The human eye is similar to a camera!! Light enters through an opening, is focused through a lens, passes through a light-tight (dark) space, and forms a smaller, inverted, real image on a light-sensitive surface at the back.
Parts of the Human Eye Cornea (clear covering) Iris (coloured disc) Pupil Cornea Iris Lens Ciliary Muscle Vitreous Humour Fovea Retina Optic Nerve Sclera
Path of Light into the Eye Cornea Transparent, outer layer of eye. Refracts light towards pupil. Pupil Black hole in the iris. Allows light to pass through to the lens. Iris Circular band of muscle and pigment. Controls the size of the centre hole (contracts or dilates the pupil).
Focusing the Light -Lens Transparent, flexible, crystalline convex lens behind pupil. Refracts and focuses (converges) light. -Ciliary Muscle Controls shape of lens to allow lens to focus.
Support Structure of Eye Sclera – White, dense outer layer of eye ball. For eye muscle attachment, holding eye shape, and to keep inside of eye dark. Vitreous humour – Transparent fluid gel that holds the shape of eye; allows light to pass from lens to retina.
7 Image Formation in the Eye Retina – Inner lining of light-sensitive cells that covers back of eye; surrounded by network of nerves. – Detects light (of the real image), and transmits this as a signal to the optic nerve. – Photoreceptive cells in the retina are referred to either as “rods” or “cones”. – Rod cells are more sensitive to light (therefore details). – Cone cells detect either red, green, or blue wavelengths of light. (therefore colour vision).
About 10% of males have a colour perception defect, but this is rare in females.
9 Fovea – Area of retina which contains the highest concentration of photoreceptive cells. Optic Nerve – Bundle of all the nerves from the retina, located at the back of the eye ball. Transmits all the optic signals to the brain for image processing. Image Formation in the Eye
Accommodation The distance between the lens and the image (d i ) is constant in the eye. However, the eye can focus on objects far away or very close to the eye. How is this possible?
Accommodation Accommodation: the ability of the eye to change the focus between objects at different distances by altering the curvature of the lens. What changes the shape of the lens in our eyes?
12 Accommodation When the ciliary muscles contract, the lens is stretched so that less refraction takes place. This allows us to see objects that are far. When the ciliary muscles relax, the lens thickens so that more refraction takes place. This allows us to see objects that are near. Note: This is UNLIKE a camera, where the lens is moved forward or backward to focus.
13 Accommodation Not Perfect Either by heredity or age, accommodation of the human eye can be flawed. In general, people can either suffer from Myopia (near-sightedness) or Hyperopia (far-sightedness). People can also suffer from Astigmatism or develop Presbyopia.
Astigmatism Cornea is oval shaped instead of spherical. This causes light to focus on two or more spots.
Fixing Eye Problems 1. Glasses 2. Contacts 3. Surgery
1. Glasses for Near-Sighted (Myopia) People Use a Concave Lens
1. Glasses for Far-Sighted (Hypermetropia) People Use a Convex Lens
2. How a contact lens works Contact lens works just like a pair of glasses, it bends light in a specific direction in order to have a correct light projected on the retina.Contact lens works just like a pair of glasses, it bends light in a specific direction in order to have a correct light projected on the retina.
Disease caused by wearing the contact lenses improperly
Corneal Ulcer - Bacterial infections cause corneal ulcers and are common in people who wear contact lensesCorneal Ulcer - Bacterial infections cause corneal ulcers and are common in people who wear contact lenses It is a very serious disease and it only can be cured by the cornea transplantat ion.
Giant Papillary Conjunctivitis -It is caused by the uncleanness of the lenses.
7. Conjunctivitis -It is caused by the invasion of the bacteria, it will caused the inflammation of the cornea and it is an infectious disease.7. Conjunctivitis -It is caused by the invasion of the bacteria, it will caused the inflammation of the cornea and it is an infectious disease.
2. What is LASIK? Procedure uses computer controlled laser to reshape cornea Surgical procedure to correct –Myopia –Hyperopia –Astigmatism LASIK is acronym for laser assisted in situ keratomileusis
Slits are cut in the eye to correct myopia (decreasing curvature) or astigmatism.
Video on Laser Eye Surgery http://www.mayoclinic.org/procedure/lasik- eye-surgery/multimedia/lasik-eye- surgery/vid-20084660http://www.mayoclinic.org/procedure/lasik- eye-surgery/multimedia/lasik-eye- surgery/vid-20084660