|Year : 2021 | Volume
| Issue : 1 | Page : 56-60
Corneal endothelial cell characteristics and central corneal thickness in patients with type 2 diabetes mellitus
Rajani Kadri, Namrata Sasalatti, Sudhir Hegde, Ajay A Kudva, Devika Parameshwar, Akansha Shetty
Department of Ophthalmology, A. J. Institute of Medical Sciences and Research Centre, Mangalore, Karnataka, India
|Date of Submission||28-Jun-2020|
|Date of Acceptance||05-Jul-2020|
|Date of Web Publication||19-Apr-2021|
Dr. Rajani Kadri
Department of Ophthalmology, A. J. Institute of Medical Sciences and Research Centre, Mangalore - 575 004, Karnataka
Source of Support: None, Conflict of Interest: None
Purpose: To evaluate the morphological features of corneal endothelium and central corneal thickness (CCT) in patients with type 2 diabetes mellitus (DM) and to correlate them with the duration of diabetes and patients glycemic status. Design: This was a prospective, cross-sectional, comparative, hospital-based study. Materials and Methods: The present study was conducted on 192 diabetics and 192 age- and sex-matched healthy controls. Corneal endothelial cell characteristics, CCT were measured using a specular microscope. Statistical comparisons were done between the case and controls using the appropriate parametric or nonparametric test. The associations between the various parameters were studied using the Pearson coefficient of correlation. Results: The mean corneal endothelial cell density (CECD) in the diabetic group (2521.3 ± 300.7 cells/mm2) was significantly lower compared to the nondiabetic group (2629.3 ± 221 cells/mm2) ( P < 0.001). The mean CCT in diabetic group was significantly higher (532.00 ± 24.88 μm) compared to control group (499.47 ± 24.76 μm) ( P < 0.001). The co-efficient of variation though higher and hexagonality though lower in diabetics was not statistically significant. CCT showed a significant positive correlation with duration of DM (r = 0.566, P<0.001). A weak positive correlation was observed between CCT and HBA1C ( r = 0.271, P<0.001) No correlation between CECD and CCT for diabetics with a duration of >10 years when compared with those with a duration of <10 years was observed. Conclusion: Diabetic patients in our study had thicker corneas, decreased CECD, and hexagonality, more irregular cell size than that of age matched controls. However, duration of the disease and the glycemic control did not affect these parameters.
Keywords: Central corneal thickness, corneal endothelium, diabetes mellitus, duration
|How to cite this article:|
Kadri R, Sasalatti N, Hegde S, Kudva AA, Parameshwar D, Shetty A. Corneal endothelial cell characteristics and central corneal thickness in patients with type 2 diabetes mellitus. Kerala J Ophthalmol 2021;33:56-60
|How to cite this URL:|
Kadri R, Sasalatti N, Hegde S, Kudva AA, Parameshwar D, Shetty A. Corneal endothelial cell characteristics and central corneal thickness in patients with type 2 diabetes mellitus. Kerala J Ophthalmol [serial online] 2021 [cited 2021 Jun 18];33:56-60. Available from: http://www.kjophthal.com/text.asp?2021/33/1/56/314109
| Introduction|| |
Corneal endothelial cell changes in diabetic patients have been explained by the assessment of polyol (sorbitol–aldose reductase) pathway in the diabetic cornea. Earlier studies have documented that high glucose levels led to increased activity of the aldose reductase, causing sorbitol build up in the corneal epithelial and endothelial cells. This sorbitol acts as an osmotic agent and leads to the swelling of endothelial cells. Furthermore, diabetes mellitus (DM) diminishes Na+–K+ ATPase activity of the corneal endothelium. This results in the morphological and permeability changes in a diabetic cornea. Endothelial pump function was proven to be affected by decreased ATP production as a result of slowing down of the Krebs cycle in a diabetic cornea.
Corneal endothelial cell studies on diabetic patients have shown variable results. Many studies have shown that even minor changes in the morphology of the endothelial cells may manifest in the disturbances in the tightness of the endothelial barrier., An arrest of the human endothelial cells in G1 phase results in the loss of endothelial cells being compensated by expanding of the neighbouring cells. This, over a period of time results in corneal edema due to the lack of tightness. The questions that need to be pondered are if these changes are transient during the time of increased blood sugars in the body or permanent, affected by the duration of the disease and if glycemic control has any effect on these changes. There are very few studies correlating the endothelial parameters with the duration and glycemic control, again with conflicting reports.,,
We planned to compare the morphological features of corneal endothelial cell in type 2 DM with age-matched, nondiabetic controls using Specular Microscope Tomey EM-4000 (Tomey Corporation, Japan) and correlate these corneal changes with the duration of DM and glycemic control (glycated hemoglobin [HbA1c] level).
| Materials and Methods|| |
This prospective, hospital-based, comparative study protocol was approved by the University's Institutional Ethical Committee. Our study was conducted in accordance with the declaration of Helsinki. Written informed consent was obtained from all patients before their enrollment in this study. The diagnosis of DM was based on the criteria of the American Diabetes Association (ADA). Patients diagnosed as diabetics, at least 1 year prior to the study and started on anti-diabetic drugs were included as cases. Recruitment of the subjects was based on the medical history and treatment taken by the patients attending the outpatient clinic.
