your brother in law is sufferring from VKH syndrome which has got eye symptoms, skin involvement and nervous system involvement. From history it is found out that he is taking steroid
eye drops for eye disease. Since the disease can cause variety of eye diseases like uveitis
, retinal detachmnet and others. The cause for loss of vision in left eye has to be investigated. Many investigations are available to fin d out the ocular involvement like ultrasound
examination, fluorescein angiography
... So i recommend you to consult a nearest ophthalmologist for further evaluation. Nothing to worry the overall prognosis for the eye disease is fairly good with appropriate treatment. so do consult nearest ophthalmologist at the earliest.