Correlation between Corneal Endothelial Cell Characteristics and Dry Eye Disease

Purpose: To correlate corneal endothelium cell density with dry eye disease compared to an age-matched control group. Materials and Methods: In this cross-sectional study, a total of 150 eyes of 75 female students aged 19-25 years who did not have any history of eye injuries or eye disease affecting the corneal endothelium cell density, were recruited from KSU Female Campus. They were divided into groups based on their dry eye disease severity. All subjects undergone full ophthalmic examinations assessing their endothelium cell count using specular microscope and dryness level using Non-invasive Break up Time (NIBUT) using Keratograph4. Results: The mean endothelial cell density was significantly lower in subjects with severe dryness (2620.3 ± 252.2 cell/mm2) and moderate dryness (2801 ± 221.6 cell/mm2) than normal subjects (3067± 196.7 cell/mm2), p=.000.In addition, the mean cell area was lower in normal subjects (327.4± 21.5 μm2) and increased with severity of dryness, in subjects with moderate dryness (358.9 ±27.1 μm2) and in subjects with severe dryness (384.8 ±33.7 μm2), p=.000.There was variation in the mean cell volume, in normal subjects was (25±3.6) and (27.2±4.3) in moderate dryness and (25.5±3.6) in severe dryness, p=.009. Conclusion: Results succeeded to demonstrate that in moderate to severe dryness, there was a significant reduction in the corneal endothelial cell density as compared to the ageand sex-matched control group. Correlation between corneal endothelial cells Characteristics and dry eye disease Correlation between corneal endothelial cell Characteristics and dry eye disease.

International Dry Eye Workshop's (DEWS2007) provided the following definition: "Dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance, and tear film instability with potential damage to the ocular surface. It is accompanied by increased osmolality of the tear film and inflammation of the ocular surface" [14].
Any interruption to the Lacrimal Functional Unit, (a system composed of the lacrimal glands, ocular surface (cornea, conjunctiva and meibomian glands), lids, and the sensory and motor nerves that supplies them [15] can destabilize the tear film leading to hyperosmolarity and eventually to ocular surface disease. These two considered to be the core mechanisms of the dry eye that can initiate, intensify, and alter dry eye prosperities with time [14].
Dry eye disease is classified to two major classes' aqueous deficient dry eye and Evaporative dry eye. Both lead to tear hyperosmolarity [16]. Aqueous deficient dry eye ADDE is induced by decreased lacrimal tear production and volume leading to tear hyperosmolarity followed by inflammation [17,18]. It is caused by disease in the lacrimal gland (e.g. Sjögren syndrome), obstruction to lacrimal gland outflow (e.g. cicatricial pemphigoid), homeostatic disturbance induced by blockage of the afferent pathway (e.g. topical anesthesia or trigeminal nerve section), and by blockage of efferent pathway (e.g. damage to the pterygopalatine gangli on and third order neurones) [19]. It also can becaused by systemic drugs uptake [20]. ADDE is divided to Sjögren Syndrome Dry Eye (SSDE) and non-Sjögren Syndrome Dry Eye (NSSDE) [16]. Evaporative dry eye EDE is induced by increased tear evaporation rate with normal function of the lacrimal gland. It can be caused by lid related or ocular surface related diseases, also referred to as intrinsic and extrinsic EDE, respectively [16]. Dry eyes can be diagnosed non-invasively using Non-Invasive Tear film Breakup Time (NITBUT) and tear meniscus assessment. NITBUT is measured as the time between the last blink and the breakup of a reflected image of a target on the tear film ( Figure 4). Tear meniscus assessment carries 75% to 90% of the total tear film volume. Thus, it is used to diagnose aqueous tear deficiency. Tear meniscus parameters used for tear film volume are Tear Meniscus Height TMH (the commonest) and tear meniscus radius of curvature. TMH is measured from the eye lid to the top of the meniscus, the cutoff value is <0.1mm [21] ( Figure 5). Clinical examination involves the use of specular microscope and keratograph4, as non-invasive procedures, to correlate corneal endothelial cell characteristics with eye dryness.

Study population and Examination
Endothelium cell count using specular microscope. Subjects with break up time  10 seconds were considered to have dryness Subjects with ocular allergic disease, keratitis, ocular surface disease, contact lens wear, glaucoma, previous ocular surgery or injury or subjects with systemic orocular treatment were excluded from this study.

Statistical Analysis
Statistical analysis was performed using SPSS version 21.0. All variables were expressed as Mean±Standard deviation. The normality of the data was first assessed using the Shapiro-Wilk test. Levene's test was used to determine homogeneous of the data. Owing to the normal distribution and homogeneous of the data, oneway ANOVA test was used to compare the means of endothelium cell characteristics between control group and DED groups. To assess the statistical significance of differences between means using a set of confidence intervals 95% multiple comparison post hocScheffe was used. The Pearson correlation analysis was used to estimate the correlations between the means of endothelium cell characteristics and the level of the NITBUT. The probability values of <0.05 were considered statically significant.

Ethical consideration
The protocol of the study was explained to each participant at the time of recruitment and informed consent was obtained according to the Declaration of Helsinki. The research was approved by the research ethical committee at College of applied medical sciences, King Saud University.

Medical & Surgical Ophthalmology Research
CA showed higher statistically significant difference between normal to severe DED with mean difference (-57.35µm²) (P=.000) than between normal to moderate DED with mean difference (-31.53 µm²) (P=.000) and between moderate to severe DED with mean difference (-25.82 µm) (P=.000).  CV showed higher statistically significant difference between normal to moderate DED with mean difference (-2.24%) (P=.013) than between normal to severe DED with mean difference (-1.99%) (P=.049) with no statistically significant between moderate to severe DED with mean difference (0.25%) (P=.94).
HEX showed no statistically significant difference between normal to moderate DED with mean difference (2.15%) (P=.15) and between normal to severe DED with mean difference (2.88%) (P=.05) and between moderate to severe DED with mean difference (0.73%) (P=.78).
The ECD showed statistically significant negative correlation with the NITBUT level (rs=-.6, P=0.000), CA showed statistically significant positive correlation with the NITBUT level (rs=.61, P=0.000), CV showed weak positive correlation with the NITBUT level (rs=.191 P=0.19), HEX showed weak negative correlations with the NITBUT level (rs=-.194P=0. 18), and CCT showed irrelevant (very weak) negative correlations with the NITBUT level (Table 4). This cross-sectional study showed That in moderate to severe DED, there was a significant reduction in the corneal endothelial cell density (ECD) as compared to the age-and sex-matched control group. ECD showed significant correlation with clinical severity of the disease, as judged by the level of non-invasive tear breakup time test. In addition, in DED there is a significant reduction in percentage of hexagonal cells (Polymegathism) and an increase in endothelial cell area and coefficient of variation (pleomorphism) that correlates

Heidelberg Retina Tomography3
With the Rostock Cornea Module.

Eyes with DED displayed a
Significant reduction in corneal ECD indeed that correlates with clinical severity of the disease and Significant lower sub basal nerve density than did those in the control group.

Specular microscopy
It has been reported that there is a negative correlation between endothelial cell density and an endothelial cell area and pleomorphism. Pleomorphism.