38

Common eye diseases and their treatment: sty dry eyes pterygium Ptosis retinal tear Glaucoma cataracts diabetic retinopathy macular degeneration thyroid

Embed Size (px)

Citation preview

eyes

Your eyes are your body's most highly developed sensory organs. In fact, a far larger part of your brain is dedicated to the functions of eyesight than to those of hearing, taste, touch or smell. We tend to take eyesight for granted, yet when vision problems develop, most of us will do everything in our power to restore our eyesight to normal.

eye: camera

The eye functions much like a camera. Light passes through the cornea and the lens of the eye and is focused on the retina in much the same way that an image is focused on the film of a camera.

                                                                     

parts The eye is protected by 3 layers: sclera, choroid, and the retina.

• The sclera is the white covering of the eye. It is continuous with the cornea in the front.

• The middle layer, the choroid, is a vascular layer lining the posterior (back) 3/5 of the eyeball. It is continuous with the ciliary body and the iris, which is the colored part of your eye.

• The intermost layer is the retina, which is light-sensitive and has rods and cones.

parts you can see…

The pupil is the small black opening in the iris. The iris controls the size of the pupil with 2 muscles: dilator muscle, which enlarges the pupil and the sphincter muscle, which makes the pupil smaller. The iris is the colored disk which is right behind the cornea. It's color comes from melanin. The more melanin there is and the closer it is to the surface, the darker the iris.

sagittal section of the eye

the lens is like a magnifying glass The lens is transparent and

helps to focus light rays onto the retina in the back of the eye. The macula is the bull's-eye center of the retina. Though the macula makes up only a small part of the retina, it is one hundred times more sensitive to detail than the peripheral retina and allows us to see tiny detail, to read fine print, recognize faces, thread a needle, read the time, see street signs, see grains of salt being poured from a shaker, etc.

Red Eyes

The "red eye" effect shown in this photograph is due to light reflection by the retina

muscles of the eye

There are two different types of muscles in your eye -- Intrinsic and Extrinsic! Intrinsic muscles in the eye are the iris and ciliary muscles. Extrinsic muscles are the six muscles that control eye movement and make it possible for the eye to follow a moving object.

functions of extrinsic muscles

• Lateral Rectus -- allows eye to move horizontally and laterally (sideways)

• Medial Rectus -- allows eye to move horizontally and medially (middle)

• Superior Rectus -- allows eye to elevate (up)• Inferior Rectus -- allows eye to depress (down)• Inferior Oblique -- allows eye to elevate and turn

laterally• Superior Oblique -- allows eye to depress and turn

laterally

eye movementThe muscles of the eye are all innervated by the III cranial nerve (oculomotor), except for the superior oblique, innervated by the IV cranial nerve (trochlear), and the lateral rectus, innervated by the VI cranial nerve (abducent).

protective structures of the eye

The exterior structures include: eyelids, eyelashes, eyebrows, and the

orbit.

The interior structures are the conjunctiva, lacrimal organs, and the Meibomian glands.

                                     

visual acuity test Normal vision is measured at 20/20. This

means that you can see clearly at 20 feet what should normally be seen at that distance. If you have 20/100 vision, that means that you must be as close as 20 feet to see what a person with normal vision can see at 100 feet. 20/20 vision is not perfect vision, it just indicates the visual acuity. There are many other things such as peripheral vision, eye coordination, depth perception, focusing ability and color vision that affect overall vision ability.

pupillary response

is another exam used to survey your visual system. A light beam will be directed at and away from your eye to observe if your pupils constrict and dilate as expected.

                            

normal focus of image on the retina

If your visual acuity is normal you are described asemmetropic

common forms of vision impairment

The most common forms of vision impairment are errors of refraction -- the way light rays are bent inside the eye so images can be transmitted to the brain. Nearsightedness, farsightedness and astigmatism are examples of refraction disorders. Retinal detachment, color blindness and night blindness are disorders of the functional eye and its processing units that lead to distorted or inaccurate vision.

myopia and hyperopia

• Nearsightedness and farsightedness have to do with the way the eye brings images into focus on the back of the eyeball, where 10 layers of light-sensitive nerve tissue make up the retina.