Nondiabetic patients used as controls underwent two casual blood glucose tests in accordance with the recommendations of the ADA to disclose undetected diabetes. Data collected included the duration of diabetes and HbA1c levels.
The exclusion criteria included patients not willing to give written informed consent, postoperative patients, contact lens users, patients with corneal diseases or dystrophies, any ocular traumas such as blunt and penetrating injuries, history of any other systemic illness, patients with glaucoma and retinal diseases not associated with diabetes, any other ocular disease such as dry eye, anterior uveitis, primary angle closure glaucoma, evidence of any corneal pathology on slit-lamp biomicroscopy, and high refractive errors.
The right eye of all the patients was examined using a noncontact specular microscope, Tomey EM-4000 (Tomey Corporation, Japan) with an autoshot option by fixed frame method. The patient was positioned on a chair in front of the specular microscope and made to fix inside the device till the instrument automatically took a clean image of corneal endothelium and measured the parameters. Parameters that were recorded included corneal endothelial cell density (CECD), average cell area (AVG), coefficient of variation (CV) of cell area, percentage of hexagonal cells (6A), and central corneal thickness (CCT). An average of 3 reading was taken for the analysis. Cell density was recorded as the number of cells per square millimeter. The CV of hexagonal cell in the analyzed area was used as an index of variation in cell shape (polymegathism). The percentage of hexagonal cells indicated pleomorphism. CCT varies over the day with cornea being thickest in the morning and gradually becoming thinner. Specular microscopy and CCT were hence measured at the same time of the day 10 p.m. to 12 pm, to reduce the errors related to diurnal variation.
The primary outcome variable studied was the relationship of corneal endothelial cell characteristics in diabetic patients and healthy controls.
The secondary outcome measures included the effect of duration of diabetes and glycemic control on the diabetic cornea.
All data distribution analysis was checked using the Kolmogrov–Smirinov test. Data were evaluated using the descriptive statistics which were presented using mean and standard deviation (SD). Statistical comparisons were done between the case and controls using an appropriate parametric or nonparametric test. The Mann–Whitney test or t-test was used as and when required for finding the association between various parameters in diabetic patients and healthy controls. The associations between the various parameters were studied using the Pearson Coefficient of Correlation®. Multivariable regression analysis was used for identifying the influencing factors for cell density with respect to different predictors. These predictors were checked for the modal fit by adding or removing the predictors at each level. The predictors included age, sex, CCT, and percentage of hexagonal cell in the final modal. All the data values of beta coefficients and its standard errors were analyzed. Multi-collinearity was checked analyzing variance inflation factors (VIF). If a high VIF was observed, then the predictor would not be considered in the model. For the regression model, the P = 0.25 was (adjusted P = 0.05, adj-P, P/number of predictors in the model) considered for statistical significance. Statistical analysis was performed using Minitab® 17.1.0, © 2013 Minitab Inc.
| Results|| |
In this study, corneal endothelial cell parameters of 192 diabetic patients were compared with 192 healthy controls. The mean (±SD) age of the study group was 58.86 (±7.90) years, and of the controls were 57.95 (±8.79). The mean duration of DM was 7.86 (±5.69) years. Mean HBAIC was 10.12 (±2.69). [Table 1] includes the corneal endothelial cell characteristics of right eyes of cases and controls as recorded by a specular microscope. [Figure 1] shows (a) specular microscopic image of normal and (b) specular microscopic image of diabetic cornea. The mean endothelial cell density in the diabetic group (2521.3 ± 300.7 cells/mm2) was significantly lower compared to the nondiabetic group 2629.3 ± 221 cells/mm2 (P < 0.001). [Figure 2] shows the comparison of corneal ECD between diabetics and nondiabetics. The mean CCT in diabetic group was significantly higher (532.00 ± 24.88 μm) compared to the control group (499.47 ± 24.76 μm) (P < 0.001). Mean corneal ECD and mean CCT in patients with DM duration >10 years when compared with those with DM duration ≤10 years were found to be insignificant.
|Table 1: Corneal endothelial cell characteristics of right eyes of case and controls as recorded by specular microscope|
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|Figure 1: Specular microscopic image of (a) Normal cornea. (b) Diabetic cornea|
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|Figure 2: Comparison of corneal endothelial cell density between diabetics and nondiabetics|
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Correlation analysis of various predictors such as cell density, average cell area, hexagonality and CCT in diabetics with age, duration, and HBA1C was done. Cell density (r = −0.167, P = 0.021) showed a significant negative correlation with age. CCT showed a significant positive correlation with duration of DM (r = 0.566, P < 0.001). A weak positive correlation was observed between CCT and HBA1C (r = 0.271, P < 0.001).The comprehensive list of correlation coefficients is presented in [Table 2].
