A 52-year-old woman with a five-year history of type 2 diabetes mellitus and hypertension presented to the retina clinic with decreased vision in her left eye for four months. At presentation, her best-corrected visual acuity (BCVA) was 6/24 in the right eye and counting fingers at 1 m in the left eye. Anterior segment examination revealed clear lenses and normal intraocular pressures in both eyes. Dilated fundus examination of the right eye showed multiple fronds of neovascularization elsewhere (NVE), extramacular fibrovascular proliferations along the retinal arcades with minimal vitreous hemorrhage, consistent with high-risk PDR. The left eye demonstrated advanced PDR with sclerosed retinal vessels, predominantly in the inferior quadrants, and a subtotal macula-off combined retinal detachment (Fig. 1A, B).

Colour fundus photograph of both eyes at presentation: A: Dilated fundus examination of the right eye reveals multiple fronds of retinal neovascularization and extramacular fibrovascular proliferations along the retinal arcades, accompanied by minimal vitreous hemorrhage, consistent with high-risk proliferative diabetic retinopathy. B: The left eye demonstrates high-risk PDR, characterized by sclerosed retinal vessels predominantly in the inferior quadrants and a subtotal macula-off combined retinal detachment

After thorough counselling regarding treatment options and prognosis, the patient underwent aggressive pan retinal photocoagulation over multiple sessions for the right eye. For the left eye, a 25-gauge vitreoretinal surgery was performed, including membrane peeling to relieve retinal traction, subretinal fluid drainage through the primary retinal break and a drainage retinotomy, followed by endolaser to the retinal breaks and retinal periphery and silicone oil tamponade (Aurosil 1500 centistokes, Aurolab, India). The procedure was uneventful. Postoperative day one examination of the left eye revealed a completely attached retina with well-lasered, flat retinal breaks and silicone oil in situ (Fig. 2A, B). By the 12th postoperative day, her BCVA in the left eye improved to 6/24, with normal intraocular pressure and a well-attached retina. However, early hard exudates were observed in the inferotemporal quadrant (Fig. 2C, D). Subsequent follow-ups at week 3 and month 3 showed a well-attached retina and stable BCVA of 6/24 in the left eye. However, there was a significant increase in the density and extent of hard exudates in the inferotemporal quadrant over time. Optical coherence tomography scans through the hard exudates showed the subretinal location of the lipid exudates. The right eye showed stable PDR with an adequately lasered retina (Fig. 2E-I). Systemic evaluations, including glycosylated haemoglobin (HbA1C = 6.2%), blood pressure and renal function assessments, were conducted to rule out contributing systemic factors, but no abnormalities were identified. The patient was advised to optimize glycaemic control and review after two months.

Postoperative retinal findings and progression of hard exudates. A, B: Postoperative day one examination of the left eye demonstrates a completely attached retina with well-lasered, flat retinal breaks and silicone oil in situ. C, D: On the 12th postoperative day, the left eye shows an attached retina with silicone oil in situ; minimal hard exudates are observed in the inferotemporal quadrant. E-H: Follow-up examinations at week 3 and month 3 reveal a stable, well-attached retina with a notable progression of hard exudates in the inferotemporal quadrant. I: Optical coherence tomography (OCT) imaging through the area of hard exudates confirms their subretinal location, indicative of lipid exudation

At the month 5 follow-up, BCVA remained 6/24 in the left eye, with a well-attached retina, silicone oil in situ, and a decrease in hard exudates (Fig. 3A-C). Wide-field fluorescein angiography revealed temporal capillary dropout and leakage in the inferotemporal quadrant, corresponding to the areas of hard exudates seen clinically (Fig. 3D-G). The findings were consistent with a diagnosis of secondary Coats’ response possibly following vitreoretinal surgery and PDR. Silicone oil removal was performed with additional intraoperative endolaser to the leaking areas identified on angiography. At the end of surgery, fluid air exchange was performed and 0.4 mg/0.1 mL of intravitreal triamcinolone acetonide was injected.

Resolution of Coats-Like Response in the Left Eye: Pre- and Postoperative Outcomes Following Silicone Oil Removal and Retinal Laser Photocoagulation. A-C: At the 5-month follow-up, dilated fundus examination of the left eye shows a well-attached retina with silicone oil in situ and a reduction in hard exudates. D-G: Wide-field fluorescein angiography reveals temporal capillary dropout and leakage in the inferotemporal quadrant, corresponding to the areas of hard exudates observed clinically. These findings are consistent with a secondary Coats-like response, likely associated with vitreoretinal surgery and proliferative diabetic retinopathy. H, I: Two weeks post-silicone oil removal, the patient’s best-corrected visual acuity (BCVA) in the left eye deteriorated to 6/60, attributed to the rapid progression of posterior subcapsular cataract. Fundus examination shows a well-attached retina with complete resolution of hard exudates. J: Optical coherence tomography (OCT) confirms the resolution of subretinal lipid exudation, marking a successful resolution of the Coats-like response

Two weeks post-silicone oil removal, the patient’s BCVA in the left eye had deteriorated to 6/60, attributed to rapid progression of a posterior subcapsular cataract. The intraocular pressure remained normal, and fundus examination showed a well-attached retina with complete resolution of hard exudates. OCT scans confirmed the resolution of the subretinal lipid exudation (Fig. 3H-J). The patient was counselled for requiring cataract surgery in the future and was advised to follow up with the retina clinic after 4 weeks.