I ninja identity we're gonna talk about light and dark adaptation so why is it important to talk about it you guys are probably all experienced this let's say that you guys went to go watch a movie all right you guys we're in the dark watching this movie the whole time then you guys decided okay I'm going to go outside now the movies over and what happens you walk outside and it's just like ah you get hit with a beam of white light right cuz you're going from the dark to the light same thing could happen let's say that you're actually going from light into a very very dark room okay so all the lights are off on your house but for whatever I'm sorry all the lights on your house and you go from a really really light room into a really really dark room where you go down to the basement your eyes are constantly adjusting to the light and the dark I want to talk about how that's happening okay so let's go and get started so first off where are we going to find these structures if you guys watched our video on the phototransduction cascade you'll know what these are basically called right we're going to call this bad boy here we're going to call this a rod okay so this is called a rod and then this sucker over here is called a cone okay and if you remember rods were basically important because these are photoreceptors they consist of a chemical called rhodopsin and then cones consists of a chemical called fo top Singh and if you remember it has different fo toxins that responds to different wavelengths of light specifically that around blue green and red which allows for to have color vision and visual acuity so now I'm going to write down a term here rods are very important for our retinal sensitivity so they are important for retinal sensitivity okay and again what was that for more of the dim light vision more being able to see within the dark what kind of vision did we call that we said that that was for Scott opaque vision okay first go taupey vision some of this will be a review of what we talked about in the phototransduction cascade so cones what are they very very very good for tones are very important for visual acuity okay so for visual acuity so very very specific precise edge detecting vision okay being able to determine the shapes of some object being able to determine whether or not it can actually uh if it's square or if it's circular right being able to see color so also color so it's also important for color vision okay so cones are good for color vision they're also good for visual acuity now we said oh and last thing what kind of vision would you call this for visual acuity and color vision and bright vision a lot of stuff this is called photo Pig mission photo Pig vision right now let's do the example that we said first let's say that we do going from a movie theater which is really really dark okay you just watched whatever you watch the new spider-man movie and you're coming out and you get hit with a beam of light how what's going to happen not only do you get blinded with a light glare of light a lot of things happens so let's go through this this is called dark to light adaptation okay so first thing first thing that happens within this dark to light adaptation you guys should notice this right away with any individual is whenever you're going from a dark room into a light room what happens to the pupils they constrict okay so the first thing is that the pupils are going to constrict I'll talk about why they do that in just a second okay next thing that's going to happen is what do you see whenever you get hit with a really really bright light usually you might see a white glare okay you might see a white glare but what happens is the reason why you have that white glare is because you're bleaching your photo pigments you're bleaching the photo pigments what I mean by your bleaching them what am I taking Clorox and pouring on them no I'm not doing that there's a specific mechanism if you guys remember we had what's called rhodopsin let's use the rod as an example here let's say that we had that rhodopsin right and if you remember rhodopsin when we hit it with light right what happened it broke the rhodopsin down right specifically what was the rhodopsin in the form of originally it was in 11 sis retina which was bound with opsin it was tightly bound with this protein called opsin which is how like a g-protein coupled receptor when we hit it with light we hit this with light what did we do we switched it from 11 sis right now into all trans and then opsin was released so this gets converted into all trends right now and then opsin gets released okay and he gets active you know it can activate the transition proteins which we're going to activate phosphodiester races so this is like the bleaching event where the actual rhodopsin is getting broken down into the all trans right now and opsin now what happens is you have special enzymes that can actually regenerate this okay so this is the regeneration process so special enzymes are functioning to regenerate this but this regeneration can take a little bit of time okay can take a little bit of time so when you get hit or blasted with really really bright light and you were in a dark room the rhodopsin starts getting broken down excessively not only just rhodopsin but also the actual pigments within the cones the foe Thompson okay so this also would get broken down now as this is getting broken down something really weird happens let me explain come over here to the rod for a second if you guys remember we had this molecule right here let's say that this is our rhodopsin and then what did we do we hit this rhodopsin with light rays okay so we hit it with photons and then what did it do it's split the actual off here you got the actual what all trans retina formed from what structure 11 sis okay right now it gets converted from 11 sis right now into all trans then what else gets released opsin obscene