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

Tear function in patients with diabetes mellitus: A systematic review and meta-analysis

PURPOSE

To examine tear function in patients with diabetes mellitus (DM).

DESIGN

Systematic review and meta-analysis.

METHOD

We searched Embase and PubMed from database inception to March 16, 2022. We included observational studies that compared tear function between patients with and without DM. Tear function was measured using invasive tear breakup time (ITBUT) and Schirmer's 1 test. Pooled results are presented as standard mean difference (SMD) with 95% confidence interval (CI) based on random-effects models.

RESULTS

We included 59 studies (7,234 eyes) comparing the tear function between patients with and without DM. This meta-analysis indicated that patients with DM had worse tear function than those without DM (ITBUT: SMD: -0.98, 95% CI: -1.27 to -0.69; Schirmer's 1 test: SMD: -0.45, 95% CI: -0.64 to -0.26), and the results remained consistent in patients with different types of DM (e.g., type 1 DM and type 2 DM) and from different ethnic backgrounds (e.g., Asian vs. non-Asian). Patients with DM under poor glycemic control had worse tear function than those of the non-DM group (ITBUT: SMD: -1.26, 95% CI: -1.86 to -0.66; Schirmer's 1 test: SMD: -0.25, 95% CI: -0.48 to -0.02), whereas there were no significant differences in tear function between patients with DM under optimal glycemic control and non-DM groups.

CONCLUSIONS

We found that patients with type 1 or type 2 DM had significantly reduced tear function. The level of tear function could be determined by glycemic control, and therefore, our findings suggest that glycemic control in patients with DM is critical for maintaining tear function.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero, identifier CRD42021250498.

Canine Diabetes Mellitus Associated Ocular Disease

Diabetes mellitus (DM) is a commonly encountered disease in companion animal veterinary practice. Ocular complications in dogs with DM are thought to be common but there are no reports of the overall incidence of DM-associated ocular disease. Some complications, such as cataracts and ocular surface disease, can lead to vision loss and significant morbidity among DM patients, therefore early recognition and intervention are essential for successful outcomes. The purpose of this article is to provide a review of several currently known or suspected ocular diseases associated with DM.

Tear exchange and contact lenses: a review

Tear exchange beneath a contact lens facilitates ongoing fluid replenishment between the ocular surface and the lens. This exchange is considerably lower during the wear of soft lenses compared with rigid lenses. As a result, the accumulation of tear film debris and metabolic by-products between the cornea and a soft contact lens increases, potentially leading to complications. Lens design innovations have been proposed, but no substantial improvement in soft lens tear exchange has been reported. Researchers have determined post-lens tear exchange using several methods, notably fluorophotometry. However, due to technological limitations, little remains known about tear hydrodynamics around the lens and, to-date, true tear exchange with contact lenses has not been shown. Further knowledge regarding tear exchange could be vital in aiding better contact lens design, with the prospect of alleviating certain adverse ocular responses. This article reviews the literature to-date on the significance, implications and measurement of tear exchange with contact lenses.

Tear glucose analysis for the noninvasive detection and monitoring of diabetes mellitus

One approach to the noninvasive monitoring of blood glucose concentration is to monitor glucose concentrations in tear fluid. While several methods for sensing glucose in tear fluid have been proposed, controversy remains as to the precise concentrations of tear glucose in normal and diabetic subjects and as to whether tear fluid glucose concentrations correlate with blood glucose concentrations. This review covers the present understanding of the physiology of glucose transport in tears, the regulation of the aqueous tear fraction, and studies of tear glucose concentration over the last 80 years. The various tear collection methods employed greatly influence the measured tear glucose concentrations. Studies that involve mechanical irritation of the conjunctiva during sampling measure the highest tear glucose concentrations, while studies that avoid tear stimulation measure the lowest concentrations. Attempts to monitor tear glucose concentration in situ by using contact lens-based sensing devices are discussed, and new observations are presented of tear glucose concentration obtained by a method designed to avoid tear stimulation. These studies indicate the importance of the sampling method in determining tear glucose concentrations. On the basis of these results, we discuss the future of in vivo tear glucose sensing and outline the studies needed to resolve the remaining questions about the relationship between tear and blood glucose concentrations.

A flexible and wearable biosensor for tear glucose measurement

A flexible and wearable amperometoric glucose sensor was fabricated and tested. Also, the sensor was utilized to tear glucose monitoring. The sensor was constructed by immobilizing GOD onto a flexible oxygen electrode (Pt working electrode and Ag/AgCl counter/reference electrode), which was fabricated using "Soft-MEMS" techniques onto a functional polymer membrane. In purpose of bioinstrumentation, adhesive agents were not used for constructing the flexible biosensor. Linear relationship between glucose concentration and output current was obtained in a range of 0.025-1.475 mmol/l, with a correlation coefficient of 0.998. Current dependences on pH and temperature were also evaluated. The current was largest at pH 7.0 and the current increased when temperature increased. This indicates that the output current depends on enzyme activity. Based on the basic characteristics investigation, the glucose sensor was applied to measurement of glucose in tear fluids on an eye site of a Japan white rabbit. The change of tear glucose level induced by oral-administration of glucose was monitored as a current change of the sensor attached on the eye site. In this investigation, the tear glucose level varied from 0.16 to 0.46 mmol/l. Although there was a delay of several tens of minutes towards blood sugar level, it is considered to be possible that non-invasive continuous glucose monitoring can be realized using the flexible biosensor.

