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An example of the Landolt C eye chart (also known as the Japanese eye chart). Numerous types of eye charts exist and are used in various situations. For example, the Snellen chart is designed for use at 6 meters or 20 feet, and is thus appropriate for testing distance vision, while the ETDRS chart is designed for use at 4 meters. [16]
Some clinics do not have 6-metre eye lanes available, and either a half-size chart subtending the same angles at 3 metres (9.8 ft), or a reversed chart projected and viewed by a mirror is used to achieve the correct sized letters. In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres.
A manual pupillometer measures pupil size via a comparison chart method. There are several types of manual pupillometers. The most common type is the Haab scale, or Haab's pupillometer, which is a series of graduated filled circles on a slide ruler. [2]
For an adequate test, vision must not be entirely lost. In dim room light, the examiner notes the size of the pupils. The patient is asked to gaze into the distance, and the examiner swings the beam of a penlight back and forth from one pupil to the other, and observes the size of pupils and reaction in the eye that is lit.
The Neurological Pupil index, or NPi, is an algorithm developed by NeurOptics, Inc., that removes subjectivity from the pupillary evaluation. A patient's pupil measurement (including variables such as size, latency, constriction velocity, dilation velocity, etc.) is obtained using a pupillometer, and the measurement is compared against a normative model of pupil reaction to light and ...
The more difficult the task, the greater pupil diameter observed from the time preceding the solution [58] until the task was completed. [59] While these discoveries from the 1960s sparked renewed interest in the psychological significance of pupil size, research had substantially earlier identified the relationship between pupil size and effort.
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By analogy with a camera, the pupil is equivalent to aperture, whereas the iris is equivalent to the diaphragm. It may be helpful to consider the Pupillary reflex as an 'Iris' reflex, as the iris sphincter and dilator muscles are what can be seen responding to ambient light. [2] Whereas, the pupil is the passive opening formed by the active iris.