goes and activates a protein here called what was that protein called if you guys remember was called transducin and then this transducin did what it went in activated a special enzyme located on this like disk little membrane here and this enzyme here was called phospho diester ace and if you remember phosphodiesterase did what if transducing stimulates falsehood aster ace he breaks down the cyclic GMP and if you break that down then these sodium and calcium channels can't function and then sodium and calcium can't come in right now something really weird happens that as you have this consistent breakdown of rhodopsin whenever you're going from a dark to a light room this rhodopsin starts getting broken down excessively that transducin is like frick this I can't do this anymore you guys are activating me too much and he decides that he's going to leave and he's going to come into this segment here now what is this segment here called this segment here is called the inter segment this is called the inter segment and this little ruffled part here is called the outer segment so what happens whenever this light you're going from a dark to light room transducin leaves and goes into the inner segment so he's going to go into the intersegmental stay if he goes into the inner segment to stay then what happens when transducin leaves he's like Frick desk can't do this anymore I'm not going to do this the rhodopsin the rods are going to stop functioning because now even if you try to hit this rhodopsin with light the rhodopsin is not going to respond because most of it is existing in the all trans retinal form okay we want to regenerate and bring it back to 11 sis but if we keep hitting with light that's not going to happen so because of this but because the transducing leaves the rods turn off so the rods turn off during this dark to light adaptation okay so what happens to the retinal sensitivity it decreases so the retinal sensitivity will decrease what does that mean that means your scotopic vision is going to be decreasing so that means that you're not going to be very good at being seen being able to see dim light or fuzzy light or different shades of gray then who comes to the rescue cones some of the cones within your retina where where exactly in the retina would you find these let's imagine for a second I take a nice slice the eyeball and I'm going to look in the back of the eyeball and the back of the eyeball here this is the back of the eyeball you see this structure right here that I'm drawing in blue this is the optic nerve that's where it's actually going to pierce through the back of the sclera but we don't really call it that we call it the optic disc or the blind spot a little bit more outside from that is going to be this nice pink structure here this is called the macula lutea and lutein means yellow and inside of this right in the center of it is going to be the special structure in here there's a special structure in here and that special structure in there is called the fovea centralis so inside of the macula lutea you have a structure here called the fovea centralis the fovea centralis is where the highest concentration of cones all right okay okay so you know where most of the cones are located there pretty much located within the macula lutea or inside of the fovea centralis where's the rods located the rods are more located on the peripheral parts of the retina so imagine all this that I'm kind of like drawing within this like baby bluish color here all this out here is going to be rods so you can get that we have more rods than we do cones so first off you're going to notice two things first off you're going to notice that there's going to be more mods than there are cones and you're going to notice that the laws are mobile or catabolize on the periphery whereas the cones are located within the center okay there's an importance to that and we'll talk about that okay so these are your rods so now what do we know them we know that rods they're going to be more rods than there is cones okay so we can even rewrite like this rods we know that there's going to be more of them than cones and then we also know that the rods are located in periphery okay okay so the rods are located within the periphery whereas the cones are very very concentrated or centrally located within the full decent trials within the macula lutea all right okay why is that important okay so let's say that you're going from a dark area to a light area what did we say happens your pupils constrict if your pupils constrict come over here for a second let's say right here let's put right here let's make that the macula it's actually kind of put a little bit more over here a little bit more about right here now that's the macula and we constrict the pupil I constrict the pupil then what's going to happen I'm going to focus more of the light rays in the center of the eye okay so more of the light rays that are coming in here now we're going to be centered onto a specific structure what is that structure called it's called the macula what is in the center of the macula the fovea centralis and what is the Philby's and trials primarily made up of cones so whenever you're going from a dark area to a light area the pupils constrict so they can focus the light specifically onto what onto the retina that's why the pupils constrict so the pupils constrict to focus light centrally on macula okay booyah which is where the fovea centralis is that's where the highest concentration of cones are okay that should make sense so first off what has happened so far pupils constricted so that we could focus the light specifically onto the center of the macula lutea where the fovea centralis is where the highest concentration of cones are we're bleaching the photo pigments very very rapidly because we're getting hit with a lot of light at once the rhodopsin is getting broken down continuously because the