Friday, August 12, 2005

The anatomy of an eye

Yesterday, I had 2 lessons- Optimisation and HR Management. There was a short break between the classes, so I replied a few emails, and explored the biomedical library for interesting books. I found “Prime Mover- a natural history of muscle” by Steven Vogel. The first chapter looks promising enough.

I then went into my lecture theatre, only to see a guest lecturer introducing himself. He then started to discuss the anatomy of the human eye. Shit… this does not look like Human Resources Management. Ruffling through my feathers papers, I found my timetable and realised I was an hour early. So I sat and listened about the human eye.

No wonder the eye is used as an argument for proof of a supreme being’s existence!

Stepping back from theology, here are some key points (minus the correct jargon) that I remember (not with 100% accuracy):

Tears consist of 3 secretions- an oily component, mucus, and the watery bit. Eyelids do not slam shut straight downwards. Instead, the edges furthest from the nose shuts first, and the upper lid sort of comes down like a guillotine. As such, a wiping action is developed upon blinking, pushing the tear film towards the middle of the face. At the ‘inner’ tip of the eye is a little hole which drains the tears into the nasal cavity. Ladies (and some gentlemen) who use eye-liner are advised not to colour that little hole.

The optical nerve carrying visual information out of each eye consists of two channels, one for the left half of the field of vision. Optical nerves from both eyes meet somewhere before arriving at the two half-brains, and they cross over. As such, the right brain received signals from both eyes, but only information about the left half from each eye. Similarly, the left brain receives signals from both eyes, but only information from the right half of each eye.

If you cut a nerve between the eye and the crossing point, the entire eye becomes blind since the information cannot be sent out.

If you cut the crossing point, to sever the crossing nerves, you would blind the patient’s victim’s periphery vision. The right eye can only see left, and the left eye can only see right.

If you cut a nerve after the crossing, the patient cannot see to one side. For example, cutting the nerves leading into the right half brain would cause the victim to be blind to objects on the left side.

I’ll be there next week.

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