chapter 25: The senses

Blepharoptosis

A disorder of the eyelid that occurs when muscles of the eyelid aren't strong enough to raise it.

Нурeгоpia (farsightedness)

Light focuses behind the retina. objects that are close to the eye are harder to decipher and blurred. It is easierto see things farther away.

Myopia (nearsighnedness)

Light focuses in front of the retina. objects farther away tend to be blurry and difficult to see. It is easierto see objects that are closerto the eye.

Anatomy of the Eye

The eye is made up of the eyeball and its internal structures, which perform the complex process of translating light into images, and the external structures that support and protect the eyeball Canal of Cornea Iris Pupil Anterior chamber

orbit

eyeball is housed in a cavity in the skull called

Blepharitis

is an inflammation of the eyelids, particularly near the eyelash hair follicles. It can be caused by skin disorders such as seborrheic dermatitis, rosacea, or lice. It can also be caused by allergies. Signs and symptoms - include redness, itching, and swelling of the eyelids. Burning sensations are common as is the development of crust that covers the eye, sometimes making it difficult to separate the eyelids. Treatment - with warm wet compresses and ophthalmic antibiotic therapy.

The Eye

• The eye is spherical, fluid-filled organ composed of specialized structures that work together to facilitate vision • Light rays pass through the cornea, pupil, lens, vitreous humor to the retina, where they stimulate sensory receptors

Retinopathy

- a disease of the retina that is caused by either recurring or acute damage. - Patients with diabetes are prone to diabetic retinopathy. Nerve damage can result from hypertensive retinopathy, caused by high blood pressure, and can lead to permanent blindness. X - - Sickle cell disease, trauma, and other disorders can cause general retinopathy. Symptoms vary based on the type of retinopathy that is diagnosed, and treatment lies in treating the underlying condition causing the disorder.

Strabismus

(crossed eyes) the eyes are misaligned and do not focus on the same image. One or both eyes turn in, out, up, or down. caused by abnormal neuromuscular control and weakness in the external ocular muscles of the eye. Signs and symptoms - poor depth perception and double vision, which is also known as diplopia. Treatment- include eyeglasses, eye exercises, wearing a patch over the stronger eye to force the weaker eye to become stronger, and surgery to realign the eyes.

Hordeolums

- Also known as sties - are very common and frequently contagious. - caused by the Staphylococcus bacterium. - Sties may accompany blocked or infected eyelid glands or inflamed eyelids. Contaminated fingers that touch the eye area may also cause the infection. - Painful hordeolums can also occur under the eyelids Signs and symptoms - Early signs and symptoms include redness and tenderness followed by itching, swelling, and discomfort in the upper or lower eyelid. The stye, or hordeolum, develops as a pus-filled swelling at the base of an eyelash. Treatment - often resolve on their own. - A warm, wet compress applied to the area may help relieve the pain. - It is important to tell patients to avoid touching the affected eye, and never to squeeze the hordeolum. - Antibiotic creams or ointments may be applied to accelerate healing. - In some cases, a physician may need to lance and drain the hordeolum to assist in the healing process; particularly if vision is affected.

