Macula lutea
the small yellowish area, lying slightly lateral to the center of the retina, that constitutes the region of maximum visual acuity and is made up almost wholly of retinal cones
Macular degeneration, dry
age-related macular degeneration (ARMD or AMD); atrophic degenerative process of the pigment epithelial cells in the central area of the retina, the macula, causing a subsequent loss of function of the overlying photoreceptor cells; can cause complete loss of central vision and legal blindness; affects about 90 percent of those with the disease but accounts for about 10 percent of all severe vision loss from ARMD
Macular degeneration, wet
age-related macular degeneration (ARMD or AMD); caused by abnormal blood vessel growth (choroidal neovascularization or CNV) and leakage of blood and fluid beneath the central area of the retina, the macula, often in response to the damage done from dry ARMD; can cause complete loss of central vision (more devastating than in dry ARMD) and legal blindness; can be treated with a laser to seal off leaking blood vessels and help to prevent further vision loss, but damaged areas are lost permanently; affects about 10 percent of those with the disease
Malignant melanoma
cancer that forms in melanocytes, typically in the skin, but also in the choroid, iris, and sometimes conjunctiva; may metastisize to other parts of the body
Marcus Gunn pupil
a relative afferent pupillary defect (RAPD) in which the pupil of a diseased eye will dilate, rather than constrict, whenever a light being alternated from one pupil to the other (the “swinging flashlight test”) is shined into the affected pupil; commonly found in an eye with optic nerve disorders (such as optic neuritis, ischemic optic neuropathies, glaucoma, traumatic optic neuropathy, inherited optic neuropathy, optic nerve tumor, orbital disease, radiation optic nerve damage, optic atrophy, and surgical damage to the optic nerve); less commonly found in ischemic retinal disease, ischemic ocular disease, retinal detachment, severe macular degeneration, intraocular tumor, retinal infection, severe amblyopia, and cerebral vascular disease)
Medial rectus muscle
an extraocular muscle in the orbit, originating in the annulus of Zinn; innervated by the oculomotor nerve (cranial nerve III); adducts the eye
Meningitis
inflammation of the meninges, and especially of the pia mater and the arachnoid, of the brain; can be caused by various infectious agents, including viruses, fungi, and protozoa, but bacteria produce the most life-threatening forms
Mesoopic range
the moderately-illuminated range of light, between 0.034 cd/m² and 3.4 cd/m² (candela per meters squared), in which both cones and rods in the retina respond; most commonly present at dawn or dusk
Microaneurysm
a saccular enlargement of the venous end of a retinal capillary, especially associated with diabetic retinopathy
Microcysts
incompletely formed cells which move through the epithelium with normal cellular turnover; most likely due to hypoxia, as from extended contact lens wear
Monovision fit
a method of fitting contact lenses, especially for a presbyopic person, where the contact lens on one eye focuses that eye at far distance and the contact lens on the other eye focuses that eye at near, enabling the person to see far and near without glasses, but at the expense of optimum depth perception
Mucoid layer
mucin layer; the hydrophilic inner layer of the tear film coating the anterior surface of the cornea; produced by goblet cells in the bulbar conjunctiva
Multiple sclerosis (MS)
disease of the brain and spinal cord caused by an unknown agent that gradually destroys the myelin covering, or sheath, of nerve fibers, resulting in a temporary interruption or disordered transmission of nerve impulses, particularly in pathways concerned with vision, sensation, and the use of limbs; disruption of impulse transmission may cause mild to moderate symptoms (numbness in the limbs to complete and permanent paralysis); onset generally occurs between ages 20 and 40, with symptoms appearing at irregular intervals for years
Myopia
nearsightedness; a condition in which visual images come to a focus in front of the retina of the eye and vision is better for near than for far objects; may be due to the surface(s) of the cornea and/or crystalline lens having excessive (too steep) curvature, an eyeball which is too long, and/or an index of refraction of one of the ocular media that is too high
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
Neuropathy, Leber’s hereditary optic (LHON)
see Leber’s hereditary optic neuropathy (LHON)
Nevus
a raised freckle, usually present at birth, on the skin, choroid, or iris; contains melanocytes; sometimes can develop into a malignant melanoma
Nucleus
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
Nystagmus
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
Oblique muscle
either of two muscles, the superior oblique (a long thin muscle that arises just above the margin of the optic foramen, is inserted on the upper part of the eyeball, and moves the eye downward and rotates the top of the eye nasally) or the inferior oblique (a short muscle that arises from the orbital surface of the maxilla, is inserted slightly in front of and below the superior oblique, and moves the eye upward and rotates the top of the eye temporally)
Ophthalmologist (M.D.)
