A comparative study of retinal vein occlusion and serum 25-hydroxy Vitamin D in a tertiary care hospital

Dear Editor,

We would like to thank the authors for their interest and for taking the time to express their observations in our research article, “A comparative study of retinal vein occlusion and serum 25 hydroxy Vitamin D at a tertiary care centre.”[1]

Our study participants were selected from the outpatient clinic of our institution over a period of 1½ years (from September, 2022 to March 2024), and a thorough general, systemic and complete ocular examination was done on the very first visit and in every subsequent follow-up. Although blood samples were collected once, appropriate treatment, including administration of anti-Vascular Endothelial Growth Factor injections, was done whenever required during the study period, and they are still under follow-up even after the study. Hence, the study design was stated as an institution-based prospective case–control study.

Risk factors include elderly age, hypertension, diabetes, dyslipidemia, positive history of smoking. The authors have expressed their interest to know how many patients with low serum Vitamin-D levels had one or more of these risk factors. Table 1 shows the Spearman’s rho correlation with the risk factors and Vitamin D.

Table 1.

Spearman’s correlation between the risk factors and Vitamin D

Group	Vitamin D level
Spearman’s rho
Control
Age
Correlation coefficient	0.390
P	0.005*
IOP-affected eye
Correlation coefficient	−0.231
P	0.106
SBP
Correlation coefficient	0.291
P	0.041✝
DBP
Correlation coefficient	0.079
P	0.586
PP
Correlation coefficient	0.177
P	0.220
PPBS
Correlation coefficient	−0.074
P	0.612
HDL
Correlation coefficient	−0.071
P	0.627
LDL
Correlation coefficient	−0.314
P	0.026‡
Total cholesterol
Correlation coefficient	−0.200
P	0.164
Triglycerides
Correlation coefficient	−0.092
P	0.523
RVO
Age
Correlation coefficient	−0.147
P	0.309
IOP-affected eye
Correlation coefficient	−0.113
P	0.433
SBP
Correlation coefficient	0.017
P	0.906
DBP
Correlation coefficient	0.132
P	0.360
PP
Correlation coefficient	−0.063
P	0.662
PPBS
Correlation coefficient	0.198
P	0.168
HDL
Correlation coefficient	<0.001
P	0.998
LDL
Correlation coefficient	0.117
P	0.418
Total cholesterol
Correlation coefficient	0.083
P	0.566
Triglycerides
Correlation coefficient	0.033
P	0.820

*Significant positive correlation; older subjects had higher Vitamin D, ^✝SBP and Vitamin D shows weak positive correlation, ^‡Significant negative correlation with higher Vitamin D to lower LDL. IOP: Intraocular pressure, SBP: Systolic blood pressure, DBP: Diastolic blood pressure, PP: Pulse pressure, PPBS: Postprandial blood sugar, HDL: High-density lipoprotein, LDL: Low-density lipoprotein, RVO: Retinal vein occlusion

Table 2 shows a comprehensive statistical analysis comparing the CONTROL and retinal vein occlusion (RVO) groups across linear regression and logistic regression models. The logistic regression models did not identify any statistically significant predictors for the outcome variable in either the CONTROL or the RVO group based on the standard P < 0.05 threshold. The predictors were total cholesterol, diastolic blood pressure, postprandial blood sugar, systolic blood pressure, low density lipoprotein. But in our study, statistically significant low levels of mean serum Vitamin D (25 OH vit D) were found in cases of RVO in comparison to age-matched controls with an odds ratio of 1.137; 95% confidence interval (1.074–1.203). Thus, the association of Vitamin D levels with RVO can be established.

Table 2.

Statistical analysis comparing control and retinal vein occlusion groups across linear regression and logistic regression models

Variables in the equation
Group	B	SE	Wald	df	Significance	Exp(B)	95% CI for EXP(B)
							Lower	Upper
Control
SBP	0.042	0.045	0.848	1	0.357	1.043	0.954	1.140
DBP	−0.053	0.061	0.752	1	0.386	0.949	0.843	1.068
PPBS	0.014	0.012	1.414	1	0.234	1.014	0.991	1.039
LDL	0.109	0.076	2.041	1	0.153	1.115	0.960	1.296
Total cholesterol	0.004	0.047	0.007	1	0.933	1.004	0.915	1.101
Constant	−15.030	10.960	1.881	1	0.170	0.000
RVO
SBP	2.139	2647.250	0.000	1	0.999	8.491	0.000
DBP	−2.150	2647.250	0.000	1	0.999	0.116	0.000
PPBS	−0.011	0.007	2.433	1	0.119	0.989	0.976	1.003
LDL	−0.035	0.034	1.112	1	0.292	0.965	0.904	1.031
Total cholesterol	−0.010	0.030	0.118	1	0.731	0.990	0.933	1.050
Constant	6.995	6.024	1.348	1	0.246	1090.922
PP	−2.144	2647.250	0.000	1	0.999	0.117	0.000

B: Coefficient, SE: Standard error, Df: Degrees of freedom, Exp(B): Exponentiated coefficient, CI: Confidence interval, SBP: Systolic blood pressure, DBP: Diastolic blood pressure, PP: Pulse pressure, PPBS: Postprandial blood sugar, LDL: Low density lipoprotein

We agree that the sample size is too small and the inclusion of serum homocysteine levels would have improved our study. Multiple risk factors, including hyper-homocystenemia, hypercoagulation disorders, protein C, S deficiency and many more, are associated with RVO, but tests which were available in our institution were only included in our study. We consider them to be a limitation in our study, and the inclusion of all the criteria, as pointed out, would surely improve our study.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.