A flexible and wearable glucose sensor based on functional polymers with Soft-MEMS techniques

A novel biosensor for glucose measurement using functional polymers was fabricated and tested. The biosensor utilizes the physical and chemical functions of hydrophobic polydimethyl siloxane (PDMS) and hydrophilic 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymerized with dodecyl methacrylate (DMA). The glucose sensor was constructed by immobilizing glucose oxidase (GOD) onto a flexible hydrogen peroxide electrode (Pt working electrode and Ag/AgCl counter/reference electrode). The electrodes were fabricated using microelectromechanical systems (MEMS) techniques onto those functional polymers. The sensor showed novel functions of flexibility and it was stretchable so that the sensor could normally work when it was released after expanding to 120% longer than that of normal length. Also, basic characteristics of the sensor were evaluated. The output current of the hydrogen peroxide electrode was linearly related to the hydrogen peroxide concentration in a range of 0.20-2.50 mmol/l, with a correlation coefficient of 0.998. GOD was then immobilized onto the surface of the sensor using MPC polymer. In this case, the current output of the glucose sensor related to the glucose level over a range of 0.06-2.00 mmol/l, with a correlation coefficient of 0.997. The calibration range includes the reported concentration of tear glucose in normal human subject (0.14 mmol/l).

Optical-transparent and flexible glucose sensor with ITO electrode

The glucose sensor was constructed by immobilizing glucose oxidase (GOD) with glutaraldehyde solution onto the sensitive area of the transparent oxygen electrode. The oxygen electrode was fabricated by sealing KCl electrolyte solution including the Indium-Tin Oxide (ITO)-electrode with both metal-weldable film and gas-permeable membrane coated with Ag/AgCl electrode. The sensor behavior was evaluated using standard glucose solutions in a batch measurement system with a computer-controlled potentiostat at a reduction potential of -900 mV. The sensor device has flexible structure and good optical transparency (less than 0.6 abs) at the visible wavelength from 400 to 700 nm. The sensor was possible to be used for measuring glucose from 0.06 to 1.24 mmol/l (correlation coefficient: 0.999), including the reported concentration of tear glucose in normal (0.14 mmol/l), with good reproducibility.

A new technique for tear film fluorophotometry

AIM

To develop a reliable and objective non-touch technique for determination of tear volume and tear secretion by means of tear film fluorophotometry.

METHODS

10 defined concentrations of sodium fluorescein were given in an artificial chamber and measured by the Fluorotron Master (Coherent Radiation Inc). A calibration line was established and the calibration equation was programmed into the Fluorotron Master computer software. In 28 patients (56 eyes) with dry eye symptoms and 15 volunteers (30 eyes) tear volume and tear secretion were then measured directly without taking a tear sample, using the new technique.

RESULTS

The values obtained by the Fluorotron Master measuring 10 defined fluorescein concentrations within an artificial chamber are approximately 100 times lower than the actual concentrations. The calibration line led to a calibration equation: y = 36 + 0.01 x X. The mean tear secretion in 56 eyes of patients with dry eye symptoms was 2.48 microl/min, compared to 3.4 microl/min in healthy volunteers. The difference was statistically significant. Average tear volume was 7.0 microl in patients and 7.2 microl in healthy volunteers with no statistically significant difference.

CONCLUSION

The method developed is a simple and reliable non-touch technique without the need for taking a tear sample, which makes the examination faster and more comfortable for the patient.

An improved fluorophotometric method for tear turnover assessment

PURPOSE

Scanning fluorophotometry is considered the "gold standard" to determine tear turnover rates (TTR). In this study, we attempted to improve the precision of basal TTR by fluorophotometry through a number of methodological changes.

METHODS

By means of a timer program that produces audio cues, a new methodology that ensures confluence and a constant thickness of the tear film and minimization of reflex lacrimation as a result of the inhibition of the blink reflex was developed. This was compared with the standard protocol, both in a paired study and by a review of unpaired data. The minimum length of time required to monitor TTR measurements was also investigated.

RESULTS

A significant improvement in correlation coefficient (r) of the log decay curve was observed as a result of changes in the protocol in both the paired (p = 0.016) and unpaired study (p < 0.0001). We determined that it was sufficient to monitor TTR for 10 min to obtain accurate results.

CONCLUSIONS

We advocate that the changes be adopted as widely as possible for the precise and rapid measurement of basal tear turnover rates.

Is there a correlation between the severity of diabetic retinopathy and keratoconjunctivitis sicca?

PURPOSE

Patients with diabetic retinopathy (DRP) seldom report symptoms of ocular surface irritation, but evaluations of dryness are pathologic. This study was designed to evaluate the correlation between the severity of DRP and dry eyes.

