Reminder about why we are doing all this:

1. We can see objects even though the background luminance levels change over a range of more than 10 orders of magnitude (1010 ). How do we do it?

2. Reminder about why we are doing all this: • As a clinician, you need to understand the scientific basis on which measurements of vision are made and how they can be made in the future as new tests of visual function are developed and put into clinical practice. • For instance, dark adaptation rate may turn out to be a way to diagnose Age-related Macular Degeneration (AMD) very early – trials underway

3. Three main purposes of course • Learn how vision is measured • Basic facts about monocular visual function (What is normal?) • Neural basis of visual function (Why does the visual system respond as it does?)

4. Three main purposes of course - Adaptation • Learn how vision is measured • Will measure a group dark adaptation curve in lab • Basic facts about monocular visual function (What is normal?) • Different curves from different test flash & adapting light conditions • Neural basis of visual function (Why does the visual system respond as it does?) • mechanisms

7. “Typical” Dark Adaptation Curve Adapting light goes off at time = 0

8. Dark Adaptation The task: Measure the threshold intensity as the visual system dark adapts This is a “moving target” because the threshold decreases over time.

9. Dark Adaptation lab on Thursday The task: measure a “group dark adaptation curve” Everyone in the group will light adapt. Then everyone will take a turn as a subject (have your threshold measured) and as an examiner (measure the threshold intensity of your classmate) as the visual system dark adapts This is a “moving target” because the threshold decreases over time. The winning group will be awarded two six-packs* The winning group gets to decide the content of each six-pack (water, beer, Coke, Pepsi, etc.)

13. 1) Rods and cones both start dark adapting at time 0 2) the more sensitive system at that time determines the threshold 3) cones dark adapt faster than rods 4) the lowest thresholds obtained using cones are much higher than the lowest thresholds obtained with rods (rods, potentially, are more sensitive than cones) Note: If using the Method of Limits, must only use the ascending branch to avoid changing the time-course of the dark adaptation “sneak up” on threshold from below

14. The 2009 winning group

15. * = important parameters in dark * * adaptation studies * * * *

16. Variations in the dark adaptation curves help to illustrate the importance of knowing what you are doing when making psychophysical measurements. What you get depends on how you make the measures Different situations give very different results

18. In order to see both the rod and cone branches during dark adaptation, the adapting light and test spot must stimulate both rods and cones Fig. 2.1

19. Retinal Location (2 deg spot) (μmillilamberts) Broadband 300 millilambert adapting field, 2 min exposure 2° Spot flashed 1 s every 2 s

20. Retinal Location (2 deg spot) (μmillilamberts) Broadband 300 millilambert adapting field, 2 min exposure 2° Spot flashed 1 s every 2 s

21. Test flash size (centered on fovea) (μmillilamberts)

22. Effects of Test Flash Wavelength on the Shape of the Dark Adaptation Curve Peak rod absorption | | 400 nm 500 nm 600 nm 700 nm

23. Effects of Test Flash Wavelength on the Shape of the Dark Adaptation Curve -Rods absorb poorly at long wavelengths Peak rod absorption 400 nm 500 nm 600 nm 700 nm |

24. Effect of Test flash Wavelength “decibels” (dB) is a log scale

25. Adapting Light Wavelength | | | 400 nm 500 nm 600 nm 700 nm Test flash

26. Effect of Adapting Light Wavelength | | | 400 nm 500 nm 600 nm 700 nm | Test flash

27. Adapting light wavelength (blue test flash) (μμlamberts)

29. Adapting light intensity Illuminance (μTroland)

30. Adapting light duration Luminance (millilamberts) 333 millilamberts

31. Luminance needed to detect grating orientation (millilamberts) If you need cones to do the task, then do not get a rod branch

33. Illuminance (trolands)

35. Response to threshold test flash alone All of these action potentials are needed to see the test flash Response to adapting light offset alone Test flash long before adapting light offset Test flash just before adapting light offset Test flash same time as adapting light offset Test flash long after adapting light offset

36. Response to threshold test flash alone All of these action potentials are needed to see the test flash Response to adapting light offset alone Test flash long before adapting light offset Test flash just before adapting light offset The response to the test flash is “cut off”; not enough APs to detect Test flash same time as adapting light offset Test flash long after adapting light offset

37. Response to threshold test flash alone All of these action potentials are needed to see the test flash Response to adapting light offset alone Test flash long before adapting light offset What happens when the test flash is presented at different times, relative to the adapting light offset? Remember, we are looking at the response of just ONE neuron, responding to BOTH the test flash and the adapting light offset. Test flash just before adapting light offset The response to the test flash is “cut off”; not enough APs to detect Test flash same time as adapting light offset Test flash long after adapting light offset

39. Response to threshold test flash alone All of these action potentials are needed to see the test flash Response to adapting light offset alone Test flash long before adapting light offset Test flash just before adapting light offset How do you make the test flash visible again? Raise the intensity to restore the needed number of action potentials The response to the test flash is “cut off”; not enough APs to detect Test flash same time as adapting light offset The response to the test flash is supporessed; not enough APs to detect Test flash long after adapting light offset

41. Response to threshold test flash alone All of these action potentials are needed to see the test flash Response to adapting light offset alone Test flash long before adapting light offset Test flash just before adapting light offset The response to the test flash is “cut off”; not enough APs to detect Test flash same time as adapting light offset The response to the test flash is supporessed; not enough APs to detect How do you make the test flash visible again? Raise the intensity to restore the needed number of action potentials Test flash long after adapting light offset

43. Response to threshold test flash alone All of these action potentials are needed to see the test flash Response to adapting light offset alone Test flash long before adapting light offset Test flash just before adapting light offset The response to the test flash is “cut off”; not enough APs to detect Test flash same time as adapting light offset The response to the test flash is suppressed; not enough APs to detect Test flash long after adapting light offset How do you make the test flash visible again? Raise the intensity to restore the needed number of action potentials

45. Response to threshold test flash alone All of these action potentials are needed to see the test flash Response to adapting light offset alone Test flash long before adapting light offset Test flash just before adapting light offset The response to the test flash is “cut off”; not enough APs to detect Test flash same time as adapting light offset The response to the test flash is suppressed; not enough APs to detect Test flash long after adapting light offset

46. Illuminance (trolands)

49. New research (Greg Jackson, just moved from CEFH, UAB) suggests that dark adaptation is slower in people who are developing age-related macular degeneration Clinical trial ongoing on HPB 4th floor

50. Dark Adaptation