Glaucoma

- affects people of all ages and all races. - characterized by increased pressure in the eye. - Left untreated, the pressure can lead to damage of the optic nerve and eventual blindness. An excessive amount of aqueous humor causes the increased intraocular pressure (IOP) that can lead to glaucoma. - Risk factors for developing IOP and glaucoma include age (those over 60 are at higher risk), race (African-Americans are at higher risk), a family history of glaucoma, and those with vascular diseases. two basic types of glaucoma. - In open-angle (acute) glaucoma, a blockage gradually develops within the drainage canal from the anterior segment of the eye, slowing the drainage of aqueous humor and causing a gradual buildup of pressure. - About 90 percent of glaucoma cases are of this open-angle type. - In closed-angle (chronic) glaucoma, which is considered more serious, the space between the iris and the cornea narrows, causing the entrance to the drainage canal to narrow or close completely. - pressure can rise very quickly. - Approximately 80,000 people are totally blind as a result of glaucoma, another 250,000 are blind in one eye, and over 1.2 million people have some degree of visual loss. Signs and symptoms - Open-angle glaucoma is a chronic condition sometimes referred to as primary glaucoma. It is asymptomatic (without symptoms) and is often referred to as the "silent thief" of vison. Eventually the patient may experience tunnel vision. However, once this symptom begins to occur, damage is already severe. - Acute, closed-angle glaucoma (also referred to as narrow-angle glaucoma) may present signs and symptoms that include sharp eye pain, decreased hazy vision, and red swollen eyes. A test called tonometry, which measures the intraocular pressure of the eye, is performed on patients when glaucoma is either suspected or the patient is at high risk for developing the disorder. Treatment medications such as eye drops to lower intraocular pressure as well as with laser and conventional surgery.

Nystagmus (nystaxis)

- involuntary, repetitive, rhythmic eye movements. - inherited or acquired and usually results in some loss of vision. Signs and symptoms - Uncontrolled eye movements, which may be lateral, horizontal, or even circular. Treatment - address the underlying cause, which might be a tumor, a lesion, alcohol abuse, or retinal maldevelopment.

Cataracts

- is a clouding or opacity of the lens that prevents light from entering the eye. - Although there is not a clear and specific etiology for all cases, there may be a correlation between the formation of cataracts and smoking, diabetes, use of specific drugs, excessive exposure to sunlight, and the overall aging process of the eye. Signs and symptoms - As the cataract begins to form and the cloudiness begins to develop, vision begins to decrease. Patients may complain of fuzzy, blurred, or filmy vision. - Sufferers may also experience a lack of color intensity as well as seeing halos around lights. - Night vision suffers because of the decreased amount of light that is able to enter the eyes. The patient may also experience double vision or problems with bright lights. If left untreated, the cataract may eventually cloud the lens enough to block vision completely. Treatment - For early or immature cataracts, eyeglasses, magnifying lenses, and stronger lighting may be sufficient. - If this is not successful, surgery is the only effective treatment. - Cataract removal is a very common surgery; it is also extremely safe and effective, with a cure rate of 90 percent.

corneal abrasion

- is a lesion or scratch on the cornea. - many causes of corneal abrasions. - Most result from infection or injury. Other causes include improperly fitting contact lenses and foreign matter becoming stuck in the eyelid. Signs and symptoms - can be very painful and irritating. - Other symptoms include blurred vision, excessive tearing, gritty feeling on the cornea, and possibly headache. - The patient will be very sensitive to light and will have difficulty opening the affected eye. Treatment - mild analgesics and resting the eyes. If the abrasion becomes infected, antibiotic eye drops or ointments are given.

Amblyopia

- lazy eye, - improper developement of the nerve pathway from the eyevto the brain is etiology of this disorder. This improperly developed nerve pathway causes the affected eye to send incorrect images to the brain. - may have a hereditary factor. - The leading cause is strabismus (crossed eye or wall eye) - The brain tends to ignore the image from the misaligned eye, and amblyopia develops as the nerve pathway from the affected eye fails to fully develop. - It is important to note that not everyone who suffers from strabismus will also suffer from amblyopia, and not all cases of amblyopia are caused by strabismus. Signs and symptoms - eyes that appear to turn in or out, decreased vision, and faulty depth perception. Treatment - Early diagnosis and treatment are essential to a positive and lasting outcome. - If not corrected early, the underdevelopment of the nerve from the affected eye tends to become permanent. - Treatment for underlying conditions, such as strabismus or refractive disorders, must first be completed. A patch may be worn over the strong eye to force the brain to interpret the images from the afflicted eye to foster development of the nerve pathway from that eye.

