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Related Concept Videos

Vision01:24

Vision

Vision is the result of light being detected and transduced into neural signals by the retina of the eye. This information is then further analyzed and interpreted by the brain. First, light enters the front of the eye and is focused by the cornea and lens onto the retina—a thin sheet of neural tissue lining the back of the eye. Because of refraction through the convex lens of the eye, images are projected onto the retina upside-down and reversed.
Photoreceptors and Visual Pathways01:22

Photoreceptors and Visual Pathways

At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category, whereas...
Color Vision01:24

Color Vision

Color perception begins in the retina, the light-sensitive layer at the back of the eye. Two main theories explain how colors are seen: the trichromatic theory and the opponent-process theory. The trichromatic theory, proposed by Thomas Young in 1802 and extended by Hermann von Helmholtz in 1852, suggests that color vision is based on three types of cone receptors in the retina. These cones are sensitive to different but overlapping ranges of wavelengths corresponding to red, blue, and green.
Focusing of Light in the Eye01:16

Focusing of Light in the Eye

Light rays enter the eye through the cornea, a transparent dome-shaped tissue that is the eye's outermost layer. The cornea bends or refracts, light rays traveling to the pupil. The shape of the cornea determines how much of the light is bent and whether the image will be focused correctly on the retina at the back of the eye. Once the light has passed through both refraction layers, it converges into a single focal point onto a small area. This is where photoreceptors start transforming...
Visual Agnosia01:12

Visual Agnosia

Visual agnosia is a condition characterized by the inability to recognize visually presented objects despite having normal vision. For instance, a person with visual agnosia can describe the shape and color of an object but cannot identify or name it. This impairment does not affect their visual field, acuity, color vision, brightness discrimination, language, or memory. An example of this condition in a social setting is someone at a dinner party asking for "that silver thing with a round end"...
Anatomy of the Eyeball01:20

Anatomy of the Eyeball

The eye is a spherical, hollow structure composed of three tissue layers. The outer layer — the fibrous tunic, comprises the sclera — a white structure — and the cornea, which is transparent. The sclera encompasses some of the ocular surface, most of which is not visible. However, the 'white of the eye' is distinctively visible in humans compared to other species. The cornea, a clear covering at the front of the eye, enables light penetration. The eye's middle layer, the vascular tunic,...

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Related Experiment Video

Updated: May 27, 2026

Visualizing Visual Adaptation
04:43

Visualizing Visual Adaptation

Published on: April 24, 2017

Color vision defects in school going children.

R K Shrestha1, M R Joshi, S Shakya

  • 1Department of Ophthalmology, Nepal Medical College Teaching Hospital, Jorpati, Kathmandu, Nepal. drrajeshr1@yahoo.com

JNMA; Journal of the Nepal Medical Association
|November 5, 2011
PubMed
Summary

A study found 2.1% of students in Nepal have color vision defects, with males being more affected. This prevalence is comparable to global findings, highlighting the significance of this condition.

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Area of Science:

  • Ophthalmology
  • Genetics
  • Public Health

Background:

  • Color vision defect is linked to optic nerve and retinal diseases.
  • Inherited red-green color deficiency affects a significant population.
  • Understanding prevalence is crucial for early detection and management.

Purpose of the Study:

  • To determine the prevalence of color vision defects among students in Nepal.
  • To identify potential demographic variations in color vision deficiency.

Main Methods:

  • A cross-sectional descriptive study was conducted.
  • Purposive sampling included students from various schools in Kathmandu Valley.
  • Ishihara Isochromatic color plates were used for evaluation.

Main Results:

  • 2001 students (1050 male, 951 female) were examined.
  • Overall prevalence of color vision defects was 2.1%.
  • Male students showed a 3.9% prevalence, while no female students exhibited deficiency.

Conclusions:

  • The prevalence of color vision defect in Nepal is significant.
  • Findings are comparable to international studies.
  • Further research may be warranted to explore contributing factors.