|Table 2: Correlation coefficients between corneal endothelial cell parameters and the predictors in diabetics|
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Regression analysis of corneal ECD with age, percentage of regular hexagonal cells (6A), CV, CCT, and duration of DM found predictor factor average cell area and CV to influence the CECD, as depicted in [Table 3]. The model was adequate with R2 and R2-adjusted nearly 50%. There was no multicollinearity in the model observed with VIF 1–2.
|Table 3: Regression analysis of corneal endothelial cell density with predictor variables|
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| Discussion|| |
Corneal changes have been observed in patients with hyperglycemia of long duration as a result of compromise in the functioning of the layers of the cornea. All corneal layers are involved in DM in different ways such as corneal endothelial damage, recurrent corneal erosions, superficial keratitis, ulcers, diminished corneal sensitivity, and delayed wound healing. Folds in Descemet's membrane were detected earlier in diabetic patients compared to nondiabetic elderly people. However, the brunt is taken by corneal endothelial cells. Our study demonstrated a significant reduction in corneal ECD in patients with type 2 DM. This finding was comparable to many other studies.,, However, Schultz et al. found no difference in ECD in type 2 DM, but demonstrated a significantly higher rate of cell loss in type 1 DM. Módis et al. studied corneal endothelium in type 1 and type 2 diabetic patients. They found a statistical reduction in ECD in type 1 in comparison with healthy controls.
Storr-Paulsen et al. showed CCT to significantly increase in diabetes. Our study also demonstrated a significant increase in thickness. This increase in CCT in diabetes was interpreted as a minimal corneal swelling and could be the earliest detected change in diabetics. The accumulation of sorbitol due to increased activation of the polyol pathway resulting in oxidative and osmotic stress to the endothelial cells has been proposed to be the causative factor. This results in decreased functioning of the endothelial cells and subsequent edema. However, Inoue et al. and Choo et al. found no association between the CCT of diabetics and nondiabetics.
Corneal morphological changes have been further correlated with duration of the disease and the glycemic control. Urban et al. studied type 1 diabetic corneas in the age group of 15–34 years, and they found the duration of diabetes to significantly affect ECD and CCT. Anbar et al. studied endothelial cell morphology in children with type 1 diabetes. They found an increased CCT and decreased corneal ECD in diabetics that significantly correlated with the duration of diabetes. In our study that evaluated only type 2 DM cornea's, there was no association between corneal ECD and duration.
On evaluating of the mean values of CCT, ECD in patients with DM duration ≤10 years and those with DM duration >10 years, no significant difference was found between the two groups in our study well supported by other studies.,, On the other hand, Lee et al. found significantly higher CCT and CV in patients with DM duration >10 years than those with DM duration ≤10 years, without any significant difference in ECD and hexagonality between the two groups.
HbA1c levels are based on glycemic control of an individual over a period of 3 months. Allan Storr-Paulsen et al. correlated glycemic status by taking an average of 4 HbA1c tests with an interval of 3 months as a reflection of long term glycemic status and found that HBA1c had no impact on CCT; however, higher HBA1C values were associated with decreased ECD. Módis Jr. et al. demonstrated an inverse relationship between corneal ECD and HBA1C in the type 1 diabetic patients. In type 2 diabetic individuals, no significant difference was observed in the evaluated values. This suggested the more vulnerability of the type 1 diabetic corneas. Matsuda et al. reported a positive correlation of CCT with the duration of diabetes and negative correlation of corneal ECD with HbA1C. Busted et al. documented the positive association of HbA1c with CCT. In our study, CCT correlated positively with the duration of disease and only a weak correlation was found with HbA1c. However, there was no such correlation between HbA1C and corneal ECD. The absence of correlation between HbA1c levels and corneal endothelial parameters suggest that these parameters may not be related to short-term glycemic control. Inoue et al. claim that although they did not show the influence of duration on the morphology of the corneal endothelium, the relation may not occur during the examination, but it may appear some years later. It has been proposed that in a chronic disease such as DM, subtle changes could develop over a long period of time. Corneal endothelial cell alterations may not correlate to HbA1c measured at one point of time. These findings may suggest the possibility of insult to the endothelium at any time during the course of the disease due to the fluctuating high blood sugars, resulting in a permanent damage to the endothelial cells. This could be one of the reasons for the absence of correlation with duration of the disease and glycemic status. Endothelial cells of diabetic corneas are always at risk of damage as most often blood sugars are only controlled at intermittent intervals by the diabetics. Specular microscopic examination of the cornea should be a regular preoperative investigation in diabetic patients undergoing intraocular surgery even though the blood sugars are well controlled at the time of surgery.
| Conclusion|| |
Type 2 DM corneas have decreased CECD and increased CCT. Neither duration nor glycemic controls affects the alterations in the corneal endothelial cells. CCT correlates positively with duration of DM.
We would like to acknowledge the assistance of Dr. Thrivikrama Padur Tantry, Professor and HOD, Department of Anaesthesiology, A. J. Institute of Medical Sciences and Research Centre, Mangalore for statistical analysis.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]