medical doctor (physician and surgeon) specializing in the structure, functions, and diseases of the eye, treating with medications, surgeries, and lasers
Optometric physician (O.D.)
optometrist specializing in the structure, functions, and diseases of the eye, often treating with medications, surgeries, and lasers
Optometrist (O.D.)
doctor of optometry concerned with examination, diagnosis, and treatment of the eyes and related structures and with determination and correction of vision problems using lenses and other resources, such as low vision aids and visual therapy
Optical infinity
the least distance (simulating a virtually infinite distance) at which there is no significant accommodation by a viewer’s crystalline lens
Optic atrophy
degeneration of the optic nerve, causing severe vision loss and even blindness
Optic chiasm
optic chiasma; the X-shaped partial decussation on the undersurface of the hypothalamus through which the optic nerves are continuous with the brain
Optic disc (or disk)
optic nerve head in the eye, in which no photoreceptors are present, thus resulting in a blind spot in the visual field
Optic nerve
cranial nerve II; the sensory nerve which carries electrical impulses from visual stimuli in the retina out of the eye, across the optic chiasm, and to the ventral part of the diencephalon, on their way to the visual cortex in the occipital cortex of the brain for interpretation
Optic neuritis
inflammation of the optic nerve within the eyeball (papillitis) or behind the eyeball (retrobulbar optic neuritis)
Optic neuropathy
an abnormal and usually degenerative state of the optic nerve
Optic neuropathy, ischemic
“stroke” of the optic nerve; a sudden loss of central vision and/or side vision because of reduced blood flow to the optic nerve; can be arteritic (due to an inflammation of the arteries supplying the optic nerve, such as temporal arteritis) or non-arteritic (due to disorders such as diabetes, malignant hypertension, eclampsia (high blood pressure during pregnancy), migraine, and systemic lupus erythematosus, arteriosclerosis, shock, carotid artery disease, and collagen vascular disease)
Optic neuropathy, non-ischemic
optic nerve damage caused by such things as toxicity (from overdose of drugs such as barbiturates, DDT, alcohol, lead, aniline dyes, and medical drugs such as digitalis, ergotamine, inderal, and ethambutol), nutritional deficiency, glaucomatous optic nerve disease, and Leber’s hereditary optic neuropathy
Optic radiation
the portion of the optic fibers between the lateral geniculate body, located in the thalamus of the brain, and the striate cortex (or Brodmann’s Area 17) in the occipital lobe of the brain
Optic tract
the portion of the optic fibers between the optic chiasm and the lateral geniculate body, located in the thalamus of the brain
Optician
a maker of or dealer in optical items and instruments; a person who reads prescriptions for visual correction, orders lenses, and dispenses eyeglasses and contact lenses
Optometrist
a doctor of optometry who examines the eyes and associated structures to determine refractive errors, extraocular muscle imbalances, and pathological conditions, prescribing glasses or contact lenses, eye exercises, and in some cases topical and systemic drugs to treat ocular disorders
Ora seratta
the serrated junction between the retina and the ciliary body; marks the transition from the simple non-photosensitive area of the retina to the complex, multi-layered photosensitive region
Orbit
eye socket; the bony cavity of the skull that contains the eye
Outer nuclear layer
layer of the retina containing the cell bodies of the photoreceptors (cones and rods)
Outer plexiform layer
layer of the retina containing the axons of photoreceptor (cone and rod) cells, as well as the dendrites of horizontal cells and bipolar cells
