Not Every Blur Is A Cataract: Junctional Scotoma Revealing A Chiasmal Macroadenoma

To remind cataract surgeons that significant lens opacity may coexist with neuro-ophthalmic diseases and that chiasmal lesions do not always present with classic bitemporal hemianopia. This case highlights the role of visual field testing in preventing misdiagnosis and inappropriate cataract surgery.

A tertiary eye care center equipped with access to automated perimetry and neuroimaging facilities.

A 60-year-old female presented with gradually progressive blurred vision in both eyes for one year, more severe in the right eye. Best-corrected visual acuity was 1/60 in the right eye and 0.3 in the left eye. Slit-lamp examination revealed bilateral grade 3 senile cataract. However, a notable diagnostic 'red flag' was the degree of visual impairment, which appeared disproportionate to the lens opacity. This inconsistency, combined with a positive relative afferent pupillary defect on the right eye despite an unremarkable optic disc examination, raises a suspicion. Automated visual field testing was therefore performed, revealing a junctional scotoma with a central scotoma in the right eye and a superotemporal visual field defect in the left eye.

Contrary to the classic expectation of bitemporal hemianopia in chiasmal lesions, this atypical pattern raised suspicion of anterior chiasmal involvement. MRI of the brain demonstrated a large chiasmal macroadenoma compressing the optic chiasm. The patient was referred for neurosurgical evaluation, and cataract surgery was deferred.

Cataract should not be assumed as the sole cause of visual loss when clinical findings are incongruent. Chiasmal lesions do not invariably present with bitemporal hemianopia. Atypical visual field defects, including junctional scotoma, may be the initial manifestation, particularly in anterior chiasmal compression. Routine visual field assessment in selected cataract patients can prevent misdiagnosis, avoid unnecessary surgery, and facilitate the timely detection of serious neuro-ophthalmic diseases.