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Bell's palsy
It is a disorder involving unilateral facial weakness or paralysis. The condition usually has its onset over a two- to five-day period. During that time, the patient may experience a loss of facial sensation, a numbness, drooling, delay in blinking, inability to close an eye, excessive tearing, paralysis of one side of the face, or noticeable drooping of the mouth or face. Half of those with Bell's palsy experience pain behind the ear, but the condition does not cause hearing impairments. The symptoms of Bell's palsy, named for Sir Charles Bell, the 19th century physician who first described the disease, may be confused with those of a stroke. Bell's palsy symptoms, however, usually affect the entire side of the face from the forehead to chin, whereas stroke symptoms are usually located below the eye. Bell's palsy symptoms also do not include the classic stroke symptoms of weakness in limbs, slurred speech, or double vision.

Bell's palsy is caused by a swelling of the facial nerve resulting from immune disorders or a viral disease. The nerve is constricted, the blood supply is limited, and the nerve becomes ischemic, or anemic, from lack of blood flow. Nerve degeneration may follow. Individuals who contract the disorder are typically in good health but have a history of diabetes, sarcoidosis, or Lyme disease. It has also been associated with influenza, colds, and headaches and may be triggered by such illnesses. Bell's palsy may occur to either sex at any age but is most prevalent after the age of 40. The disorder poses the greatest threat to the eye's cornea, the clear protective cover of the eye. When the eyelid, which normally protects the cornea, functions incorrectly, the cornea becomes dry and is vulnerable to the elements. Constant exposure may result in keratitis (corneal infection), ulceration or injury, causing a loss of vision.

The eye may be treated with occasional applications of artificial tears during the day and a lubricating cream or ointment at night. The eye may be taped shut or protected with an eyeshield. Dryness or irritation, increased sensitivity to light, or symptoms of infection may develop and require further treatment. A partial tarsorrhaphy, a surgical procedure in which the upper and lower eyelids are stitched together at the corner, may be performed. The surgery is reversible and may be a temporary measure but may also cause corneal breakdown, irritation to the cornea from eyelashes, or scars along the lashline. The treatment for Bell's palsy may include physical therapy, a combination of heat application and facial massage or facial exercises. In severe cases, corticosteroids may be prescribed for up to fourteen days. In 85% of the cases, recovery begins to occur within ten days to three weeks. The remaining 15% may require up to a year to recover. The condition tends to recur in 10% of cases and usually affects the opposite side of the face. Pregnancy and multiple sclerosis have been linked to recurrences.

Bifocals, or bifocal lenses
They contain two prescription lenses put together into one lens. Each contact or eyeglass lens has two focusing abilities, one for seeing near objects and one for seeing distant objects. Bifocals are usually needed after the age of forty. They are a common aid in the treatment of presbyopia -- ageing eyes. As the eye ages, the lens loses the ability to focus on close objects. Although one prescription for reading glasses would solve the problem, they would have to be removed to see distant objects. The constant switching is inconvenient, and bifocals eliminate this problem. Bifocals are custom-designed. The reading and distance segments of each lens may be small or large and placed high or low in the frame. The lens size and placement are determined by the needs of the wearer. Using an updated method of polishing, bifocals today can be made without a noticeable line. These are called "blended bifocals", and are preferred by many people. Wearers must adopt new head movements to use the lenses correctly and safely.

Biomicroscope, or slit lamp
It is an instrument used to examine the eye. It magnifies the anterior chamber of the eye, including the cornea, iris, and lens. A biomicroscope examination is a painless one-step in a routine eye exam. The patient places his/her chin on a chin rest centered at the bottom of an open square-shaped frame. A bright light in front of the frame shines a vertical beam of light through the cornea. The light that is reflected back gives an illuminated, magnified cross-section of the front part of the eye. The biomicroscope examination is used to check for abrasions, erosion or scarring, inflammation, presence of blood vessels, or change of shape in the cornea, as well as inflammation or thinning of the sclera, inflammation or irregularities of the iris, and subluxated or shifted lens and cataracts. The biomicroscope may also be used to examine the eye during such tests as those to determine intraocular pressure (tonography) or the junction of the cornea and iris (gonioscopy). It is also used as a tool in some laser treatment procedures.

Bioptics
They are optical aids that consist of small telescopes fused onto the upper portion of spectacles, on one or both lenses. The bottom portion of the spectacles contains the individual's corrective prescription. The bioptics involving both eyes enable the low-vision user to view distances when walking or driving or to view closer objects or material, if magnification is needed. The bioptics that involve one eye only are used for near and intermediate distance viewing for reading material. Bioptics are prescribed by an ophthalmologist or low-vision expert and must be properly centered to the eyes of the wearer. Magnification may extend to six times normal size when used for distance viewing. Wide-angle lenses may be incorporated into the device. Regulations vary from state to state, but the majority of them now permit driving with the aid of bioptics.

Blepharitis, or eyelash dandruff
It is a common condition of the eyelids. An inflammation of the eyelids along their edges, blepharitis is mainly caused by an excessive production from oil glands near the eyelashes. The oil encourages the growth of bacteria, which can make the eyelids irritated and itchy. Causes of blepharitis are unknown; but it is often associated with allergies, a disorder in the lipid layer of the tear film, or seborrhoea of the scalp. Seborrheic dermatitis is a chronic condition that involves an abnormal secretion of oil in the skin, particularly around the scalp and face. Some lash loss may occur, but in milder cases the lashes grow back. In severe cases, the lash follicles are destroyed and permanent lash loss results.People with rosacea, dandruff, or dry eyes are likely to develop blepharitis as well.

