Has anyone asked their vet if they have experience with nocturnal animals having light sensitivity? Articles I am reading (including what
eden posted) point out that cats are nocturnal-active animals with slit pupils but I have yet to see a healthy cat who is damaged by sunlight. I have seen owls, a distinctly nocturnal bird, flying in the daytime and they have enormous eyes well-adjusted to their nocturnal lifestyle. Perhaps they are not
comfortable exposed to bright light for long periods but even on sunny days they are still seen out and about and do not appear damaged when they hunt at night. Articles I found touched on "nocturnal animals have light-sensitive eyes so be cautious when exposing to bright light" but only show that the methods nocturnal animals use to protect their eyes are pupil constriction.
Are we arguing that gliders as nocturnal animals CANNOT be exposed to light because it will harm them or that they should not be exposed to direct, harsh, BRIGHT light for
extended periods?
If you take a photo of a glider in a dark room and let the flash go off that can be considered exposure to harsh light because their pupils have adjusted to a dim setting and are not prepared for a bright flash. Take a photo of a glider who has had time to adjust to ambient lighting in a typical room with sun-lit window and the flash is much less harsh on their eyes because their pupils are already smaller from adjusting to the ambient light. If your camera has "no redeye" mode this works best because it conducts a series of pre-flashes that are meant to make the subject's pupil contract to adjust for the actual flash and reduce red-eye (light bouncing off the retina). Is this considered harmful? Or is this an example of "appropriate" light for gliders?
A quip from an article from
BioMEDIA Associates:
Back In The Daylight
But what happens to these night-time specialists during the day? Most nocturnal animals are largely inactive during the day to avoid over-stimulating their highly sensitive eyes. Nocturnal animals have specialized pupils to shut out damaging bright light.
Pupils are usually circular; it's the most effective shape for allowing light into the eye. Indeed, nocturnal animals dilate their pupils to their circular maximum at night.
But by day, the circular pupil is inefficient at blocking light. Instead, a variety of pupil shapes have evolved that limit incoming light, the most advanced being the vertical slit. The slit pupil can shut out all light except a narrow band. Its vertical orientation is of significance too, as it works well with eyelids. As an animal squints, partially closing its lids at right angles to the vertical slit pupil, it further reduces the amount of light entering its eye. Perhaps the most noteworthy of all pupils is the stenopeic pupil of the gecko, a vertical slit lined with notches on each margin. When the pupil is entirely closed, tiny pinholes allow light to pass through to the retina creating sharp overlapping images.
Gliders have a circular pupil, several articles mention that this is the least efficient pupil shape for blocking out light. Does this mean they are by nature more adapted to adjust to light or does it mean they are more prone to sunlight damage when exposed?
Light is important to nocturnal mammals as well as diurnal because of our circadian rhythms. If we (humans) didn't experience night-time on the cycle we are accustomed to our bodies would have a difficult time adjusting our sleep patterns, we rely on it getting dark out to tell our bodies "ok, time to shut down and sleep" while nocturnal animals use daylight as their signal to bed down. If we didn't expose our gliders to
any light at all wouldn't that mess up their cycles?
An
article about flash photography and light damage to eyes:
Phototoxic retinopathy, or permanent damage to retinal nerve cells as a result of light energy, has been studied in humans and other animals. Extreme unfiltered bright light, focused onto the retina through surgical microscope lenses has been documented to produce permanent retinal damage. To cause either microscopically evident or grossly visible lesions, the light must be held in focus on a single area of the retina for an extended period of time. This situation generally occurs in specialized surgery, when anesthetic agents prevent the movement of the eye. Operating microscopes for ophthalmology are now all equipped with specialized filters to prevent phototoxic retinopathy even with extended procedures.
