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V

Vernal Conjunctivitis

Definition:
It is a condition which is caused by an allergic reaction during the warm weather months.

Who can get it?
Vernal conjunctivitis typically occurs in children during the summer months.

What are the symptoms?
Severe itching and a thick discharge from the eyes. White spots or ulcers may form on the cornea and large papillae may form under the upper lid.

What is the treatment?
A trip to the optometrist is recommended, and antihistamines may be prescribed to reduce itching and discharge.

Vision Therapy
A process used to improve a person's visual perception and coordination.
Visual Acuity

Visual acuity refers to a standard that represents the clearness or sharpness in vision or sight. Visual acuity may be refered to as the "resolution" in vision.

The most common standard for measuring visual acuity is "Snellin Acuity." The Snellin standard is usually used to define "distance" visual acuity. Under the Snellin standard the object is placed 20 feet from the observer. The measurement is always in reference to this 20 foot distance. As an example, consider a person who is said to have 20/40 visual acuity. 20/40 means that the person being tested had to move up to 20 feet from the object in order to see a letter which was actually placed 40 feet from the observer.

The test objects that are traditionally used to subjectively test visual acuity are: Capitol letters, Rotating "C"s, Tumbling "E"s (for children).

Another standard for measuring visual acuity is JAEGER acuity. This is defined in terms of a metric reference. The jaeger standard is most often used in measuring "near point" vision, rather than distance vision.

Technical Definition:
The reciprocal of the minimum angular separation of two lines just resolvable. It is measured in minutes.

Visual field
Region or area visible to the eye in a specific position.
Visual Field Test
A test used to help diagnose Glaucoma that produces a map of the complete field of vision. Small vision changes can be detected by having the patient look straight ahead and indicate when a moving object or light is seen out of the corner of the eye. See Perimetry.
Visual Pathway

The visual pathway is remarkable. When you view an object (for example, a potted plant) light rays reflected by that object enter the eye and pass through its lens. The lens projects an inverted image of the plant onto the retina at the back of the eye. Vision is generated by photoreceptors in the retina, and signals produced by rod and cone cells in the retina then leaves the eye by way of the optic nerve, and there is a partial crossing of axons at the optic chiasm. After the chiasm, the axons are called the optic tract. The optic tract wraps around the midbrain to get to the lateral geniculate nucleus, where all the axons must synapse. From there, the LGN axons fan out through the deep white matter of the brain as optic radiations. These optic radiations travel to the primary visual cortex, which curves around a deep fissure at the back of the brain. From there, signals fan out to "higher" areas of cortex that process more global aspects of the plant such as its shape, color, or motion.

Visual Pathway
Posterior Vitreous Detachment

A vitreous detachment occurs when the vitreous gel separates from the retinal surface of the eye. A Vitreous Detachment can often be no cause for concern, but can result in retinal tears, leading to retinal detachment. It is because of this reason that Vitreous Detachments are carefully monitored.

A Vitreous Detachment frequently occurs with aging as the vitreous liquifies, or in high-risk diseases such as diabetes and high myopia.

Additional keywords and misspellings:
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vitreousdetach-ex

Vitreous Surgery

VIT-tree-uss SIR-jah-ree

A surgical procedure performed under general anesthesia, to remove the vitreous and replace it with a compatible clear fluid or with air. Vitreous surgery is necessary in situations when a retinal detachment is so severe, it can not be treated with other methods.

The Eye Encyclopedia is a collection of eye care terminology created by practicing optometrists and ophthalmologists. The information provided is not intended to be a substitute for regular medical care or to diagnose or treat any medical condition, and should be used only as a supplemental source of information. Please consult your doctor if you have any questions or concerns about your eye health.