Dr. Ben, it’s the chameleon again!” exclaimed my younger colleague as he stared into the lady’s eye with the ophthalmoscope. For a brief moment, I was at sea. What’s he talking about – a chameleon in the eye? I quickly came to my senses. He must be speaking figuratively.
As he completed his examination, he looked at me as if he had discovered something worthy of a Nobel Prize and repeated with pride. “It is the chameleon. I saw her for the first time yesterday morning. I was completely baffled when she gave me her story. Nothing she had said prepared me for these findings. As a matter of fact, I was thinking of something completely different,” he said.
My thoughts went some miles ahead trying to work out the various eye conditions that could behave like a chameleon. Chameleons are fascinating creatures. There are about 160 different types in nature.
Three things are peculiar to them all. The first is the chameleon’s eyes. Each eye can rotate in a different direction. The second feature is their long tongue which is about one and a half their body length. Imagine a six-foot person, having a nine-foot long tongue! The third and perhaps the best known feature is the ability of the chameleon to change its colour.
Which of these three features has aroused the interest of my colleague? The lady’s eyes are fixed. I can see them! Her tongue looks nothing like the chameleons and neither can she change the colour of her skin!
At least she hasn’t looked any different since I have been in the room over 15 minutes. The feature therefore must be in the inner recesses of her eyes. My anxiety was further heightened after he had taken the lady’s intraocular pressure and he exclaimed, Dr. Ben, the pressures are within normal limits.
What then can he be talking about? Glaucoma is usually associated with a higher than normal intraocular pressure. Just as it would be right to say you cannot have hypertension without a raised blood pressure, it would be unusual to have glaucoma with normal pressure! I couldn’t stand the suspense anymore. “Doctor, what is it then if it is not glaucoma?” I asked in a voice that conveyed my disenchantment for keeping me anxious about his findings.
“Dr Ben, it is glaucoma! She has glaucoma!” Now, I am even more confused. He saw my bewilderment and explained further, “She complained of blurring of vision when reading. She had no problem seeing distance clearly and no other symptoms. She is 45 years old and her symptoms are typical for normal people of her age. Since there are no specific symptoms attributable to chronic glaucoma in the early stages, patients with glaucoma often present with misleading irrelevant history.”
“How then did you come about the diagnosis of glaucoma?,” I probed further. “For a diagnosis of glaucoma, at least two of three things must be present. There must be evidence of damage to the nerve at the back of the eye. Secondly, there must be a higher than normal intraocular pressure for that eye. Thirdly, there must be functional evidence to explain the structural change observed within the optic nerve.”
I looked at him and I could see that he was passionate about the subject. But I wasn’t done with him yet. “Which of these three things you have mentioned are present in this lady?”, I asked. “I have two of three,” he replied. “No! You have only one,” I interjected.
“First, I can see evidence of structural damage to the optic nerve at the back of the eye. Yesterday morning, the intraocular pressure was 10 mmHg. This is the lower border of normal, but this afternoon it is 20 mmHg. That is clearly double! I am certain the test of function of the optic nerve we call visual field will show damage consistent with my findings to meet all three criteria.”
It is not always easy to make a diagnosis of glaucoma especially in the early stages. Quite often it behaves like a chameleon. Painstaking examination is required to make a diagnosis in the early stages. Fortunately there are newer and more accurate structural tests that can be done to ascertain presence of the disease before serious damage occurs.
and then