Diabetes, a chronic metabolic disorder characterized by high blood sugar levels, poses a significant and escalating health threat to India. The country is often termed the "diabetes capital of the world" due to its rapidly increasing number of cases(1–3). Current estimates suggest that India has over 77 million individuals with diabetes, making it the second-highest number of people living with diabetes in the world. This number is projected to rise further, posing a significant public health challenge(1–3).

Cataract surgery, particularly the small incision cataract surgery (SICS), is a common and generally safe procedure to restore vision impaired by cataracts(4–6). Small incision cataract surgery (SICS) represents a pivotal advancement in ophthalmic surgery, offering patients a safer, quicker, and less invasive option for cataract removal(4–6). Small incision cataract surgery is a technique where the cataract is removed through a small incision (usually around 6-8mm) made on the side of the cornea(4–6). The lens is then replaced with an intraocular lens (IOL) (4–6). Compared to older procedures, SICS is preferable because it has a shorter recovery period and a lower chance of problems. However, the presence of systemic conditions like diabetes mellitus can influence the outcome and recovery from this surgery(7). Despite the procedure's high success rate and general safety, certain postoperative complications remain a concern, particularly for patients with conditions such as diabetes mellitus. Among these complications, clinically significant macular edema (CSME) is of paramount importance due to its potential to impair visual recovery(4–6).

Diabetic patients generally have impaired wound healing due to factors like reduced collagen synthesis, altered immune response, and potential microvascular complications(8,9). This slower healing process can impact the recovery period following SICS, potentially leading to prolonged inflammation and increased risk of infection. Diabetics are at a high risk of developing postoperative complications such as infections, hemorrhage, or macular edema(8,9). Diabetic retinopathy, a common complication of diabetes, can also worsen after cataract surgery, affecting visual outcomes. Although SICS generally results in improved vision, diabetic patients may experience less significant improvements compared to non-diabetics(10,11). Diabetes-related eye conditions, like macular edema or retinopathy, can limit the improvement in vision even after successful cataract removal (10,11). Non-diabetic patients typically have a smoother and faster recovery from SICS due to the absence of systemic complications that can affect healing and visual recovery(12,13).

CSME refers to the accumulation of fluid in the macula, leading to swelling and thickening of this central part of the retina, which is crucial for sharp, detailed vision(14). The condition is termed "clinically significant" when it threatens vision, necessitating intervention. In the context of cataract surgery, CSME is considered a form of postoperative macular edema, sometimes specifically called pseudophakic macular edema or Irvine-Gass syndrome(15). The pathogenesis of CSME following SICS involves a complex interplay of factors. Surgical intervention, despite being minimally invasive in the case of SICS, disrupts the blood-aqueous barrier, leading to inflammation and the release of pro-inflammatory cytokines and growth factors(16). These substances increase vascular permeability, resulting in fluid leakage into the macular region. In diabetic patients, pre-existing microvascular damage and chronic inflammation exacerbate this process, making them more susceptible to CSME. The present study delves into a crucial yet under-explored area with significant implications for patient care and clinical practice. The aim of the present study was to assess and compare the macular thickness changes using optical coherence tomography in diabetic and non-diabetic patients after uncomplicated small incision cataract surgery.

This single-centre, prospective, comparative, observational study with a 1:1 allocation was conducted over 18 months in the Department of Ophthalmology at MM Medical College and Hospital, Kumarhatti, Solan, after obtaining approval from the Institutional Ethics Committee. Written informed consent was obtained from all participants. A total of 100 patients scheduled for small incision cataract surgery (SICS) were enrolled using non-probability convenience sampling, comprising 50 patients with diabetes mellitus and 50 non-diabetic controls. Diabetic patients with senile immature cataract and no, mild, or moderate non-proliferative diabetic retinopathy were included, while patients with prior ocular surgery, co-existing ocular pathologies affecting macular thickness, macular diseases, or poor OCT signal strength (<2) were excluded. The primary independent variable was diabetes status, and the dependent variable was central macular thickness (CMT). All participants underwent detailed pre-operative evaluation, including visual acuity assessment and baseline CMT measurement using spectral-domain optical coherence tomography (CIRRUS HD-OCT 500, Carl Zeiss Meditec, USA); diabetic patients additionally underwent blood glucose and HbA1c estimation. Standard SICS was performed, with intraoperative details documented. Post-operative evaluation was carried out at 12 weeks, including repeat OCT-based CMT measurement, visual acuity assessment, and fundus examination. OCT measurements focused on central subfield thickness derived from a 6 × 6 mm macular scan. Data were analyzed using descriptive statistics, independent sample t-tests for intergroup comparisons, and repeated measures ANOVA for within-group temporal changes, with statistical significance set at p < 0.05. The study received no external funding, and the authors declared no conflicts of interest.

