Light and Dark Adaptation

in StemSocial2 months ago

Greetings to all and sundry,

It is another beautiful day today, hello to February the month of love and seasons greetings to all hivers and our amazing writers in the science community. In the month of love let's learn to celebrate in moderation and be safe in whichever activities we find ourselves doing.


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So the weekend is fast approaching and as you know me already if I am here then I have something to share regarding our eyes. I love the idea of sharing what I know and helping others the work of eyecare practitioners better, it not only makes our work easier but also helps patients be more compliant and understanding and so I do hope you enjoy today's reading too.


Today I had a patient who came in with his main concern being that whenever he moves from his room out into the open it takes a while before he can look around because the sun tends to hurt the eye and then everything seems too bright he can't help it. But then it gets worse when he moves from the sun to his room.

After spending time outdoors he enters his room and he cannot see anything, it is like he has gone completely blind for a while and he tends to panic and get afraid and so he is in to make sure that there's nothing wrong with him because he is afraid he may be losing his sight since he hasn't really taken notice of this happening to him previously.


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After spending time to check his eyes and any other parameters to ensure that there was no underlying condition I used the rest of the time to explain the diagnosis which wasn't much of a diagnosis because he wasn't actually sick he was just becoming more observant of something that has always been. Apparently, where he always stayed he didn't have to move between two different illuminations before.

Now he has his own place and his room is not as bright as when he steps out, he prefers a dim room because it helps him feel more comfortable at home and helps him fall asleep easily and so I went ahead to explain what we call light and dark adaptation to him and it made him feel so much better, he went home smiling and he would also be on the lookout for other changes which suggest an underlying condition popping. And so I felt the urge to not only share this story with you but the explanation I gave him hoping it helps someone today.

Light and Dark Adaptation

Two main cells within the retina are responsible for vision, these are known as the rods and the cones. The cones are used mainly for what we term color vision whereas the rods are used for black and white vision let me put it that way or we can also use the term monochromatic for the technical individuals.

The rods are concentrated around the area of the retina known as the macular which is used for central vision. This is the part of the retina at play when you are looking directly at an object or that friend or watching that movie, the peripheral part of your vision thus when you looking at a friend and could still someone coming over from the corner of your eye, yes that part is mostly by the help of the rods.


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And so the rods have a higher number as compared to the cones and are more sparsely placed all around the retina. In very good illumination the cones are the only ones working to give you the best vision, 1080p or UHD whichever you would want to use, just for emphasis, this happens because the rods tend to bleach so quickly that when illumination is bright they don't get to work.

When the way is turned, the rods would be working at the expense of the cones, when it is dim almost no cone would be working because not enough light is available for the cones to work be bleached. Because the rods are highly sensitive, they can pick on the minute amount of light in the environment to produce electricity for some form of vision.

And so in the dark, you tend to see more shapes and ghostly appearances because there is not enough light to make things out well, also vision is black and white because cones ain't at play here, and so if you already knew the color of your friend's shirt before you entered into a dark room you could discern but you would still be seeing it in monochrome.

Now due to the nature of these two cells' movement from one extreme end of illumination to the other means there has to be a switch from one active type of cell to the other. There are times when both may be working together though, this happens during the twilight session, where we get mesopic vision, the light is not so bright and yet not so dark and so you can see some color and some black and white too.

When you suddenly move from a very bright area into a more dim room, your vision may be dazed for a while before you can see again or make figures. After staying in this illumination for a while you realize that things start to become more clear and at a point, you can see so well as if there was good illumination there, whiles you may not be seeing so beautiful or colorful as when you were outside you could move about freely without bumping into any objects.

The whole scenario describes what is referred to the as dark adaption of the eye. The switch from cones to rods. This switch activates within a few minutes but only peaks at about 25 minutes into the dim illumination. At this point, the illumination now feels or becomes normal for you. Dark adaption is a normal thing and no one can escape or FastTrack this process any more than the eye itself can, you just have to wait it out. The time-lapse will depend on the extremeness of the two illuminations.

In the same vein, when one moves from a dark room or dark environment into a bright environment their vision experiences disability glare for a while. If you do not know what disability glare is I recommend you read my previous article it would clear up a lot of things for you. After being in this bring to light for a while though you start to get accustomed and within a short time, you feel ok and can go about your activity.

This is what happens with light adaption and just as I explained above, it simply depicts the retina's switch from rods to cones function. Unlike rods though, cone adaption is quite fast and occurs within a shorter time frame peaking around 5 minutes of being in bright light. This is attributed to their tolerance for light impulses, not getting bleached as easily as rods, and the wavelength within which they function.


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You cannot escape this any more than you can escape dark adaption and you cannot fast forward the discomfort too however, please know that this is actually very normal, every single human being experiences this, and you are not going blind or anything like that. There are instances where some conditions can make matters worse though and so it is never a bad thing to go in for a checkup just to be sure especially if you feel like it is not normal just like my patient came and went home with a smile on his face.

Conditions such as Xerophthalmia about inadequate vitamin A in our system would literally bring about what we know as night blindness, where dark adaption seems to take forever and we still find it difficult to see in the dark. Retinitis pigmentosa would equally make things worse both in bright and dark illumination but worse in dark illumination though. And so whiles light and dark adaptation may be normal, there is no harm in verifying with an Optometrist, after all, it is better safe than sorry right?


As I wrap up on this I would like to remind you that having regular eye care exams would do more at putting your mind at ease than just assuming, remember that the purpose of these writeups is not so you can diagnose yourself of any particular condition or do self-medication but add understanding to whatever care your Optometrist may have in store for you.


by @nattybongo

I also seek to provide an avenue where others would have the opportunity to speak to me to solicit professional advise and the like regarding their ocular health or condition etc. And so let's learn whiles taking good care of our sight by consulting a professional always. Please be safe and remember that your sight is the window to the beautiful scenery of this world. Avoid over-the-counter medication and when in doubt, always ask. It is a pleasure serving you once again.

Further Reading

Le Duc, D., & Schöneberg, T. (2016). Adaptation to nocturnality - learning from avian genomes. BioEssays: news and reviews in molecular, cellular and developmental biology, 38(7), 694–703.

Brasil, A., Tsai, T. I., da Silva Souza, G., Herculano, A. M., Ventura, D. F., de Lima Silveira, L. C., & Kremers, J. (2019). Pathway-specific light adaptation in human electroretinograms. Journal of Vision, 19(3), 12.

Pant, M., Zele, A. J., Feigl, B., & Adhikari, P. (2021). Light adaptation characteristics of melanopsin. Vision Research, 188, 126–138.

Dirkx J. (1993). Adaptation to permanent night work: the number of consecutive work nights and motivated choice. Ergonomics, 36(1-3), 29–36.


Whoops!!, so when I started reading, I was reading through, I thought you were trying to describe this experience as an eye problem, you have no idea how relieved I feel knowing that, oh it is actually normal and I am good. Thanks for sharing this knowledge with us.

Haha, sorry for scaring you within that moment, now you don’t have to panic because all is well right? Don’t be afraid to come in though if you feel there’s some change aside what you are used to observing though

Yes, I am relaxed now. I won't hesitate to come in friend if I notice any form of change.

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