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As the first comprehensive reference for the eye, its support structures, diseases, and treatments, Encyclopedia of the Eye is an important resource for all visual.
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• Recording and contextualizing the science of embryos, development, and reproduction.
• DK Human Body: Eye
• CLEVELAND EYE BANK | Encyclopedia of Cleveland History | Case Western Reserve University

The smooth muscle of the eyelids and orbit is activated by the sympathetic division of the autonomic system. The secretion of epinephrine adrenaline during such states of excitement as fear would also presumably cause contraction of the smooth muscle, but it seems unlikely that this would lead to the protrusion of the eyes traditionally associated with extreme fear.

It is possible that the widening of the lid aperture occurring in this excited state and the dilation of the pupil create the illusion of eye protrusion.

Blinking is normally an involuntary act, but it may be carried out voluntarily. The more vigorous full closure may be evoked as a reflex response. Reflex blinking may be caused by practically any peripheral stimulus, but the two functionally significant reflexes are 1 that resulting from stimulation of the endings of the fifth cranial nerve in the cornea , lid, or conjunctiva—the sensory blink reflex, or corneal reflex—and 2 that caused by bright light—the optical blink reflex. The corneal reflex is rapid 0.

The reflex is said to be under the control of a medullary centre. The optical reflex is slower; in humans, the nervous pathway includes the visual cortex the outer substance of the brain ; the visual centre is located in the occipital—rear—lobe.

In the waking hours, the eyes blink fairly regularly at intervals of two to 10 seconds, the actual rate being a characteristic of the individual. The function of this is to spread the lacrimal secretions over the cornea. It might be thought that each blink would be reflexly determined by a corneal stimulus—drying and irritation—but extensive studies indicate that this view is incorrect.

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This is not to deny that the blink rate is modified by external stimuli. There is a strong association between blinking and the action of the extraocular muscles. Eye movement is generally accompanied by a blink, and it is thought that this aids the eyes in changing their fixation point. The exposed surface of the globe eyeball is kept moist by the tears secreted by the lacrimal apparatus , together with the mucous and oily secretions of the other secretory organs and cells of the lids and conjunctiva; these have been described earlier.

The secretion produces what has been called the precorneal film, which consists of an inner layer of mucus, a middle layer of lacrimal secretion, and an outer oily film that reduces the rate of evaporation of the underlying watery layer. The normal daily hour rate of secretion has been estimated at about 0. Chemical analysis of the tears reveals a typical body fluid with a salt concentration similar to that of blood plasma. An interesting component is lysozyme , an enzyme that has bactericidal action by virtue of its power of dissolving away the outer coats of many bacteria.

Tears are secreted reflexly in response to a variety of stimuli—e. In addition, tear flow occurs in association with vomiting , coughing , and yawning. The secretion associated with emotional upset is called psychical weeping. Severing of the sensory root of the trigeminal fifth cranial nerve prevents all reflex weeping, leaving psychical weeping unaffected; similarly, the application of cocaine to the surface of the eye, which paralyzes the sensory nerve endings, inhibits reflex weeping, even when the eye is exposed to potent tear gases. Managing your diabetes may help slow diabetic retinopathy and other eye problems.

Control your blood sugar glucose level by:. Treatments can reduce vision loss. They do not cure diabetic retinopathy or reverse the changes that have already occurred. Call for an appointment with an eye doctor ophthalmologist if you have diabetes and you have not seen an ophthalmologist in the past year. Good control of blood sugar, blood pressure, and cholesterol are very important for preventing diabetic retinopathy. Preferred Practice Pattern Guidelines.

Diabetic retinopathy. Accessed August 18, American Diabetes Association. Microvascular complications and foot care. Diabetes Care. PMID: www. Philadelphia, PA: Elsevier Saunders; chap 6. A slit-lamp, which is a specialized magnifying microscope, is used to examine the structures of the eye including the cornea, iris, vitreous, and retina.

Recording and contextualizing the science of embryos, development, and reproduction.

The slit-lamp is used to examine, treat with a laser , and photograph with a camera the eye. Diabetes causes an excessive amount of glucose to remain in the blood stream which may cause damage to the blood vessels. Within the eye the damaged vessels may leak blood and fluid into the surrounding tissues and cause vision problems.

Editorial team. Doctors St. E-mail Form. Diabetes and eye disease Retinopathy - diabetic; Photocoagulation - retina; Diabetic retinopathy. Diabetes Diabetes is a chronic disease in which the body cannot regulate the amount of sugar in the blood. Type 1 Type 1 diabetes is a lifelong chronic disease in which there is a high level of sugar glucose in the blood. Type 2 diabetes Type 2 diabetes is a lifelong chronic disease in which there is a high level of sugar glucose in the blood.

Cataract A cataract is a clouding of the lens of the eye.

Glaucoma Glaucoma is a group of eye conditions that can damage the optic nerve. Retinal detachment Retinal detachment is a separation of the light-sensitive membrane retina in the back of the eye from its supporting layers. Floaters There are many types of eye problems and vision disturbances, such as: HalosBlurred vision the loss of sharpness of vision and the inability to see Tonometry Tonometry is a test to measure the pressure inside your eyes.

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Slit lamp exam The slit-lamp examination looks at structures that are at the front of the eye. Fluorescein angiography Fluorescein angiography is an eye test that uses a special dye and camera to look at blood flow in the retina and choroid. Eye exams Diabetic retinopathy - eye exams; Diabetes - eye exams; Glaucoma - diabetic eye exam; Macular edema - diabetic eye exam. Resources The following sites provide further information on diabetes:American Diabetes Association -- www.

Appointment with an eye doctor ophthal Open References. All Video Images Tog. Slit-lamp exam - illustration A slit-lamp, which is a specialized magnifying microscope, is used to examine the structures of the eye including the cornea, iris, vitreous, and retina. Slit-lamp exam illustration. Diabetic retinopathy - illustration Diabetes causes an excessive amount of glucose to remain in the blood stream which may cause damage to the blood vessels.

Diabetic retinopathy illustration. A Closer Look. Diabetes - type 2 In-Depth. Talking to your MD. Type 2 diabetes - what to ask your doctor. Self Care.

Diabetes eye exams Type 2 diabetes - self-care Long-term complications of diabetes Diabetes - keeping active Diabetes and exercise. Tests for Diabetes and eye disease. A1C test Orbit CT scan.

• DK Human Body: Eye.
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Related Information. Retina Special Topic. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions.