ABNORMAL EPITHELIAL FRAGILIGY IN DIABETES AND IN CONTACT LENS WEAR

Diabetes and contact lens wear

The literature suggests that diabetic patients may have altered tear chemistry and tear secretion as well as structural and functional changes to the corneal epithelium, endothelium and nerves. These factors, together with a reported increased incidence of corneal infection, suggest that diabetic patients may be particularly susceptible to developing ocular complications during contact lens wear. Reports of contact lens-induced complications in diabetic patients do exist, although a number of these reports concern patients with advanced diabetic eye disease using lenses on an extended wear basis. Over the past decade or so, there have been published studies documenting the response of the diabetic eye to more modern contact lens modalities. The results of these studies suggest that contact lenses can be a viable mode of refractive correction for diabetic patients. Furthermore, new research suggests that the measurement of tear glucose concentration could, in future, be used to monitor metabolic control non-invasively in diabetic patients. This could be carried out using contact lenses manufactured from hydrogel polymers embedded with glucose-sensing agents or nanoscale digital electronic technology. The purpose of this paper is to review the literature on the anterior ocular manifestations of diabetes, particularly that pertaining to contact lens wear.

The Glenn A. Fry award lecture 2010: Ophthalmic markers of diabetic neuropathy

Diabetic peripheral neuropathy (DPN) is a debilitating condition that affects about 50% of diabetic patients. The symptoms of DPN include numbness, tingling, or pain in the arms and legs. Patients with numbness may be unaware of foot trauma, which could develop into a foot ulcer. If left untreated, this may ultimately require amputation. Currently, the only method of directly examining peripheral nerves is to conduct skin punch or sural/peroneal nerve biopsies, which are uncomfortable and invasive. Indirect methods include quantitative sensory testing (assessing responses to heat, cold, and vibration) and nerve electrophysiology. Here, I describe research undertaken in my laboratory, investigating the possibility of using a range of ophthalmic markers to assess DPN. Corneal nerve structure and function can be assessed using corneal confocal microscopy and non-contact corneal esthesiometry, respectively. Retinal nerve structure and visual function can be evaluated using optical coherence tomography and perimetry, respectively. These techniques have been used to demonstrate that DPN is associated with morphological degradation of corneal nerves, reduced corneal sensitivity, retinal nerve fiber layer thinning, and peripheral visual field loss. With further validation, these ophthalmic markers could become established as rapid, painless, non-invasive, sensitive, reiterative, cost-effective, and clinically accessible means of screening for early detection, diagnosis, staging severity, and monitoring progression of DPN, as well as assessing the effectiveness of possible therapeutic interventions. Looking to the future, this research may pave the way for an expanded role for the ophthalmic professions in diabetes management.

Corneal markers of diabetic neuropathy

Diabetic neuropathy is a significant clinical problem that currently has no effective therapy, and in advanced cases, leads to foot ulceration and lower limb amputation. The accurate detection, characterization and quantification of this condition are important in order to define at-risk patients, anticipate deterioration, monitor progression, and assess new therapies. This review evaluates novel corneal methods of assessing diabetic neuropathy. Two new noninvasive corneal markers have emerged, and in cross-sectional studies have demonstrated their ability to stratify the severity of this disease. Corneal confocal microscopy allows quantification of corneal nerve parameters and noncontact corneal esthesiometry, the functional correlate of corneal structure, assesses the sensitivity of the cornea. Both these techniques are quick to perform, produce little or no discomfort for the patient, and are suitable for clinical settings. Each has advantages and disadvantages over traditional techniques for assessing diabetic neuropathy. Application of these new corneal markers for longitudinal evaluation of diabetic neuropathy has the potential to reduce dependence on more invasive, costly, and time-consuming assessments, such as skin biopsy.

Safety of contact lenses in patients with diabetes

The purpose of the present study was to determine if increased complications exist among patients with diabetes as compared with individuals without diabetes who wear soft disposable contact lenses for daily wear. Complications among daily-wear contact lens wearers who have worn soft contact lenses for 1 year or more were reported from a retrospective review of records. Eyes from 254 patients with diabetes and 254 individuals without diabetes (control), one eye for each subject, from six clinical practices were compared using chi2 and exact Wilcoxon analyses as appropriate. The overall incidence of complications was 49.8% among eyes of patients with diabetes and 48.0% among controls. The respective values for occurrence of corneal abrasions were 7.9% and 5.9%, those for corneal staining were 3.2% and 5.5%, and those for pain at some time while wearing a contact lens were 17% and 19.7%. No significant difference in complications, corneal abrasions, corneal staining, or experience of pain was found between daily-wear contact lens wearers with diabetes and controls. Thus patients with diabetes showed no increased complications over patients without diabetes for daily-wear soft contact lens wear.

Risk factors for contact lens associated microbial keratitis

Although the risk of developing contact lens associated microbial keratitis is small, the potential consequences of this condition, such as vision loss, are serious. This paper presents an analysis of the risk factors that have been identified for contact lens induced microbial keratitis, which include extended wear, hypoxia, non-compliance, blepharitis, diabetes mellitus, epithelial trauma, steroid use, therapeutic lens use, tobacco use, and possibly travel to warm climates. By remaining mindful of these risk factors, practitioners can take action and offer advice to patients so as to optimize the safety of contact lens wear.

