Med Term Ch 17: the eyes

xanthelasma

A raised yellowish plaque on the eyelid, caused by a lipid disorder, is called xanthelasma.

astigmatism

Astigmatism is an abnormal condition in which light rays cannot come to a single point of focus on the retina because of irregular curvature of the cornea or lens. The condition usually can be treated with glasses or contact lenses that correct the refractive error.

strabismus

Before turning our attention to diagnostic and treatment options for Sara, let's discuss a few more eye disorders, beginning with disorders of movement. One movement disorder prevalent in children is called "lazy eye," or *strabismus*. Strabismus involves the inability of the eyes to focus simultaneously on the same object. Different forms of strabismus include *esotropia*, characterized by an inward (eso-) deviation or turning (-tropia) of one eye; *exotropia*, in which one eye turns outward (exo-); and hypertropia, wherein one eye deviates upward; in this context, the prefix hyper- means above. Other visual conditions attributable to muscle weakness include *diplopia*, double (dipl/o) vision (-opia), and *amblyopia*, a partial loss of vision (ambly/o means dull or dim).

cones

Cone cells, of which there are about 6.5 million, produce vision in bright light and help us to see color. There are three types of cone cells in the retina, each sensitive to one of the three primary colors: red, blue, and green.

refractive correction

Corrective lenses, either in the form of glasses or contact lenses, are the most common ways to treat refractive errors. Surgical methods for refractive correction include *photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK)*, in which an excimer laser is used to reshape the cornea and thus correct the refractory error.

blepharitis

Disorders of the eye have a variety of causes and a range of specific effects. Infection and inflammation commonly affect the structures of the eye, disrupting their sight-producing or protective functions. Impairment of the ocular muscles can interfere with the synchronous movement of the eyes. Trauma, systemic illness, certain medications, and the process of aging can cause damage or deterioration to the eye and threaten the loss of vision. Let's start with inflammation. A simple inflammation of the eyelid is called blepharitis. However, inflammation of the eyelid (blephar/o) can become far more complicated than that.

xerophthalmia

Dry eye, or xerophthalmia, is a lack of adequate tear production and eye lubrication: -ia = condition; xer/o = dry; -ophthalm/o = eye

ocular examinations

Elevated intraocular pressure results in damage to the optic nerve and to the retina. The condition causes the optic disk to become wider, deeper, and paler. *Ophthalmoscopy*, which allows visualization of changes to the optic disk, is one of several procedures used to diagnose glaucoma and is the primary procedure that has led Dr. Green to suspect glaucoma in Sara.

general sense organs

In Module 10 we learned about afferent sensory neurons that respond to stimuli in our external environment. Some of these sensory receptors, known as general sense organs, are widely distributed throughout the body. They enable us to detect pain, pressure, and changes in temperature. The special senses—smell, vision, hearing, taste—are characterized by closely grouped receptors that are located in complex organs. In this module, we'll look at two of those special sensory organs: the eye and the ear. Various kinds of specialties focus on the ears and eyes, and physicians may specialize in the following: Eyes, ears, nose, and throat (EENT) Ears, nose, and throat (ENT) Head, eyes, ears, nose, and throat (HEENT)

optic disk

Landmarks of the retina include the optic disk (also spelled optic disc), from which the optic nerve arises, and the macula lutea, an oval spot at the center of the retina. Cone cells are concentrated in the fovea centralis, a small depression in the middle of the macula that is the area of clearest vision. The optic disk, also called the blind spot, is the only area of the retina that is not sensitive to light.

Treatment of Diabetic Retinopathy

Methods of treating diabetic retinopathy include *laser photocoagulation and vitrectomy*. Laser photocoagulation uses a precisely focused laser to seal leaky blood vessels and to prevent the growth of new ones. With vitrectomy, a saline solution replaces the vitreous humor in which blood and scar tissue have accumulated. In cases of diabetic macular edema, treatments involve the use of corticosteroids and other agents injected into the vitreous jelly to promote regression of abnormal blood vessels and to reduce fluid leakage and the formation (-ation) of new (neo-) blood vessels (vascul/o), called *neovascularization*.

