these studies have documented that diabetic cornea is vulnerable to many abnormalities such as corneal endothelial damage , recurrent corneal erosions , punctate epithelial keratopathy , persistent epithelial defects , impaired corneal sensitivity , ulcers , slowed wound repair , and superficial keratitis.13 morphological features of the corneal endothelium in diabetic patients recognized by a number of studies include a decrease in endothelial cell density ( ecd ) and polymorphism ( decrease in the percentage of hexagonal cells [ the normal percentage > 50% ] ) as well as polymegathism , which means increased coefficient of variation ( cv ) of cell area ( cv values measured between 0.22 and 0.31 are considered normal and above 0.4 are abnormal ) and increased central corneal thickness ( cct).46 em-3000 specular microscope ( cbd / tomey , phoenix , az , usa ) is a noncontact specular microscope that avoids some disadvantages of the classic contact specular microscopes such as corneal ulceration and transmission of infectious diseases .
it has the ability to assess corneal endothelium features and measure cct at the same time with accuracy of 10 m.7 the aim of this study was to compare corneal ecd , morphological features , and cct in type 2 dm with age - matched , nondiabetic control subjects using em-3000 specular microscope .
in addition , correlation between these corneal changes and the duration of dm and severity of diabetic retinopathy ( dr ) and glycemic control ( glycated hemoglobin [ hba1c ] level ) were also assessed .
it got the approval of research ethics committee of college of applied medical sciences , king saud university , and security forces hospital , riyadh , saudi arabia .
all the participants signed comprehensive consent after explanation of the possible consequences of the study prior to investigations .
the study included 57 patients ( 27 males and 30 females [ 57 eyes ] ) with type 2 dm and 45 control ( nondiabetic ) subjects ( 45 eyes [ 22 males and 23 females ] ) .
the age range of diabetic group was 4280 years ( mean : 57.088.37 years ) , and the age range of the control group was 4076 years ( mean : 50.808.39 years ) .
all patients were recruited from ophthalmology department at security forces hospital , riyadh , saudi arabia , by nonrandomized convenience sampling method from february to april 2015 .
the diagnosis of type 2 dm was based on the criteria of the world health organization ( who).8 control patients did not have diabetes was confirmed by random blood sugar test .
the mean duration of dm was 12.878.03 years ( range : 140 years ) , and the mean value of hba1c was 8.57%2.09% ( range : 6.3%17.2% ) .
exclusion criteria included presence of high myopia , history of past intraocular surgery or corneal disease or dystrophy such as fuch s endothelial dystrophy , active or previous eye infection or inflammation , previous ocular surgery or trauma , previous retinal photocoagulation , pterygium , entropion , trichiasis , contact lens wear , regular usage of any eyedrops or known tear - interfering systemic drugs ( such as hormone replacement and antihistamines ) , systemic illness such as rheumatoid arthritis and systemic lupus erythematous that are known to impair tear function , pregnancy , labor , and glaucoma .
age , gender , duration of diabetes , most recent hba1c value , status of dr , other medical illness , and current medical treatment were recorded . in this study , only the right eye of each patient was tested .
all subjects underwent a complete ophthalmic examination that included visual acuity assessment using the snellen chart , refraction using auto - refractometer ( topcon , tokyo , japan ) , and intraocular pressure measurement using air puff tonometer , slit - lamp biomicroscopy , and fundus examination . the corneal endothelial structure and cct
were examined in all eyes by noncontact specular microscopy using em-3000 specular microscope , and this examination was done by a single examiner .
the endothelial structure was studied by measuring a variety of factors , including ecd , cv , and percentage of hexagonal cells .
his / her chin was placed on the chin rest and his / her forehead rested on the special head area .
the patient was asked to fixate his / her eye for a few seconds on the red light coming from inside the device until the instrument automatically took a clear image of the corneal endothelium and measured the cct at the same time .
the diabetic eyes were classified into 3 groups according to the status of dr ( group without dr , group with nonproliferative dr [ npdr ] , and group with proliferative dr [ pdr ] ) .
also , they were divided into 2 groups according to dm duration ( group with a duration of 10 years and group with a duration of > 10 years ) and according to hba1c value ( group with hba1c 7.5% and group with hba1c > 7.5% ) .
the data were analyzed using spss 21 for windows software ( ibm , armonk , ny , usa ) .
an independent sample t - test was performed to compare the means of cct and corneal endothelium features in diabetic and control groups .
the differences among 3 or more groups were analyzed by one - way analysis of variance .
pearson correlation test was performed to find the relationship between corneal changes and dm duration , hba1c% , and dr status .