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

The purposes of this study are to characterize the pathophysiological effects of benzalkonium chloride and gentamicin on corneal epithelial cells and to determine the concentration dependent effect of these agents on membrane currents of these cells. Rabbit corneal epithelial cells were isolated and subdivided into small, medium and large cells according to their cell capacitance. Using whole cell clamp technique, potassium current of corneal epithelial cells was recorded. Transmembrane current was measured again after bathing in benzalkonium chloride 1, 3, 10, 30 and 100 micrometer ml(-1)for 3 min. The effect of gentamicin was tested at concentrations of 0.4, 1.0, 2.0, 4.0 and 10 mg ml(-1). Synergistic effect of gentamicin of the above mentioned concentrations in the presence of benzalkonium chloride 1 microgram ml(-1)was also measured. We found that small corneal epithelial cells had the highest depolarization-gated, outward potassium current density and large cells had the lowest current density, while medium cells had a current density in between. Benzalkonium chloride induced a concentration dependent increase in the leak current with increasing concentration from 1 to 100 microgram ml(-1). The increase of leak current in medium and large cells was less than that in the small cells. Gentamicin also caused a concentration dependent increase in leak current density from 0.4 to 10.0 mg ml(-1). The increase in leak current density was statistically significant when the concentration was 2.0 mg ml(-1)or higher in small corneal epithelial cells and 1.0 mg ml(-1)or higher in the medium and large cells. Benzalkonium chloride 1.0 microgram ml(-1)augmented the effect of gentamicin on epithelial cell membrane. The extent of enhancement was more prominent in larger than smaller cells. Using whole-cell clamp technique, we were able to determine the threshold concentration of gentamicin and benzalkonium chloride on the integrity of corneal epithelial cell membrane. The toxic action of both agents is mediated by an increase in leak current. We propose that the whole-cell clamp technique is a sensitive and useful tool in determining cytotoxic effects of various agents.

Epithelial inclusions in association with mucin ball development in high-oxygen permeability hydrogel lenses

Debris trapped behind contact lenses may be associated with adverse reactions in extended wear. Although streaks and clumps of cellular material have been reported after overnight wear of conventional materials, recent experience with several high-oxygen permeability (Dk), silicone-containing hydrogel lenses indicates that certain participants are prone to the development of a unique back surface debris. This debris forms as spherical, translucent entities and results in depressions within the ocular surface after lens removal. Little information is known about these spherical bodies, particularly with respect to their composition and development. In this report, we provide photographic evidence of this debris (sometimes termed "mucin balls" or "lipid plugs"), discuss its differential diagnosis and describe a case in which material seems to be embedded in the epithelium as a direct consequence of their presence.

Determination of basal tear turnover in insulin-dependent diabetes mellitus patients by fluorophotometry

The tear turnover was determined by fluorophotometry in 25 insulin-dependent diabetes mellitus (IDDM) patients without retinopathy and 29 IDDM patients with (pre-)proliferative retinopathy. The results were compared with those in 34 healthy controls, to investigate the lacrimal gland function in diabetic patients. The tear turnover was calculated from the decay of the relative tear fluorescein concentration values measured after instillation of one microliters of fluorescein. The tear turnover values in both patient groups did not correlate significantly with age or diabetes duration (linear correlation coefficients: r less than 0.3). The tear turnover values in patients both without retinoplathy and with (pre-)proliferative retinopathy did not differ significantly from those in healthy controls (mean +/- SD in %/min: 13.7 +/- 4.5, 14.7 +/- 5.8 and 15.5 +/- 5.1, respectively; P greater than 0.16). The tear turnover was significantly decreased in eyes having a BUT shorter than 10 seconds compared with eyes having a BUT longer than 10 seconds (P less than 0.05). The tear turnover values correlated significantly with the HbA1c and Schirmer-test values in patients with (pre-)proliferative retinopathy (r = 0.7 and r = 0.4, respectively; P less than 0.02) and with the blood glucose values in patients without retinopathy (r = 0.41, P = 0.04). Since the tear turnover was not significantly decreased in IDDM patients in comparison with healthy controls the corneal disorders which are more frequently seen in these patients than in a healthy population may not be attributed to a decrease in tear production.

Corneal epithelial oxygen uptake rate in diabetes mellitus

Corneal epithelial oxygen uptake rate (CEOUR) has been measured using a non-invasive polarographic electrode technique in patients with diabetes mellitus (DM), all with varying degrees of retinopathy. CEOUR was found to be significantly reduced in diabetic patients when compared to age-matched non-diabetic controls--Type I diabetics p less than 0.001; Type 2 diabetics p less than 0.01. Known duration of DM and assay of instantaneous, medium and long term glycaemic control showed no significant correlation with CEOUR in the patients studied. These results give further evidence of abnormal corneal metabolism in DM. Reduced CEOUR may be a contributory factor in the pathogenesis of diabetic corneal epitheliopathy.

Corneal pathophysiology with contact lens wear

Contact lens wear induces a wide spectrum of changes in the appearance and function of the cornea. The most salient effect of lens wear is the hypoxically induced reduction in the rate of metabolic activity of the corneal epithelium and its sequellae. Other important alterations to corneal health associated with contact lens wear may be caused by antigenic and toxic stimuli, mechanical forces, osmotic effects and carbon dioxide retention. Perhaps the most important task facing the contact lens clinician is to distinguish between an acceptable state of physiological modification and an anomalous or pathological state of hypofunction. In this article, we review the assortment of corneal changes primarily on the basis of the causative agents and time scale with reference to the physical and chemical processes leading to the observed signs or symptoms. This procedure allows a strong foundation for understanding the etiology and management principles for the variety of effects that contact lenses may have on the cornea.

The influence of age on the fragility of the cornea

Corneal fragility was measured with the Cochet-Bonnet aesthesiometer on 171 eyes of various ages. It was found to remain the same until about age 40. It increased significantly and progressively afterwards. It was compared to corneal sensitivity which diminishes significantly after about the same age.