The Human Eye

The Human eye is a remarkable instrument with respect to both sensitivity and resolution

In clear air a candle flame is just visible at a distance of ten miles

Figure - Human eye: Anatomy of the human eye (from Fischler and Firsheim, 1987)


Some of the parameters of the human visual system are:

  • 120 million rod cells in each eye
  • 6 million cone cells in each eye
  • 2000 cone cells in each fovea in the region of maximum uniform density
  • 1 million nerve fibers in the optic nerve exiting each eye
  • 250 million receptor cells in the two eyes versus 250 000 elements in a TV picture
  • Distance from effective center of lens to fovea: 17mm
  • Interpupillary distance: 50 to 70mm
  • Visual angle subtended by fovea: 20 min of arc for region uniform max. cone density , 1-2 deg for rod-free area
  • Angle with respect to visual axis of eye at which rod density is maximum: 15 to 20 degrees
  • Rod cells are about 500 times more sensitive to light than cone cells
  • Wavelength of visible part of electromagnetic spectrum : 0.4 to 0.7 micrometers
  • Wavelength of maximum rod sensitivity: 0.51 micrometers (green)
  • Wavelength of maximum cone sensitivity: 0.56 micrometers (orange)
  • Intensity range : 10 exp 16 (160 decibels)
  • Minimum visual angle at which points can be separately resolved: 10 to 60 seconds for dots
  • Object distance from eye for stereoscopic depth perception: 10 in to 1500 ft
  • Involuntary eye movements: 10 to 15 seconds of arc for tremor, slow drift of up to 5 min of arc
  • Wavelength of maximum cone sensitivity: 0.56 micrometers (orange)


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Last modified on April 05, 1999, G. Scott Owen,