the study included 36 eyes without dr , 14 eyes with npdr , and 7 eyes with pdr .
there were 26 eyes with dm duration of 10 years and 31 eyes with dm duration of > 10 years .
also , there were 24 eyes with hba1c 7.5% and 33 eyes with hba1c > 7.5% .
ecd was significantly lower in the diabetic cornea group ( 2,491.98261.08 cell / mm ) than in the control group ( 2,629.68293.45 cell / mm ) ( p=0.014 ) .
cv was higher in the diabetic cornea group ( 0.410.07 ) than in the control group ( 0.370.08 ) ( p=0.008 , which was considered statistically significant ) .
diabetic cornea group had lower percentage of hexagonal cells ( 33.24%10.25% ) than control group ( 34.24%8.73% ) , but the difference was not statistically significant ( p=0.603 ) .
also , cornea was thicker in the diabetic group ( 545.6130.39 m ) than control group ( 539.4229.22 m ) , but not statistically significant ( p=0.301 ) .
a comparison of the mean values of cct , ecd , cv , and hexagonality between control and diabetic eyes is shown in table 3 .
eyes with dm duration of 10 years had higher ecd ( 2,509.38303.49 cell / mm ) than eyes with dm duration of > 10 years ( 2,477.38223.61 cell / mm ) ( p=0.658 ) , and they also had more hexagonality ( 35.61%9.87% ) than those with dm duration of > 10 years ( 31.26%10.29% ) ( p=0.111 ) , but the differences were not significant . also , there were no significant differences in cct ( p=0.431 ) and cv ( p=0.927 ) between the 2 groups .
a comparison of the mean values of cct , ecd , cv , and hexagonality between the diabetic groups according to the duration of dm is shown in table 4 .
specular microscope pictures taken from diabetic eyes with dm duration of > 10 years and 10 years are shown in figures 2 and 4 .
diabetic patients with hba1c% 7.5 had higher , but not statistically significant , ecd ( 2,537.62311.86 cell / mm ) than those with hba1c% > 7.5 ( 2,458.78216.06 cell / mm ) ( p=0.293 ) and higher hexagonality ( 35.58%10.09% ) than the other group ( 31.54%10.17% ) ( p=0.144 ) .
the mean of cv was significantly lower ( p=0.017 ) in diabetic patients with hba1c% 7.5 ( 0.390.05 ) than in the other group ( 0.430.07 ) .
also , there was no statistically significant difference in cct between the 2 groups ( 0.789 ) .
a comparison of the mean values of cct , ecd , cv , and hexagonality between the diabetic groups according to hba1c% is shown in table 5 .
in addition , there were no significant differences between cct , ecd , cv , and hexagonality percentage of the corneal endothelial cells in diabetic patients without dr , with npdr , and with pdr ( p=0.344 , 0.806 , 0.284 , and 0.500 , respectively ) ( table 6 ) .
pearson correlation analysis showed that dm duration , hba1c levels , and severity of dr had no significant correlations with cct , cv , hexagonality , or ecd ( table 7 ) .
diabetic cornea may give the impression that is healthy , but actually it may suffer from many morphological features affecting its function later on .
this fact was evidenced by several studies.16 in this study , we found that diabetic corneas showed a statistically significant reduction in mean corneal ecd of 5.24% ( p=0.014 ) compared to the corneas in the control group .
this was similar to the results of choo et al4 of 4.5% significant reduction in ecd ( p<0.01 ) in malaysian type 2 dm patients .
also , the results of inoue et als9 study of the corneal endothelium and cct in type 2 dm in japan showed similar results of 4.1% ( p=0.016 ) significant reduction in ecd in the diabetic group .
however , results of storr - paulsen et als6 and siribunkum et als10 studies of corneal endothelium morphology in type 2 dm according to ecd were not consistent with our findings .
the cv of corneal endothelial cells was found to be significantly increased in diabetic patients ( p=0.008 ) .
this increase indicated the presence of polymegathism , in which endothelial cells enlarge to fill the gaps between adjacent cells .
this result was concordant with those obtained by shenoy et al11 and lee et al,12 but not similar to those of sudhir et al5 and chen et al.13 also , our study demonstrated no significant difference in the percentage of hexagonal cells between the diabetic patients and the controls , which was in agreement with the results of sudhir et al,5 storr - paulsen et al,6 and inoue et al,9 and in disagreement with those of choo et al,4 and lee et al.12 many studies4,14,15 have explained the morphological features of diabetic cornea .
this was established by the assessment of polyol ( sorbitol  aldose reductase ) pathway in diabetic cornea .
these studies documented that high glucose levels lead to increased activity of the aldose reductase , causing sorbitol buildup in the corneal epithelial and endothelial cells .
