Question

1. Describe 3 dark adaptation experiments that are designed to obtain the following:

1. Pure cone dark adaptation curve
   • Describe the stimulus. Where in the retina is it presented?
   • Describe the subject. Do they have normal vision or not?

2. Pure rod dark adaptation curve
   • Describe the stimulus. Where in the retina is it presented?
   • Describe the subject. Do they have normal vision or not?

3. Both rod and cone dark adaptation curve
   • Describe the stimulus. Where in the retina is it presented?

• • Describe the subject. Do they have normal vision or not?

Answer 1

When stimuli of different wavelengths are used, the dark adaptation curve is affected. On the other hand, when light of short wavelength is used,the rod-cone break is most prominent as the rods are much more sensitive than the cones to short wavelengths once the rods have dark adapted. Factors affecting dark adaptation: intensity and duration of the pre-adapting light, size and position of the retinal are used in measuring dark adaptation, wavelength distribution of the light used, rhodopsin regeneration.

The retinal location used to register the test spot during dark adaptation will affect the dark adaptation curve due to the distribution of the rod and cones co the retinal. When the small test spot is located at the fovea (eccentricity of 0°), only one branch is seen with a higher threshold compared to the rod branch. When the same size test spot is used in the peripheral retina during dark adaptation, the typical break appears in the curve representing the cone bramch and the rod branch.

When stimuli of different wavelengths are used, the dark adaptation curve is affected. A rod-cone break is not seen when using light of long wavelengths such as extreme red. This occurs due to rods and cones having similar sensitivities to light of long wavelengths.

Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of colors. They are also able to perceive finer details and more rapid changes in images because their response times to stimuli are faster than those of rods.