enucleation

Neoplastic disease may affect any of the structures of the eye. Although many malignancies can be managed with radiation and chemotherapy, enucleation—removal of the entire eyeball—sometimes becomes necessary. Surgical excision of the eye may also be warranted in some instances of glaucoma, infection, or trauma. Following surgery, a permanent *ocular prosthesis* can be inserted.

glaucoma

Normally there is a balance between the production of aqueous humor and its outflow through the eye's filtration structures at the junction of the iris and cornea. In glaucoma, outflow of the aqueous humor is blocked, causing an increase in *intraocular pressure (IOP)*. Glaucoma may occur as a primary disorder (e.g., as *primary open-angle glaucoma or POAG*) or it may develop secondary to systemic illness or trauma. Blockage of the outflow channels for aqueous humor may happen suddenly, causing acute glaucoma, or may progress at so slow a pace that the loss of vision is not recognized until it becomes extensive. Acute glaucoma is a medical emergency; it is accompanied by extreme ocular pain, blurred vision, a red discoloration of the eye, dilation of the pupil, and, possibly, nausea and vomiting.

myopia

Refractive error is the most common visual problem, and myopia, or nearsightedness, is the most frequently occurring type of refractive error. Causes of myopia include elongation of the eyeball and excessive deflection of light by the refracting media such that the rays are focused in front of the retina. This condition interferes with visual acuity, producing a blurred or fuzzy image. Snellen chart for vision test

Snellen chart/visual acuity test

Refractive errors are detected by measuring the ability of the eyes to distinguish small details at a given distance. In a visual acuity test, the Snellen chart, which contains letters of decreasing size, is often used to measure visual sharpness. The person being tested sits or stands 20 feet from the chart and tries to read the smallest line of letters possible, using first one eye, then the other. That performance is compared with what an individual with normal vision would see. Visual acuity is recorded as a fraction. The numerator, 20, is the distance from the chart; the denominator is the distance from which the person being tested can read the letters. The larger the denominator, the poorer a person's vision. The standard used for normal vision is 20/20.

retinal damage disorders

Several visual disorders are characterized by damage to the retina. Four of these, which we'll consider now, are diabetic retinopathy, macular degeneration, retinal detachment, and glaucoma.

changes in eye shape

Sometimes a change in elasticity or shape of the eyelid can occur. For example, a drooping of the eyelid (as seen in the illustration), called *blepharoptosis*, is caused by neuromuscular difficulties—either congenital or acquired by trauma. *Ectropion* is an outward (ec- = out or outside) sagging, or eversion, of the eyelid (-tropia means to turn), which can lead to improper lacrimation and corneal drying and ulceration. Its opposite, *entropion*, is an inversion (en- = in or within) of the eyelid in which the eyelashes actually rub against the eye, leading to possible corneal *abrasion*.

iris and pupil

The iris and pupil also play important roles in making sight possible. When the muscles of the iris contract, the pupil constricts, eliminating light rays that cannot be sufficiently refracted to focus on the retina. This simple process not only promotes sight, but also protects the retina in that, when the iris contracts in specific response to very bright light, the pupil's constriction naturally protects the retina.

the retina

The retina is the innermost covering of the eye. It is a thin, delicate membrane that is continuous with the optic nerve, through which light impulses are transmitted to the brain. The retina itself is a multilayered structure, the outermost layer of which contains light-sensitive cells called *rods and cones*. A cone is a photoreceptor cell in the retina that transforms light energy into a nerve impulse. Cones are responsible for color and central vision. A rod is a photoreceptor cell of the retina essential for vision in dim light and for peripheral vision.

visual field test

The visual field test measures the area within which objects are seen when the head and eyes are fixed and the eyes look only straight ahead—in other words, this test measures peripheral vision. What happens is this: Sara sits down in a darkened room before a machine that looks like a big white sphere inside. A patch is put over one eye at a time, and she is asked to stare at a spot on the back of the rounded screen. She is given a cord with a button to push every time she sees a tiny white flash of light in her peripheral vision. A machine records her score, mapping out a graph of where her peripheral vision is no longer functioning. This helps to pinpoint the site of any damage.

