Facts and Figures concerning
the human retina


1. Size of the retina.

2. Size of optic nerve head or disc.

3. Degrees and distance in micometers.

  • One degree of visual angle is equal to 288 µm on the retina without correction for shrinkage (Drasdo and Fowler (1974).

4. Foveal position.

  • 11.8o or or 3.4 mm temporal to the optic disk edge

5. Cross diameter of the macula.

  • 3 mm of intense pigmentation, surrounded by 1 mm wide zone of less pigmentation (Polyak, 1941).

6. Cross diameter of the central fovea from foveal rim to foveal rim.

  • 1.5 mm (Polyak, 1941)
  • 1.2-1.5 mm (Ahnelt and Kolb, unpublished data)


Fig. 2a. Vertical section of the human fovea (59 K jpeg image)
Fig. 2b. Vertical section of the monkey fovea
(78 K jpeg image)

7. Cross diameter of central rod free area.

  • 400-600 µm (Polyak, 1941)
  • 750 µm (Hendrickson and Youdelis, 1984)
  • 570 µm (Yamada, 1969)
  • 250 µm (Ahnelt et al., 1987)

8. Vertical thickness of the fovea from ILM to ELM.

  • In the foveal pit 150 µm (Yamada, 1969)
  • foveal rim 400 µm

9. Central region of fovea where there are no cone pedicles.

  • 250 µm (Yamada, 1969)
  • 200 µm, (Hendrickson and Youdelis, 1984)
  • 300 µm (Ahnelt and Pfug, 1986).

10. Length of foveal axons (Henle fibres).

  • 150-300 µm (Ahnelt and Pflug, 1986).

11.Age when fovea is fully developed.

  • Not before 4 years of age (Hendrickson and Youdelis, 1984).

12. Highest density of cones at center of the fovea (50 x 50 µm).

  • 147,000/mm2 (Osterberg, 1935)
  • 178,000-238,000/mm2 (Ahnelt et al., 1987)
  • 96,900-281,000/mm2 mean161,900/mm2 (Curcio et al., 1987).

Fig. 3. Hexagonal packing of cone mosaic in central human fovea (59 K jpeg image)

13. Total number of cones in fovea.

  • Approximately 200,000. 17,500 cones/degree2. Rod free area is 1o thus there are 17,500 cones in the central rod-free fovea.

14. Total number of cones in the retina.

    6,400,000 (Osterberg, 1935).

15. Total number of rods in the retina.

  • 110,000,000 to 125,000,000 (Osterberg, 1935).

16. Rod distribution.

  • Rods peak in density 18o or 5mm out from the center of the fovea in a ring around the fovea at 160,000 rods/mm2
  • No rods in central 200 µm.
  • Average 80-100,000 rods/mm2
  • Rod acuity peak is at 5.2o or 1.5 mm from foveal center where there are 100,000 rods/mm2 (Mariani et al.,1984).

Fig. 4. Density plot of rods and cones on the horizontal meridian of the human retina (59 K jpeg image)

17. Number of axons in the optic nerve.

  • 564776-1,140,030 (Bruesch and Arey, 1942)
  • 800,000-1,000,000 (Polyak, 1941)
  • 1,200,000 (Quigley et al., 1982; Balaszi et al., 1984).

18. Number of cones to ganglion cells in the fovea.

  • 1 cone to 2 ganglion cells out to about 2.2o (Schein, 1988).

19. Number of cones/retinal pigment epithelial cell (RPE).

  • 30 cones/RPE in fovea (Rapaport et al., 1995).

20. Number of rods/retinal epithelial cell (RPE).

  • In periphery 22 rods/RPE cell

  • In rod peak (4-5 mm from foveal center) 28 rods/RPE cell (Rapaport et al.,1995).

21. Useful Units in Vision Science (Wandell, 1995).

  • Radiometric units represent a physical measurement e.g., radiance is measured in watts sr -1 m-2.

  • Calorimetric units adjust radiometric units for visual wavelength sensitivity e.g., luminance is measured in candela per square meter, cd/m2.

  • Lux are units of illumination. Thus a light intensity of 1 candela produces an illumination of 1 lux at 1 meter.

    • Scotopic luminance units are proportional to the number of photons absorbed by rod photoreceptors to give a criterion psychophysical result.

    • Photopic luminance units are proportional to a weighted sum of the photons absorbed by L- and M-cones to give a criterion psychophysical result.

  • Typical ambient luminance levels (cd/m2):.

