hello and welcome to inside of thermology this is Dr Amrit welcoming you to another lecture today we are studying the anatomy of lens before we understand the anatomy of lens I would advise you to study the development of the lensber cycle which I have explained to you in this video on development of eye now what is lens lens is basically a transparent by convex crystalline Mass which is placed in between the iris and the witcher's body now the lens is basically situated in a saucer shape depression at the anterior phase of the vitreous which is called the patellar fosas the lens nicely sits in that patella fosa so if this is the waitress the which is anteriorly forms this cavity in which our lens will nicely sit and that is called the patella fossa and of course in front we have the iris this is the correct time to discuss the important ligaments which are associated with the lens the lens as we know is nicely sitting in the patellar fossa and in a circular region of the patella fosa the lens has a strong addition because of the presence of a circular ligament around it which is called the vegan ligament or the hilidocapsulator ligament it's called hilidocapsulator because present between a hyloid there is nothing but the waitress and the lens capsule now the lens is not firmly adhered throughout the patella fossa so there is still a part behind the lens which is Loosely attached to the hyloid face where we have a space and this space is called retro lentil space because it is present behind the lens and it is also called the burgers space so let me explain it to you so you basically have your patella fossa which is represented here in the gray color the lens is nicely sitting in the patellar fossa now along a circular margin where the vigured ligament is present the lens is firmly attached and in between that we get ligament the lenses Loosely present in a space so there's a space where the vegan ligament is not attached and that space is called the burgers space so what are the functions of the lens lens basically helps in transmitting and refracting on the light it also absorbs the ultraviolet light which is of less than 350 nanometers wavelengths so in a way our lens is basically preventing us from the damaging effect of the UV radiation and it prevents those UV radiation to reach the retina it contributes to 35 percent of the refractive power of the eye another important refractive surface of the eye is of a cornea which gives the majority of the refractive power and the second most important surface is our crystalline lens another thing is it helps in accommodation okay now let's talk about some important measurements of our leads we know that the lens has an anterior surface and then it has a posterior surface these two surfaces are going to meet at the equator okay so wherever they meet that is called a equator now as you can see in this diagram the anterior surface is much less curved compared to the posterior surface right and therefore the radius of curvature of the anterior surface is much more compared to the radius of curvature of the posterior surface okay so you must not get confused here the more curved a surface is the Lesser is the radius of curvature right so the radius of curvature of the anterior surface is about 10 mm and that of the posterior more curved surface is about 6 mm what about the equatorial diameter which is drawn here in green color the equatorial diameter that means if you draw a line from one equator to the other the equatorial diameter of the lens at the time of birth is about 6.5 millimeters and as uh you reach the second decade of life which is about 20 years 20 to 30 years okay at that time the equatorial diameter will become 9 to 10 millimeters okay and then it stays constant so the adult diameter or at the equator of the lens if someone asks you the answer is 9 to 10 millimeters now what about the lens thickness the thickness of the lens represented here by the blue line is basically a line drawn from the antidupole to the posterior pole of the lens so in a while I'll tell you what is meant by the anteropore and the posterior Port so lens thickness is about 3.5 millimeters at the time of birth and then it reaches maximum to about 5.5 millimeter it increases by a unit of 0.2 millimeters every year now the center of the anterior surface of the length and the center of the posterior surface of the lens is called the anterior pole and the posterior pole respectively now the anterior pole is situated about three millimeters from the center of the cornea so that's also a very important point now let us talk about the refractive properties of the lens the refractive index of the lens that we should remember is about 1.39 and the refractive power of the lens is about 16 to 17 diopters now the refractive power is definitely different from accommodative Power the refractive power is is basically the ability of the lens to bend the light rays and the accommodative power is the power of the lens which helps you in accommodation that means which helps you to look at closer objects right this accommodative power is maximum at the time of birth it is about 14 to 16 diopters at the time of birth and then at the age of 25 it becomes 7 to 8 diopters and then at the age of 50 and then old age sometimes it even becomes zero right so the accommodative power basically decreases gradually and this is actually