Uncomplicated Cataract surgery with CI-DME results in poor visual outcome. This may be attributable to both increase in VEGF levels which correlates with postoperative increase in CST at 1month [8, 9], and also to a breakdown of the blood retinal barrier in response to the postoperative release of inflammatory mediators.
In the present study, though both groups showed a reduction in mean CST at 6months, greater reduction was found at one month and at three months in group1(anti-VEGF group) and group 2 (dexamethasone implant) respectively. The baseline CST had a wide range of values 164-960µm compared to any other published data till now. Hence, we subclassified the baseline CST values into <300microns,300-600microns and >600microns and assessed change in P value in these subgroups. Subgroups with <300microns of CST, also received an intervention along with the cataract surgery as they were already receiving ongoing treatment either with an anti-VEGF or with the dexamethasone implant. There were significant differences in trend p in <300microns in both group 1 and group 2. 300-600 microns showed an increase in CST in both groups. In >600microns, although both groups showed decrease in mean CST, there was significant reduction in group 2 over a 6 months follow-up (p=0.043). We did not find statistically significant differences in terms of BCVA and also with no statistical heterogeneity between these two treatment arms at 6 months.
There was no significant difference in BCVA in any of these subgroups. The disparity between the CST and BCVA may be due to the chronicity of the DME and also the weak correlation shown to exist between CST and BCVA. TMV also showed no significant difference instead a slight increase in both the groups in six months follow up period.
In contrast, many studies have shown that the mean CST decrease being is maximum at one month with the anti-VEGF group [12, 13] and 3 months in case of dexamethasone implant. Khodabandeh et al in their prospective randomized clinical trial which included 71 eyes from 71 diabetic patients randomized into two groups: combined phacoemulsification and intravitreal bevacizumab injection group and only phacoemulsification group, showed that bevacizumab group had lower CMT one month after the surgery compared to control group. Furino et al in their retrospective non randomized study of 16 patients showed reduction in the central retinal thickness (CRT) maximum at 30 (120.5 µm) and 60 days (160 µm) after the implant when the dexamethasone level is expected to reach its peak in the vitreous. 
Uncomplicated cataract surgery in pre-existing Diabetic macular edema (DME) causes disruption of blood retinal barrier and release of multiple inflammatory mediators such as VEGF, interleukin 6, protein kinase C and results in endothelial dysfunction, leukocyte adhesion. This, results in increased vascular permeability and fluid accumulation within the macula. [19, 20]
Anti-VEGF and Corticosteroids are the two main modalities used to treat CI-DME. Intravitreal anti-VEGF agents such as ranibizumab, bevacizumab, and aflibercept all have been used successfully to treat DME. Many Randomized clinical trials such as READ-2, RISE/RIDE, and RESTORE trials, have shown that ranibizumab is superior to macular laser whereas the BOLT trial demonstrated bevacizumab's superiority to laser. A meta-analysis by Feng et collected six comparative studies and analyzed 283 eyes for the efficacy of intravitreal bevacizumab combined with cataract surgery in patients with diabetic retinopathy. They found that central macular thickness was significantly reduced at 1, 3 and 6 months postoperatively as compared to the control group. BCVA also showed significant improvement at 1 and 3 months follow up period whereas no such difference was found at 6 months. 
Some studies have shown improvement in visual acuity and reduction in central retinal thickness in patients with DME undergoing cataract surgery with anti-VEGF agents While some prospective studies have shown no such improvement from baseline CRT values.
Intravitreal dexamethasone implant used concurrently with the cataract surgery in patients with DME reduces the postoperative inflammation by two mechanisms, downregulating the VEGF and decrease of the inflammatory mediators thereby reducing the breakdown of blood retinal barrier system. [14, 25] Calvo et al studied twenty-four eyes of 24 patients in a prospective study followed up for 3months.Intravitreal Dexamethasone implant was given at the end of the cataract surgery in diabetic retinopathy patients. They noticed a decrease in retinal thickness at 1 week, 1 month and 3 months postoperatively. The increase in CRT was less than 50 microns in all of the postoperative visits. BCVA also showed significant improvement in all 3 visits. 
In a study conducted by Corbelli et al where they compared combined versus 1month deferred dexamethasone implant with the cataract surgery, they found no long-term difference in either anatomical or functional outcomes among the groups. They concluded that combined over deferred Dexamethasone implant was preferable as it showed protective effect from strong and acute inflammatory stimulus of cataract surgery and also reduces the number of hospital visits for the patient.
Bressler et al in a prospective and non-comparative study, showed that more than half of the eyes who underwent cataract surgery with co-existing DME had no meaningful improvement of vision or worse along with definitive worsening in CRT. On the other hand, those who did not have diabetes gained 6/12 or better vision in >95% cases. [17, 18]
However, anti-VEGF and dexamethasone delivery systems have different pharmacological properties and side-effect characteristics. Our study showed no significant adverse events such as rise in IOP or any infections (both ocular and systemic) postoperatively. Previous studies have also shown that Dexamethasone implant following cataract surgery shows no such increase in IOP and can be used safely. [26, 27]
Ours being a retrospective study design, there were few limitations: (1) small sample size (2) short follow up period. (3) Heterogeneity due to the different group of anti-VEGF therapies. The DRCR.net Protocol T compared two-year results among the three anti VEGFs and found that intravitreal aflibercept, bevacizumab, and ranibizumab were all equally effective in visual acuity improvement and reduction in retinal thickness.
The strength of the study is that both groups were comparative in their baseline demographic characteristics and mean CST and BCVA at the baseline. Even though there was a huge difference in baseline CST, this helped us to analyse the response of the treatment modality with three different sub-groups of CST values.