Optics Lexicon

 You will find below a lexicon explaining what is what in optics.

Accommodation: Adjustment made to the eye lens curve to allow a clear image in distance and near visions.

Age-Related Macular Degeneration (ARMD): Progressive degeneration of the macula, located at the back of the retina, causing loss of central vision, especially with old people.

Amaurosis: Complete loss of sight, either temporarily or permanently, caused by neurosensory damage to the retina and the optic passages. 

Amblyopia: Partial or relative dimness of visual acuity.

Ametropia: Sight defect that can be corrected with lenses.  There are three types of ametropias: myopia, hyperopia, and astigmatism.  Presbyopia is not an ametropia.

Aqueous humour: Transparent fluid occupying the space between the eye lens and the cornea.

Astigmatism: Sight defect caused by irregularities in the cornea or lens curve, creating a difference of focus between horizontal and vertical lines.  Astigmatism can be corrected by cylindrical or toric lenses. See image

Blepharitis: Chronic and reoccurring eyelid inflammation usually located on the rim.

Blepharospasm: Involuntary contractions (winks) of the eyelid muscles.  It is an acquired affection with no known cause. 

Blindness: Total or partial loss of sight.

Cataract: Partial or total clouding of the eye lens due to age or illness that causes a lack of transparency of the eye.  Cataract surgery has a 99% success rate.

Ciliary muscles: Small muscles connected to the crystalline lens and allowing accommodation.

Conjunctiva: Mucous membrane lining the inner surface of the eyelid and part of the ocular globe.

Conjunctivitis: Inflammation of the conjunctiva.

Cones: Conical photosensitive cells detecting shapes, colours, and very bright light and that enable vision fineness. See image
 

Cornea: Transparent membrane enclosed in the sclera and forming the front part of the ocular globe.

Daltonism (colour blindness): Hereditary colour vision defect, especially with red and green, more common to men than women.  It was identified by John Dalton, British physicist and chemist (1766-1844).

Eyebrows: The ridge over the eye or the hair growing on it.

Eyelashes: Fringe of hair edging the eyelid and protecting the eye against outside aggression.

Glaucoma: Eye disease marked by increased intraocular pressure that can result in damage to the optic nerve, affecting visual acuity, and that may lead to blindness.

Hyperopia: Ocular refraction defect where image focus is made behind the retina thus creating a blurred image.

Iris: Opaque contractile diaphragm perforated by the pupil and forming the coloured portion of the eye. 

Keratitis: Inflammation of the cornea, caused by a germ, a virus, an allergy or a neuroparalytic source.

Lacrimal glands: A pair of glands in each eye secreting lacrimal fluid (tears). See image


Lens: Biconvex lens located behind the iris and in front of the vitreous humour and by which visual accommodation is made. 

Lenses: Bifocal: Lens which upper part corrects distance vision and lower part corrects near vision.

Contact: Small plastic disk applied directly on the eye and that corrects vision problems.

Mineral: Made of glass (silica + various additives).  The mineral lens has excellent optical quality and is scratch-resistant.  It is however fragile and heavy.

Organic: Polymer lens, light but not scratch-resistant.  It absorbs shocks and may be coloured.

Polycarbonate: Thermoplastic lens, shock resistant and very clear.  It is also ultra light and thin. It was developed during the Second World War by the American army to replace glass and be bullet proof.

Progressive: This lens progressively links the corrections for distance, intermediate, and near visions without optical or visible breaks. 

Single vision: Single-focal lens to correct ametropias.  The optical power is the same throughout the lens surface.

Lysozyme: Enzyme present mostly in tears and able to dissolve various germs.

Macula (fovea, macula lutea or yellow spot): Small yellowish area located at the center of the retina where visual acuity is as its best.

Mariotte’s blind spot: Spot without photoreceptors located at the base of the optical nerve.

Melanin: Dark pigments responsible for the colour of skin, hair, and iris.

Nerve ganglia: Neurons located in the retina and transmitting messages from cones and rods to the brain via nerve fibers.

Ocular muscles: Muscles controlling the eyeball movements.

Ocular pressure: Pressure maintained inside the ocular globe.  An increase of ocular pressure is a sign of glaucoma.

Ocular refraction: Change of direction made by a light ray passing through the eye’s various layers before converging on the retina.

Ophthalmologist: Doctor specialised in eye disease treatments and correction of vision problems.

Optic chiasma: Crossed track of optic nerves in the brain.

Optic nerve: Either pair of cranial nerves that pass from the retina to the optic chiasma and conducts visual stimuli to the visual cortex.   

Optical addition: Lens’ optical power required for near vision that is added to the optical power of distance vision.

Optician: A maker of and dealer in optical items and instruments, such as corrective lenses and contact lenses.

Optometrist: Practitioner that measures the eye refraction and corrects refraction problems by using corrective lenses.

Orbit: Socket in the skull where are located the ocular globe, the optic nerve, the ophthalmic blood vessels and the oculomotor muscles and nerves.

Peripheral vision: Ability to see objects located in the outer edge of the field of vision without looking directly at them.  

Photochromic: With regards to lenses, the ability to change colour according to light.

Pigment: Colouring matter.

Presbyopia: Decrease in visual acuity in near vision caused by aging.  It may be combined with another visual defect.

Pupil: Contractile aperture in the iris of the eye.  By contracting or expanding, it regulates the amount of light penetrating the eye. See image

Retina: Sensory membrane the size of a post stamp. It contains the light-sensitive cells. See image

Retinitis Pigmentosa: Hereditary degeneration of the rods and cones causing a decrease of the visual field and eventually blindness.

Rods: Thin cylindrical cells located on the retina and reacting to light but not to colours.
Very sensitive, the rods enable sight in dimly lit conditions. See image

Scotoma: Spot in the visual field in which vision is absent or deficient. May be perceived or not.

Sclera: Dense fibrous white outer coat enclosing the ocular globe except the part covered by the cornea.

Stereoscopic vision: Ability to see objects in three dimensions.

Strabismus (squint): Imbalance of the ocular muscles causing a deviation of the axis of one eye compared to the other.

Tears: Clear saline fluid produced by the lacrimal glands.

Trachoma: Chronic contagious bacterial conjunctivitis commonly resulting in blindness.  It affects millions of people around the world especially in Mediterranean and tropical countries. 

U.V. (ultraviolet): Ultraviolet rays (UV rays) emitted by the sun are invisible and dangerous to the eyes, causing cell aging in the long run.

Uvea: Middle layer of the eye, between the sclera and the retina. 

Uveitis: Inflammation of the uvea, often bacterial, that may greatly alter vision.

Visual acuity: Ability of the eye to project a clear, sharp, and focused image on the retina.

Visual cortex: Sensory area located at the back of the cerebral cortex that receives and interprets nerve impulses coming from the eyes.

Visual field: Entire expanse of space visible without moving the eyes. See image

Vitreous humour or body: Clear colourless transparent jelly that fills the eyeball behind the lens. It gives the eye its shape and consistency. It represents 90% of the eye’s volume and is shock resistant.

Zonula: Fibril system tying the eye lens to the Ciliary body. .