- Schirmer’s test is an ocular exam used to determine the amount of moisture or tear production in the eye. The test is often conducted as a part of a routine eye examination or in response to patient complaint of a dry eye. The Shirmer’s test is painless and involves the placement of one folded end of a thin strip of filter paper into the lower eyelid. The uninserted end of the strip projects forward, out of the eye. The strip is left in place for one to five minutes during which time the tears of the eye wet the strip. A measurement is taken of the amount of moisture accumulated in the strip. Normal readings may be twelve millimeters or more, and dry readings may be from one to five millimeters.
Sclera is the tough, outer, leathery, protective layer of the eye. It is seen as the white portion of the eye surrounding the colored iris but it lines the entire globe of the eye. The sclera joins the transparent cornea at the front of the eye and circles around to join the optic nerve at the back of the eye. The sclera lies on top of the choroid, the vascular layer that supplies blood to the eye. The sclera may appear red as a result of an infection or disorder of the conjunctiva, the mucous membrane that lines the sclera and the inside of the eyelids. The sclera is also subject to scleritis, an inflammation of the sclera. Scleritis is closely linked to rheumatoid arthritis, gout, menstrual disorders, and collagen disease. It is particulary found among young women. Symptoms include redness, pain, and erosion of the sclera. The condition is treated with systemic anti-inflammatory agents but seldom with steroids, which destroy collagen and exacerbate scleral thinning. Scleral thinning may expose the underlying uveal pigment and, if left untreated, may lead to necrosis (death of tissue) or perforation of the globe. Although bloodshot eyes may not look nice, in some respects they are good to have at times. Because the blood vessels are enlarged, more blood can circulate through them, carrying away toxic substances and bringing additional oxygen and white blood cells to fight off infection. When the sclera turns yellowish, this usually indicates a liver disease. The yellowish tint to the eyes, and possibly the skin, is produced by an excess production of a red-yellow pigment called bilirubin. When the liver is working properly, it safely removes this pigment; but when it is not working efficiently, the pigment backs up and collects. Jaundice can result from a number of different causes, including all types of hepatitis, cirrhosis of the liver, a bile duct blockage, and certain types of anemia. Some medications can also trigger it. The only way to cure this yellowing of the eyes and skin is to treat the disease causing it. A pinguecula is a small, yellowish, raised mark on the sclera. It is usually associated with age and is a harmless condition. A pterygium is a patch of raised vascular tissue on the sclera. If the pterygium grows into the cornea, it may block vision. In 1775, Israel Putnam warned his comrades not to fire until they saw the “whites of their eyes”, advice that has been preserved in many stories ever since. However, there is little doubt that this phrase would have lasted had he used the medically correct term of not firing until they saw the “whites of their sclera”.
Scotoma is a blind spot or area of blocked vision in the visual field. Each eye contains one scotoma. This is the blind spot caused by the optic disc. The optic disc is part of the retina where the optic nerve meets the eye. It is here that the blood supply enters the eye. The optic disc contains no photosensitve rods and cones and is therefore unable to “see”. Scotomas may also be caused by an eye injury, disease or disorder, or by migraine headaches. Scotomas may be present in either the central or peripheral field of vision. Macular diseases attack the macula, the point of clearest vision in the central field. A scotoma, or blind spot, develops that permanently blocks central vision; but that usually leaves peripheral vision intact. Scotomas caused by retinitis pigmentosa and glaucoma block vision in the peripheral or side visual field. These diseases continue to destroy peripheral vision until tunnel vision results. Scotomas caused by migraines are temporary. They occur during the preheadache or prodrome stage and may forewarn of the subsequent headache. Migraine scotomas may appear in any part of the visual field and may move during the course of the prodrome or headache stages. These scotomas may simply block out vision or may be scintillating and shimmer or blink with bright or colored lights. Migraine scotomas usually last from five minutes to an hour and tend to retreat with the onset of the migraine headache.