                                                                        

nearsightedness…

Nearsightedness, or myopia, which affects about 20% of the population, is the result of images being focused in front of the retina rather than on it, so distant objects appear blurred. A nearsighted person holds a book close to the eyes when reading and has to sit in the front of the classroom or movie theater to see clearly. The condition runs in families and affects men and women equally, usually appearing in childhood and stabilizing in the twenties.

farsightedness…

Farsightedness, or hyperopia, is the opposite of nearsightedness: The lens of the eye focuses images slightly behind the retina, making nearby objects appear blurry. Children often overcome mild farsightedness as they grow up and the eye muscles contract.

astigmatism… occurs when the eye

lacks a single point of focus. The condition is a result of an uneven curvature of the cornea or, in some cases, an abnormality in the lens. People with astigmatism have a random, inconsistent vision pattern, in which some objects appear clear and others blurry.

                                                                        

test for astigmatism…

An irregular curvature of the cornea and/or lens is determined using this type of illustration. When using the test card, a person would know if he has astigmatism becausesome radial lines would be blurred.

red-green colorblindness… is a disorder of the retina's

light-sensitive cone cells, which respond to colors. Most people with color blindness see colors normally in bright light but have difficulty distinguishing reds and greens in dim light. Color blindness occurs mostly in men, afflicting 8% of the male population. It is extremely rare for someone to be totally color-blind --able to see only shades of gray.

Pseudoisochromatic plates

                                                        

others

• Presbyopia is blurred vision at normal reading distance. It typically starts at about age 40 and is the reason many older people use glasses.

• Retinal detachment occurs when a part of one of the layers of the retina is pulled out of place, or when a hole or tear occurs. Although a detached retina is not painful, it is definitely a medical emergency. If the retina is not reattached to its source of nutrients promptly, the cells die and blindness can result.

more…

• Night blindness difficulty seeing in dim light -- occurs when the retina's rod cells, which distinguish light from dark, begin to deteriorate. The precise cause is unclear, but it may be linked to a liver disorder, a vitamin-A deficiency, or a disease of the retina, such as retinitis pigmentosa, an inherited disorder.

…continuing

• Eyestrain does not affect your vision, but it accompanies some vision disorders and may bring on a headache. It is often the result of eye muscles becoming strained from holding the same focus too long. If you wear prescriptive lenses, eyestrain may be an indication that you need new glasses or a different prescription. Eye exercises or resting the eyes every 30 minutes helps relieve eyestrain, especially if you work with computers.

There are other diseases of the eye that respond in varying degrees to medical treatment, such as cataracts, conjunctivitis, glaucoma, crossed eyes or wall eye (strabismus) and lazy eye (amblyopia), and macular degeneration.

Conjunctivitis

The conjunctiva -- the transparent membrane that lines your eyeball and your eyelid -- can become inflamed for various reasons. Most cases of conjunctivitis run a predictable course, and the inflammation usually clears up in a few days. Although conjunctivitis can be highly contagious, it is rarely serious and will not damage your vision if detected and treated promptly.

more on conjunctivitis

• Bacterial conjunctivitis, commonly known as pinkeye, usually infects both eyes and produces a heavy discharge of mucus. It is treated with antibiotics, usually as eye drops.

• Viral conjunctivitis is usually limited to one eye, causing copious tears and a light discharge. This infection will resolve without treatment.

• Allergic conjunctivitis produces tears, itching and redness in the eyes, and sometimes an itchy, runny nose. Allergy medicines in the form of pills or eye drops will relieve these symptoms.

• Ophthalmia neonatorum is an acute form of conjunctivitis in newborn babies. It must be treated immediately by a doctor to prevent permanent eye damage or blindness.

flashes and floaters The flashes of light are caused by

the tugging of the vitreous where it is attached to the retina. As it liquifies and pulls away from the retina, the vitreous becomes somewhat condensed and stringy and forms strands. The patient can see these strands and strings; they appear as spots, small circles, or irregular fine threads in the vision. They seem to float and are therefore called "floaters".

vision improvers

Not everyone is blessed with perfect eyes, but that does not matter because there are many ways to fix vision defects. Several of examples are glasses, contacts, or surgery. Optometrists and ophthalmologists don't know exactly why people have eye defects, but they do know that it usually has something to do with genetics, stress, and nutrition.

Presbyopia

visual correction with a convex lens for hyperopia

visual correction with a concave lens for myopia

                                                                                                                                          

                                                                                                                                         

 

references

WebMD Inc. webmd.lycos.com/content/ article/1680.53542 Indiana University School of Optometry www.opt.indiana.

edu/clinics/ educ/iexam/main.htm Northwest Kansas Eye Clinic www.nwkec.com/005rd020.htmBiological Bases, Sensation and Perception

peace.saumag.edu/.../Courses/ GPWeiten/Chapter4SandP.html