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  • Symptoms

    Vision - night blindness

    The cornea allows light to enter the eye.  As light passes through the eye the iris changes shape by expanding and letting more light through or constricting and letting less light through to change pupil size.  The lens then changes shape to allow the accurate focusing of light on the retina.  Light excites photoreceptors that eventually, through a chemical process, transmit nerve signals through the optic nerve to the brain.  The brain processes these nerve impulses into sight.

    Night blindness is poor vision at night or in dim light. Night blindness may cause problems with driving at night. People with night blindness often have tro...

  • Symptoms

    Vision problems

    Visual acuity tests may be performed in many different ways. It is a quick way to detect vision problems and is frequently used in schools or for mass screening. Driver license bureaus often use a small device that can test the eyes both together and individually.

    There are many types of eye problems and vision disturbances, such as: Halos Blurred vision (the loss of sharpness of vision and the inability to see fine ...

  • Test

    Visual acuity test

    Visual acuity tests may be performed in many different ways. It is a quick way to detect vision problems and is frequently used in schools or for mass screening. Driver license bureaus often use a small device that can test the eyes both together and individually.

    The visual acuity test is used to determine the smallest letters you can read on a standardized chart (Snellen chart) or a card held 20 feet away. Special ch...

  • Test

    Visual field

    The eye is the organ of sight, a nearly spherical hollow globe filled with fluids (humors). The outer layer or tunic (sclera, or white, and cornea) is fibrous and protective. The middle tunic layer (choroid, ciliary body and the iris) is vascular. The innermost layer (the retina) is nervous or sensory. The fluids in the eye are divided by the lens into the vitreous humor (behind the lens) and the aqueous humor (in front of the lens). The lens itself is flexible and suspended by ligaments which allow it to change shape to focus light on the retina, which is composed of sensory neurons.

    The visual field refers to the total area in which objects can be seen in the side (peripheral) vision while you focus your eyes on a central point. Confront...

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