation in the risk assessment of BAK-preserved ophthalmic solutions.

Current concepts in crosslinking thin corneas

Corneal cross-linking (CXL), introduced by Wollensak et al. in 2003, is a minimally invasive procedure to halt the progression of keratoconus. Conventional CXL is recommended in eyes with corneal thickness of at least 400 microns after de-epithelialization to prevent endothelial toxicity. However, most of the keratoconic corneas requiring CXL may not fulfill this preoperative inclusion criterion. Moderate-to-advanced cases are often found to have a pachymetry less than this threshold. There are various modifications to the conventional method to circumvent this issue of CXL thin corneas while avoiding the possible complications. This review is an update on the modifications of conventional CXL for thin corneas.

Current perspectives on corneal collagen crosslinking (CXL)

Corneal collagen crosslinking has revolutionized the treatment of keratoconus and post-refractive corneal ectasia in the past decade. Corneal crosslinking with riboflavin and ultraviolet A is proposed to halt the progression of keratectasia. In the original "Conventional Dresden Protocol" (C-CXL), the epithelium is removed prior to the crosslinking process to facilitate better absorption of riboflavin into the corneal stroma. Studies analyzing its short- and long-term outcomes revealed that although there are inconsistencies as to the effectiveness of this technique, the advantages prevail over the disadvantages. Therefore, corneal crosslinking (CXL) is widely used in current practice to treat keratoconus. In an attempt to improve the visual and topographical outcomes of C-CXL and to minimize time-related discomfort and endothelial-related side effects, various modifications such as accelerated crosslinking and transepithelial crosslinking methods have been introduced. The comparison of outcomes of these modified techniques with C-CXL has also returned contradictory results. Hence, it is difficult to clearly identify an optimal procedure that can overcome issues associated with the CXL. This review provides an up-to-date analysis on clinical and laboratory findings of these popular crosslinking protocols used in the treatment of keratoconus. It is evident from this review that in general, these modified techniques have succeeded in minimizing the immediate complications of the C-CXL technique. However, there were contradictory viewpoints regarding their effectiveness when compared with the conventional technique. Therefore, these modified techniques need to be further investigated to arrive at an optimal treatment option for keratoconus.

Anterior Segment Biometry Changes with Cycloplegia in Myopic Adults

PURPOSE

To determine the effect of cycloplegia on corneal thickness, corneal curvature, anterior chamber depth (ACD), angle-to-angle (ATA) and white-to-white (WTW) distances, and axial length (AL).

METHODS

Changes in corneal thickness, corneal curvature, ACD, ATA and WTW distances, and AL with and without cycloplegia were analyzed in 31 eyes of 31 young myopic adults, aged 26.4 ± 3.0 years. Pentacam was used to measure the corneal thickness, corneal volume, and corneal curvatures. Visante optical coherent tomography (OCT) measured corneal thickness, ATA distance, ACD, and pupil size. The AL and WTW distance were measured using IOLMaster.

RESULTS

Cycloplegia induced significant flattening of corneal curvatures (p = 0.019, 0.001, and 0.003 for anterior sagittal, posterior tangential, and posterior sagittal curvatures, respectively). The difference in the posterior corneal curvature was greater in corneas with steeper posterior curvatures. Cycloplegia also induced significant deepening of ACD (0.08 ± 0.06, p < 0.001) and widening of both WTW (0.42 ± 0.43, p < 0.001) and ATA (0.08 ± 0.17, p = 0.015) distances. The cycloplegia-related increase in the ATA distance correlated negatively with AL (r = -0.361, p = 0.046), whereas the cycloplegia-related increase in WTW distance correlated weakly with the increase in ACD (r = 0.347, p = 0.056) but not with AL. The AL did not change with cycloplegia. Pentacam measured a slightly thicker cornea than OCT (p = 0.002). Both Pentacam and OCT detected a significant increase in corneal thickness of 4 μm, which could be attributed to reflex tearing, after cycloplegia.

CONCLUSIONS

Cycloplegia resulted in deeper ACD, greater ATA distance, and flatter corneal curvatures. Surgeons should be aware of these cycloplegia-related alterations for more accurate phakic/functional intraocular lens selection and better refraction results.

