of what we know about the function of our eyes is the result
of studies that began over 50 years ago on the large, compound
eyes of the horseshoe crab. Its eyes have a relatively simple
construction, and the optic nerve is readily accessible.
In addition, it is easy to keep Limulus alive in
the laboratory, making it an ideal animal for eye research.
In 1967, Dr. H. Keffer Hartline received the Nobel Prize for
his research on horseshoe crab vision. He discovered how sensory
cells in the retina help the brain process visual cues, enabling
horseshoe crabs to see lines, shapes, and borders. This mechanism,
called lateral inhibition, allows horseshoe crabs to distinguish
mates in murky water. Research of this type is helpful to understanding
human eye diseases like retinitis pigmentosa, which causes
tunnel vision and can lead to total blindness.
on Hartline's lateral inhibition research, Dr.
a professor of ophthalmology at the State University of New
York, is investigating the role of vision in potential mate
selection. Using computer models, Dr. Barlow analyzed how the
brain of a horseshoe crab processes signals transmitted from
the eyes and optic nerve. In the future, decoding this pathway
may provide valuable information for correcting human vision
| Horseshoe Crab Vision Research Milestones
||The cornea of Limulus eyes is first examined.
||Scientists describe the median eyes — each has a single
lens and is a simple eye.
|| Scientists investigate the anatomy of the lateral eyes
(a complex eye composed of
thousands of small hexagonal eyes called ommatidia — like in a honeybee).
|| Dr. H. Keffer Hartline studies electrical impulses in the horseshoe crab optic nerve.
||The eye of Limulus is the first in which electrical responses are recorded from a single visual receptor.
Scientists identify the visual pigment in Limulus eye to be rhodopsin.
Rhodopsin: a light-sensitive protein in the retina that helps trigger nerve
impulses between the optic nerve and the brain. Click
here for more information on rhodopsin.
||Nobel prize is awarded to Dr. Hartline for research on vision in horseshoe crabs.
||Research studies reveal that a horseshoe crab's eyes are one million times more sensitive to light at night.
||Scientists discover that the sensitivity to light of the horseshoe crab's retina to light is regulated by an internal clock.
||Studies identify a circadian clock in the horseshoe crab's brain that enhances night vision.
||It is found that the simple eyes (median ocellus) of the horseshoe crab function as UV receptors, sending signals to the lateral eyes. Changes in UV light intensity provide the cue to turn off lateral inhibition, enabling horseshoe crabs to see better at night.
||Dr. Robert Barlow and colleagues discover vision plays a role in mating behavior. The circadian clock influences perception of contrast and form, and helps male horseshoe crabs detect potential mates.
|| Dr. Barlow designs a "CrabCam" to investigate
underwater vision in horseshoe crabs.
||A computer model of the lateral eye is developed by Dr.
Barlow to understand how horseshoe crabs find their mates
in varying light conditions.