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Eye Health Glossary

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nasolacrimal duct

A canal that carries tears from the lacrimal sac into the nasal cavity.

nearsightedness

See Myopia for more information.

neovascularization

Formation of new blood vessels. While this may seem beneficial, the new blood vessels are extremely fragile and are prone to bleeding, which can impair vision. Neovascularization is a classic sign of wet macular degeneration.

nevus

Congenital birth mark or mole. Nevi are most often benign and can occur in the eye without any impact on vision.

non-contact tonometer (NCT)

An automated ophthalmic instrument that is used to measure the pressure inside the eye. Better known as the “puff test” or “glaucoma test,” the NCT machine uses a short blast of air to flatten the cornea slightly. By doing this, the amount of resistance put forth by the cornea in response to the blast of air can be measured and intracular pressure (IOP) can be determined. Although a puff from the NCT machine is rather uncomfortable, it does no harm to the eye, even with soft contact lenses in.

non-proliferative retinopathy

The stage of diabetic retinopathy in which retinal blood vessels are weakening and becoming blocked, but without evidence of neovascularization occurring. Learn more about the stages of Diabetic Retinopathy.

nuclear cataract

Formation of a cataract in the nuclear region (center) of the crystalline lens. Nuclear cataract is also known as nuclear sclerosis and is a common eye condition that occurs in people over age 60. Nuclear cataract is one of the three types of cataracts. Learn more about the different types of cataracts.

nystagmus

Rapid, rhythmic, uncontrollable movement of the eyeballs. The nature of this involuntary jerking of the eyes can be a helpful symptom in diagnosing a variety of neurological and visual disorders.

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