    • Starlight: 0.001

    • Moonlight: 0.1

    • Indoor lighting: 100

    • Sunlight: 10.000

    • Maximum intensity of common CRT monitors: 100

  • One Troland (Td) of retinal illumination is produced when an eye with a pupil size of 1 mm2 looks at a surface whose luminance is 1 cd/m2.

  • Lens focal length: f(meters); lens power= 1/f (diopters).

22. Image formation (Wandell, 1995).

  • The eyes are 6 cm apart and halfway down the head.

  • Visual angle of common objects (degrees, deg)

    • The sun or moon = 0.5 deg

    • Thumbnail (at arm's length) = 1.5 deg

    • Fist (at arm's length) = 8-10 deg

  • Visual field (measured from central fixation)

    • Monocular: 160 deg (w) x 175 deg (h)

    • Binocular: 200 deg (w) x 135 deg (h)

    • Region of binocular overlap: 120 deg (w) x 135 deg (h)

  • Range of pupil diameters: 1-8 mm.

  • Refractive indices.

    • Air: 1.000
    • Glass: 1.520
    • Water: 1.333
    • Cornea: 1.376

  • Optical power (diopters).

    • Cornea: 43
    • Lens (relaxed): 20
    • Whole eye: 60
    • Change in power due to accomodation: 8

  • Axial chromatic aberration over the visible spectrum: 2 diopters.

  • Visible spectrum: 370-730 nanometers (nm)

  • Peak wavelength sensitivity:
    • Scotopic: 507 nm
    • Photopic: 555 nm

  • Spectral equilibrium hues:
    • Blue: 475 nm
    • Green: 500 nm
    • Yellow: 575 nm
    • No spectral equilibrium: red

    References.

    Ahnelt, P. K. and R. Pflug (1986) Telodendrial contacts between foveolar cone pedicles in the human retina. Experientia 42, 298-300.

    Ahnelt, P. K., Kolb, H. and Pflug, R. (1987) Identification of a subtype of cone photoreceptor, likely to be blue sensitive, in the human retina. J. Comp. Neurol., 255, 18-34.

    Balaszi, A. G., Rootman, J., Drance, S. M., Schuttzer, M. and Douglas, G. R. (1984) The effect of age on the nerve fibre population of the human optic nerve. Am. J. Ophthal., 97, 760-

    Bruesch, S. R. and Arey, L. B. (1942) The number of myelinated and unmyelinated fibres in the optic nerve of vertebrates. J. Comp. Neurol., 77, 631-

    Curcio, C. A., Sloan, K. R., Packer, O., Hendrickson, A. E. and Kalina, R. E. (1987) Distribution of cones in human and monkey retina: individual variability and radial asymmetry. Science 236, 579-582.

    Drasdo, N. and Fowler, C. W. (1974) Non-linear projection of the retinal image in a wide-angle schematic eye. Br. J. Ophthal., 58, 709-714.

    Hendrickson, A. E. and Youdelis, C. (1984) The morphological development of the human fovea. Ophthalmol. 91, 603-612.

    Mariani, A.P., Kolb, H. and Nelson, R. (1984) Dopamine-containing amacrine cells of rhesus monkey prarallel rods in spatial distribution. Brain Res. 322, 1-7.

    Michels, R.G., Wilkinson, C.P. and Rice, T.A. (1990) Retinal detachment. p 17. The C.V. Mosby Company.

    Osterberg, G. (1935) Topography of the layer of rods and cones in the human retina. Acta Ophthal., suppl. 6, 1-103.

    Penkhus, J. (1965) The ora serrata and its anatomical variations. M.S. Thesis, Univ. of California, Los Angeles.

    Polyak, S.L. (1941) The Retina. University of Chicago Press, Chicago.

    Quigley, H. A., Addicks, E. M. and Green, W. R. (1982) Optic nerve damage in human glaucoma: III Quantitative correlation of nerve fibre loss and visual defect in glaucoma ischemic neuropathy and toxic neuropathy. Arch. Ophthal., 100, 135-

    Rapaport, D.H., Rakic, P., Yasamura, D. and LaVail, M.M. (1995) Genesis of the retinal pigment epithelium in the macaque monkey. J. Comp. Neurol. 363, 359-376.

    Schein, S. J. (1988) Anatomy of macaque fovea and spatial densities of neurons in foveal representation. J. Comp. Neurol., 269, 479-505.

    Van Buren, J.M. (1963) The retinal ganglion cell layer. Charles C. Thomas, Springfield, Illinois.

    Wandell, B.A. (1995) Foundations of Vision. Sinauer Associates, Inc. Sunderland, Massachussets.

    Yamada, E. (1969) Some structural features of the fovea centralis in the human retina. Arch. Ophthal., 82, 151-159.