Glossary

A glossary of terms in alphabetical order is provided for Patients as follows.

Accommodation – ability to change lens shape to obtain clear near (and distance) vision; accommodation is lost progressively as the eye ages, necessitating use of reading glasses in most adults over age 45; stronger magnification is required for clear near vision as progressive loss of accommodation occurs

Astigmatism – distorted vision due to unequal focusing power in different areas of the cornea and/or lens; in technical terms, astigmatism is one type of optical aberration that may blur vision

Binocular uncorrected distance visual acuity (Binocular UDVA) – the visual acuity of both eyes (without aid of spectacles or contact lenses) used simultaneously for distance vision – typically measured using an eye chart with a Snellen scale for distance visual acuity

Binocular uncorrected near visual acuity (Binocular UNVA) – the visual acuity of both eyes (without aid of spectacles or contact lenses) used simultaneously for near vision – typically measured using an eye chart with a Jaeger scale for near visual acuity

Conductive keratoplasty (CK) – cornea reshaping by a “poke in the eye with a sharp stick” procedure that heats cornea tissue with radiofrequency energy emanating from the stick (needle) to change cornea shape

Cornea – the “window” of the eye – a transparent curved tissue that provides most of the focusing power of the eye; the lens provides almost all the remaining focusing power and has the ability (in youth) to “accommodate” its shape (hence, focusing power) for distance, intermediate and near vision requirements

Cornea epithelium – the outer layer of cornea cells – the epithelium has many important ocular functions, including maintenance of cornea hydration state, protection from microbial attack, and foundation for the tear film (i.e., the actual interface with air that produces refraction and focusing of light)

Cornea stroma – the structural tissue of the cornea that accounts for over 90% of the cornea thickness

Diopter (D) – a measure of focusing power, equal to 1 divided by the focal length of the lens measured in meter (m) units – the normal eye has ca. 43 D of focusing power for distance vision and requires an additional 3 D for near (“reading”) vision

Distance vision – vision required to see distant [i.e., 3 meters (10 feet) or farther] objects clearly

Emmetropia – The condition of the normal eye when parallel rays are focused exactly on the retina and vision is perfect; perfect distance vision

Hyperopia – farsightedness (AKA longsightedness) – inadequate eye focus for distance vision

Jaeger scale – a near vision scale in which:

  • J1+ is fine “normal” near vision (equivalent to 20/20 in Snellen terms) - the ability to read the bottom line (in 3-point font letters) on a near vision eye chart;
  • J1 is good near vision (equivalent to 20/25 in Snellen terms) - the ability to read the next-to-bottom line (in 4-point font letters) on a near vision eye chart;
  • J2 and J3 are fair and functional near vision, respectively (equivalent to 20/30 and 20/40, respectively, in Snellen terms) - the ability to read lines 3 and 4, respectively, from the bottom on a near vision eye chart – J3 is “reading vision” for 6-point font letters

Keratoplasty – cornea reshaping

Laser – acronym of Light Amplification by Stimulated Emission of Radiation; a light source with enhanced characteristics such as coherence, monochromaticity and spectral brightness

Laser thermal keratoplasty (LTK) – cornea reshaping by laser heating of cornea tissue

Monovision – using one eye for distance vision and the fellow eye for near vision

Multifocal – having more than one focusing power

Myopia – excessive eye focus for distance vision

Near vision – vision required to see near (e.g., 0.5 meter distance or closer) objects clearly; “reading” vision is usually considered to be that required to read text in 6-point font letters at ca. 0.35 meter (14 inches) from the eye – “short arm syndrome” occurs as presbyopia advances progressively with age

Optimal Keratoplasty (Opti-K®) – cornea reshaping to provide optimal vision for both distance and near vision tasks

Plano – without refractive error for distance vision

Presbyopia – Greek for “old eye” – inadequate near vision due to insufficient lens accommodation

Refraction – change of direction of light rays passing through an interface such as the air/tear film interface

Snellen scale – a distance vision scale in which:

  • 20/16, 20/12.5 or 20/10 is superlative distance vision – the ability to read lines 3, 2 or 1, respectively from the bottom on a distance vision eye chart;
  • 20/20 is fine “normal” distance vision – the ability to read line 4 from the bottom on a distance vision eye chart;
  • 20/25 is good distance vision – the ability to read line 5 from the bottom on a distance vision eye chart;
  • 20/32 and 20/40 are fair and functional distance vision, respectively – the ability to read lines 6 and 7, respectively, from the bottom on a distance vision eye chart – 20/40 vision is required in most states to drive a vehicle without corrective lenses

Treatment (Tx) – for Opti-K®: noninvasive procedure performed to change cornea shape

Uncorrected distance visual acuity (UDVA) – the visual acuity of an eye (without aid of spectacles or a contact lens) for distance vision – typically measured using an eye chart with a Snellen scale for distance visual acuity

Uncorrected near visual acuity (UNVA) – the visual acuity of an eye (without aid of spectacles or a contact lens) for near vision – typically measured using an eye chart with a Jaeger scale for near visual acuity

Visual Acuity – the "sharpness" of vision – in technical terms, the ability to resolve images (such as letters on an eye chart); refractive blur or other problems (such as lens opacification) may adversely affect visual acuity (VA) – see also Jaeger scale and Snellen scale entries above