sclera

Three fibrous layers cover the eyeball itself and are among the internal structures of the eye. The sclera is the tough (scler/o means hard) outer membrane that helps to maintain the size and shape of the eyeball and attaches to the muscles that move the eye. The sclera is what we recognize as the white of the eye. The anterior portion of the sclera is the cornea (corne/o, kerat/o)—a convex, transparent structure through which light passes to other parts of the eye. Recall that the combining form kerat/o also means hard, horny in the context of the integumentary system and the skin. In the context of this module, kerat/o means cornea.

ophthalmologist

a specialist (-ist) in the study (log/o) and treatment of disorders of the eye (ophthalm/o).

the eye

(ocul/o, ophthalm/o, optic/o, opt/o) is one of a pair of special sense organs that converts the energy of light into electrical nerve impulses and transmits those signals to the brain where they're interpreted as sight. It is through the eye that we gain most of our information about our external environment. The structures of the eye don't merely receive a light stimulus; they adjust the incoming light and adapt to it to form the clearest image vision (optic/o, opt/o)

cataract

A cataract is a progressive, abnormal condition of the lens characterized by a loss of transparency. Most cataracts are produced by degenerative changes that accompany the aging process; however, cataracts may be congenital or may be caused by trauma, certain medications, infection, or other diseases. The condition leads to a gradual blurring of vision as the lens clouds over and results in eventual loss of sight.

treatments for glaucoma

Conservative treatment for glaucoma—the one Dr. Green recommends and Sara chooses—involves the use of eye drops (*miotics*) to improve drainage of aqueous humor and to decrease its production. If conservative treatment fails, surgery may be used to modify the outflow channels or to create a new opening for the escape of aqueous humor from the anterior cavity. This filtering procedure is called *trabeculectomy*. If miotics fail, one of the most effective treatments for narrow-angle glaucoma is laser therapy, which works by creating a hole in the iris (iridotomy) to improve aqueous humor outflow. In chronic glaucoma, laser therapy (trabeculoplasty) causes scarring in the drainage angle, which improves outflow to reduce intraocular pressure. Congenital glaucoma can cause scarring and the formation of opacities on the cornea, requiring replacement of that structure by a procedure known as keratoplasty.

rods

The rods and cones of the retina contain chemicals that undergo change in the presence of light. These chemical changes produce nerve impulses, which are transmitted to the brain and interpreted as a visual image. Rods are cylindrical cells that enable the detection of low-intensity light. Most of the 120 million rods in the eye are located around the periphery of the retina.

hemianopsia

is caused by brain damage (often from stroke) in which damage to nerve cells in one cerebral cortex (right or left) will cause loss of vision in the opposite visual field (VF); hemi = half; an- = without; and -opsia = vision condition.

chronic glaucoma

that fourth type of retinal disorder—chronic glaucoma. Chronic glaucoma may produce no symptoms initially. Eventually, headaches, blurred vision, and eye pain may be present, in addition to the loss of peripheral vision. Glaucoma draws its name from the dull gray color (glauc/o) of the eye in advanced cases; the suffix -oma means mass or collection of fluid.

sty

the "bump" is called a hordeolum, or sty, and is caused by a bacterial infection of the sebaceous glands of the eyelid. The affected area of the lid becomes red, swollen, and tender. Dr. Green gives Sara antibiotic drops (also available as an ointment) to treat the infection.

conjunctiva

a healthy pink color and adequate moisture along the conjunctiva—a mucous membrane (conjunctiv/o) lining the inner surface of the eyelids and the anterior part of the eye. Dr. Green also checks the lacrimal glands, which produce the tears (lacrim/o, dacry/o) that moisten the eye and the eye muscles.

presbyopia

As we age, the structures of the eye undergo a loss of elasticity. That loss reduces the ability of the lens to accommodate variations in distance. As a result, an age-associated hyperopia, called presbyopia, develops (presby/o means old age). Using corrective lenses for near vision compensates for this

conjunctivitis

However, one of the most common of the inflammatory conditions is conjunctivitis, or inflammation of the conjunctiva (conjunctiv/o)

retinal detachment

The third retinal disorder we'll look at, retinal detachment, is a separation in the layers of the retina. As the separation becomes complete, fluid accumulates between the layers and blindness can result. Detachment of the retina may occur suddenly, as in the case of trauma, or slowly, such as when the vitreous shrinks during aging and pulls on the retina, producing retinal tears. Signs of retinal detachment are floaters in the visual field—clumps of vitreous humor that look like black spots in the field of vision; patients may also see bright flashes of light (phot/o), a condition called photopsia (-opsia means vision condition)

tonometer

The tonometer is used to measure intraocular pressure. The gonioscope assesses the angle of the anterior chamber.