Table 1 describes the baseline characteristics of the study participants in the diabetic and non-diabetic groups. Among diabetic patients, males constituted 62% (n=31) and females 38% (n=19), whereas the non-diabetic group had a higher proportion of females at 52% (n=26) and males at 48% (n=24). The mean age was comparable between the two groups, being 64.0 ± 8.10 years in diabetics and 65.38 ± 7.40 years in non-diabetics. The mean body mass index was higher in the diabetic group (27.5 ± 3.65 kg/m²) compared to the non-diabetic group (25.7 ± 3.41 kg/m²). Mean HbA1c levels were elevated in diabetics (7.04 ± 0.832) as expected, while lower values were observed in non-diabetics (5.26 ± 0.498). Hypertension was present in 18% of participants in both groups (n=9 each). Obesity was more frequent among diabetics, affecting 32% (n=16), compared to 16% (n=8) in the non-diabetic group.

Among diabetic participants, the majority had no retinopathy, accounting for 34% (n=17) of the sample. Mild non-proliferative diabetic retinopathy (NPDR) was observed in 36% (n=18) of diabetic participants, followed by moderate NPDR, affecting 30% (n=15) of individuals. In contrast, among non-diabetic participants, all individuals had no retinopathy, representing 100% (n=50) of the sample. Among diabetic participants, the majority had Grade II cataracts, accounting for 66% (n=33) of the sample, while Grade III cataracts were observed in 34% (n=17) of diabetic participants. Similarly, among non-diabetic participants, Grade II cataracts were predominant, affecting 68% (n=34) of the sample, followed by Grade III cataracts, which were observed in 32% (n=16) of non-diabetic participants (p = 0.832). (Table 2)

The mean pre-operative CMT was slightly higher in diabetic patients (263.16 µm, SD=31.00) compared to non-diabetic patients (251.78 µm, SD=30.76). However, the difference in mean CMT between two groups was statistically not significant (p=0.193). At 12 weeks post-operation, both groups exhibited an increase in mean CMT. The mean CMT for diabetic patients was 286.92 µm (SD=31.25) and for non-diabetic patients, it was 261.10 µm (SD=31.101). Although the diabetic group continued to show a higher mean CMT than the non-diabetic group, the difference was statistically significant (p=0.036). (Table 3)

Among diabetic participants, 84% (n=42) did not develop macular edema, while 16% (n=8) experienced its occurrence. In contrast, among non-diabetic participants, the incidence of macular edema was notably lower, with 96% (n=48) not developing macular edema and only 4% (n=2) experiencing its occurrence (p = 0.046). (Table 4)

In this study, we investigated the changes in macular thickness with help of optical coherence tomography (OCT) in diabetic and non-diabetic patients following uncomplicated small incision cataract surgery. Our findings reveal several significant insights into postoperative macular changes in both diabetic and non-diabetic populations. One of the key observations of our study is the notable increase in macular thickness post cataract surgery in both diabetic and non-diabetic groups. This postoperative macular thickening has been well-documented in literature and is attributed to various factors such as surgical trauma, inflammation, and fluid accumulation within the retina. Interestingly, our study also revealed that diabetic patients exhibited a greater increase in macular thickness compared to non-diabetic individuals postoperatively. This finding propose that diabetic status may exacerbate inflammatory response and fluid dynamics within the retina post cataract surgery.

In this study, we observed significant increases in CMT from preoperative levels to 12 weeks postoperatively, with a statistically significant difference between diabetic and non-diabetic patients. A study by Wang et al. observed that the mean postoperative CMT in non-diabetic patients generally increased by about 10-20 µm from the preoperative baseline, which is slightly lower than the increase we observed in our non-diabetic cohort (an increase from 251.78 µm to 271.10 µm)(17). The greater increase in our study could be influenced by factors such as differences in surgical technique, the OCT equipment used, or patient demographic factors such as age and general health status.

In diabetic patients, the literature suggests a more pronounced increase in postoperative CMT. A study by Singh N et al., noted increase in CMT that aligns closely with that observed in our diabetic group(18). These studies all together suggest that diabetic patients are at a increased risk of developing significant macular thickening post-surgery, likely due to pre-existing microvascular abnormalities exacerbated by the surgical procedure.