METHODS

We included 144 eyes of 72 patients. Severity of retinopathy was graded according to the Early Treatment Diabetic Retinopathy Study. The examinations for dry eyes included Schirmer's test, break-up time, lipid layer thickness, fluorescein and rose bengal staining of the cornea, impression cytology, and a questionnaire. A sicca severity score was calculated using a point system of the results of these tests. Patients were divided into three groups: postpanretinal laser coagulation (PPL), postcentral laser coagulation (PCL), and those with no laser treatment (0-L). For statistics, we used the correlation coefficient to determine relationships and the unpaired Student t test for statistical difference.

RESULTS

The correlation (c) of keratoconjunctivitis sicca (KCS) and DRP after laser treatment was c = 0.24 and after central laser treatment was c = 0.22; the correlation without laser treatment was 0.54. The best correlation is 1 or -1, the worst was 0. The score of those patients with mild to moderate retinopathy was compared to that of patients with severe to proliferative disease. There was a significant statistical difference in the sicca severity score between both groups, (p < 0.006. Student t test).

CONCLUSION

KCS represents another manifestation of diabetes mellitus and its severity--measured by a many-membered score--correlates with the severity of the DRP.

Tear secretion and tear film function in insulin dependent diabetics

BACKGROUND

Diabetic patients often complain of dry eye symptoms, such as burning and/or foreign body sensation. The aim of the present study was to investigate whether diabetes mellitus is correlated with tear film dysfunction and/or tear hyposecretion.

METHODS

In 86 consecutive insulin dependent diabetics with retinopathy and 84 non-diabetic controls (age and sex matched) we performed fluorophotometry of tear secretion, the Schirmer test, and impression cytology of the conjunctival epithelium and determined the tear film break up time.

RESULTS

When compared with the healthy control group diabetics showed decreased Schirmer test readings (-37%, p <0.001) and significantly more frequent and pronounced signs of conjunctival metaplasia. None of the other values differed between groups.

CONCLUSION

In insulin dependent diabetics, reflex tearing was demonstrated to be significantly decreased. In contrast, unstimulated basal tear flow and tear film break up time were found to be normal. However, a majority of insulin dependent diabetics shows distinct signs of conjunctival surface disease.

Correlation of tear clearance rate and fluorophotometric assessment of tear turnover

BACKGROUND

The study sought to determine dynamic changes and theoretical bases of a clinical diagnostic test, the tear clearance rate.

METHODS

Thirty four healthy subjects ranging in age from 22 to 84 years underwent examination of tear clearance rate, the Schirmer test with anaesthesia, as well as fluorophotometric measurement of tear turnover, tear volume, and tear flow. By applying 0.5% fluorescein into the conjunctival sac and subsequently measuring colour fades on a Schirmer strip, the tear clearance rate for assessing tear drainage was divided into nine grades. The results of the tear clearance rate were compared with those of the basal tear turnover and tear flow obtained from fluorophotometry.

RESULTS

Significant relations were found between the tear clearance rate and the basal tear turnover or tear flow (r = 0.91 and 0.79, respectively, p = 0.0001). Considering the grades of progression from low to high, each grade of tear clearance rate showed a 12.5% increase in basal tear turnover (3.59%/min) and tear flow (0.38 microliter/min). There was no significant correlation between age and the basal tear turnover, tear volume, tear flow, or the tear clearance rate.

CONCLUSION

The tear clearance rate is proposed as a simple and useful way to estimate basal tear turnover and tear flow, and measure tear drainage indirectly.

Analysis of tear fluid proteins in insulin-dependent diabetes mellitus

Secretory immunoglobulin A, lactoferrin, lysozyme and tear specific pre-albumin were analyzed in stimulated tear fluid of 25 diabetic patients without retinopathy and in 29 diabetic patients with (pre) proliferative retinopathy using high performance liquid chromatography. Results were compared to those obtained in 26 healthy controls to determine the effect of diabetes mellitus on the exocrine function of the main lacrimal gland. Sodium dodecyl sulfate polyacrylamide gel electrophoresis onto minigels was performed on 20 tear samples for verification of high performance liquid chromatography fractions recorded. The mean total protein values in tear fluid (Bradford assay) of diabetics without retinopathy, with retinopathy and healthy controls did not differ significantly (mean in mg/ml +/- SD: 6.4 +/- 2.2, 5.9 +/- 2.0 and 5.7 +/- 1.7, respectively; Mann-Whitney; p > 0.02). High performance liquid chromatography showed an increased secretory immunoglobulin A and decreased peak 5 OD280 (+56% and -38%, respectively; p < 0.02) in patients without retinopathy, whereas in patients with retinopathy lysozyme was increased (+27%; p < 0.01) and tear specific pre-albumin and peak 5 OD280 decreased (-24% and -42%, respectively; p < 0.04), when compared to healthy controls. These inconsistent differences do not uniformly suggest an exocrine dysfunction of the main lacrimal gland in diabetic patients.