nystagmus

a condition characterized by repetitive, rhythmic eye movements of one or both eyes—is usually caused by brain tumors or diseases of the inner ear.

chalazion

A chalazion is another abnormal condition involving the eyelid. It is a small localized swelling, or granuloma, caused by chronic inflammation of the lid's sebaceous glands (also called meibomian glands), which are located along the margin of the eyelid. A chalazion may develop from a hordeolum or may occur as a primary inflammatory response. While its initial treatment is similar to that for a sty, surgical correction—incision and drainage—is frequently necessary.

Age-Related Macular Degeneration (AMD)

A second retinal disorder is also one for which Sara seems a natural candidate—that of age-related macular degeneration (AMD). AMD is the leading cause of blindness in the elderly. It is the progressive deterioration of the macula of the retina and the choroid layer of the eye. Two types of macular degeneration occur. The "wet" type is characterized by the formation of new and fragile vessels that leak blood; the "dry" type involves atrophy and deterioration of retinal cells, along with deposits of clumps of extracellular debris, or *drusen*. Macular degeneration can result in severe loss of central vision, as the illustration demonstrates. There is no cure for macular degeneration. Treatment includes vitamin and mineral therapy and smoking cessation as ways to try to slow the disease.

surgical treatment for cataract

Cataracts are now commonly treated with surgical removal of the lens. The lens may be extracted by *aspiration*—insertion of a hollow needle to withdraw the lens tissue—followed by irrigation of the anterior chamber. Another procedure for extracting the lens is by *phacoemulsification*, the use of ultrasonic vibration to break up the lens. The entire lens may be excised, a procedure known as *intracapsular extraction*, or an *extracapsular extraction* may be performed, leaving in place the back part of the thin capsule that surrounds the lens. A foldable *intraocular lens (IOL)* is usually implanted in the eye at the time of cataract removal. If an IOL cannot be implanted, external lenses—glasses or contact lenses—must be worn.

slit-lamp microscopy

Diabetic retinopathy, glaucoma, and retinal detachment can sometimes be identified by slit-lamp microscopy. The slit lamp is an instrument that combines a microscope and a light source, allowing magnified examination of the interior of the eye. Diabetic retinopathy can also be detected using *fluorescein angiography*, which involves the injection of dye to assess the retinal vessels.

visual activity (VA)

In Section I we learned that as light rays pass through the eye, they are refracted by certain eye structures so that they focus to form a clear image on the retina. Sometimes defects of the refractive media interfere with visual acuity (VA), that is, the sharpness of visual perception. These defects include irregularities in the curvature of the cornea, the focusing power of the lens, and the length of the eye.

hyperopia

In hyperopia, also called hypermetropia and farsightedness, the rays of light entering the eye are brought into focus at a point behind the retina, which causes the perceived image to appear blurred. Hyperopia occurs when the lens lacks adequate focusing power or the eyeball is too short.

accommodation

In the previous lesson, we learned that the ciliary body changes the size and shape of the lens by contracting and relaxing. This refractory adjustment to focus as an object draws near is *accommodation*. Muscles of the ciliary body produce flattening of the lens for distance vision and thickening and rounding of the lens for close vision.

dacryocystitis

Inflammation can occur in a lacrimal or tear (dacry/o) gland (aden/o), called dacryoadenitis, but if it occurs in the lacrimal sac, it is called dacryocystitis

how we see

Now that we have reviewed the structures of the eye and their functions, let's consider the sequence of events that result in our ability to see. As we now know, light rays enter the eye and are refracted by the *cornea, aqueous humor, lens, and vitreous humor*. The rays are focused on the retina where they stimulate the rods and cones, causing chemical changes and producing impulses. These impulses are conveyed along the optic nerves, which merge to form the *optic chiasm*. At this juncture, fibers from each optic nerve cross over to the other side. Fibers from the left visual field of each eye form the left optic tract. Impulses move along these fibers to the left visual cortex in the *occipital lobe*—an area in the posterior of the brain where visual stimuli is interpreted. Fibers from the right visual fields form the right optic tract and transmit impulses to the right occipital cortex. When these images from both eyes fuse in the brain, they produce a single 3-D image, the result being called *binocular vision. Convergence* is the movement of the eyes in unison toward a common point of fixation. It is because of convergence that we have binocular vision, the ability to see one image using both eyes

