The Senses Sight and Hearing

Vision – Anatomy of the eye

Vision – evolution of sight

Vision – A natural Reflex Accommodation reflex: –The lens can modify its shape based on the distance you are trying to focus with –For close elements short and fat the lens curves and thickens –For far elements long and thin the lens moves so light lands properly on the retina

Vision – Far away

Vision – close up

Passageway from front to back –Cornea – aqueous humour – pupil – lens – vitreous humour – retina – choroid – sclera - opaque Transparent medium –Aqueous humour –Vitreous humour –Cornea –Lens

Vision – How do we see? Light: –is the reason we see. Light has lower density than the cornea. So as it enters the cornea the light wave refracts as it goes though it continues to refract because the lens and humours. When the image hits the retina it is turned upside down. The brain gets the message from the optic nerve upside down but turns it right side up. –We only see when the message gets to the brain. Our eyes are a tool for the brain. When you are looking t something unknown you stare at it longer because the brain is trying to analyse what you are seeing.

Vision – Snellen Chart 20/20 what you should see is located at the bottom what you do see is at the top. Go forward by 1 foot until line number seven becomes clear (13/20) Some people have above normal vision (25/20)

Vision – Eye Problems Astigmatism: –lens and cornea are not symmetrical and light does not land on the right area of the retina Glaucoma: –Increase of level of aqueous –This build up should be expelled by the eye ducts but dusts gets blocked so there is a blockage –Worst case: The eye duct do not drain so the pressure increases. If left untreated the pressure becomes so high that the eye explodes Rods and comes don’t get O2 and die = blind Cataract: –the lens becomes opaque so light does not go through anymore

Vision – Other common ailments Near sightedness (myopia): –A person can see things from close clarly but not from far. 2 reasons why people are myopic a) congenital malformation (you are born with it, it didn’t form properly as a fetus) problem: The eye is too long so the image does not reach the retina properly so the images are blurry Accomodation reflex does not work properly. The muscles of the lens are weak and the leans stays in the short and fat position. So you see clearly from close but not from far. It can get better if you always wer your glasses –Solution: Concave lense. They work because they give the extr layers light needs to reach the retina

Farsightedness: – person can see from far and not from close : Prebyopic –2 reasons a) congenital malformation: Eye is too short. Born with this problem. The light ays fall behind the retina so you see bleurry Lens always stays in the long and thin position. Often happes as a person gets older. When looking at something close it is bleurry but from far is is clear –Solution: convex lenses. The shape of the lens that is missing. Image begins to be refracted earlier so image lands on retina.

Vision – Care of the eye read at cm away Look away to curve the lens to focus at different positions Vitamin A promotes good vision (vegtables, meat) Daily eye care