Unilateral Vision Loss in a Patient with Newly Diagnosed Graves' Disease

Case at a Glance

A 34-year-old male with recently diagnosed Graves' disease presenting with acute unilateral vision loss in his functionally dominant left eye, with no structural abnormalities found on initial ophthalmologic examination.

Patient's Story

The patient, previously healthy except for seasonal allergies and seborrheic dermatitis, began experiencing classic hyperthyroid symptoms in April including palpitations, unintentional weight loss, muscle weakness, fatigue, and sleep disturbances. In May, he noticed gradual decline in vision in his left eye, which progressed to sudden significant visual impairment 3-4 weeks prior to presentation. He described the vision as blurry with uneven clarity, occasional brief moments of improved sharpness lasting only seconds, and periorbital discomfort. Notably, the patient had untreated amblyopia in childhood affecting his right eye, making him functionally dependent on his left eye for vision.

Initial Assessment

Physical examination revealed a thin male (BMI 21.7) with signs consistent with hyperthyroidism. Ophthalmologic examination showed severe vision loss in the left eye (visual acuity 0.2+ with correction, compared to baseline near-normal vision). Autorefraction demonstrated significant myopic shift (-23.75/-2.50x63 degrees). Pupillary examination was normal with no relative afferent pupillary defect. No diplopia or pain with eye movement was present.

The Diagnostic Journey

Comprehensive ophthalmologic evaluation including slit-lamp examination and dilated fundoscopy revealed no retinal pathology, hemorrhages, detachment, or optic disc abnormalities. Color vision testing with Ishihara plates was normal. Laboratory studies confirmed severe hyperthyroidism with suppressed TSH (<0.02), markedly elevated free T4 (>100), positive TRAb (17), and elevated TPO antibodies (186). CRP was mildly elevated at 10. Advanced imaging including OCT and orbital MRI/CT had not yet been performed despite the clinical presentation being concerning for dysthyroid optic neuropathy.

Final Diagnosis

Graves' disease with severe hyperthyroidism and suspected dysthyroid optic neuropathy (DON), pending confirmatory orbital imaging.

Treatment Plan

Antithyroid therapy was initiated with methimazole 30mg daily along with propranolol for symptom control. Given the high clinical suspicion for DON despite normal pupillary responses, urgent orbital imaging was recommended to evaluate for extraocular muscle enlargement and optic nerve compression. Consideration for corticosteroid therapy pending imaging results.

Outcome and Follow-up

The case highlights the importance of maintaining high clinical suspicion for dysthyroid optic neuropathy in Graves' patients with vision changes, even when initial ophthalmologic examination appears normal. Urgent orbital imaging and possible intervention are crucial to prevent permanent vision loss, particularly in patients who are functionally monocular due to pre-existing conditions.