The observed increase in CMT postoperatively in both groups, with a more substantial and statistically significant increase in diabetics, can be partly attributed to natural inflammatory responses to surgical trauma. However, in diabetics, these changes are likely magnified due to underlying diabetic retinopathy or subclinical microvascular damage not evident during preoperative assessments.  In comparing preoperative and postoperative CMT values, the progression in diabetics raises concerns about potential delays in visual recovery or even long-term visual deterioration if the edema persists or worsens. This contrast underscores the importance of preoperative screening and postoperative monitoring of macular thickness, particularly using OCT, as a standard part of care for diabetics undergoing cataract surgery(6).

In evaluating the changes in central macular thickness (CMT) postoperatively, the scientific community has presented mixed findings. Notably, the literature can broadly be divided into two separate groups according to observed outcomes of cataract surgery on CMT: one group reports statistically significant increase in CMT similar to our study, while the other finds no statistically significant differences. Ikegami Y et al., (2020) observed a significant increase in CMT postoperatively up to 3 months, particularly highlighting an increase in aqueous flare values in diabetic individuals which was significant at 3 months post-surgery(19). Singhi A and Baishya K (2015) found that diabetics who had retinopathy had significantly higher foveal thickness at 6 weeks post-surgery compared to those without retinopathy, with higher incidence of macular edema in diabetics(20). Rathore P et al., (2020) reported a substantial increase in mean CMT in both diabetics and non-diabetics one month post-surgery, with significantly higher incidence of clinically significant macular edema in diabetics(21). Spoorthy S et al., (2023) observed a steady increase in macular thickness over time, with a statistically significant difference in diabetics at 6 weeks post-operative(22). Paraskar NJ et al., (2023) reported significant differences in CMT at various time points post-surgery, highlighting that these changes were reversible and peaked at 1 month(23).

Guliani BP et al., (2019) reported no significant difference in mean CMT between normal and diabetic subjects without diabetic retinopathy preoperatively and in the early postoperative period(24). Gomez de Segura MG et al., (2022) noted no significant difference in macular thickness between diabetic and non-diabetic patients before or after surgery(25). Kumar MMR et al., (2023) found no statistically significant difference in the mean foveal thickness between diabetic and control groups postoperatively, with values returning to near-normal at 3 months(26). Ratha S et al., (2023) concluded that the overall change in macular thickness was insignificant at 3 months postoperatively(27).

Non-Diabetic Group: In this group, 48 out of 50 participants (96%) did not develop macular edema, while only 2 participants (4%) experienced this condition. Diabetic Group: Conversely, a higher incidence of macular edema was observed among diabetic participants, with 8 out of 50 (16%) reporting edema, whereas 42 participants (84%) did not demonstrate any signs of edema. The P-value of 0.046 indicates a statistically significant difference in the incidence of macular edema between diabetic and non-diabetic groups post-surgery. This finding is consistent with established clinical understanding that diabetes is risk factor for development of macular edema, particularly following surgical procedures such as cataract surgery. The higher incidence of macular edema among diabetics can be credited to several diabetes-related pathophysiological mechanisms.

Diabetes can cause chronic inflammation and vascular changes that compromise the integrity of the blood-retinal barrier, making it more susceptible to fluid leakage post-surgery(28). Diabetics often suffer from microvascular complications that can exacerbate the risk of fluid accumulation in the macula(28). Surgical interventions can trigger an inflammatory response, which may be more pronounced in diabetic patients due to their altered metabolic state, leading to increased risk of edema. The significant difference in the incidence of macular edema between diabetic and non-diabetic groups post-surgery not only underscores the impact of underlying systemic conditions such as diabetes on surgical outcomes but also highlights the need for tailored perioperative care protocols to manage and mitigate risks associated with diabetic patients undergoing surgery(28).

The study investigated changes in macular thickness and the incidence of macular edema 12 weeks post small incision cataract surgery in diabetic and non-diabetic patients. Results showed a significant increase in macular thickness postoperatively in both groups, with a more pronounced increase in diabetic patients. Diabetic patients also had a higher incidence of macular edema. Demographic factors did not influence these outcomes. The findings emphasize the importance of vigilant preoperative assessment and postoperative monitoring in diabetic patients to prevent complications and preserve vision. Personalized management strategies for diabetic individuals are crucial for optimizing surgical outcomes. Further research is needed to explore additional factors and develop targeted interventions for improving long-term visual outcomes in diabetic patients.

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