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Hapnic sense refers to the sense of touch used extensively by blind and visually impaired individuals to gather information. The senses of hearing, taste, smell, and sight are associated with a central organ to receive the information and transmit it to the brain. The haptic sense is not centrally located but receives information throughout the body via the skin. The haptic sense defines temperature, shape, size, texture, moisture and consistency, movement, and presence. It is used as a compensation for sight, as in the performance of tasks, or perceptually, as in reading braille or using an abacus. Early stimulation of the haptic sense is especially important to blind infants and children. It helps to link the infant to the surrounding world and to indicate the presence of a protective or loving person. Blind infants and children rely heavily on the haptic sense for developmental progress. Since the lips and hands of the body have large concentrations of sensitive haptic receptors, blind children tend to mouth and handle objects longer than sighted children in an effort to gain information. Blind and visually impaired children rely on the haptic sense for aid in movement and exploration, essential developmental activities. Such tactual experiences as fondling a stuffed animal may be stimulating for a blind child and alleviate the need to develop such self-stimulating behaviors as rocking. Such factors as the ability to move the hands, finger dexterity, wrist flexibility, and motor control may affect the effectiveness of the haptic sense. If the haptic sense itself is impaired, information gathering may also be impaired. Those who have lost sensitivity of touch in the fingertips because of diabetic neuropathy may be unable to feel the detail necessary to read braille, and those with motor-control problems may be unable to direct the hands in place to gather information.

Hemianopsia is a loss of vision in one-half of the eye. This results in a loss of the right or left half of the vision field. Objects or people in the field of vision may appear to be cut in half. Hemianopsia is a common symptom of migraine headaches and occurs during the preheadache or prodrome stage. The loss of vision may be accompanied by shimmering zigzag light patterns and blind spots called scotomas. Hemianopsia accompanying migraines usually lasts from five minutes to an hour with the lost vision returning with the onset of the headache. Retinal migraine occurs when a spasm happens in the blood vessels in the retina of one eye. One half of the vision of the affected eye is lost, but the unaffected eye retains full vision. The condition is temporary and abates with the migraine. Hemianopsia is also associated with strokes when vision may be blurred or lost in one-half of the vision field, or the entire vision in one eye may be lost. Recovery of this visual loss depends on the damage done during the stroke and the progress made during recovery. As a result of a focal transient ischemic attack (TIA), a temporary disruption of the flow of blood to the brain and eye, the vision may be lost and then may suddenly return in a matter of minutes. Usually, the vision lost because of these attacks is completely recovered within twenty-four hours.

Hordeolum, or sty, is red lump of infection on the outside or inside of the eyelid and may resemble a boil or a pimple. An external hordeolum is an infection of an eyelash follicle. It generally stems from a bacterial infection near the root of an eyelash which develops over several days. It fills with pus and becomes painful to touch but is usually harmless to the eye. About a week after it first appears, the sty ruptures, relieving the pain. The swelling will go down in another week or two. Applying warm compresses until the sty opens is the best treatment. Never squeeze it! Once the sty has opened, wash the eyelid thoroughly to prevent the bacteria from spreading. Remember, all pus, anywhere on the body, is loaded with bacteria. An internal hordeolum is a sty on the inside of the eyelid. It is the result of a glandular infection. If untreated, the hordeolum becomes inflamed and swollen. It is then called a chalazion. These chalazia normally do not affect vision unless they are located in the middle of the upper eyelid where they can flatten the central cornea and distort sight. Sties can be treated by holding a warm, damp cloth over the area for twenty minutes, three or four times a day (chamomile tea is wonderful). Most sties and chalazia go away on their own, without medication.