Retinal detachment

- occurs when a retina has separated from the underlying choroid layer (a vascular layer of connective tissue between the retina and sclera). - Damage may start as small holes or tears and later, if left untreated, develop into full detachment. When such a separation occurs, vision is damaged. However, if the detachment is detected early, it can be repaired and the vision saved. If the retina has already detached, vision can frequently be restored by surgery and laser therapy. - Causes of retinal detachment include shrinking of the vitreous that makes the retina tug and possibly tear, inflammatory eye disorders, advanced stages of diabetes, and injury to the eye. Signs and symptoms - an increase in floaters (particles that float slowly within the viewer's eyes), or flashes of light in the field of vision. - The individual may feel as if a curtain has obscured part of the vision. Treatment - Early treatment is ideal. Therefore, anyone experiencing the symptoms retinal detachment should seek professional help as soon as possible. - Treatment for small holes or tears is usually laser surgery or cryotherapy (application of intense cold to induce a scar); for retinal detachment, more invasive surgery requiring a hospital stay is generally recommended.

Macular Degeneration

- the deterioration of the macula, which is the central portion of the retina. - an incurable disease that affects more than ten million Americans and is one of the leading causes of blindness among people over the age of 55. - there is not a specific etiology for macular degeneration. - There are various risk factors associated with age-related macular degeneration. Some of these factors include being Caucasian and having lighter pigmentation, smoking, obesity, a familial history, exposure to sunlight, and gender, as women are more likely to develop macular degeneration. The two types of macular degeneration are dry and wet. The dry (atrophic) - occurs in 85 to 90 percent of cases. - small yellow deposits called drusen form under the macula, causing it to thin and dry out, leading to a loss of central vision - slower progression than does the wet type; however, in some cases dry atrophic macular degeneration may develop into wet macular degeneration. wet macular - degeneration, abnormal new blood vessels grow under the retina and the macula. They may then bleed and leak fluid, which causes the macula to bulge or lift up, impairing or destroying the central vision. Vision loss may be rapid and severe. Signs and symptoms - dry macular degeneration include a decline in central vision, increasing haziness of overall vision, and a need for brighter illumination for reading and close work. - wet macular degeneration include visual distortions and a blurry spot in the central vision. Treatment - There is no known treatment or cure for dry macular degeneration. - If performed early, laser surgery may halt the progression of wet macular degeneration, thus preventing a total loss of vision. Although this outcome cannot be guaranteed, laser surgery is currently the best treatment for wet macular degeneration.

Exophthalmos

A disorder that causes the bulging, bug-like appearance of one or both eves

Entropion

A disorder that causes the lower eyelid to turn inward.

Ectropion.

A disorder that causes the lower eyelid to turn outward.

Presbyopia

A loss of elasticity in the lens; generally a result of aging. Difficulty seeing objects that are close. Specifically relatedcto aging

Conjunctivitis

Pink eye - is one of the most common and treatable eye infections, affecting both children and adults., - this highly contagious condition - inflammation of the conjunctiva, Etiology includes viruses, bacteria, sexually transmitted infections (STIS), allergens, and irritants such as chlorine, dirt, or smoke. Signs and symptoms - Early recognition extremely important. - early symptom is the feeling of a foreign object in the eye, such as a speck of dust or sand. Other common symptoms include redness in the sclera, increased tear production, a thick yellow discharge that crusts over the eyelashes, itchy eyes, burning eyes, blurred vision, and greater sensitivity to light. Treatment - Early treatment of conjunctivitis is equally important. Cleansing the eyes and applying warm compresses is an effective home remedy for treating pink eye. - Over-the-counter eye drops are used to keep eyes lubricated. - If the infection is bacterial, or if it is caused by an STI, prescription eye drops may be prescribed. Isolation during the first 24 hours of antibiotic therapy is recommended because of the highly nature of the infection.

