Glossary

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Accommodation:

 An ocular adjustment for the sharp focusing of objects viewed at different distances is termed as accommodation.

Amblyopia: 

Amblyopia is defined as unilateral or bilateral partial loss of sight without any ophthalmoscopic sign. 

Amsler Grid: 

It is a test featuring horizontal and vertical lines, usually white on black background, used to test central visual field defects like Macular Degeneration. 

Antioxidants: 

They are micronutrients, which destroy or neutralize free radicals, molecules, which have been implicated as one causative factor in the stimulation of abnormal cellular reproduction (cancer) and cellular destruction (aging). 

Aqueous: 

It is a clear watery fluid that bathes the inside of the front part of the eye, providing nutrition to the cornea and the lens. 

Age Related Macular Degeneration:  

It is an age related breakdown of the macula that causes a loss of central vision and even blindness in advanced cases. 

Astigmatism: 

Astigmatism is that condition wherein the refraction varies in the different meridians of the eye. 

Binocular vision: 

It is the simultaneous use of the two eyes. Normal binocular vision yields a stereoscopic image and parallax-induced depth perception. 

Blind spot, physiological blind spot: 

It is a small white oval shaped area on the retina of the eye from which the optic nerve emerges, the spot is insensitive to light because it lacks nerve endings that are responsive to light, which can be seen through an ophthalmoscope. It is not noticed in binocular vision because a sensitive area in the other covers the blind spot in the visual field of one eye. 

Cataract: 

A cataract is a cloudy or opaque area in the natural lens of the eye. As the opacity thickens, it prevents the light rays from passing through the lens and being focused on the retina. 

Colour Vision:  

It is the ability to perceive differences in colour, including hue, saturation and brightness. 

Conjunctivitis: 

Conjunctivitis, commonly known as "pink eye", is an inflammation of the membrane (conjunctiva) that covers the eye and lines the inner surface of the eyelid. 

Conjunctiva: 

The conjunctiva is a clear membrane that is the tough, leathery outer coat of the eye. 

Convergence/ Divergence: 

It is the turning of the eyes inwards/ outwards so that they are both “ aimed ” towards the object being viewed. 

Cornea: 

The cornea is the curved transparent front surface of the eye. It is a tough, five-layered membrane that focuses light. 

Corneal Curvature: 

It is the shape of the front surface of the eye. 

Crystalline Lens: 

The lens of the eye is a transparent, biconvex, avascular structure. It is located directly behind the iris and pupil, which focuses light onto the retina. It has the ability to vary its power to accommodate and focus light from objects at all distances. 

Depth Perception: 

The ability of the visual system to perceive the relative positions of objects in the visual field. 

Diplopia: 

A condition in which a single object is perceived as two; it is also called double vision.  

Emmetropia: 

It is the medical term used for Normal vision. 

Glaucoma: 

Glaucoma is a symptomatic condition of the eye in which the intraocular pressure exceeds the tolerance of the affected eye resulting in optic nerve damage and irreversible visual field defects. 

Hyperopia: 

Hyperopia or Farsightedness is an error of refraction wherein parallel rays of light come to a focus behind the retina. A hyperopic person will have no problem seeing objects in the distance, but there will be difficulty in focusing clearly on near objects.

Intraocular Pressure:

The fluid pressure within the eye created by the continual production and drainage of aqueous fluid in the anterior chamber is known as the Intraocular Pressure. 

Iris:

The iris is the pigmented structure that gives our eyes their colour. 

Keratitis: 

It is the inflammation of the cornea. 

Monovision: 

Monovision is a situation where one eye (usually the dominant eye) is corrected for distance, and the other eye is corrected for reading. 

Myopia: 

It is the dioptric condition of the eye in which parallel rays of light form infinity come into focus in front of the retina. A Myopic person can see clearly objects upclose, but everything in the distance is blurred. 

Neovascularization: 

The formation of new blood vessels, often fragile and inappropriate for the location. 

Ocular Hypertension: 

It is the elevated fluid pressure. The normal pressure is about 10 to 20mmHg, with the majority of people falling between 13 and 19. Over 20 is considered “suspicious”, over 24 “cautiously concerned” and warranting immediate investigation, and over30 is considered to be “urgent” and a potential emergency situation. 

Optic Nerve, Optic Nerve Head: 

It is a bundle of nerve fibers that connects the eye to the brain. It is a part of the visual pathway. The optic nerve carries the impulses formed by the retina to the brain, which interprets them as images. 

Ophthalmoscopy: 

It is an examination of the internal structures of the eye using an illumination and magnification system.  

Orthokeratology: 

A non-surgical procedure using contact lenses to alter the shape of the cornea to effect a change in the refractive error. 

Photophobia: 

Sensitivity to light is known as Photophobia.

Presbyopia: 

Presbyopia which is also known as the aging eye is the condition when one starts to experience difficulty in reading and focusing on things close up, it is usually noticed first around the age of 45 and is a progressive condition. 

Pupil:

The pupil is an aperture in the middle of the iris that determines the amount of light entering the eye. 

Refraction: 

Determination of the optical refractive errors of the eye is known as Refraction. 

Refractive Error:

It is the degree to which images received by the eyes are not focused on the retina, e.g.: Myopia, Hyperopia and astigmatism. 

Retina: 

The innermost layer of the eyeball is known as the retina. It is the tissue that transforms light into electrical impulses that are transmitted to the brain to create our sense of vision. 

Retinal Detachment: 

It is the separation of the retina from its normal location covering the inner surface of the back portion of the eye. 

Strabismus: 

Strabismus is the medical term relating to a misalignment of the eyes. It is a lack of coordinated muscle movement or focusing ability between the eyes, causing the eyes to point in different directions. 

Ultraviolet Radiation: 

During the 19^th century, scientists discovered that beyond the violet end of the spectrum radiation could be detected that was invisible to the human eye but that had marked photochemical action; this was termed as ultraviolet radiation. 

Visual Acuity:

The clearness of vision, which depends upon the sharpness of the retinal image.

Visual Field:

The area or extent of space visible to an eye in a given position of gaze. There is central visual field, that is directly in front of us, the target at which we are looking and a peripheral visual field, which we perceive as our “side vision”. The fields of each eye partly overlap. We do not perceive the blind spot from each eye because the area that is missing in one eye is present in the other.

Vitreous:

The gel like transparent fluid substance filling the posterior four fifths of the globe between the crystalline lens and retina. 

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