rhodopsin is getting broken down continuously what happened to the rods the rods turn off then what happens then to the retinal sensitivity retinal sensitivity for the dim light or the fuzzy light or the different shades of gray kind of light the retinal sensitivity decreases what structures turn on the cones turn on and as the cones turn on the less sensitive cones to the actual bright lights the less sensitive cones as those cones turn on then what happens to the visual acuity their visual acuity increases and so does your color vision and then what type of vision is going to be occurring at this point time photopic vision now if you guys have noticed you go from a dark room to a light room it's not going to happen immediately it takes a little bit of time sometimes it can take about five to ten minutes right so for this event it might take about five to ten minutes for your eyes to completely and perfectly adjust okay from going from a dark room into a light area all right so again to cross it all out just to review it's over that confused pupils constrict to focus the light onto the macula or the highest concentration of cones are where the fovea centralis is because of the light hitting it from going into this dark to very very bright light the rods were pretty active but now they're going to get bleached so the rhodopsin is going to get excessively broken down and where's transducing going to go it's going to go to the inner segment so even if light is hitting rhodopsin can't be broken down to generate some of those activities so then if that happens and even some of the so tops and it's broken down in the higher like more sensitive cones and then again because the road Asin is excessively broken down and transmission goes into the inner segments the rods turn off retina sensitivity decreases and then the less sensitive cones are going to turn on and their visual acuity increases in the color vision becomes very precise and that might take about five to ten minutes so that covers that that covers the dark to light now let's say that you're like oh man you know what I remember he was so great I'm gonna go back in again and watch it again okay now what happens all right so you say all right I'm going to go back in and watch that movie again so now we got to talk about light to dark adaptation okay and it's pretty much just the reversal so it's not really going to be that confusing it's just going to be the exact opposite of everything we did over there so the first thing that's going to happen is when you go from a light room to a dark room what happens to the pupils okay the pupil should dilate okay okay so now that we have a good understanding of what we see within the back of the retina this pupil dilation should make a lot of sense so now let's put our macula right here and again what's going to be within the center of the macula you're going to have the full these and travels where the highest concentration of cones are and then again spread out all around the rat in here is going to be the rods here right and again this part right here I actually should get rid of and the reason why this is the optic disk so really there is no photoreceptors there okay now we dilate the pupils if we dilate the pupils let's make these soccers huge okay look at this these pupils are freaking huge now look what happens all the light rays that are coming in can spread out to all different parts of the retina so not only can the light hit this actual macula but the light can hit D what the outer peripheral parts if you can hit the outer peripheral parts which photoreceptors are going to be activated now the rods okay so you're going to be hitting a lot of rods so now because of the dilation of people so pupils dilate if the pupils dilate what is that going to do it's going to allow more light into eye reaching periphery why and which parts are there what is in the periphery of the eye the rods okay so we're going to be able to hit some more of that light on the rods instead of completely focusing onto the macula lutea where the fovea centralis is that's the first thing second thing transducin is like alright you know what I'll make a truce I'll come back so rhodopsin starts accumulating again okay because what happens is this takes a little bit of time this is not as fast as going from dark to light if you guys have ever noticed that it takes a while for your eyes to get adjusted going from a light to a dark room it takes a little bit it's not easy okay so it does take a little bit and that's because this rhodopsin has to accumulate a little bit so now what happens is transducing that was out here in the inter segment he comes back up he comes back out to the outer segment and as he does that it allows for the accumulation of the rhodopsin again so now the read opsin is sensitive to the light again okay this dim light this dark light the different shades of gray type of light so now that the rhodopsin accumulates it's now going to be sensitive to the light now so now what happens to the retinal sensitivity for this dim light or fuzzy light or different shades of gray type of light the retinal sensitivity will increase all right now the rhodopsin accumulates because the transducing comes back as the relapse and accumulates it becomes more sensitive to the light and whenever it's sensitive to the light then whenever the light hits the rhodopsin the dim light of the fuzzy light it can initiate this type of cascade event that would allow for the activation of these rods right now so the rods are going to be turned on so rods turn on in this case third thing that's going to happen now the cones the cones are going to get turned off here's why the cones have a certain threshold of wavelength that they'd like to be hit with dark light is a low wavelength okay so low wavelength of lights aren't going to be really activating these cones so because this low wavelength of light it's not