Diabetes mellitus (DM) has emerged as one of the most significant global health challenges of the 21st century, with rapidly increasing prevalence across both developed and developing nations. India, in particular, bears a substantial portion of this burden, with a large and growing diabetic population. The chronic hyperglycemic state in diabetes leads to multiple microvascular and macrovascular complications, among which diabetic retinopathy (DR) remains the most common and vision-threatening ocular manifestation.^1-3

Diabetic retinopathy is a progressive microangiopathy characterized by structural and functional changes in the retinal vasculature. It encompasses a spectrum ranging from non-proliferative diabetic retinopathy (NPDR) to proliferative diabetic retinopathy (PDR), the latter representing an advanced stage associated with neovascularization. The risk of progression from NPDR to PDR is strongly influenced by factors such as duration of diabetes, glycemic control, hypertension, and other systemic comorbidities.^4-7 In the natural course of the disease, nearly 50% of patients with severe NPDR progress to PDR within one year if left untreated.⁸

Proliferative diabetic retinopathy is characterized by the formation of new, fragile blood vessels arising from ischemic retina. These neovessels are prone to bleeding, leading to vitreous hemorrhage, fibrosis, and tractional retinal detachment, which can culminate in irreversible vision loss. The underlying pathophysiology involves retinal hypoxia-induced release of angiogenic factors such as vascular endothelial growth factor (VEGF), which stimulates abnormal vascular proliferation.⁹

Panretinal photocoagulation (PRP) remains the gold standard treatment for PDR and has been extensively validated through landmark clinical trials. The Diabetic Retinopathy Study (DRS) demonstrated that PRP reduces the risk of severe visual loss by approximately 50–60% in eyes with high-risk characteristics. Similarly, the Early Treatment Diabetic Retinopathy Study (ETDRS) provided guidelines regarding the timing and indications for laser therapy and emphasized the role of early intervention in improving visual outcomes.¹⁰

The mechanism of action of PRP involves selective ablation of ischemic retinal tissue, thereby reducing metabolic demand and decreasing the production of angiogenic mediators. This leads to regression of neovascularization and stabilization of the disease process.¹¹ Although PRP is highly effective in preventing severe visual loss, it is not without limitations. Potential adverse effects include peripheral visual field constriction, decreased night vision, exacerbation of macular edema, and, in some cases, transient reduction in central visual acuity.^12,13

Several studies have evaluated the long-term visual outcomes following PRP. While many have demonstrated stabilization or improvement in vision, others have reported variable outcomes depending on baseline visual acuity, severity of disease, and associated complications such as macular edema or vitreous hemorrhage.^14-16 Therefore, real-world evaluation of visual outcomes following PRP remains essential, particularly in tertiary care settings where patients often present at advanced stages of the disease.

Given the increasing burden of diabetes and diabetic retinopathy in India, and the continued reliance on PRP as a primary treatment modality in resource-limited settings, it is important to assess its effectiveness in routine clinical practice. This study was undertaken to evaluate the visual outcomes following panretinal photocoagulation in patients with proliferative diabetic retinopathy at a tertiary care hospital in Eastern India.

STUDY DESIGN AND SETTING

This was a prospective, interventional, hospital-based study conducted in the Retina Clinic of the Department of Ophthalmology at Nil Ratan Sircar Medical College and Hospital (NRSMCH), Kolkata, over a period of 18 months.

STUDY POPULATION

A total of 110 patients diagnosed with proliferative diabetic retinopathy (PDR) were included in the study. All patients were aged above 40 years and had type 2 diabetes mellitus. Both male and female patients were enrolled.

INCLUSION CRITERIA

• Patients diagnosed with proliferative diabetic retinopathy
• Age >40 years
• Best corrected visual acuity (BCVA) better than 6/24 in the study eye
• Willingness to provide informed consent

EXCLUSION CRITERIA

• Advanced proliferative diabetic retinopathy
• Media opacities significantly affecting vision (e.g., dense cataract, corneal opacity, vitreous hemorrhage)
• Presence of diabetic maculopathy or prior laser photocoagulation
• Associated systemic complications such as nephropathy
• Other ocular conditions affecting visual acuity

PRE-LASER EVALUATION

All patients underwent a detailed clinical and ophthalmic evaluation, including:

• Best corrected visual acuity (BCVA) assessment using Snellen’s chart
• Measurement of intraocular pressure using Schiotz tonometry
• Slit-lamp biomicroscopy
• Fundus examination using direct and indirect ophthalmoscopy
• Slit-lamp biomicroscopy with +90D lens
• Fundus fluorescein angiography (FFA) in all cases

Relevant systemic parameters such as duration of diabetes, hypertension status, treatment history, and family history were also recorded.

INTERVENTION: PANRETINAL PHOTOCOAGULATION (PRP)

Panretinal photocoagulation was performed in all patients using a 532 nm frequency-doubled diode-pumped laser (Zeiss Visulas 532s).

