The desire to see more causes larger telescopes to appear and more frequent trips to the dark mountains to be made in order to grasp as many photons as the clear haze-free sky will allow to enter into our telescopes and then into our eyes.
But little thought is given to maximising the human physiological potential in order to see more. More importantly, little is done to stop impairing our seeing ability.
The photons that strike our retinas are only as useful as the retina's ability to respond to the incoming light. Colour sensitivity decreases and black and white perception increases as we go from the retina center to the periphery.
We all use averted vision to use the more sensitive peripheral retina, but let me address myself to what can decrease the sensitivity of the retina over all of its area.
It is easy to demonstrate that blood vessels are caused to constrict by various chemicals: If a naked person stands in a room about 75°F, his skin temperature will equilibrate at about 92°F (internal body temperature 98.6°F ± 1°F). All areas of the skin will be within 1°F as noted by infra-red photography.
After smoking ONE cigarette, the hands and feet darken on infra-red photographs, and the skin temperature over these areas is lower by 6 - 10°F compared to before smoking one cigarette. (Consider this effect on potentiating the likelihood of frost bite or simply discomfort on a cold winter night). A marked decrease in blood flow to these areas is easily demonstrable.
More sophisticated techniques have been used to measure the decrease in calibre of the retinal arteries (vessels that supply blood to the retina) in response to smoking one cigarette. The decrease is significant and results in raising the threshold of light perception. Consequently, if all else is equal, the non-smoker will see dimmer objects and details compared to a smoking companion. Nicotine is responsible for this.
The effect of nicotine starts within minutes of the smoke inhalation and lasts for about four hours. The nicotine is absorbed through the lungs and the moist mucous membranes of the mouth and throat, so those who do not inhale still experience the decrease in seeing ability. Therefore, TWO well-placed cigarettes can diminish your dark adaption for an entire night.
Aviators have been advised not to smoke until after night flights for the above reason.
No permanent diminution of dark adaption has been demonstrated to date, though in heavy smokers (2 packs per day) a 24 hour period of abstinence may be necessary for return to full dark adaptability.
Note...I have not been able to find a study that relates visual acuity with the use of marijuana. It would be interesting to know if one's seeing is impaired by marijuana in the same way as it is with tobacco.
Alfred Monkowski, M.D.