Difference Between Rods and Cones

The human retina has two types of photoreceptors to gather light namely rods and cones. While rods are responsible for vision at low light levels, cones are responsible for vision at higher light levels. The light levels where both are functional are known as mesopic.

Rods

  • Capable of scotopic vision (low light levels), they have a low spatial acuity and do not mediate color
  • Populated at the periphery of the retina.
  • They are rod-shaped, facilitating vision during dim light/night
  • Contain rhodopsin pigment rich in vitamin A responsible for the night vision hence making rods sensitive to light

Cones

  • Capable of photopic vision(higher light levels), they are responsible for high spatial acuity and responsible for color vision
  • They are populated in the central fovea region and mostly found in retina
  • Help distinguish color and other fine details and are cone-shaped
  • They are of three types – long-wavelength sensitive cones(L-cones), middle-wavelength sensitive cones (M-cones) and short-wavelength sensitive cones (S-cones)
  • These contain iodopsin pigment known as violet pigment

Difference Between Rods and Cones

Following are some of the important differences between rods and cones.

Rods Cones
What it means?
Rod-shaped photoreceptors found in the eye imparting twilight vision Cone-shaped photoreceptors found in the eye and are lesser in number compared to rods
Colour vision
Do not impart color vision and are not differentiated Imparts color vision and can be differentiated into three types – red, blue and green
Integration time
Long, slow response Short, fast response
Directionally selective
No Yes
Amplification
High Less
Convergence of retinal pathways
Highly convergent Less convergent
Acuity
Low High
Location
Periphery of the retina Centre of the retina
Quantity – Out of 125 million photoreceptors found in human eye
120 million photoreceptors out of the total About 5 million photoreceptors out of the total
Outer segment – shape/pigment
Cylindrical. Comprises of rhodopsin pigment (made of vitamin A) Conical. Comprises of iodopsin pigment
Sensitivity to wavelength
Sensitive – 480nm

Insensitive – greater than 640nm

Sensitive – 420nm, 534nm, 563nm
Deficiency
Lack of rhodopsin pigment may cause night blindness Lack of iodopsin pigment may cause blindness

 

Stay tuned with BYJU’S for more on information on rods and cones and other related concepts.

 

 

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