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Related Concept Videos

The Retina01:32

The Retina

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The retina is a layer of nervous tissue at the back of the eye that transduces light into neural signals. This process, called phototransduction, is carried out by rod and cone photoreceptor cells in the back of the retina.
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Photoreceptors and Visual Pathways01:22

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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,...
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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...
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Color Vision01:24

Color Vision

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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.
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Unrenewable Cells00:50

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In humans, the photoreceptor cells of the eye and sensory hair cells of the ear lack stem cells. These cells are thus unrenewable and cannot be replaced when they are damaged or destroyed.
Photoreceptors
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Vision01:24

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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.
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Related Experiment Video

Updated: Mar 20, 2026

Transretinal ERG Recordings from Mouse Retina: Rod and Cone Photoresponses
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Transretinal ERG Recordings from Mouse Retina: Rod and Cone Photoresponses

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Why are rods more sensitive than cones?

Norianne T Ingram1, Alapakkam P Sampath2, Gordon L Fain3,4

  • 1Department of Integrative Biology and Physiology, University of California, Los Angeles, CA, 90095-7239, USA.

The Journal of Physiology
|May 25, 2016
PubMed
Summary
This summary is machine-generated.

The evolution of the duplex retina involved stepwise increases in photoreceptor sensitivity. Molecular and anatomical differences between rods and cones, including outer-segment discs, contributed incrementally to enhanced vision.

Keywords:
conesphotoreceptorrhodopsinrodsvision

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Area of Science:

  • Vision science
  • Evolutionary biology
  • Retinal physiology

Background:

  • The duplex theory of vision, proposed 150 years ago, posits two photoreceptor types: rods for dim light and cones for bright light and color.
  • This division is fundamental to retinal and visual processing in vertebrates.
  • Cone-like cells are ancient, but rod emergence was crucial for vertebrate eye evolution.

Purpose of the Study:

  • To investigate the evolutionary origins and functional basis of the duplex retina.
  • To determine which molecular and anatomical differences between rods and cones are essential for enhanced sensitivity.

Main Methods:

  • Analyzing molecular differences in protein isoforms and expression levels between rods and cones.
  • Investigating anatomical distinctions, such as membranous discs in rods.
  • Conducting experiments involving expressing cone proteins in rods and altering expression levels.

Main Results:

  • Many molecular differences in response activation and decay likely contributed incrementally to increased sensitivity during evolution.
  • Rod outer-segment discs were not essential for initial single-photon detection and evolved later.
  • Gene duplication and rod-specific proteins were key to forming the duplex retina.

Conclusions:

  • The evolution of the duplex retina was a stepwise process with incremental increases in sensitivity.
  • Molecular and anatomical adaptations in rods and cones, including outer-segment discs, collectively explain the enhanced sensitivity and the conserved physiology of the duplex retina.