Purpose <p>To describe a patient with electronegative ERGs in association with probable TRPM1-related cancer associated retinopathy.</p> Methods <p>A 67-year-old female presented with progressive visual disturbances, including night blindness, cloudy vision, color vison problems, and scotomas. Initial ophthalmic examination revealed mild retinal vasculitis and an epiretinal membrane in one eye. Visual acuity was bilaterally normal. Electroretinography (ERG) showed electronegative waveforms. Subsequent systemic investigation revealed a lung mass, later confirmed to be a small cell carcinoma, with metastases. Western blot analysis and immunohistochemistry were performed. The patient received cisplatin and etoposide chemotherapy, and sub-Tenon triamcinolone injections (STTA).</p> Results <p>ERGs showed an electronegative waveform with features suggesting pan-retinal loss of On-bipolar cell function. Serum Western blot analysis and immunohistochemistry identified anti-retinal autoantibodies to TRPM1 with binding specificity to the C-terminal region. Further systemic evaluation detected a lung mass, which was later confirmed as small cell lung cancer with metastases. Although initial visual field deterioration was noted, subsequent follow-up showed almost total improvement in visual function, including ERG recovery. Best-corrected visual acuity remained stable at 20/20. Despite the ocular improvements, the patient succumbed to her systemic illness 29&#xa0;months after the initial visit.</p> Conclusion <p>Electronegative ERGs are unusual in CAR, which usually affects photoreceptor function. This case, associated with anti-retinal autoantibodies to TRPM1, highlights the need for full systems review in a patient with possible paraneoplastic disease, even in the absence of systemic symptoms.</p>