Corneal collagen cross-linking (CXL) in thin corneas

Corneal collagen cross-linking (CXL) is a therapeutic procedure aiming at increasing the corneal stiffness in the keratoconus eyes by induction of cross-links within the extracellular matrix. It is achieved by ultraviolet-A (370 nm) irradiation of the cornea after saturation with the photosensitizer riboflavin. In the conventional CXL protocol, a minimum de-epithelialized corneal thickness of 400 μm is recommended to avoid potential irradiation damage to the corneal endothelium. In advanced keratoconus, however, stromal thickness is often lower than 400 μm, which limits the application of CXL in that category. Efforts have been undertaken to modify the conventional CXL procedure to be applicable in thin corneas. The current review discusses different techniques employed to achieve this end and their results. The overall safety and efficacy of the modified CXL protocols are good, as most of them managed to halt the progression of keratectasia without postoperative complications. However, the evidence of safety and efficacy in the use of modified CXL protocols is still limited to few studies with few patients involved. Controlled studies with long-term follow-up are required to confirm the safety and efficacy of the modified protocols.

A review of collagen cross-linking in cornea and sclera

Riboflavin/UVA cross-linking is a technique introduced in the past decades for the treatment of keratoconus, keratectasia, and infectious keratitis. Its efficacy and safety have been investigated with clinical and laboratory studies since its first clinical application by Wollensak for the treatment of keratoconus. Although its complications are encountered during clinical practice, such as infection inducing risk, minimal invasion merits a further investigation on its future application in clinical practice. Recently, collagen cross-linking in sclera shows a promising prospect. In present study, we summarized the representative studies describing the clinical and laboratory application of collagen cross-linking published in past decades and provided our opinion on the positive and negative results of cross-linking in the treatment of ophthalmic disorders.

Safety and efficacy of epithelium removal and transepithelial corneal collagen crosslinking for keratoconus

This review aims to assess the efficacy and safety of epithelial removal (ER) and transepithelial (TE) corneal collagen crosslinking (CXL) for the treatment of keratoconus. We used MEDLINE to identify all ER and TE CXL studies on keratoconic eyes (n≥20, follow-up ≥12 months). Ex vivo and studies for non-keratoconus indications or in conjunction with other procedures were excluded. Data on uncorrected (UDVA) and corrected (CDVA) distance visual acuity, refractive cylinder, maximum keratometry (Kmax), and adverse events were collected at the latest follow-up and 1 year. Only one randomised controlled trial (RCT) qualified inclusion. Forty-four ER and five TE studies were included. For logMAR UDVA, CDVA, mean spherical equivalent, refractive cylinder and Kmax, at latest follow-up 81, 85, 93, 62, and 93% ER studies vs 66.7, 80, 75, 33, and 40% TE studies reported improvement, respectively. Whereas at 1 year, 90, 59, and 91% ER studies vs 80, 50, and 25% TE studies reported improvement, respectively. The majority of studies showed reduced pachymetry in both groups. Treatment failure, retreatment rates, and conversion to transplantation were reported to be up to 33, 8.6, and 6.25%, respectively, in ER studies only. Stromal oedema, haze, keratitis, and scarring were only reported in ER studies, whereas endothelial cell counts remained variable in both groups. Both ER and TE studies showed improvement in visual acuity, refractive cylinder but Kmax worsened in most TE studies. Adverse events were reported more with ER studies. This review calls for more high quality ER and TE studies with comparable parameters for further assessment of safety and efficacy.

Effect of acacia honey on cultured rabbit corneal keratocytes

BACKGROUND

Acacia honey is a natural product which has proven to have therapeutic effects on skin wound healing, but its potential healing effects in corneal wound healing have not been studied. This study aimed to explore the effects of Acacia honey (AH) on corneal keratocytes morphology, proliferative capacity, cell cycle, gene and protein analyses. Keratocytes from the corneal stroma of six New Zealand white rabbits were isolated and cultured until passage 1. The optimal dose of AH in the basal medium (FD) and medium containing serum (FDS) for keratocytes proliferation was identified using MTT assay. The morphological changes, gene and protein expressions of aldehyde dehydrogenase (ALDH), marker for quiescent keratocytes and vimentin, marker for fibroblasts were detected using q-RTPCR and immunocytochemistry respectively. Flowcytometry was performed to evaluate the cell cycle analysis of corneal keratocytes.

RESULTS

Cultured keratocytes supplemented with AH showed no morphological changes compared to control. Keratocytes cultured in FD and FDS media supplemented with 0.025% AH showed optimal proliferative potential compared with FD and FDS media, respectively. Gene expressions of ADLH and vimentin were increased in keratocytes cultured with AH enriched media. All proteins were expressed in keratocytes cultured in all media in accordance to the gene expression findings. No chromosomal changes were detected in keratocytes in AH enriched media.

