Retinal vein occlusion (RVO) is a retinal vascular condition characterised by the obstruction of the retinal venous system. This condition is often associated with hypertension and coagulation abnormalities [1, 2]. Visual impairment among the elderly is a widespread condition globally. [3]This condition is classified into three types according to the blockage's location: central retinal vein occlusion (CRVO), branch retinal vein occlusion (BRVO), and hemi retinal vein occlusion (HRVO) [4]. Additionally, both central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO) can be classified into two subtypes: non-ischemic and ischaemic. This classification is predicated on the degree of retinal capillary perfusion [5]. Macular oedema (ME) is a notable complication in individuals with ischaemic retinal vein occlusion (RVO), potentially resulting in considerable impairment of central vision [6]. A variety of treatment modalities have been utilised in the management of ME. Among these therapeutic alternatives, anti-vascular endothelial growth factor (VEGF) therapy has proven to be both safe and effective, as evidenced by prior studies [7-10]. Eyes impacted by retinal vein occlusion (RVO) may display anomalous choroidal vasculature, attributable to hydrostatic pressure and concentrations of vascular endothelial growth factor (VEGF) [11]. Multiple studies have investigated the subfoveal choroidal thickness (SFCT) in eyes impacted by central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). Nevertheless, the results from these studies have been inconsistent and contradictory. Numerous studies have demonstrated that there is no statistically significant difference in subfoveal choroidal thickness (SFCT) between eyes with retinal vein occlusion (RVO) and their unaffected counterparts [11]. Previous research has demonstrated that the subfoveal choroidal thickness (SFCT) in eyes with retinal vein occlusion (RVO) is significantly greater than that in unaffected fellow eyes [12] [13]. Moreover, the alterations in SFCT subsequent to anti-VEGF therapy have been reported as inconsistent in prior studies [14, 15]. Most studies demonstrated a notable reduction in subfoveal choroidal thickness (SFCT) subsequent to anti-vascular endothelial growth factor (anti-VEGF) treatment [12, 16], whereas a few studies indicated no reduction in SFCT following anti-VEGF treatment [9]. Consequently, these contradictory results require further investigation.

The research determined that VEGF levels were the principal factor influencing alterations in subfoveal choroidal thickness (SFCT) [11]. An increase in vascular endothelial growth factor (VEGF) expression may lead to enhanced permeability and leakage in the retina and choroid [2, 17]. This phenomenon is pivotal in the progression of macular oedema (ME) as a secondary effect of retinal vein occlusion (RVO) [18, 19]. Franco-Cardenas et al. (20) noted an elevated ischaemic index in central retinal vein occlusion (CRVO) relative to branch retinal vein occlusion (BRVO). Yasuda et al. (21) additionally reported a markedly elevated concentration of vascular endothelial growth factor (VEGF) in the aqueous humour of eyes with central retinal vein occlusion (CRVO) relative to those with branch retinal vein occlusion (BRVO). The findings collectively demonstrate that retinal ischaemia is more pronounced in CRVO compared to BRVO. Consequently, it is hypothesised that the subfoveal choroidal thickness (SFCT) in eyes with central retinal vein occlusion (CRVO) may be greater than that in eyes with branch retinal vein occlusion (BRVO). This claim is conjectural and necessitates empirical verification. The main aim of this study was to perform a detailed analysis of the subfoveal choroidal thickness (SFCT) in eyes impacted by central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). The study also sought to evaluate the immediate response of SFCT after a single intravitreal ranibizumab injection. It is more important to compare the alterations in subfoveal choroidal thickness (SFCT) before and after intravitreal injection of anti-vascular endothelial growth factor (IVR) in eyes with central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO).

