Vision Related Words and Terms Glossary of Terms

  • Acuity
    Clearness, sharpness. The ability to recognize small detail. This is not the same as the ability to detect objects.
  • Alternating Attention
    The ability to focus attention between different types of tasks. For example, reading a map while driving.
  • Binocular Vision
    Vision from both eyes simultaneously.
  • Contrast Sensitivity
    The ability to detect object of low contrast (objects similar in color or shape). For example, detecting an oncoming car on a foggy day or recognizing a street sign parallel to a fence.
  • Cornea
    The clear, transparent coating over the lens and iris.
  • Decreased Acuity
    Inability to see clearly. This can cause a delay in responding to the environment. For example, a person with decreased acuity may be slow to recognize signs at a distance. The ability to see clearly decreases as light levels decrease.
  • Depth Perception
    The ability to see three dimensions. If depth perception is impaired, the person may have difficulty judging distances.
  • Divided Attention
    The ability to respond simultaneously to multiple tasks. For example, maintaining the path of travel while turning the head to check blind spots.
  • Focused Attention
    The ability to respond to specific visual, auditory, or tactile stimuli.
  • Glare Disability
    Glare refers to the disruption of vision which results from the presence of a veiling light source. Problems of glare are typically greater under low light conditions.
  • Heterotropia
    Deviation of the eyes due to the absence of binocular equilibrium. In other words, the vision in one eye is not balanced with the other. This can cause double vision; seeing two of the same object.
  • Impaired Figure Ground
    Unable to distinguish foreground from background. A person affected by this impairment will have difficulty finding the stop sign among other stimuli in the environment. The driver may have difficulty finding dashboard controls quickly.
  • Iris
    The colored membrane between the cornea and the lens. The iris is a muscle surrounding the pupil.
  • Lens
    A transparent, colorless structure within the eye which focuses images and rays of light on the retina.
  • Optic Atrophy
    Deterioration of the optic nerve.
  • Optic Nerve
    The nerve that carries the impulses for the sense of sight from the eye to the brain.
  • Optic Neuritis
    Inflammation of the optic nerve.
  • Peripheral Awareness
    A person may have limited peripheral vision but can have peripheral awareness if eye scanning movements are increased to compensate for the vision deficit.
  • Pupil
    The opening at the center of the iris. It dilates in low light levels and constricts in bright light. The pupil regulates the light flow on the retina.
  • Refractive Errors
    Conditions in which the lens system of the eye is not properly focused.
  • Retina
    The inside light sensitive lining of the eye which receives the image from the lens.
  • Selective Attention
    The ability to maintain a focused attention among distracting or competing stimuli. For example, driving downtown in rush-hour traffic.
  • Snellen
    Hermann Snellen (1834-1908) was a Dutch opthamologist who introduced a method of measuring and recording visual acuity. A fraction is used to compare a person's vision to standard vision.

    Vision = distance at which the subject recognizes an object distance at which a standard eye recognizes an object.
    20/40 means a person must be twice as close to an object to see its detail compared to the standard eye.
    20/100 means a person must be five times as close to an object to see its detail compared to the standard eye.

  • Spatial Neglect
    The person does not acknowledge one side of the environment. This driver may drift to one side in his/her lane with little or no improvement when cued. This driver may also make unsafe lane changes or turns through crosswalks.
  • Spatial Relationships Deficit
    The person will be unable to determine their position in relationship to two or more objects in the road or their relationship to each other. This person may be able to drive in light traffic or in residential areas. However, as the complexity of the driving environment increases, the driver will have problems knowing what to do. This may result in the person slowing down in traffic to determine what to do next.
  • Stereoscopic Vision
    Binocular depth perception.
  • Sustained Attention
    The ability to maintain consisttention during a continuous and repetitive activity such as driving on an interstate freeway for long periods of time.