associated with the refractive condition that we see in old age and usually after 40 years of age do you know what it is it is called presbyopia so if you want to know more about about accommodation we have a video on what is accommodation and what is accommodative power of the eye now let us discuss our topic that is the anatomy of the lens we shall be discussing the anatomy of the lens and the headings of lens capsule lens epithelium and the lens fibers first you should understand how the lens develops right this was explained in detail in development of file still to summarize the optic recycle is in close contact with the surface ectoderms this is the surface ectoderm part of the surface ectoderm which is in close contact with the optic recycle will undergo thickening and will form the lens flicker okay now gradually what happens is this lens placard is going to start invaginating inside this Optical cycle converting the optical cycle into optic cup and subsequently this is going to get separated and form the circular structure surrounded by the epithelium of the surface ectoderm all throughout and this is called the lens recycle and of course your optic recycle is converted into the optic cup so this is what was explained in that video on development of I so now let us talk about the lens capsule if you would remember this diagram this is nothing but this is your lens recycle right so this lens recycle is actually surrounded all throughout by the lens epithelium okay so which will derived from the surface sector now the basal cells that means the outermost wall of these epithelial cell is actually going to secrete a membrane-like structure around it and that is called a lens capsule right so lens capsule is a thin transparent hyaline collagenous membrane which is surrounding the lens now although it does not contain any elastic fibers it is highly elastic that's important it is produced throughout the life so that is also one more important point and if you see it is produced by the basal portion that means this one the outer part is called the basal portion so it is secreted by the basal portion of the epithelium anteriorly and the basal portion of the posterior lens fibers posteriorly not the posterior epithelium so why the posterior not the posterior epithelium I'll tell you in a while before that did you know that the thickest basement membrane in a human body is nothing but it is the lens capsule okay now the lens capsule stains with periodic acids give stain so that also one more point that you should remember coming to the thickness of the lens capsule this has clinical importance as well the thickness of the lens capsule is not equal throughout the lens is thicker anteriorly compared to the posteriorly and it is thicker at the equator compared to the poles and as a matter of fact it is thinnest at the posterior pole so that brings us to a clinical nugget and that is number one in true exfoliation of lens okay that is seen in case of glass blowers disease okay and people who who are actually glass blowers or those who work at high temperature what happens is that the anterior superficial lamular of the lens capsule so basically the lens capsule gets separated into two individual laminate right one will be superficial and one will be deeper right and that you can see in this diagram so it's it looks as if the anterior capsule has actually split off into different layers because of that heat right so that is called true exfoliation syndrome now here you can see this is actually a histological slide in which uh the capsule has been stained with the past stain and you can actually see how the capsule has been you know broken into individual layers okay so this is seen in the exfoliation true exfoliation syndrome now one more clinical nugget related to the thickness of the lenses what did I tell you the thickness of the lens is leased in the posterior pool and therefore at the time of surgery the most common place where the lens capsule gives away and the most common complication as well that you see is the posterior capsular rupture right so this can happen with some instrument touch sometimes during hybrid section due to the weakness inherent weakness of the posterior capsule so this is called posterior capsular rupture which is a complication of the cataract surgery and why it happens because the posterior capsule is weakest at the posterior Pole now let us discuss about the lens epithelia here do you remember that I told you that the posterior capsule is formed from the posterior lens fibers and not from the posterior epithelium why because we do not have a positive epithelia so if you would remember this is the lens cycle right at this point the lens cycle seems to have epithelium both at the anterior surface and the posterior surface as well however what happens is that the posterior epithelial cells will now start elongating and as they elongate they will fill up this less recycle cavity and now this uh the posterior epithelial cells have elongated and completely filled up this cavity to form what is called an embryonic nucleus or an embryonic lens and therefore we do not have a posterior epithelium left after the embryonic period because a posterior epithelium of the lens has been totally used up to form the primary lens 5 fibers during the embryonic period that is up to three months of gestation so this is very