Patient X is a 49-year-old man who was referred to me by another ophthalmologist to discuss his suitability for laser refractive surgery. He had previously been diagnosed with mild cataracts by the referring ophthalmologist, and was also being treated at the time of presentation for fairly florid, active marginal keratitis (Flucon eye drops to the left eye). Patient X was known to have a previous history of right amblyopia, although the degree of amblyopia was unknown. During the consultation, Patient X reported a history of having some difficulty with driving over the preceding 18 months (no road accidents). However, his description of the visual impairment was vague – he found it uncomfortable and complained of evening glare.
At presentation, Patient X’s vision could not be improved beyond 6/12 in either eye. He had a serpiginous area of old, inactive marginal keratitis in the right eye (mid-periphery, extending from 4 o’clock to 6 o’clock). The left eye showed an area of mid-peripheral marginal keratitis, with active infiltrate extending from 6 o’clock to 8 o’clock. Patient X’s examination also demonstrated early lens opacities. There was no relative afferent pupil defect nor any colour defect, and OCT examination revealed healthy optic discs and maculae.
At his first presentation, I changed the patient from Flucon eye drops to Prednefrin Forte. A review two weeks later revealed that the keratitis was resolving. A month after his initial presentation, the keratitis had completely settled. However, Patient X’s corrected vision had not improved in either eye. I referred him to Dr Joseph Reich to consider whether he felt the cataracts were affecting Patient X’s visual acuity, particularly in the non-amblyopic left eye. Dr Reich reviewed the patient and reported that the cataracts were not consistent with the decline in visual acuity. He was subsequently sent for visual field analysis.
Analysis of Patient X’s visual fields demonstrated bitemporal hemianopia. He was immediately referred to the Alfred Hospital, where an urgent MRI revealed a space-occupying lesion compressing the optic chiasm. Patient X was admitted for neurosurgery later that week and underwent an endoscopic transsphenoidal resection of the tumour. Pathology revealed the tumour to be consistent with a craniopharyngioma. Following the surgery, Patient X’s bitemporal field loss completely resolved and he no longer notes any difficulty with driving.
Patients with this condition have visual deficits in both outer halves of the visual field. Bitemporal hemianopia is usually diagnostic of either a pituitary tumour or a craniopharyngioma, either of which can compress the optic chiasm. It is often picked up late, as the field loss on both sides is compensated by the other eye.
Visual loss that cannot be accounted for by other active diseases of the eye (in Patient X’s case, cataracts and active keratitis) certainly requires further investigation – in particular, a visual field test.
If the patient’s active eye diseases do not adequately explain the visual impairment, keep investigating.