This research was executed as a prospective longitudinal observational study in the Ophthalmology Department of IQ city Medical College Durgapur West Bengal. The research concentrated on treatment-naive individuals recently diagnosed with central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). The participants were selected from an outpatient department. The data was gathered and analysed at the centre. A minimum follow-up duration of three months was required. The study established the following exclusion criteria: individuals with a history of retinal venous occlusion, previous intravitreal treatment with anti-VEGF, corticosteroids, or retinal laser; individuals with concurrent macular or choroidal disorders; individuals with a history of uveitis; individuals with a refractive error greater than 6 diopters of spherical equivalent in either the affected or fellow eye; individuals with suboptimal image quality that obstructed the precise evaluation of SD-OCT images. Data was collected at three specific intervals: the baseline (during the acute phase), and at 3 and 9 months during the post-treatment follow-up period. The research evaluated the demographic traits and risk factors linked to retinal vein occlusion (RVO), encompassing arterial hypertension (AHT), dyslipidaemia, diabetes mellitus (DM), and glaucoma. The evaluation of Best-corrected Visual Acuity (BCVA) was performed using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. All patients were evaluated by retinal specialists (JB and SP) and received treatment through a treat-and-extend methodology utilising either anti-angiogenic or corticosteroid agents according to their specific clinical presentations.

This table compares the demographic and clinical data of patients with Central Retinal Vein Occlusion (CRVO, n=80) and Branch Retinal Vein Occlusion (BRVO, n=120). BRVO patients were significantly older (mean age: 70.15 ± 10.15 years) than CRVO patients (58.00 ± 18.90 years, *P* = 0.008). Both groups had a similar sex distribution, though BRVO showed a slight female predominance (60% vs. 50%). Arterial hypertension (AHT) was more prevalent in BRVO (63.3%) than CRVO (50%, *P* = 0.063), as was diabetes mellitus (25% vs. 12.5%, *P* = 0.164) and glaucoma (16.7% vs. 8.8%, *P* = 0.239), though these differences were not statistically significant. Dyslipidemia affected 35% of BRVO and 17.5% of CRVO patients (*P* = 0.535). The mean intraocular pressure (IOP) was comparable in both groups (CRVO: 15.79 ± 5.67 mmHg, BRVO: 15.38 ± 3.38 mmHg, *P* = 0.735). The median time from symptom onset to baseline was slightly shorter in CRVO (42 days) than BRVO (62 days, *P* = 0.079). At 3 and 9 months, the mean number of intravitreal injections (IVI) was similar between groups, with no significant differences observed.

Table 1 Demographic and Clinical Data Comparison Between CRVO and BRVO

*p <0.05: statistically significant. Key:CRVO: Central Retinal Vein Occlusion,BRVO: Branch Retinal Vein Occlusion,AHT: Arterial Hypertension,DM: Diabetes Mellitus,IOP: Intraocular Pressure,IVI: Intravitreal Injection

Table 2: SD-OCT Thickness Measurements During the Follow-Up in Patients with CRVO and BRVO

*p <0.05: statistically significant.

Abbreviations: CRVO, central retinal vein occlusion; BRVO, branch retinal vein occlusion; PPCT, peripapillary choroidal thickness; SFCT, subfoveal choroidal thickness; pRNFL, peripapillary retinal nerve fiber layer; CMT, central macular thickness.

This table presents SD-OCT thickness measurements for 200 patients with Central Retinal Vein Occlusion (CRVO) and Branch Retinal Vein Occlusion (BRVO) across baseline, 3 months, and 9 months of follow-up. In CRVO, the peripapillary choroidal thickness (PPCT) in affected eyes decreased significantly from baseline (155.38±48.23 µm) to 3 months (132.43±52.64 µm, P = 0.002), with a return to near-baseline levels at 9 months (151.83±61.61 µm). Subfoveal choroidal thickness (SFCT) showed consistent reductions in affected eyes at 3 months (251.65±74.50 µm) and 9 months (246.47±69.35 µm, both significant). Retinal nerve fiber layer (RNFL) and central macular thickness (CMT) significantly decreased over time. Similarly, BRVO patients demonstrated significant reductions in PPCT, SFCT, and RNFL in affected eyes, while CMT decreased notably by 3 months (365.40±145.94 µm, P = 0.002) and stabilized at 9 months. Thickness changes were less pronounced in fellow eyes for both conditions, emphasizing the localized impact of the disease.