• Lens used: Mainster PRP lens
• Spot size: 200 µm
• Power: 200–400 mW
• Duration: 200 milliseconds
• Total burns: 1600–2000

The procedure was performed under topical anesthesia and delivered in 2–3 sittings.

Sequence OF Laser Application

1. Near the optic disc below the inferior temporal arcade
2. Around the macula to create a protective barrier
3. Nasal to the optic disc
4. Peripheral retina until completion

FOLLOW-UP PROTOCOL

Patients were followed up at:

• 1 month
• 3 months
• 6 months
• 1 year

At each visit, the following assessments were performed:

• Visual acuity (Snellen’s chart)
• Detailed fundus examination
• Slit-lamp evaluation of the macula (+78D/+90D lens)

Fundus photography was performed in selected cases. In cases with persistent or progressive lesions, repeat FFA and additional (fill-in) PRP were performed.

OUTCOME MEASURES

Primary Outcome

• Change in visual acuity following PRP at 1 year

Secondary Outcomes

• Proportion of patients with improved, maintained, or worsened vision
• Disease stabilization following PRP

STATISTICAL ANALYSIS

Data were analyzed using descriptive epidemiological methods. Results were expressed as proportions and percentages and represented using tables, bar charts, and pie diagrams.

ETHICAL CONSIDERATIONS

Written informed consent was obtained from all patients prior to enrollment. Patient confidentiality was strictly maintained throughout the study

A total of 110 patients (110 eyes) with proliferative diabetic retinopathy were included in the study. All patients underwent panretinal photocoagulation and were followed up for a duration of one year.

Baseline Characteristics

The age distribution of patients showed that the majority (60.9%) belonged to the 51–60 years age group, indicating that proliferative diabetic retinopathy was most prevalent in the middle-aged to elderly population. A smaller proportion of patients were in the younger age group (40–50 years), while a significant number (25.5%) were above 60 years, reflecting the chronic and progressive nature of diabetes-related retinal disease. This is shown in Table 1

Table 1: Age Distribution

There was a clear male predominance (69.1%) in the study population. This may reflect gender-related differences in healthcare access, disease prevalence, or health-seeking behavior in the study setting. This is shown in Table 2.

Table 2: Gender Distribution

The majority of patients (81.8%) had a duration of diabetes between 10–20 years, highlighting the strong association between prolonged duration of diabetes and the development of proliferative diabetic retinopathy. Only a small proportion had disease duration exceeding 30 years. This is shown in Table 3

Table 3: Duration of Diabetes

A high proportion of patients had coexisting hypertension (71.8%) and positive family history of diabetes (77.3%), suggesting that systemic risk factors play a significant role in the progression of diabetic retinopathy. This is shown in Table 4.

Table 4: Associated Risk Factors

Disease Characteristics

Neovascularization elsewhere (NVE) was the most common finding (64.5%), followed by neovascularization at the disc (NVD) in 26.4% of cases. A smaller subset of patients (9.1%) had both NVE and NVD, indicating more advanced disease involvement. This is shown in Table 5.

Table 5: Type of Neovascularization

The right eye (62.7%) was more commonly treated than the left eye. This distribution appears incidental and does not suggest any specific laterality pattern. This is shown in Table 6.

Table 6: Laterality of Operated Eye

Primary Outcome: Visual Acuity

At baseline, the majority of patients (61.8%) had moderate visual impairment (6/12–6/18), while 17.3% had good visual acuity and 20.9% had relatively poorer vision (6/24). This indicates that most patients presented at a stage where vision was still salvageable with timely intervention. This is shown in Table 7.

Table 7: Baseline Visual Acuity

Following panretinal photocoagulation, there was an initial shift toward lower visual acuity categories, particularly evident at the 1-month follow-up, where the proportion of patients with visual acuity ≤6/24 increased to 40.0%. This early decline is likely attributable to transient post-laser effects such as retinal edema or inflammation. Over subsequent follow-up visits, visual acuity showed a trend toward stabilization, with relatively minor fluctuations between 3 months and 1 year. By the end of one year, a substantial proportion of patients (48.2%) remained in the 6/12–6/18 category, indicating preservation of functional vision in a majority of cases. This is shown in Table 8.

Table 8: Visual Acuity at Follow-Up

VISUAL OUTCOME AT 1 YEAR

At one-year follow-up, the majority of patients across all baseline categories maintained their visual acuity, highlighting the stabilizing effect of PRP. Visual improvement was more evident among patients with poorer baseline vision (≤6/24), where 13.6% showed improvement. In contrast, no improvement was observed in patients with initially good vision (6/6–6/9), likely reflecting a ceiling effect. A proportion of patients experienced decline in visual acuity, particularly those with better baseline vision. This may be related to disease progression or known effects of PRP such as macular edema or retinal damage. This is shown in Table 9.