repair of retinal tears

Repair of retinal tears is accomplished with *laser photocoagulation and cryotherapy*, a procedure in which a freezer burn is used to create scar tissue that seals holes in the eye's innermost layer. Most retinal detachments are treated with a technique known as a *scleral buckle* (or scleral buckling). This method involves placing a silicone band over the detached area, forcing the layers of the retina together. A final treatment option is *pneumatic retinopexy*, in which a gas bubble is injected into the vitreous cavity to put pressure on the area of retinal tear until the retina is reattached.

detecting retinal detachment

Symptoms of a detached retina include flashes of light (called photopsia), floating spots or opacities, or a ring in the field of vision. As the loss of sight progresses, a sensation of a curtain being drawn across the field of vision may occur (as shown in the illustration). In addition to ophthalmoscopy, slit-lamp examination, also called slit-lamp microscopy, and ultrasonography may help to identify a separated retina if the structure itself cannot be visualized.

choroid structures of the eye

The eye's middle layer, the choroid layer, is a thin membrane with a rich supply of blood vessels. Anteriorly, the choroid is joined to the iris (irid/o, ir/o), the contractile disc that forms the colored portion of the eye, by the ciliary body (cycl/o). The pupil (cor/o, pupill/o) is the circular opening in the middle of the iris. Muscles of the iris constrict and dilate the pupil in response to the intensity of light. The lens (phac/o, phak/o), a highly elastic, transparent structure behind the iris, is surrounded and supported by fibers arising from the ciliary body. Contraction or relaxation of the ciliary body changes the shape and size of the lens.

external structures of the eye

The eyes are contained in two bony orbits at the front of the skull. About five-sixths of each eyeball lies within, and is protected by, these bony sockets. The other external structures of the eye are the eyelids (blephar/o, palpebr/o), eyebrows, and eyelashes.

diabetic retinopathy

The first of the retinal disorders we will look at is diabetic retinopathy. Diabetic retinopathy is a complication of diabetes mellitus affecting the blood vessels of the retina. Dilatation of the retinal capillaries, microaneurysms of the capillary walls, small hemorrhages, leakage of protein from the retinal vessels, and the formation of new blood vessels and connective tissue characterize this disorder, which usually occurs in those with poorly controlled diabetes. The loss of vision associated with diabetic retinopathy may be caused by scarring following the development of hemorrhages, macular edema resulting from fluid leakage from the blood vessels, or the rupture of the new blood vessels, which bleed into the vitreous, causing blurred vision.

two cavities

The interior space of the eyeball is divided into two cavities. The anterior cavity consists of anterior and posterior chambers. The chambers of the *anterior cavity* (anterior chambers) contain a clear, watery fluid, called *aqueous humor* (aque/o = water), that helps to maintain the shape of the eyeball and to nourish the iris, lens, and cornea. A humor is any body fluid, including blood and lymph. The *posterior cavity *of the eyeball occupies all of the internal space behind the lens. It contains *vitreous humor*, a gelatin-like substance (vitre/o means glassy) that also helps to preserve the eyeball's shape.

fundus

the inner posterior surface of the eye. It includes the retina (retin/o) and its structures—the optic disc (papill/o) and the macula lutea. The fundus can be visualized during a procedure called ophthalmoscopy. In this procedure, an ophthalmoscope—a device consisting of a light, a mirror, and lenses of varying strengths—is used in examining (-scopy) the eye (ophthalm/o).

refraction

visual problems—including the glare from lights at night—are the result of interference with the rays of light as they strike the lens. This is a problem of refraction. Refraction refers to the bending of light rays as they pass through the cornea, lens, and other structures of the eye en route to the retina. The angle of refraction varies with the density of the structure through which the light rays pass. The refracting media of the eye are the cornea, aqueous humor, lens, and vitreous humor. These media bend the light rays so that they focus on and stimulate the rods and cones. the lens is not as clear as it could be. This could be causing her to see halos or blurriness, particularly around lights and particularly at night.