Table 3: Comparison of PPCT and SFCT Between CRVO and BRVO (n=200)

Notes: Comparisons between CRVO and BRVO evaluated through ANCOVA (values pre- sented were corrected for age). *p <0.05: statistically significant. Abbreviations: CRVO, central retinal vein occlusion; BRVO, branch retinal vein occlusion; PPCT, peripapillary choroidal thickness; SFCT, subfoveal choroidal thickness.

This table compares peripapillary choroidal thickness (PPCT) and subfoveal choroidal thickness (SFCT) between 200 patients (80 CRVO and 120 BRVO) at baseline, 3 months, and 9 months, with adjustments for age via ANCOVA. In affected eyes, baseline and 9-month PPCT were significantly higher in CRVO compared to BRVO (P = 0.017 for both). Fellow-eye PPCT was also significantly higher in CRVO at baseline (P = 0.014) and 9 months (P = 0.001). SFCT differences were not statistically significant between groups for affected eyes at any time point, but in fellow eyes, CRVO showed higher SFCT at 9 months (P = 0.011). These findings suggest that CRVO is associated with thicker PPCT, particularly in the fellow eye and over time, compared to BRVO.

This study revealed a significant increase in baseline posterior pole choroidal thickness (PPCT) and subfoveal choroidal thickness (SFCT) in eyes with central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO) compared to their unaffected counterparts. A notable reduction in choroidal thickness was detected in both the peripapillary and subfoveal areas during the first three months post-treatment. Furthermore, our study demonstrated that patients with central retinal vein occlusion (CRVO) displayed a markedly increased thickness of the peripapillary choroid at the initial assessment in comparison to patients with branch retinal vein occlusion (BRVO), in both the affected and unaffected eyes. No statistically significant differences were detected in the subfoveal choroid between the two groups. Retinal vein occlusions create a hypoxic environment, which may result in increased intraocular expression of vascular endothelial growth factor (VEGF). Subsequently, there may be an augmentation in vascular permeability and dilation of the choroid.[22-25] The posterior pole choroidal thickness (PPCT) and subfoveal choroidal thickness (SFCT) of the affected eyes demonstrated statistically significant increases relative to the fellow eyes after central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). These results align with earlier research evaluating subfoveal choroidal thickness (SFCT) subsequent to occlusions[26-29].
Our study reveals that after the acute event, there was a sudden and statistically significant decrease in posterior pole choroidal thickness (PPCT) and subfoveal choroidal thickness (SFCT) following anti-vascular endothelial growth factor (anti-VEGF) treatment. This was noted in patients with central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). Moreover, throughout the subsequent follow-up period, thickness exhibited stabilisation. The findings may be corroborated by an abrupt decrease in the initial hypoxic stimulus and the continuous administration of anti-VEGF therapy throughout the study duration.The figures [27,28] are being referenced. The results of our study corroborate the existing data concerning the fluctuation in choroidal thickness after an occlusive event.The numbers provided by the user are [30, 29, and 31]. Conversely, the peripapillary choroidal thickness (PPCT) and subfoveal choroidal thickness (SFCT) of the fellow eyes demonstrated stable measurements over the study period, indicating that these parameters were unaffected by the event. The subsequent examination revealed that the peripapillary and subfoveal choroidal responses were similar, thereby reinforcing the hypothesis that the retinal occlusion event significantly affects the choroid.
The central macular thickness (CMT) and peripapillary retinal nerve fibre layer (pRNFL) demonstrated a predicted increase after the acute event in both groups, probably due to the subsequent development of acute oedema. Nonetheless, these measurements progressively diminished throughout the follow-up period. The peripapillary retinal nerve fibre layer (pRNFL) demonstrates a notable positive linear correlation with the pre-perimetric central thickness (PPCT) at baseline in branch retinal vein occlusion (BRVO). Nevertheless, the ensuing follow-up did not produce any significant correlations. Moreover, no correlations were observed between peripapillary choroidal thickness (PPCT) and peripapillary retinal nerve fibre layer (pRNFL), nor between subfoveal choroidal thickness (SFCT) and central macular thickness (CMT) in eyes with central retinal vein occlusion (CRVO). Consequently, we assert that the response of retinal tissue is not intrinsically connected to the response of the choroid. Similarly, it is suggested that the reduction of the hypoxic stimulus and the application of anti-VEGF therapy may produce different effects on the choroid and retina during the observation period, considering their classification as distinct vascular entities. Patients with central retinal vein occlusion (CRVO) demonstrated increased thickness in the parafoveal photoreceptor cell layer (PPCT) at the study's outset relative to those with branch retinal vein occlusion (BRVO). The pre-occlusion choroidal condition of the patients is undetermined; however, the augmented thickness of the choroid in central retinal vein occlusion (CRVO) is hypothesised to indicate a more significant ischaemic injury. This may lead to an elevated release of inflammatory mediators and vascular endothelial growth factor (VEGF), consequently resulting in a more significant increase in choroidal thickness (CT). However, during the following observation period, no significant differences in post-treatment patient care time (PPCT) were noted between the two groups, at least until the 9-month milestone. The SFCT demonstrated similar values in both groups throughout the entire follow-up period, as previously indicated.The given number is 20. It is significant that the contralateral eyes of patients with central retinal vein occlusion (CRVO) also demonstrate increased posterior pole choroidal thickness (PPCT). This finding indicates that this specific cohort of patients may possess a naturally thicker choroid, and that the occlusion itself may not be the fundamental factor contributing to the observed difference between the two groups.
No notable differences were detected regarding sex, arterial hypertension (AHT), diabetes mellitus (DM), dyslipidaemia, or the occurrence of glaucoma between patients diagnosed with central retinal vein occlusion (CRVO) and those with branch retinal vein occlusion (BRVO). Moreover, no notable differences were detected regarding baseline intraocular pressure (IOP), the interval from symptom onset to initial evaluation, and the total number of intravenous (IV) injections given in either group. While no substantial age differences were detected, it is noteworthy that CRVO patients were significantly younger than BRVO patients. Consequently, we performed a supplementary analysis to compare the groups while considering this parameter.
This study is the first to sequentially evaluate posterior pole choroidal thickness (PPCT) and subfoveal choroidal thickness (SFCT) at multiple time points in patients with central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). Nevertheless, it is crucial to recognise the constraints of our research. The main limitations of this study are its limited sample size and retrospective observational methodology. Moreover, the analysis failed to consider the presence of macular oedema or the degree of retinal ischaemia. Moreover, our study exclusively included patients with high-quality optical coherence tomography (OCT) images. The incorporation of this data may lead to selection bias, potentially omitting more severe occlusions from our analysis. Additionally, choroidal thickness varies according to factors including age, refractive error, and the time of day when measurements are conducted.The range of values is [32, 34]. To alleviate potential biases, modifications were implemented for age, notwithstanding the lack of age-specific cohorts. Furthermore, patients with a spherical equivalent exceeding 6D were omitted from the analysis. The evaluation of patients occurred solely between 2 pm and 8 pm.

In summary, central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO) are associated with a significant increase in peripapillary choroidal thickness (PPCT) and subfoveal choroidal thickness (SFCT) relative to the unaffected eye. This finding suggests a possible initial increase in choroidal thickness after the occlusion, followed by a subsequent decline during the early follow-up stages. Additional research through prolonged follow-up studies with larger sample sizes would yield a more thorough comprehension of the relationship between choroidal thickness and the incidence of retinal vascular occlusion. This study presents evidence indicating that the choroid may contribute to the pathophysiological response associated with retinal vein occlusion (RVO). Improved understanding of the relationship between choroid thickness and retinal response may provide an additional structural indicator for predicting outcomes in these individuals.

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