also , dm diminishes na  k atpase activity of the corneal endothelium , resulting in morphological and permeability changes in diabetic cornea , thereby leading to corneal destruction .
furthermore , endothelial pump function was proven to be affected by decreased atp production as a result of slowing down of the krebs cycle in diabetic cornea .
regarding cct in our study , there was no significant difference between diabetic and control groups .
this result was in concordance with those of choo et al4 and sudhir et al.5 other studies , for instance , storr - paulsen et al6 and lee et al,12 demonstrated a statistically significant increase in cct of diabetic compared to control subjects .
as regards the comparison of the mean values of cct , ecd , cv , and cell hexagonality in patients with dm duration of 10 years and those with dm duration of > 10 years , no statistically significant difference was detected in all these morphological features in this study .
this finding was in agreement with altay et al,16 who reported absence of statistically significant difference in cct between the 2 groups . however , lee et al12 documented that cct and cv were significantly higher in patients with dm duration of > 10 years compared with those with dm duration of 10 years , but there was no statistically significant difference regarding ecd and hexagonality between the 2 groups . concerning the comparison of the mean values of cct , ecd , cv , and cell hexagonality in diabetic patients with hba1c 7.5% and those with hba1c
> 7.5% in our study , no significant differences were detected between the 2 groups in cct , ecd , and hexagonality , but cv showed a statistically significant difference ( p=0.017 ) .
storr - paulsen et al6 found significantly lower ecd in patients with elevated hba1c , but without any influence on cct . however , altay et al16 documented significantly thicker cct in hyperglycemic condition than in euglycemic condition in the same patient before and after successful control of hba1c . regarding the comparison of the mean values of cct , ecd , cv , and hexagonality between the 3 diabetic groups according to the status of dr , our study found no significant differences between the 3 groups .
this finding was not in accordance with that of shenoy et al,11 who demonstrated significantly lower ecd in eyes with dr than those without dr .
pearson correlation analysis reported absence of significant correlations between dm duration , hba1c levels , and severity of dr and morphological features of diabetic cornea such as cct , cv , hexagonality , or ecd .
these results were similar to those of choo et al.4 however , siribunkum et al10 found a significant correlation between dm duration and pleomorphism , polymegathism , and cct .
this study documented that type 2 dm resulted in a significant reduction of ecd and increased cv ( polymegathism ) . also , diabetic cornea had increased cct and lower percentage of hexagonal cells than in the cornea of normal subjects , but this is not statistically significant .
in addition , our study demonstrated that dm duration , hba1c levels , and severity of dr had no significant correlations with cct , cv , hexagonality , or ecd . in this study , patients with a history of laser photocoagulation were excluded due to its influence on the corneal structures.17 this exclusion produced a small sample size because most of diabetic patients who came to the clinic had undergone laser treatments .
therefore , further studies with a large sample size are recommended to verify the extent of corneal damage caused by type 2 dm .
 purposethis study was conducted to compare the corneal endothelial cell density ( ecd ) , morphological features , and central corneal thickness ( cct ) in type 2 diabetes mellitus ( dm ) with age - matched , nondiabetic control subjects using em-3000 specular microscope.study designthis was a prospective , hospital - based , nonrandomized , case  
 control , observational , and quantitative study.subjects and methodsthe study included 57 patients ( 57 eyes ) with type 2 dm and 45 control ( nondiabetic ) subjects ( 45 eyes ) . 
 the corneal endothelial structure and cct were examined in all eyes by noncontact specular microscopy using em-3000 specular microscope . 
 the endothelial structure was studied for ecd , coefficient of variation of cell area ( cv ) , and percentage of hexagonal cells.resultsthe study included 36 eyes without diabetic retinopathy ( dr ) , 14 eyes with nonproliferative dr , and 7 eyes with proliferative dr . 
 there were 26 eyes with a duration of 10 years and 31 eyes with a duration of > 10 years . 
 also , there were 24 eyes with hba1c 7.5% and 33 eyes with hba1c > 7.5% . 
 ecd was significantly lower in the diabetic cornea than in control group ( p=0.014 ) . 
 cv was higher in diabetic cornea ( p=0.008 ) . 
 the diabetic cornea group had lower percentage of hexagonal cells than the control group , but the difference was not statistically significant ( p=0.603 ) . 
 also , diabetic cornea was thicker than control group , but not statistically significant ( p=0.301).conclusionthis study documented that type 2 dm causes a significant reduction of ecd and increased cv ( polymegathism ) . 
 also , diabetic cornea has increased cct and lower percentage of hexagonal cells than normal subjects , but without statistical significance . 