important so what is primary lens fibers primary lens fibers are the fibers which are formed by the elongation of the posterior epithelium of the lens recycled right and they are formed in the embryonic period that is about zero to three months now because we don't have any posterior lens epithelium we will be discussing only about the anterior lens epithelium the anterior lens epithelium are basically cuboidal nucleated epithelial cells so they are cuboidal nucleated epithelial cells and moreover they are the most metabolically active part of the lens they contain all the organelles so all the metabolism even the ATP production it all happens at the anterior lens epithelium if someone asks you that in the lens which part is utilizing the most amount of oxygen it is again the most metabolically active part that is the anterior lens epithelium right now the entire lens epithelium does not divide right it's only the lens epithelium cells which are present near the equator which have this capability of division So based on that there are zones in epithelium as well we have some central zone of cells which are labeled in pink then periphery to the central zone we have the peripheral Zone which are labeled in blue and then we have a germinative Zone which is labeled in green and because the germinator zone is present near the equator they also call the equatorial Zone so first let us talk about the central zone the central zone as I told you and as you can see over here they are basically cuboidal in shape okay and their number also decreases with eight just like the corneal endothelial now these cells are usually stable they do not undergo mitosis normally okay so this is the point however they can show mitosis in some pathological condition in some pathological condition these cuboidal cells will undergo metablasia and lead to development of cataract so this is your clinical nugget here example in Shield cataract in atopic dermatitis and another thing is the glaucoma flecken that you see in the acute angle closure glaucoma right in both these cases what is happening is there is metaplasia of cuboidal cells into myofibroblasts right so because of Any pathological condition these anterior capsule or the anterior epithelial cells can undergo necrosis like in the glaucoma fleckin and some amount of metaphlasia which is seen in Shield Cataract and locomophilic in both and it can lead to development of such pathological conditions okay next coming to the intermediate zone or the peripheral Zone this intermediate Zone cells are much smaller however they are more cylindrical they're located peripheral to the central zone and they rarely undergo any sort of mitosis finally we have these uh cells which are located at the equator which are also called The germinator Zone so some say they're located at the equator some cereal located just anterior to the equator which is called The pre-equatorial Zone but what is important here is that they can undergo active division okay so they undergo mitosis now this is also a Zone which is going to form your lens fibers and since these lens fibers are formed after the embryonic periods and they're not from from the posterior epithelium instead formed from a part of the anterior epithelium these are called secondary lens fibers okay so this ellipse uh sorry this equatorial zone or the germinator zone are going to lay down these fibers okay and these fibers are going to migrate from here posteriorly and then towards inside right and these cells actually will continue to divide throughout your life so that's important similarly here there's another concept of bow region so what is meant by this blue region we know that the newly laid lens fibers are laid from the germinator zone or the equatorial Zone and these lens fibers after they are laid they're going to start getting elongated now as they start getting elongated their nuclei will now become more anterior compared to their original compared to their uh compared to the cells which are present in the equatorial Zone you can see The Superficial cells have Zone here and the deeper cells actually have their nuclear present like this right so the deeper cells will have their nuclear situated more anteriorly compared to the superficial cells as this happens they take a configuration of a bow and therefore this is called a bore region now here is an important clinical Market I told you that actively dividing cells are present in the germinator zone or the equatorial Zone and therefore as we know that wherever you have actually actively dividing cells you know they are very susceptible to irradiation and therefore in case of radiation cataracts sometimes even a neurofibromatosis and myotonic dystrophy you will see dysplasia of these cells and they will not form the normal lens fibers instead they are going to form some dysplastic cells and this will lead to formation of a cataract just below the posterior capsule okay and therefore such a cataract is called a posterior subcapsular cataract as you can see in the first picture this is a retro elimination in which you can see this cataract okay this has a nice shape to it and you can see this okay this is called a posterior subcapsular cataract similarly here on the optical section this is the anterior lens capsule then you might have the lens and in the posterior part of that you can see that there is this