M

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


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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

macular dystrophy
see dystrophy, macular

macular edema
see edema, macular

macular pucker
see epiretinal membrane

macular edema
see edema, macular

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 (turns the front of the eye inward)

Meibomian glands
see glands, Meibomian

membrane, Bowman’s
see Bowman’s membrane

membrane, Bruch’s
see Bruch’s membrane

membrane, Descemet’s
see Descemet’s membrane

membrane, external limiting
see external limiting membrane

membrane, internal limiting
see internal limiting membrane

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

meshwork, trabecular
see trabecular meshwork

mesoopic range
the moderately-illuminated range of light, between 0.034 cd/m˛ and 3.4 cd/m˛ (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

monochromatism
see achromatopsia

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

mucin layer
see mucoid layer

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

muscae volitantes
see floaters

muscle, ciliary
see ciliary muscle

muscle, oblique
see oblique muscle

muscle, rectus
see rectus muscle

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


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