CONCLUSION

Corneal keratocytes cultured in media supplemented with 0.025% AH showed an increase in proliferative capacity while retaining their morphology, gene and protein expressions with normal cell cycle. The results of the present study show promising role of AH role in accelerating the initial stage of corneal wound healing.

Comparison of transepithelial corneal collagen crosslinking with epithelium-off crosslinking in progressive keratoconus

PURPOSE

To evaluate the safety and efficacy of transepithelial corneal collagen crosslinking (TE-CXL) as compared to epithelium-off crosslinking (epi-off CXL) in progressive keratoconus.

METHODS

Records of keratoconus patients treated with TE-CXL or epi-off CXL were reviewed retrospectively. Patients were included if they had at least 12months follow-up. Pre- and postoperative measurements of visual acuity, refractive errors, keratometry, corneal topography and pachymetry were assessed and compared.

RESULTS

There was no statistically significant difference between two groups at baseline in terms of demographic, refractive and corneal parameters. Mean maximum cone apex curvature (apical K) increased from 51.62±5. Eighty-four diopters (D) to 53.70±5.49 D in the TE-CXL group (n=17), and decreased from 52.02±4.07 D to 51.22±3.51 in the epi-off CXL group (n=19) at the end of the follow-up period. The difference between two groups was statistically significant (P=0.0002). An increase of≥1D in apical K was observed in two of 19 eyes (11%) in the epi-off CXL group, and 11 of 17 eyes (65%) in TE-CXL group at the last follow-up visit, compared to baseline (P<0.0001). Fourteen patients in the epi-off CXL group exhibited corneal edema that resolved without haze with topical corticosteroid treatment by 4months. No postoperative corneal edema was observed in TE-CXL group.

CONCLUSIONS

Although it is safe and well tolerated, TE-CXL does not effectively halt the progression of keratoconus. Epi-off CXL appears to be effective in stopping progression and even improves corneal parameters.

Transepithelial corneal collagen cross-linking in ultrathin keratoconic corneas

Background

The purpose of this paper was to report the results of transepithelial corneal collagen cross-linking (CXL) with modified riboflavin and ultraviolet A irradiation in patients affected by keratoconus, each with thinnest pachymetry values of less than 400 μm (with epithelium) and not treatable using standard de-epithelialization techniques.

Methods

Sixteen patients affected by progressive keratoconus with thinnest pachymetry values ranging from 331 μm to 389 μm underwent transepithelial CXL in one eye using a riboflavin 0.1% solution in 15% Dextran T500 containing ethylenediamine tetra-acetic acid 0.01% and trometamol to enhance epithelial penetration. The patients underwent complete ophthalmological examination, including endothelial cell density measurements and computerized videokeratography, before CXL and at one day, one week, and one, 6, and 12 months thereafter.

Results

Epithelial healing was complete in all patients after one day of use of a soft bandage contact lens. No side effects or damage to the limbal region was observed during the follow-up period. All patients showed slightly improved uncorrected and spectacle-corrected visual acuity; keratometric astigmatism showed reductions (up to 5.3 D) and apical ectasia power decreased (K_max values reduced up to 4.3 D). Endothelial cell density was unchanged.

Conclusion

Application of transepithelial CXL using riboflavin with substances added to enhance epithelial permeability was safe, seemed to be moderately effective in keratoconic eyes with ultrathin corneas, and applications of the procedure could be extended to patients with advanced keratoconus.

Preservative use in topical glaucoma medications

Benzalkonium chloride (BAK) is the principal preservative employed in topical ocular hypotensive medications, although alternative compounds recently have begun to be employed or examined. Individual clinical trials have shown that exposure to BAK concentrations contained in ophthalmic solutions does not produce adverse sequelae in the majority of glaucoma patients, but concerns continue with regard to its long-term use. These concerns have resulted from an extensive research effort, including preclinical studies with in vitro and in vivo models, as well as recent clinical investigations dedicated specifically to this issue. The aim of this systematic literature review of both preclinical and clinical data was to determine the relevance of these findings to clinical practice. Most preclinical studies reported negative effects of BAK exposure, but with few exceptions, BAK concentrations and exposure times greatly exceeded those likely to be experienced by patients, given the normal physiological dilution by the tear film. In addition, consistent evidence of BAK-related toxicity did not emerge from our review of dedicated clinical investigations. Thus, taken together, current evidence supports the safety of BAK for most glaucoma patients, although subpopulations with abnormal tearing may benefit from alternative preservative compounds or preservative-free formulations. Further studies to identify these populations are needed.