opacification that means your posterior capsule the posterior subcapsular area is getting affected so this is a posterior sub capsular capture again another clinical nugget here is that sometimes after cataract surgery what happens is even though we remove the anterior capsule we do leave a rim of the anterior capsule after cataract surgery and that remove the anterior capsule still Harbor some of the germinative cells right so these epithelial cells from The germinator Zone can actually migrate towards the posterior capsule behind the intraocular lens and they can cause what is called posterior capsular opacification right so these cells basically can form two types of posterior capsule or specification which are called PCO okay so these two types can be else nickels or it could be summer Rings Rings now how does each happens is that the residual epithelial cells if they migrate posteriorly and they get differentiated into some balloon-like cells or wing-like cells also called the Weddell cells these metal cells are also seen in your bladder okay so if they differentiate into such cells they will look like these pearls on the posterior capsule behind the iol and these are called the else Nick Pearl so each Pearl is actually a failed epithelial cell which was supposed to become a lens fiber okay so that is your else neck oil now sometimes they are going to take a shape of a ring okay or a donut shape rig so that is called a summary ring so both of these are basically posterior capsular specifications so I hope that is clear now if you want to know more about this little lamp examination of a lens and the optical section of the lens I would advise you to visit this video on slit lamp techniques diffuse versus focal the third part in which we'll study the anatomy is the lens fiber so we discussed about the capsule we discuss about the epithelium now we're discussing about the fibers of the lens the lens fibers are actually arranged in a zonal Arrangement okay in zones So based on the zones roughly we have a nucleus and we have cortex however the nucleus is also divided into further zones let me tell you now here the concept of primary lens fibers and secondary length fibers is very important so what are these primary lens fibers primary lens fibers or the fibers which develop before three months of age from the posted epithelium whereas the secondary lens fibers are the fibers which are developing from the equatorial zone or the germinative zone so these are your primary lens fibers and these are your secondary lens fibers the primary lens fibers are basically going to form the embryonic nucleus and the secondary lens fibers are going to form a lot of layers okay and each of these layers are actually given different names okay based on when they develop so here the basic idea that you should get is the oldest nucleus or the oldest cells are going to be present in the center right and the new cells are laid from The Superficial area right from the periphery and therefore all the new cells will be present in the periphery and the youngest one will be present in the most periphery the oldest one will be present in the center the fibers of the lens are basically split into regions depending upon the age of the origin so as I told you the embryonic lens is formed at three months of the embryonic life from the posterior epithelium and forming the embryonic nucleus right so those are the primary lens fibers now whatever is formed afterwards is called secondary lens fiber okay so the embryonic nucleus is a primary and then we have the secondary now the part of the secondary lens fibers which are formed during the fetal life that is three to eight months of fetal life is called the fetal nucleus okay and obviously the embryonic nucleus will be in the center and Fetal nucleus will be around the embryonic nucleus then next what we have is the infantile nucleus from the last month of the intrauterine life which is probably from the ninth month up till the puberty what we get is the infantile nucleus then after the uh puberty till uh let's after the puberty that is like early at at life whatever you get from there on is called the adult nucleus right and then the most youngest fibers which are present the most periphery they're called the cortex right so here let us try to label that suppose this is the structure of a lens in a 40 years old right so let us label it so the most outside one which is labeled as one is the anterior capsule right now just below that will be your actually epithelium and then you will have the cortex right now here the cortex is labeled in the pink color inside the cortex you will have the adult nucleus just inside that we will have the infantile nucleus then we have the fetal nucleus and then the most innermost part is called the embryonic nucleus so I hope that is clear so here you can see the anterior aspect and the lateral aspect of a cut open lens right so you can see the center most part is the embryonic nucleus surrounding that is a fetal then we have the infant type then adult and surrounding that we have cortex then we have the epithelium and then the epithelial secretes what is called the capsule now you should know that the after the embryonic nucleus is actually secreted then we have the fetal nucleus coming up so the initial fibers which are formed surrounding that embryonic nucleus are actually arranged in