Sickle-cell retinopathy is a common, serious result of sickle-cell disease. As vessels within the peripheral sections of retina become blocked, the retina becomes starved for oxygen and develops new vessels that tend to be weak and hemorrhage. This neovascularization may cause leakage into the vitreous or retinal detachment, resulting in a loss of vision. Photocoagulation therapy (laser treatments) is performed after neovascularization has begun. This may stop the hemorrhaging but can cause complications such as vitreal neovascularization. Cryotherapy (freezing treatments) may be performed on the smaller areas of neovascularization. Sclera buckling may be used to reduce the traction that causes retinal detachment. This normally simple procedure is difficult in cases of sickle-cell disease because there may be overlying bleeding that interferes with localization of the hemorrhage source, and the procedure may trigger necrosis (localized tissue death), in anterior areas.
Slit-lamp examination allows the doctor to see, under magnification, the structures at the front of the eye. The microscope-type instrument, called a slit-lamp, uses an intense line of light (a slit) to provide oblique illumination of the cornea, iris, and lens of the anterior chamber. It also allows the doctor to view these structures in a cross section so he can detect any abnormalities. When examining corneal problems, the doctor may use fluorescein dye which spreads across the eyes and appears as a bright yellow when hit with a blue light (screened through a blue filter). This causes tiny cuts, scrapes, tears, foreign material, or infections on the cornea to stand out.
Snellen chart is the eye chart routinely used in eye examinations to determine central vision acuity. It has lines of increasingly smaller letters. Developed in 1864 by the Dutch ophthalmologist, Herman Snellen, each line of the chart corresponds to a different level of vision – 400, 200, 100, 70, 40, and 20. The vision of each eye is expressed as a fraction. The top number represents the testing distance from the chart, commonly 20 feet and the bottom number represents the smallest line the patient can see. If an individual can read all nine lines, the vision is measured as 20/15, or is able to read at 20 feet what a normally sighted person can read at 15 feet. If the person can read only the top line, or the big “E”, that vision is measured as 20/200, meaning that person is able to read at 20 feet what a normally-sighted person can read at 200 feet. This is classified as legally blind. The Snellen chart has been criticized for inaccuracy since each line on the chart must cover a wide range of visual acuity. Those with borderline vision may fall between two lines of ability and be incorrectly classified. Each line corresponds to a degree of visual acuity:
- Line one corresponds to 20/200 vision
- Line two, 20/100
- Line three, 20/70
- Line four, 20/50
- Line five, 20/40
- Line six, 20/30
- Line seven, 20/25
- Line eight, 20/20
- Line nine, 20/15
Snow blindness refers to an eye injury caused by intense light reflected off snow. The bright light in prolonged exposure situations produces an ultraviolet burn on the cornea of the eye. Symptoms appear in both eyes and include extreme pain, a feeling of sand in the eyes, and severe sensitivity to light. The symptoms are usually delayed two to nine hours after exposure but heals itself within two to three days. Antibiotic or steroid drops may be prescribed to ease discomfort and discourage infection. Snow blindness can be prevented by wearing protective glasses or goggles. Although the rays that cause snow blindness are the same as those that cause sunburn at the beach, sunbathers rarely get snow blindness because most of the rays at the beach are coming from above and the eyes are afforded some protection by the eyelids, eyelashes, and eyebrows. In cases of snow blindness, the rays are reflected from the snow and enter the eye from below, a relatively unprotected position.
Sorsby’s fundus dystrophy (SFD) is a rare genetic disorder that causes macular degeneration to occur at an early age, usually between the ages of 30 and 40. Researchers are interested in SFD because of its clinical similarity to age-related macular degeneration. Symptoms include retinal edema, hemorrhages, and exudates in the macular area. As the disease progresses, considerable scarring may occur. Symptoms usually occur first in one eye, with the other eye developing symptoms months or even years later. As with age-related macular degeneration, central vision is affected first. The disorder was first addressed in 1949 in a study of five British families who were were afflicted with the disease. It has also been identified in patients in Europe, North America, South Africa, Australia, and Japan.
