Clinical characteristics of retinal venous occlusions occurring at different sites.

AIMS: To identify the contributory factors associated with different sites of occlusion and the presence or absence of optic nerve head swelling (ONHS).
METHODS: 874 cases of retinal venous occlusion (RVO) were prospectively examined at a tertiary referral centre and classified according to three defined sites of occlusion: arteriovenous crossing RVO (AV-RVO); optic cup RVO (OC-RVO); and optic nerve sited RVO. Optic nerve sited RVOs were further divided on the basis of presence (ONHS-RVO) and absence (NONHS-RVO) of ONHS. RVOs not occurring at any of the defined sites were grouped as no-site RVO (NS-RVO). Important clinical parameters were compared among four of the five subgroups by multivariate analysis of variance and chi(2) test (NS-RVO excluded).
RESULTS: The overall multivariate analysis of variance for differences in the mean age, systolic and diastolic blood pressure, body mass index, and intraocular pressure (IOP) among the four subgroups were highly significant (p <0.0001). The F ratios indicated that the differences in the mean age and IOP accounted for this statistical trend. The mean age was statistically significantly lower in the ONHS-RVO group compared to the rest of the groups (p <0.0001). The mean age was significantly higher in OC-RVO compared to the AV-RVO group (p <0.05). The mean IOP was significantly higher in OC-RVO than in the rest of the groups (p <0.01 to 0.0001), while it was also higher in the NONHS-RVO group compared to the ONHS-RVO and AV-RVO groups (p <0.0001). The prevalence of primary open angle glaucoma (POAG), sex, laterality, involvement of the fellow eye, smoking and hypertension were compared by chi(2) tests. POAG was significantly more prevalent in the OC-RVO group than in the rest of the groups (p <0.0083), while it was also significantly more prevalent in the NONHS-RVO group compared to AV-RVO or ONHS-RVO (p <0.0083) groups. Smoking was significantly more prevalent in AV-RVO than in the rest of the groups (p <0.05). The proportion of male sex was significantly higher in ONHS-RVO compared to the AV-RVO group (p <0.05). Hypertension was significantly more prevalent in the AV-RVO than in the ONHS-RVO or NONHS-RVO groups (p <0.05).
CONCLUSION: A new classification of RVO based on the site of occlusion and ONHS has been evaluated. The higher prevalence of hypertension and smoking in AV-RVO suggests a particular importance of cardiovascular risk factors in this group. The association of POAG with CRVO has been confirmed, but only for those cases without ONHS. A distinctive relation between raised IOP and OC-RVO has been demonstrated, suggesting a causal association. RVOs with ONHS tend to occur in younger people, with a higher proportion of males, and a lower prevalence of hypertension and POAG, suggesting that other causal factors may be important in this group. The new scheme resolves the confusion in the literature regarding classification of RVO, and has diagnostic, causal, prognostic, and therapeutic implications.