Why some people suddenly go blind

Why do people suddenly go blind,” asked the unidentified voice on the phone? I could discern a glint of anxiety in the voice.
I paused a little, not knowing from where to commence my response. It was a straightforward question and the answer also simple but explaining the nitty-gritty of the symptom on the phone was quite complex.
   I could immediately think of over 200 possible causes of sudden painless loss of vision and another 100 causes of sudden painful loss of vision. Reeling out these causes to the faceless person at the other end of the phone was meaningless.
 The anxiety in his voice was a warning that this was not supposed to be a teacher-student interaction. It meant there was someone with an urgent problem requiring some crucial advice. So I decided to ask some searching questions.
“Sir, do you have anyone in particular in mind?” I asked. “My 70-year-old aunt,” he replied. “How sudden is ‘sudden’?” I questioned. In the over four decades of practising medicine in this part of the world, I have learnt that several words which are supposed to have definite meanings are used with such laxity that they lose their significance.
“I was in her house two weeks before and she opened the door for me. She cooked me a really delicious meal without any assistance from anyone. Her housekeeper came in later to tidy the table and wash the dishes. Then two days ago, she phoned me that she had to grope, in broad day light, to find her way inside the same house!” he said. “That’s a helpful piece of information,” I replied with satisfaction. “’Sudden’ here might just be sudden,” I surmised.
 “By the way is she diabetic or hypertensive?” I asked again. “Not to my knowledge. She has never been ill in the last five years!” he replied confidently. My task was still very difficult even though through those questions I had already excluded over two dozen possibilities! “You have to bring your aunt to my office for examination and investigations,” I demanded. 
The following day, he breezed into my office with his aunt. “Doctor, your patient is here,” said he, introducing his aunt. As she was led to the examination chair, I had doubts if this was actually a case of sudden loss of vision. But there was no need for guessing now since she was with me. Auntie could barely see my hand waving very close to her face. I shone my torch on her eyes and was greeted with a brisk wink in each eye by a nice round pupil in response to the bright light. Now something else caught my attention! It was least expected, yet common place. Behind each pupil was a whitish opacity.
“Cataract!” I blurted out in disbelief. Cataract blindness is usually never sudden! Blindness is typically gradually progressive. Could there be other co-existing and more devastating disease in the eyes? I reviewed the information provided earlier and conducted a few more tests.

Certainly, Auntie had straightforward cataracts. Why then is her visual loss sudden? From the evidence gleamed from the eye examination, the cataract in her left eye started first. I estimated the near total visual loss in that eye had occurred not less than two years before. She had been seeing through a small clear window in the cataract in her right eye until a few days ago when it sealed up plunging her into near total darkness. 
This is an unusual case! What then are the common causes of sudden painless loss of vision? The commonest cause in this area is bleeding into the eye. It is not infrequent in sicklers especially those with SC haemoglobin between the ages of 15 and 55 years.
Diabetes and hypertension are some of the other causes of bleeding into the eye that  can also cause sudden loss of vision through several other mechanisms. I remember seeing recently a young man who lost vision in both eyes after ingestion of wood alcohol (Methyl Alcohol) and another who suffered the same fate from quinine. 
Sudden painless loss of vision can be dramatic and alarming to both the patient and the doctor. In some cases, immediate attention and diagnosis within a few minutes after occurrence may determine if or not the eye will ever see again. An accurate history is just as important as the clinical examination. Do not hold anything back from your doctor including the history of recent or past illnesses, medications, contraceptive use and drug abuse.

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