Done by: natalie bahsous and Charlie khalil Sense of sight Done by: natalie bahsous and Charlie khalil

introduction The eye is a sphere filled with two fluids The skeletal muscles that move the eye are called the rectus muscles and the oblique muscles. Only 1/6th of the eye’s anterior surface can normally be seen. Protection for the eye The rest of the eye is enclosed in a bony orbit. A cushion of fat surrounds most of the eye. It has two basic structures Eyeball Accessory structures

pupil Pupil is a central opening of the iris Regulates the amount of light entering the eye during: Close vision and bright light – pupils constrict Distant vision and dim light – pupils dilate Changes in emotional state – pupils dilate when the subject matter is appealing or requires problem-solving skills

lens Biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary body Light passing through a convex lens is bent so that the rays converge to a focal point When a convex lens forms an image, the image is upside down and reversed right to left

retina Extends anteriorly only to the ciliary body. Contains receptor cells (photoreceptors) Rods Cones Signals leave the retina toward the brain through the optic nerve. No photoreceptor cells are at the optic disk, or blind spot

rods Hundreds of times more sensitive to light than cones Provide vision in poor light. Produce colorless (black and white) vision. Nerve fibers converge so impulses produce more general outlines.

cones Provide vision in good light. Produce colored and sharp vision Nerve fibers do not converge as much so impulses produce more detailed images.

There are three types of cones Different cones are sensitive to different wavelengths Color blindness is the result of lack of one cone type

Cones contain iodopsins A group of pigments sensitive to light waves of different frequencies.

Physiology of EYE Light waves from an object enter the eye first through the cornea, The light then proceed to the pupil Fluctuations in incoming light change the size of the pupil.  When the light entering the eye is bright enough, the pupil will constrict due to the pupillary light response.

Vision interpretation The light continues through the vitreous humor then, ideally, back to a clear focus on the retina, behind the vitreous.  The small central area of the retina is the macula, which provides the best vision of any location in the retina. Within the layers of the retina, light impulses are changed into electrical signals.  Then they are sent through the optic nerve, along the visual pathway, to the occipital cortex .  Here, the electrical signals are interpreted or “seen” by the brain as a visual image.

How we can test our sense of vision ?

Test of visual acuity It is a measure of the smallest retinal images which can be appreciated By using a Snellen’s chart we can recode the visual acuity for distance and for near

A visual acuity test is a measure of how well you see or the sharpness and clarity of your vision. Your eye doctor will ask you to read letters on a chart while standing 20 feet away. The smallest letters you are able to read will be recorded as your acuity. Your visual acuity may be written as 20/20 or (6/6) if your vision is normal. If your vision is reduced, it might be recorded as less than 20/20, such as 20/100.

Test of Color Vision Red and Green color vision can be assessed using Ishihara test plate. These colored spots forming numbers which the patient reads out

Pupillary Examination Examine the pupil for the shape and symmetry Ask the pt to fix the eye on a distant point straight ahead Bring a bright torchlight from the side to shine on the pupil Look for constriction of that pupil ( direct light reflex) and for the constriction of the opposite pupil ( consensual light reflex )