Table 9: Visual Outcome by Baseline Vision

stage of diabetic retinal disease and remains a major cause of preventable blindness. The present study evaluated the visual outcomes following panretinal photocoagulation (PRP) in patients with PDR and demonstrated that PRP primarily results in stabilization of vision rather than significant improvement, which is consistent with existing literature.8,10 In this study, the majority of patients presented with moderate visual impairment (6/12–6/18) at baseline. This finding reflects the typical presentation pattern in tertiary care settings, where patients often seek medical attention at relatively advanced stages of disease. Similar baseline characteristics have been reported in previous studies evaluating PRP outcomes in PDR.^16,17

Following PRP, an initial decline in visual acuity was observed during early follow-up, followed by stabilization over time. This transient deterioration may be attributed to laser-induced retinal inflammation, macular edema, or redistribution of retinal blood flow. Such early worsening has also been described in previous studies and is considered a known short-term effect of PRP.^14,15 At one-year follow-up, the majority of patients in this study maintained their baseline visual acuity, with a smaller proportion showing improvement or deterioration. These findings are consistent with earlier reports suggesting that the primary goal of PRP is to prevent further visual loss rather than restore vision. The Diabetic Retinopathy Study (DRS) demonstrated that PRP reduces the risk of severe visual loss by approximately 50–60% in patients with high-risk PDR.¹⁰

Visual improvement was observed predominantly in patients with poorer baseline vision (≤6/24). This may be explained by regression of neovascularization and resolution of retinal ischemia following PRP, allowing partial functional recovery. Similar trends have been reported in earlier studies, where patients with worse initial vision demonstrated greater relative improvement after treatment.^14-16 Conversely, a subset of patients, particularly those with better baseline vision, experienced decline in visual acuity. This may be attributed to factors such as progression of diabetic macular edema, laser-induced retinal damage, or underlying disease severity. PRP is known to be associated with certain adverse effects, including exacerbation of macular edema and peripheral visual field loss.^12,13 These factors may contribute to reduced central vision in some cases despite adequate laser treatment.

The overall findings of this study reinforce the role of PRP as an effective modality for disease stabilization in PDR. The mechanism involves ablation of ischemic retina, thereby reducing angiogenic stimuli and promoting regression of neovascularization.8 This aligns with the fundamental principles established by landmark trials such as DRS and ETDRS, which form the basis of current treatment guidelines.¹⁰ Importantly, colour vision remained largely unaffected in this study, suggesting that PRP, when appropriately applied, does not significantly impair this aspect of visual function. Additionally, no major procedure-related complications affecting visual outcomes were observed, supporting the safety profile of PRP when performed under standardized protocols.

However, variability in visual outcomes across studies has been reported. Some studies have shown more favorable visual improvement, while others have reported stabilization or even deterioration in certain cases.^14-16 This variability may be due to differences in baseline disease severity, presence of macular edema, laser parameters, and follow-up duration.¹⁵ Overall, the findings of the present study are in agreement with existing evidence that PRP is highly effective in preventing progression of proliferative diabetic retinopathy and preserving useful vision, particularly when applied in a timely manner.

The present study has several limitations. First, it was conducted at a single tertiary care center, which may limit the generalizability of the findings to broader populations. Second, the study utilized a moderate sample size (110 patients), which may not fully capture the variability in disease presentation and outcomes. Third, the analysis was primarily based on descriptive statistics, without advanced inferential analysis to assess statistical significance between subgroups. Additionally, important factors such as glycemic control (HbA1c levels), severity grading of diabetic retinopathy, and presence of diabetic macular edema were not quantitatively correlated with visual outcomes. The follow-up period of one year, although adequate to assess short- to mid-term outcomes, may not reflect the long-term effects of PRP, including late complications or disease progression. Furthermore, subjective assessment tools such as Snellen’s visual acuity, while widely used, may introduce measurement variability.

Future research should focus on larger, multicentric studies to improve the external validity of findings and better represent diverse patient populations. Incorporation of longer follow-up periods would help in understanding the sustained impact of PRP on visual outcomes and disease progression. Further studies should aim to correlate visual outcomes with systemic parameters such as glycemic control, duration of diabetes, and comorbid conditions like hypertension. Comparative studies evaluating PRP with newer treatment modalities, including intravitreal anti-VEGF therapy or combination approaches, may provide deeper insights into optimizing management strategies. Additionally, the use of objective imaging modalities such as optical coherence tomography (OCT) and wide-field angiography could enhance the precision of outcome assessment. Patient-centered outcomes, including quality of life and functional vision, should also be incorporated into future research.

Panretinal photocoagulation remains an effective and reliable modality in the management of proliferative diabetic retinopathy. The findings of the present study demonstrate that PRP primarily contributes to stabilization of visual acuity, with a majority of patients maintaining their baseline vision over a one-year follow-up period. Although improvement in visual acuity was limited, particularly among patients with good baseline vision, a subset of patients with poorer initial vision showed measurable gains. Importantly, PRP was effective in preventing further visual deterioration, thereby preserving functional vision in most cases. These results reinforce the role of PRP as a cornerstone treatment in PDR, especially in resource-limited settings, where it continues to be widely accessible and cost-effective. Early diagnosis and timely intervention remain critical in optimizing visual outcomes.

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