Role of benzalkonium chloride in DNA strand breaks in human corneal epithelial cells

PURPOSE

To investigate the toxic effects of benzalkonium chloride (BAC), a preservative commonly used in ophthalmic preparations, on DNA single- and double-strand breaks in immortalized human corneal epithelial cells (HCEs).

METHODS

HCEs were treated with BAC in concentrations ranging from 0.00005% to 0.001% for 30 min. Cells were examined immediately after BAC exposure and after 24-h recovery. Alkaline comet assay was used to detect DNA single-strand breaks (SSBs). Immunofluorescence microscope detection of the phosphorylated form of histone variant H2AX (γH2AX) foci indicated DNA double-strand breaks (DSBs). Cell viability was measured by the MTT test.

RESULTS

A significant increase of SSBs, detected by alkaline comet assay, was observed in a dose-dependent manner with BAC exposure in HCEs at concentrations of 0.00005% and higher. Such BAC treatment also exhibited a dose-dependent increase in DSBs, evaluated by number of γH2AX foci. In addition, a significant change in the relative cell survival rate of HCEs was observed after exposure to 0.001% BAC for 30 min. Although the toxic effects of BAC could be partly repaired after 24 h of cell recovery, SSBs and DSBs in HCEs were still present after BAC removal.

CONCLUSIONS

The results demonstrated that exposure to BAC in HCEs, even at low concentrations, could induce DNA strand breaks, which were present after BAC removal. Cell survival analysis indicated that BAC-induced DNA damage was correlated with the cytotoxic effects.

The impact of artificial tears containing hydroxypropyl guar on mucous layer

PURPOSE

The aim of this study was to investigate the effect of lubricant eyedrops containing propylene glycol 400 (PEG) and polyethylene glycol (PG) with hydroxypropyl guar (HP-guar) as a gelling agent on the precorneal mucous layer in vivo.

METHODS

Sixteen New Zealand white rabbits were randomly assigned to 1 of 4 groups. All rabbits received PEG/PG/HP-guar tear products in the right eye. PEG/PG/HP-guar with Polyquad, 0.1% hyaluronate sodium, 0.5% carboxymethylcellulose, or phosphate-buffered saline was placed in the left eyes of animals in each group. All eyedrops were used 4 times a day for 7 days. An additional 8 rabbits were randomly assigned to 1 of 2 groups. One group received PEG/PG/HP-guar products 4 times a day for 7 days (long-term exposure group), and the other group received PEG/PG/HP-guar products 3 times at 5-minute intervals (short-term exposure group). Fifteen minutes after the last drop was administered, each cornea was immediately excised and mucous layer thickness measured by transmission electron microscopy.

RESULTS

Mucous layer thickness was significantly greater in eyes treated with PEG/PG/HP-guar products compared with those treated with 0.1% hyaluronate sodium, 0.5% carboxymethylcellulose, or phosphate-buffered saline (all P values < 0.001). There were no significant differences in mucous layer thickness between PEG/PG/HP-guar products and PEG/PG/HP-guar with Polyquad or in the long- and short-term exposure animals.

CONCLUSIONS

This study demonstrates that even a short exposure to PEG/PG/HP-guar tear product increased precorneal mucous layer thickness.

Transepithelial corneal collagen cross-linking in keratoconus

PURPOSE

To evaluate the clinical effects of transepithelial corneal cross-linking (CXL) on keratoconic eyes pre-treated with substances enhancing epithelial permeability.

METHODS

Prospective, consecutive, single-masked, paired-eye study on 51 patients. The eye with more severe keratoconus was treated; the fellow eye served as the control. Gentamicin, benzalkonium chloride, and ethylenediaminetetraacetic acid were instilled for 3 hours, then oxybuprocaine for 30 minutes. Riboflavin 0.1% in 20% dextran T500 and oxybuprocaine were instilled for 30 minutes. Finally, ultraviolet A irradiation to the central 7.5 mm of the cornea was applied for 30 minutes, while riboflavin was instilled every 5 minutes.

RESULTS

Mean corrected distance visual acuity improved by 0.036 logMAR after CXL and worsened by 0.039 logMAR in the control eyes (P<.05). Safety index was 1.05 after CXL and 0.96 in the control group. Mean spherical equivalent refraction decreased by 0.35 D (less myopic) after CXL and increased by 0.83 diopters (D) in the control eyes (P<.05). Mean apex curvature on tangential videokeratography increased by 0.51 D after CXL and by 1.61 D in the control eyes (P=.16). Mean average simulated keratometry decreased by 0.10 D after CXL and increased by 0.88 D in the control eyes (P<.05). Mean index of surface variance increased (worsened) by 0.9 after CXL and 5.3 in the control eyes (P<.05). Mean endothelial cell density was unchanged.