The Inner Layer of the Eyeball retina, rods cones fovea centralis retinae macula lutea, optic nerve optic disk

Retina - The innermost layer of the eye is the the back of the eyeball, behind the vitreous humor. Rods and cones - Photosensitive cells in the retina translate light rays into nerve impulses that are transmitted to the brain. Rods - react to dim light and are used in night vision; cones - are sensitive to bright light and are used to see color. Fovea centralis retinae - contains only cones and is located in the middle of the macula lutea, a yellow spot on the back of the eye. Optic nerve - enters at the optic disk and carries incoming infirmation from the eye to the brain Papilledema - inflammation at the optic nerve, increases pressure in the eye and can be cuased by multiple factors including diseases, increased intracranial pressure and frontal lobe tumors

aqueous humor,

The eyeball itself can be divided into two cavities: a front, or anterior, cavity filled with a watery fluid

vitreous humor.

a back, or posterior, section located behind the lens and filled with very thick fluid in the,

Astigmatism

a condition caused by an irregularity in the curvature of the cornea and lens. rounder in shape, a cornea that is more football shaped is often present in those with astigmatism. irregular shape causes light not to focus on the retina but rather to spread out over an area. Signs and symptoms - characterized by blurry near or distant vision. It may be accompanied by squinting and headaches. Treatment - generally consists of corrective lenses (glasses or contact lenses) or surgery to reshape the cornea.

The Middle Layer of the Eyeball Choroid, iris, lens, ciliary body

composed of the following structures: • Choroid - Lines the sclera and absorbs extra light entering the eye. • Iris- Contains the pigment, or eye color, and has a "hole" in the center called the pupil. The muscular tissue that makes up the iris and pupil allows the pupil to constrict and dilate, which is how the pupil controls the amount of light that enters the eye. • Lens - Colorless structure behind the iris, sharpens the focus of light rays onto the retina. The lens is important to a reflexive process called accommodationP, which adjusts the eye's optical powers to maintain a clear image at various distances. • Ciliary body - Responsible for holding and moving the lens; secretes aqueous humor, which provides nutrients to the cornea, lens, and other tissues.

vitreous humor. The surface of the eyeball is made up of three layers:

outer, middle, and inner.

The External Structures of the Eye palpebrae, palpebral fissure, canthus conjunctiva lacrimal apparatus lacrimal gland, lacrimal canaliculi, lacrimal sac. nasolacrimal duct,

palpebrae (eye lids) - close over the eyeballs, protecting them from intense light, foreign matter, and impacts. Eyelids are composed of dense connective tissue, muscle, and skin. They also keep the eyes moist by preventing moisture in the mucosal membrane surface of the eye from evaporating. Using its muscular tissue, the eyelid performs the blinking action that helps prevent bacteria and harmful substances from entering the eye. palpebral fissure - Light enters through, the opening between the superior and inferior (upper and lower) eyelids. Eyelashes in the margins of the eyelids further protect the eye from foreign matter. the canthus - where thevsuperior and inferior palpebrae meet at each corner of the eye. The conjunctiva - is a mucous membrane that lines the underside of the eyelids and the anterior part of the eyeball. It serves a protective function by helping to keep the eyeball moist and decreasing the opportunity for bacteria to grow. lacrimal apparatus - where tears are produced, stored, and removed by the structures that make up the lacrimal apparatus Lacrimal gland - above the outer corner of each eye, which secretes tears through ducts on the surface of the conjunctiva of the upper lid. lacrimal canaliculi - at the inner corner of each eye are two ducts, which collect and drain the tears into the lacrimal sac. The lacrimal sac - empties into the nasolacrimal duct, which empties into the nasal cavity.

The Outer Layer of the Eyeball Sclera, cornea, limbus

sclera - or "white" of the eye. Light is unable to penetrate the sclera. The cornea - is frequently referred to as the "window" of the eye because it allows the light to enter. limbus - , or corneal-scleral junction, is the area of the eye where the cornea and sclera meet.