The Retina: gross anatomy

Items refer to the human eye unless otherwise specified. This section leans heavily on Wyszecki and Stiles (1982) an excellent book.

• In most primates the retina is about 200-250 micrometers thick.
• The primary layers of the retina from outermost surface to innermost surface:
  • Pigment epithelium - supporting cells for the neural portion of the retina (photopigment regeneration, blood) it is also dark with melanin which decreases light scatter within the eye.
  • Rod and cone layer/Bacillary layer,Layer of photoreceptor cells - contains the outer segments and inner segments of the rod and cone photoreceptors.
  • Outer limiting membrane -
  • Outer Nuclear Layer (ONL) - cell bodies of rods & cones
  • Outer Plexiform Layer (OPL) - rod and cone axons, horizontal cell dendrites, bipolar dendrites
  • Inner Nuclear Layer (INL) - Nuclei of horizontal, bipolar and amacrine cells
  • Inner Plexiform Layer (IPL) - axons of bipolars (and amacrines), dendrites of ganglion cells
    ~35 um thick in vitro Macaque Monkey (Dacey, 1989)
    ~25 um thick in rabbit - may include shrinkage (Famiglietti, 1992a)
    • Sublamina A/Outer/Upper two thirds/substrata s1 & s2,near INL: Off-center (Famiglietti & Kolb, 1976; Nelson et al., 1978)
    • Sublamina B/Inner/Lower one third/substrata s3, s4 & s5, near GCL: On-center (Famiglietti & Kolb, 1976; Nelson et al., 1978)
    • Famiglietti breaks each strata further into an alpha, beta and gama with alpha being closest to the INL and gamma being closest to the GCL (for example, Famiglietti 1992a)
  • Layer of Ganglion cells (GCL)- Nuclei of the ganglion cells and displaced amacrine cells
  • Layer of optic nerve fibers - fibers from ganglion cells traversing the retina to leave the eyeball at the optic disk.
  

  Retinal Layers and Neurons

  Layer	Dendrites	Somas	Axons
  Photoreceptor layer	rods red green blue cones
  ONL		rods red green blue cones
  OPL			rods red green blue cones
  INL	dendrites	ChAT Amacrine (non)	axons
  IPL - A/"off" - s1	Off Midget Amacrine A2 A8~PA2	AII	Off Midget Amacrine
  IPL - A/"off" - s2	ChAT Amacrine (non/disp) A2 A3 A4 A8 A10 A19 Axon-bearing GABA Amacrine	somata	AII
  IPL - B/"on" - s3	AII Axon-bearing GABA Amacrine A3 A4 A8 A10 On Alpha	Axon-bearing GABA Amacrine	Axon-bearing GABA Amacrine
  IPL - B/"on" - s4	AII A8 A10 ChAT Amacrine (non/disp) PA2 On Alpha Dopaminergic Amacrine	somata	Dopaminergic Amacrine
  IPL - B/"on" - s5	AII A8 A10 A13 A17 A18 Dopaminergic Amacrine PA2 On Alpha	somata	Dopaminergic Amacrine
  GCL	dendrites	ChAT Amacrine (disp)PA2	axons

• Polyak 1941's retinal regions
  • Central Island - .17-.24 degrees 50-75 micrometers; longest cones and rod-free. Free of Blue cones (Williams, MacLeod & Hayhoe, 1981)
  • Foveola - 1.4 degrees, 400 micrometers; the flat pit of the fovea; about 25,000 cones
  • Blood vessel-free area - 1.4 - 2.3 degrees
  • Rod-free area - 1.7-2.0 degrees (Polyak) 1.0 degrees (Oesterberg) 500-600 micometers
  • Fovea - 5.2 degrees, 1,500 micrometers; about 110,000 to 115,000 cones
  • Parafovea - 8.6 degrees, 2,500 micrometers
  • Perifovea - 19.0 degrees, 5,500 micrometers
• Optic disk/blind spot (Example found on the net), (Photo found on net)
  • Point at which the ganglion cell axons leave the eye ball
  • oval which is taller than it is wide
  • 1.5 - 1.8 mm x 2 - 2.4 mm
  • 5 - 6 degrees x 7 - 8 degrees
  • Location
  • 4.8 mm nasal of visual pole and .47 mm above horizontal median
  • 16 degrees temporal and 1.6 degrees below in external field. (I think it is closer to 12.5 degrees in my right eye)
  • 15 degrees from foveal center in Macaque (de Monasterio et al., 1985)

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