CONCLUSIONS

A limited but favorable effect of transepithelial CXL was noted on keratoconic eyes, without complications. The effect appears to be less pronounced than described in the literature after CXL with de-epithelialization.

Barriers to glaucoma drug delivery

Topical medications remain the mainstay of glaucoma treatment. This review will aim to cover the pharmacokinetics of topically applied drops, the ocular barriers to drug delivery, and the role of ophthalmic drug formulation in enhancing drug delivery to the target tissue while minimizing side effects and increasing patient compliance. Recent advances in surgical techniques, therapeutic approaches, and material sciences have produced exciting new therapies for ocular diseases. The development of new vehicles and drug formulations that require less patient compliance is also discussed, as are the routes of drug delivery for neuroprotection.

Investigation of tear film change after recovery from acute conjunctivitis

PURPOSE

To study the changes of tear film after recovery from acute conjunctivitis.

METHODS

This study involved 73 eyes of 56 consecutive patients who complained of dry eye after recovery from acute conjunctivitis at the Zhongshan Ophthalmic Center. Excluded were other factors that could affect the stability of the tear film. Tear film breakup time (BUT), Schirmer 1 test (S1T), tear meniscus height (TMH), and fluorescein staining (FL) were performed on both recovered and healthy eyes. The scores were measured at 3, 7, 14, 21, and 30 days after recovery.

RESULTS

Compared with the results of the healthy eyes, most scores of BUT, S1T, TMH, and FL were all abnormal until day 30 after recovery from acute conjunctivitis. BUT decreased at 3, 7, 14, and 21 days (P < 0.05). S1T decreased at 3, 7, and 21 days (P < 0.05). TMH values became less than normal at 3, 7, and 14 days (P < 0.05). FL increased significantly at 7, 14, and 21 days (P < 0.05). At 30 days after recovery, all of the test scores returned to normal (P > 0.05).

CONCLUSIONS

During acute conjunctivitis, inflammation and topical therapeutic agents can alter the tear film secretion, resulting in dry eye for nearly 1 month in recovered eyes. To minimize the effect of topical agents to the tear film, individualized treatment instead of frequent instillation of topical agents is recommended for acute conjunctivitis.

The effect of moxifloxacin on the normal human cornea

OBJECTIVE

To investigate the effects of moxifloxacin on the cornea of normal human eyes using confocal microscopy and slit-lamp biomicroscopy.

METHODS

This study enrolled adult volunteers who had a normal baseline ophthalmic examination. The dose regimen, similar to that of patients undergoing cataract extraction, was one drop of moxifloxacin in one eye four times a day for 3 days. The untreated fellow eye served as the control. Subjects had a baseline examination (Visit 1), started moxifloxacin the next day, and were examined 24 h (Visit 2) and 72 h (Visit 3) after starting medication. At each visit, visual acuity and adverse effects were recorded, slit-lamp examination with fluorescein was used to measure tear break-up time, and endothelial and epithelial cell counts were determined using confocal microscopy.

RESULTS

Fifteen volunteers (mean age 37 +/- 7 years) enrolled. No significant difference in visual acuity, tear break-up time, endothelial or epithelial cell counts was noted between the treated and fellow eye. Subjects experienced no significant decrease in visual acuity, tear break-up time, or endothelial cell counts during the 3-day treatment period in either eye. Epithelial cell counts were stable at Visits 1 and 2, and decreased similarly in the treated and control eye at Visit 3.

CONCLUSIONS

Moxifloxacin was safe for use during the 3-day treatment period. Moxifloxacin causes no significant epithelial or endothelial toxicity, and has no effect on visual acuity or ocular surface integrity in healthy subjects treated using a dosing regimen that simulated prophylactic use following cataract surgery.

