According to the univariate logistic regression analysis results of our study, patients with non-O blood group and HT patients show a predisposing effect in terms of retinal venous occlusion. This effect is not statistically significant in multivariate analysis.
There are 2 studies on the subject in the literature. In the study of White in 1978, no relationship was found between ABO blood groups and retinal vein occlusions. Interestingly, individuals with blood type A have been reported to have worse visual prognosis than other blood groups . Borella et al. stated that non-O blood group and thrombophilia were observed more in RVO patients . The difference of our study from this study is that some demographic and systemic features that may affect the development of RVO are evaluated by regression analysis.
The relationship between ABO blood group differences and vascular occlusions has been researched for many years and studies have been carried out by many different disciplines. When the published reviews on this subject are examined, it is seen that vascular occlusions of both arterial and venous system can be affected by the patient's blood type [14, 22]. A large-scale study with more than 1.5 million blood donors also showed that there was a significant difference between O type and non-O type blood groups in terms of both arterial and venous thromboembolic events, and those with non-O group were at higher risk for thromboembolic events. When A, B and AB groups were evaluated among themselves in the same study, it was stated that the group that created the most susceptibility to vascular occlusions was the AB group and the tendencies of groups A and B to vascular occlusions were found to be similar . Although this relationship has been demonstrated in many studies, it can be said that the events related to venous vascular structures are affected more with ABO blood groups when the venous and arterial originated events are examined .
There are few studies in the literature investigating the relationship between Rh blood group and vascular occlusions. In an article published in 1973, no relationship was found between myocardial infarction and Rh blood group . Similarly, in another previous study, no relationship was found between coronary artery disease and Rh positivity . In our study, results consistent with the literature were obtained.
It is well known that advanced age, hypertension and diabetes mellitus are risk factors for vascular occlusions. This has also been shown for both retinal artery and vein occlusions. In the reviews published on retinal vascular occlusions, it was stated that advanced age and cardiovascular risk factors increase the risk of all retinal vascular occlusions [1, 25]. Similarly, in studies conducted specifically for retinal vein occlusions, advanced age, hypertension and diabetes mellitus were reported to be risk factors [8, 9]. In our study, too hypertension was identified as a predictive factor for retinal venous occlusions. However, diabetes mellitus was found to have no significant effect.
The most important limiting factor of our study is its retrospective design. Apart from this, the relatively low number of patients is another limiting factor. However, the incomplete records of the patients who were examined for thrombophilia caused many patients to be excluded from the study. Despite these limitations, our study is important, because it is the first study in which the effect of ABO blood groups on retinal venous occlusions was evaluated by regression analysis.
Consequently, non-O blood type may predispose to retinal venous occlusions. Randomized controlled trials will guide in this regard.