Hyperopia (See Farsightedness)

Hypertension means persistently high blood pressure. In adults, this generally means a relatively consistent systolic pressure (top number) greater than 140 mm Hg and a diastolic pressure (bottom number) greater than 90 mm Hg. High blood pressure can cause damage to three parts of the eye – the optic nerve, the choroid, and the retina. There is a direct relationship between hypertension and atherosclerosis. Both are both risk factors for vein and artery occlusions in the eye. The back lining of the eye, the retina, contains blood vessels that provide nourishment to the eye. These tiny blood vessels are susceptible to closure from within by clotted blood and cholesterol plaques. At other places, a “hardened artery” may pass across a vein and press on the vein from the outside, causing an occulsion – something like stepping on a garden hose. Dramatic vision loss can occur from a central retinal artery or central retinal vein occlusion. The carotid arteries carry blood upward to the head and are extremely important to the eyes. One of the branches of the carotid artery is the ophthalmic artery, which is the main source of blood to the eyes. If this artery (there is one on each side of the head supplying blood to each eye) becomes clogged, as a result of arterial disease, and blood is not able to pass to the eye, tissues become diseased and may lose function. The most common problem affecting the carotid artery is atherosclerosis, a hardening. This often prevents blood from passing through the artery to the retina and the brain. When this happens, it can result in a stroke.

Hypertropia is a condition of strabismus, or misaligned eyes. Often termed “squint” or “crossed-eyes”, strabismus may cause visual problems or loss of vision. Hypertropia is a type of strabismus in which one eye turns upward. Hypotropia is a condition in which one eye turns downward. As in all types of strabismus, the eyes fail to converge on an object and view two different subjects. The brain receives two images, and double vision results. Often, in an effort to reconcile the two pictures, the brain may suppress one completely, causing partial vision loss. This results in a condition called amblyopia. Treatment may include the prescription of eye drops, eyeglasses or bifocals, or exercises. Exercises or eye patching may be prescribed if amblyopia is present. Surgery may be necessary to completely align the eyes.

Hyphema is a bleeding into the anterior chamber of the eye. Hyphemas may occur as a result of an injury or following intraocular surgery. Hyphemas may appear spontaneously because of diabetes-related neovascularization, tumor, juvenile xanthogranulomatosis, or previous vascular occlusions. Hyphemas caused by injury are caused by damage to blood vessels in the iris or ciliary body. In most cases, the bleeding slows and then ceases, and the blood is reabsorbed within the eye over a period of a week or two. Secondary bleeding that starts one to five days following the injury may fill the anterior chamber and elevate intraocular pressure. The raised intraocular pressure of secondary bleeding may cause secondary glaucoma, a serious result for which children are particularly at risk. The cornea may also become permanently bloodstained, causing an opacity or clouded area. Hyphemas caused by surgery are common but less likely to result in secondary bleeding. The bleeding recedes within days, and no further treatment of hyphema is necessary. Hyphemas are treated initially to prevent secondary bleeding and its consequences. Treatment varies according to the practitioner; but patients may be admitted to the hospital, confined to bed rest for several days, treated with cycloplegics (which widen the pupil) or with steroids or undergo patching of the eyes. Secondary bleeding may be treated surgically and medication given to reduce intraocular pressure. The hyphema may be removed or flushed out of the eye with a saline solution.

Hysterical blindness is an emotionally caused condition of blindness which occurs as a result of the need to physically resolve an emotional upset or shock. It is also known as psychogenic or psychic blindness. This type is usually bilateral and often occurs suddenly. Frequently, the blindness is not total and is restricted to a particular field. Additional symptoms of hysterical blindness include a lack of regard for the loss of sight, ability to travel within surroundings, and normal blink response. An eye examination is necessary to diagnose hysterical blindness. The examination reveals that the pupils react normally, and the fundus (back of the eye) appears normal, discounting damage to the optic nerve, cortical blindness, chiasmal lesions, or other ocular disease. The condition is usually diagnosed in light of information gathered through the eye exam and study of the patient’s psychological history. Treatment may include reassurance that the condition will right itself, presentation to the patient of the ability to see, and placebo medication therapy. The patient may recover from the condition only to replace it with another physical illness. Psychiatric counseling is often recommended to address the underlying emotional problem. Hysterical blindness is not to be confused with malingering, a condition of feigned blindness often undertaken as an attempt to receive continued compensation for an accident or injury.