Although blepharitis is a difficult condition to treat, it rarely results in a loss of vision. It is important to keep the eyelid area very clean in order to cut the buildup of secretions. Signs and symptoms include a gritty, burning sensation in the eyes, watery or red eyes, swollen eyelids, and flaking of skin around the eyes. The eyelids appear greasy and crusted with scales that cling to the lashes. This debris causes the eyelids to stick together during the night but is nothing to be alarmed over. Cleaning the area well several times a day is the best treatment. Ophthalmologists may treat the symptoms with antibiotics; but since there is no cure, the disorder becomes chronic; and chronic use of antibiotics is not advised. The best treatment is washing the area with a weak solution of warm chamomile tea several times a day. If not treated, chronic blepharitis may lead to conjunctivitis and inflammation of the cornea.

Blindisms
This is the term used to describe stereotypical mannerisms or behaviors of blind children or infants. The term is misleading since the mannerisms are also stereotypical of children with such other disabilities as autism. These behaviors include rocking, shaking, or turning the head; shaking the hands; mouthing the hands or objects; and eye poking or pressing. The repetitive and unconsciously performed mannerisms are most often found in those who are congenitally blind but may be acquired by those with adventitious blindness. Some studies indicate that children create these mannerisms of self-stimulation to compensate for the lack of sensory stimulation and activity in their lives. Others cite the lack of opportunity and ability of blind children to imitate the acceptable behavior of others and to develop a sense of unacceptable behaviors.

Behaviors related to vision loss may appear to be blindisms. A child may hold the head unnaturally to one side in order to make the best use of residual vision or a reduced visual field or may grimace in an effort to see an image. Blindisms may lead to social segregation if the mannerisms are considered distracting or unsightly. They may falsely indicate to others the presence of mental retardation, autism, or emotional disorders. Blindisms may become injurious to the individual, since eye rubbing and poking can cause bruising and callous formation. Blindisms may be prevented with the use of stimulating, physical activity (including the use of such motion furniture as rocking chairs and swings), development of an interest in the environment and frequent opportunities for new experiences. Established blindisms may be corrected if the child is given a substitute activity for the physical movement. The effort of flapping the hands may be redirected to playing an instrument or fondling a stuffed toy.

Blind spot
It is a point of blindness or blocked vision found in normal peripheral vision. This spot is caused by the optic disc, a spot on the retina where the optic nerve meets the eye. The retina, the light-sensitive layer of the back of the eye, contains cells called "rods and cones," which receive light and provides information about the viewed object. The retina encodes this information into electrical impulses, which are sent to the brain via the optic nerve (a cord of nerve fibers that connects the brain to the eye and supplies blood to the retina). The brain translates the impulses into an image. The optic nerve is joined to the retina at the optic disc, which is devoid of photosensitive rods or cones. Therefore, it is unable to collect information about an object and, as a result, the disc is "blind."

Since the blind spot is small and located within the peripheral field of vision, it does not interfere with normal central vision. The optic disc may be observed during an ophthalmologic exam or by moving an object into the field of the blind spot. This is easily accomplished by marking a piece of white paper with an X. Approximately two inches to the right of the X, mark a dark circle. Close the left eye and look directly and steadily at the X. Move the paper forward or back until the circle disappears. This circle lies in the sphere of the optic disc.The blind spot does not affect normal vision. Constant eye movements deflect attention from the blind area, and the brain compensates for its lack by completing any incomplete lines and filling in any gaps.

Blocked tear ducts
They can be problematic. The tear-producing glands, called the lacrimal glands, are located under the brow bone, just above the eyes. During blinking, the upper eyelids spread tears over the surface of the eyes and pump excess fluid into the ducts that drain into the nose, which explains why the nose runs during a crying spell. If a tear-duct becomes blocked, fluid builds up and spills over the eyelid, causing tears to run down the cheek. This condition is rare but it can be associated with aging, inflammation of a nasal passage, or injury to the nose. Usually only one eye is affected. About five percent of babies are born with a blocked tear duct. This congenital blockage often disappears within six months.

A blocked tear duct can become infected from bacteria in the stagnant tears at which time it will be called dacryocystitis. Tissue between the inner angle of the eye and the bridge of the nose becomes swollen and tender. If the eye constantly waters over a period of several days, an eye doctor should be consulted as he might be able to probe and flush the duct. Applying warm compresses several times a day will also help relieve the discomfort. If the condition is severe, the doctor may recommend surgery to create a new tear duct. In this procedure, the doctor may use thin silicone tubing to keep the new tear duct open during healing. In rare cases, the blockage may beyond repair and an artificial tear duct (a Jones tube) will have to be surgically implanted. This is made of unbreakable glass and placed in the inner corner of the eyelid.

Braille
(See separately.)

Brailon
It is the trade name for the paper used in a thermoform duplicator. Each plastic sheet is placed on top of a page of brailled paper or tactual paper and inserted into the thermoform machine. The machine heats the Brailon plastic sheet and creates a duplicate of the tactual sheet. Brailon is used to make duplicates of bralle books and such other tactual materials as tactile maps. The Brailon exchange is the agreement of many educational agencies or organizations for the blind to provide a braille copy of a book in exchange for an equal number of Brailon sheets.

B-scans
They are ultrasound tests performed prior to cataract surgery to view the retina. Cataracts may be too dense to permit any useful view of the retina with the binocular indirect ophthalmoscope. In these instances, a painless, ultrasonic B-scan is used to obtain a picture of the hidden retina. The B-scan is more effective than the A-scan and gives a picture of the eye behind the cataract. The health of the retina must be determined before cataract surgery to rule out the possibility of a detached retina. Without this knowledge, the surgery could successfully remove the cataracts, only to reveal a hidden detached retina or severe macular degeneration. Although it cannot detect macular degeneration, it can alert the doctor to the presence of a retinal detachment before the surgery takes place.