“N” selections in the Glossary of Terms for
Anatomy, Physiology & Pathology of the Human Eye

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nanometer (nm)
millimicron; one billionth of a meter

nearpoint stress
stress placed on the ciliary muscles of the eyes from weeks or months of prolonged near work without sufficient rest; can cause eyelid twitching, eyestrain, headaches, and even myopia or increased myopia

see myopia

nerve, optic
see optic nerve

neuritis, optic
see optic neuritis

neuropathy, Leber’s hereditary optic (LHON)
see Leber’s hereditary optic neuropathy (LHON)

neuropathy, optic
see optic neuropathy

a raised freckle, usually present at birth, on the skin, choroid, or iris; contains melanocytes; sometimes can develop into a malignant melanoma

the central, most dense portion of the crystalline lens; a specialized organelle of eukaryotic cells that is essential to cellular functions (as reproduction, metabolism, and protein synthesis), is composed of nuclear fluid and a nucleoprotein-rich network from which the genetic material (chromosomes and nucleoli) arise, and is enclosed in a definite membrane; a mass of gray matter or group of nerve cells in the central nervous system

involuntary, rhythmical, repeated oscillations of one or both eyes, in any or all fields of gaze; may be pendular (with undulating movements of equal speed, amplitude, and duration, in each direction) or jerky (with slower movements in one direction, followed by a faster return to the original position); reduced acuity caused by the inability to maintain steady fixation; exact cause unknown

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