Thymosin beta4 inhibits benzalkonium chloride-mediated apoptosis in corneal and conjunctival epithelial cells in vitro

Thymosin beta-4 (Tbeta(4)) is known to promote ocular wound healing, to decrease ocular inflammation, and to have anti-apoptotic effects on corneal epithelium. In this study, the effect of Tbeta(4) on the survival of human ocular surface epithelial cells exposed to benzalkonium chloride (BAK) was measured. Human conjunctival epithelial cells (HC0597) or human corneal epithelial cells (HCET) were treated with 0%, 0.001%, 0.01%, or 0.1% BAK for 15 min. After 3 or 24h of recovery in culture medium containing 1 microg/ml Tbeta(4), a dosage that has been demonstrated effective in several published studies, DNA synthesis was measured using a colorimetric BrdU incorporation assay. Both conjunctival and corneal epithelial DNA synthesis was inhibited by BAK in a dose-dependent manner. Tbeta(4) did not protect the epithelial cells from BAK-induced inhibition of proliferation. To assess the ability of Tbeta(4) to prevent apoptosis, epithelial cells were treated with 0.01% BAK+Tbeta(4) and cell death was measured using a colorimetric assay. BAK-induced apoptosis increased throughout the duration of the assay, which was carried out to 5 days in culture. Treatment of HC0597 cells with Tbeta(4) significantly inhibited the apoptosis shown to be initiated by BAK. Treatment of non-transformed human corneal epithelial cells (HCEC) with Tbeta(4) also significantly inhibited the apoptosis shown to be initiated by BAK at later times in culture. Ocular solutions containing BAK as a preservative are typically used for extended periods of time. This study suggests that Tbeta(4) may be able to overcome the apoptotic side effect of BAK, and may be a useful additive to solutions containing this preservative.

The effects of epithelial viability on stromal keratocyte apoptosis in porcine corneas stored in Optisol-GS

PURPOSE

To investigate the effect of corneal epithelium on the viability of corneal stromal keratocytes in Optisol-GS.

METHODS

After sterilization, corneoscleral buttons were excised and stored in Optisol-GS for various time periods. Group 1 corneas (n = 40) underwent mechanical corneal epithelial debridement before storage while group 2 corneas (n = 40) were stored with intact epithelium. Changes in corneal thickness, keratocyte density, and keratocyte apoptosis were investigated immediately, at 4 hours, and on days 1, 2, 3, 5, 7, and 14 in the preservation medium. The differences between group 1 and 2 corneas were analyzed.

RESULTS

Corneal thickness increased significantly in the second week of preservation in both groups, though more substantially in group 1. Significant corneal epithelial apoptosis was noticed in the first week in group 2 corneas. Corneal stromal keratocyte density decreased with prolonged preservation time. DNA laddering was detected by ligation-mediated polymerase chain reaction throughout the experiment periods in both groups, but the increase of keratocyte apoptosis was more significant after 5 days of preservation, especially in group 1.

CONCLUSIONS

Stromal keratocytes underwent apoptosis in Optisol-GS. The absence of corneal epithelium during preservation further increased the stromal keratocyte apoptosis.

Change of Potassium Current Density in Rabbit Corneal Epithelial Cells During Maturation and Cellular Senescence

BACKGROUND

Voltage-gated potassium (K+) channels may participate in cellular developmental regulation, including cell differentiation, proliferation and apoptosis. This study investigated the change of K + current densities in corneal epithelial cells during maturation and cellular senescence.

METHODS

New Zealand white rabbits were divided into three age groups: newborn (<or= 7 days old, n = 18); young (8-12 weeks old, n = 59); and adult (20-28 weeks old, n = 16). Rabbit corneal epithelial cells were subdivided into the following three groups: small cells with capacitance < 6.0 pF; medium cells with capacitance 6.0-10.0 pF; and large cells with capacitance > 10.0 pF. Using a whole-cell clamp technique, K+ current was recorded and current densities were calculated. Differences in K+ current densities among newborn, young and adult rabbits, as well as differences among small, medium and large cells, were analyzed.

RESULTS

We delineated two types of cells manifesting different amplitudes of depolarization-activated K+ outward currents. The averaged current density of type 1 response cells was significantly larger than that of type 2 cells in newborn, young, and adult groups. For newborn epithelial cells, the depolarization-gated outward K+ current density decreased from small to medium to large cells (p = 0.049, at a membrane potential of 140 mV). A similar pattern of change in current density was also delineated for these cell sizes in young and adult rabbit corneal cells (p < 0.001 for both young and adult rabbits). An increase in depolarization-gated outward K+ current density was also delineated from newborn to young to adult rabbits (p < 0.001, p < 0.001 and p < 0.006 for small, medium and large cells, respectively, at a membrane potential of 140 mV).

CONCLUSIONS

Corneal epithelial cells expressed K+ channel densities that were distinct from basal to superficial cells and from newborn to adult rabbits.