Stargardt’s disease, or juvenile macular degeneration is an inherited disease that causes young people to lose central vision, usually in the first or second decade of life. Doctors estimate that as many as 25,000 people in the US have the disease, which typically starts between the ages of 6 and 15. Some children lose most of their central vision quickly, while others experience a slow and gradual loss of sight. Researchers in May 1998 identified a gene that is the source of the disease. This gene causes cells to produce a protein that functions only in the retinas of the eyes. Discovery of this gene is significant for several reasons. It will allow doctors to develop specific tests for the disease, which is frequently confused with other vision problems, and it may move researchers closer to finding the cause of age-related macular degeneration.
Sty (See Hordeolum.)
Subluxation of the lens occurs when the crystalline lens becomes partially displaced as the result of a break in the fibers of the zonules that hold it in place. The condition may be congenital or acquired. It may be caused by a blow to the eye or other injury, Marfan’s syndrome, ageing, or homocystinuria (a metabolic congenital disorder associated with mental retardation). Symptoms include rapid changes in vision and increased myopia (nearsightedness) because of the increased mobility of the lens. On examination, the iris may appear wobbly or tremulous, and the lens may be visible in the pupil. The lens may subluxate (partially dislocate) up an out, as in Marfan’s syndrome, down and in, as in homocystinuria, backwards into the vitreous, a condition called posterior subluxation, or forward into the anterior chamber, a condition called anterior subluxation. Subluxated lenses may develop cataracts or may become trapped in the pupil. Aqueous fluid production forces the trapped lens into the anterior chamber, where it may cause a rise in intraocular pressure, or secondary glaucoma. When the lens has drifted to the anterior chamber, the pupils are dilated and the patient is set into a supine position to encourage the lens to fall back into place behind the iris. If the lens falls into place, the pupils are immediately constricted with miotic drops, although recurrences are common. If the lens fails to move into position, it is surgically removed, or a peripheral iridectomy is performed to allow aqueous flow. When the lens moves into the posterior chamber, it may be left untouched if it does not cause uveitis or cataract. In such cases, the lens may be removed. If the lens moves from the central pupil area, becomes completely dislocated or detached, or is removed, the eye becomes aphakic, or without a lens. Such aphakic characteristics as lack of accommodation, enlarged image, and color distortion can be corrected with prescription contact lenses or spectacles.
Sympathetic ophthalmia is a rare condition in which one eye becomes inflamed as a result of an injury or trauma to the other eye. The condition is most common among children and occurs following a perforation injury or surgery. It can also occur if a foreign body remains in the eye, causing great irritation. Sympathetic ophthalmia can also occur when the injured eye remains inflamed and infected due to insufficient or delayed cleansing. Over a period of two weeks to several months, an inflammatory response occurs in the uvea. Examination of the choroid reveals the presence of eosinophils, giant cells and lymphocytes, which are serious signals that threaten the sight in the eye. After a period of two weeks to several years, the inflammation spreads to the unaffected eye. Symptoms of blurred vision or photophobia develop. An eye examination with the slit lamp reveals the presence of granulomatous keratic precipitates on the posterior surface of the cornea, a condition that endangers vision. It can be prevented by earnest attention to cleansing and care of an affected eye or by enucleating (surgically removing) the initially injured eye within a two-week period following the injury. If sympathetic ophthalmia occurs after the two-week time period, the condition may be treated with local and systemic steroids. However, the treatment is often successful for a time, but the condition is inclined to recur. Any severely injured eye that remains inflamed or infected up to a two-week period may need to be removed in order to prevent further problems for the remaining eye.
Synechiae is a condition in which the iris adheres to either the cornea or the lens. The iris/cornea adhesion is termed anterior synechiae and the iris/lens adhesion is termed posterior synechiae. Either type may be caused by anterior uveitis, an inflammation of the iris and/or ciliary body. Anterior synechiae may be caused by perforation of the cornea or injuries. Posterior synechiae may cause a blockage of aqueous flow and an iris bombe, in which the iris bows forward unnaturally. This interferes with the flow of aqueous fluid and causes secondary glaucoma, a disease in which the accumulation of aqueous fluid causes a rise in intraocular pressure. Symptoms of synechiae include redness, pain, oversensitivity to light, pus in the anterior chamber on examination, constricted pupils, and the inability of the pupil to dilate. Synechiae is treated according to the cause.