Laser, by definition a highly focused beam of light energy, may produce retinal damage. In fact, in the treatment of diabetic retinopathy, retinal detachments and other diseases of the eye, laser is employed to purposefully burn selected areas of the retina. It is capable of doing this, even with very brief periods of exposure, because the light is highly focused. Therefore, when considering the possible damage to the retina by any light source, both its intensity and degree of focus must be assessed.
For more than 20 years, researchers and clinicians have used the ERG test (electroretinogram) to study function and diseases of the retina. This test involves using a strobe light stimulator to record electrical signals originating from the rods and cones. Protocols vary by testing laboratories. The rod cells are usually tested by first dark-adapting the subject, i.e., placing the subject in a dark room from 5-20 minutes, and then subjecting the retina to a dim flash of light. The light is increased to full power and then flickered at 40Hz to isolate the cone cells for testing. The stimulator or strobe light is generally positioned within a few centimeters of the cornea for testing. Grass stimulator units produce diffuse light like a camera strobe, but of much greater intensity. For cone testing, the full power flash is flickered 40 times per second for several seconds in duration. Although the light is intense and positioned close to the subject, it is not highly focused and, consequently, does not permanently damage the retina.
On
flash and animals, nocturnal included:
Fill-flash involves the balance of ambient and artificial lighting. In situations when fill-flash is used, cone cells are active, and they are designed to work in all but dim light. Because of this, the use of fill-flash on animals and birds is not likely to have any effect on their visual systems. Cone cells do not bleach to a nonfunctional state in bright light as the rod cells do.
Flash as main light in dim light conditions can produce a temporary reduction in vision but not permanent damage.
In total darkness, use of flash may cause a temporary reduction in vision for 5-20 minutes. It takes one hour of dark conditioning to achieve maximum electrical responses from rod cells in the retina. The regeneration of rod function even after "bleaching" by a bright light is not linear with time. Animals and birds probably have 50% return of function in the first five minutes, and 75% in another five minutes. The rods are rapidly moving from zero function to full sensitivity during that time, with the greatest return of function per time unit occurring in the first 10-15 minutes.
Because of the initial impairment of vision from flash in total darkness, repeated flash of birds or animals in this situation is not advocated. Ethical nature photographers avoid altering their subject’s behavior. The judicious use of flash in completely dark situations causing a brief vision alteration must be offset by the educational value of the photograph made. Technically excellent pictures of owls and other animals in their natural environment made at night with flash may, in the end, benefit the species as a result of increased public awareness. In select situations, the use of flash may be justified. Many nocturnal species rely upon other senses in combination with vision during dim or dark conditions; for example, the auditory capabilities of owls at night are probably far more important for hunting as compared with the visual sense.
In summary, to produce phototoxic retinopathy, or permanent damage, a focused intense light must be held in one location on the retina for a time several magnitudes greater than the duration of a camera flash. Fill-flash is not likely to have any effect on visual systems; flash as main light in dim light conditions may produce a temporary reduction in vision but not permanent damage. Flash on nocturnal subjects during nighttime should be used sparingly due to brief impairment of vision.
Flash does not cause permanent damage to the eyes of animals or people, even at close range. The eye is developed to handle bright light, such as the sun. This is the reason the rod cells "turn off" in bright light. Flash is diffused light when it reaches the subject. Only very highly focused light, like looking at the sun through your telephoto, or laser application, would be expected to cause permanent retinal damage.
These articles pretty much state that while nocturnal animals are adjusted to a dark environment they are also equipped with protective measures to prevent excess light from entering the eyes and damaging them. Pupils will constrict. The second article touches on the
amount and
intensity of light needed to cause DAMAGE in humans and animals. It appears that normal exposure to sunlight and OCCASIONAL exposure to camera flash in dim-lit situations is not enough to
permanently damage the eyes, but may cause temporary decrease in sensitivity. If you've ever had your picture taken in a dark room and weren't prepared you probably know the feeling--blobs in your vision, trouble focusing, speckles..it goes away quickly though. It seems in that situation the same goes for gliders..they may have temporary vision problems but no permanent damage.