going to not activate cones okay so because the light intensity okay we could even say this there's besides the decreasing wavelengths we can say decreased light intensity so as the intensity of light decreases it doesn't activate the cones the full tops as much so they get turned off so now what happens to the visual acuity the visual acuity will decrease what happens to the color vision decrease in color vision okay now I'm talking a complete dark room obviously if you go back in to watch a movie there will be in lights and all that stuff like that but just imagine going from very bright room into a dark room okay you turn all the lights off in your house instantly let's say it's dark at night it's nine o'clock at night you're going to bed and you were in a bright light room okay and you shut the lights off immediately boom complete pitch prep pitch-black you can't see anything why because your aura Dobson has to start accumulating that's why I said it takes a little bit more time and it might take a while before you start seeing anything okay so the rhodopsin has to start accumulating it and when it starts accumulating the retina sensitivity will increase and then the Roz will finally turn on what else happens the pupils dilate so that more light hits the periphery to activate those rods because your rods are for your scotopic vision your dim light vision the fuzzy vision for different shades of gray then our cones turn off because they're not going to respond to that decrease light intensity from the dim light okay now if you notice if it's complete pitch-black would I be able to notice the color of this marker or the shape of this marker that well no not as much as I would be able to notice it in this light and darkness I might not be able to see that very well so I might not be able to see the color that well and I might not be able to see the actual complete shape of it perfectly so that's what's going to happen during the actual going from this light to dark adaptation this takes a little bit longer this could actually take up in certain situations on average about twenty to thirty minutes okay for this light to dark adaptation to occur okay our last thing guys to finish up on cones you know there's a certain situation you know it controls your photo provision or your color vision you guys probably heard of color blindness well color blindness is actually an x-linked recessive disorder usually okay so it's usually an excellent recessive disorder so it's again it's going to be more common within the males right and in this situation what can happen is you're actually going to be lacking certain types of photons and using the most common types of photons that are affected is going to be that of the red okay that are responding to the red wavelengths as well as those responding to the green wavelengths so this is the red-green color blindness where they have a hard time being able to see red and green within the different shades right that's a hard thing there for these some of these people so they might have certain types of x-linked recessive disorders where their actual fo thompson's are completely mutated or deficient where they don't produce the actual foot tops and to respond to red wavelengths of light or green wavelengths of light all right and that can cause the color blindness alright another thing what if people don't ever adapt they can't ever see anything in the dark so you go from a light and then you go in the dark and they never they never form anything that they can actually see at all complete pitch-black they never adjust this is a terrible condition and this is called Nick right it's called Nick tilapia okay Nick tilapia or night blindness okay this is usually due to a decrease in the production of vitamin A or decreased intake of vitamin A because if you remember I talked about this in the phototransduction cascade vitamin A is actually oxidized remember we rule off the two protons and we convert this into right now specifically like the eleven cysts form right now if I have a decreased vitamin A I'm going to make less retinol and I'm going to be able to I'm not going to be able to respond to light as much right because remember 11:6 retina has to get converted into all trans right now and then it has to get regenerated back into this but again vitamin A is feeding into this so there's a decrease in vitamin A there's a decrease in the photo pigment so you're not going to be able to respond to the actual dim light because you're not going to have as many of them oh and then there's another one that's actually affecting this it's called retinitis retinitis pigmentosa retinitis pigmentosa this is actually another situation here you know um if you guys remember from the phototransduction cascade we had this cells back here the pigmented epithelium which was rich in melanin and they were basically helpful for being able to absorb any scattering light rays or provide nutrients and blood flow to the nutrients to the actual photoreceptors and what was another thing I was doing remember the rods it was recycling a lot of the tips from them that were actually coming off it was phagocytosis and recycling it in retinitis pigmentosa they're not able to recycle and phagocytose these actual tips from the rods if they can't phagocytose this actual tips and then recycle them what happens to the actual rods then they start degenerating as the rods degenerate do you think these people are going to be able to see well at night no and again this could actually cause this actual night blindness also okay all right ninja nerds in this video we did a lot of information okay about light and dark adaptation we talked through interest a little bit of clinical correlation in that I hope all of it made sense I hope you guys really did enjoy if you guys did please hit the like button comment on the comment section and please subscribe as always an engineer until next time