such a way that as they actually reach together so they're going to grow from one end to the another they're going to grow from one end to another as you reach each other these fibers are going to now start getting flattened up at the ends and as they flatten up at the ends they're going to meet at forming a suture the suture is called a y suture so they're going to terminate in that y area right so anteriorly you have an upright y that is a normal weight how you write a y so until you will have an upright by suture and posteriorly it is actually an inverted y okay so if you flip this wide upside down let's call it inverted or a posterior wire suture so what is the clinical significance of these wise suture so antilly as you can see it's a normal erect okay upright y suture and posterior you're going to have this posterior white suture these are nothing but basically the fetal nucleus fibers which are coming and as they are meeting they're going to flatten up and they're going to join with each other on the either side forming the sutures right suture is nothing but it's a junction right and what is joining here it is the lens fibers which are joining in the shape of Y the importance here is sometimes you can get this cataracts which is called smutral cataract so around the suture you will have this opacification of the lens and this is called a sutral Catra next we shall be discussing about the suspensory ligaments or the zonules of Zinn so what is meant by the zonules of zit now lens is basically held in its place okay the lens is not just free floating obviously it's sitting in the patellar fossa it has its vigored ligament but still it needs to have some support and some connection from the celery body and from the ciliary processes basically and especially for the purpose of accommodation so the lens is connected to the ciliary body why are these strands okay which which are actually going to join together and form lamillae and these strands are called The Zone news okay or the zonular laminate so what did I tell you the lens is situated basically between the iris and it is situated between the vitreous behind Okay so now as you can see here we have the Siri body the celery body basically has two part it has a convoluted part which is called the pars placator and then it has a flatter part which is called the pars planner right so between the ciliary body and between the lens you are going to have what is called the zonular fibers the zonular fibers most of them are going to come from your past planner and behind the past planner what you have you have Retina and the anterior part of the retina is called the oracerita right so now in the recent study it has shown that most of the zonings are actually arising from the past planner and the ursareta so they're going to arise like this and now getting inserted at the equator of the lens okay so we are going to arise like this and insert our equator arise and insert at the Equator so that is how your zones are present they are present between the ciliary body and the equator of the lens so that's important so as I told you that the recent concept is that these zonules are basically arising most of them from the parts planner and also up to 1.5 millimeters from the aura serrator right and the zonules is not just a single zone it's basically a complex and that complex has been divided into four parts so we have a parse or nucularis limb so let me tell you what are all these four parts so first of all just look at the first picture the part of the zonules which are coming from the uh from the pars planner okay the plain part of the scenery body and the uracilator that is part of the retina the parts which is coming from the past planner is called the purse orbicularis right and these part of the genres which have Arisen from the parts of the killaris now they are going to reach the parts like it apart now since the Placita part is more complex part you can remember so the zone is also going to be more complex there they're going to be more interlacings women form of plexus and therefore this part is called it's only the plexus part right now as they reach as they are form the plexus or a base at the pass placeta now they're ready to divide now before they divide they need to consolidate and form this angulation and this is called the zonila coke okay so this trident thing that you can see those are the zonular limbs and where the need is called zonular Fork now from that zone love Fork you're going to get the three limbs outside which is one is the anterior limb one is a posterior Limb and one is the equatorial zonular limb so this is also very important the zonular limbs when I talk about first we talk about the anterior Zone the anterior Zonda limb is consisting of these zonial fibers which are coming from the parts planner that is posterior part and they're inserting onto the pre-equatorial part of the lens that means they're going and inserting anterior to the part of the lens okay the posterior zonular limb means that they're inserted on the posterior part of the lens posterior to the equator but they are arising from where the arising anteriorly not from the past planet that is from the parts placeta and the equatorial is only limb is directly arising from the past blackator and getting inserted onto the lens Equator so I hope that is clear right so we have a parts orbicularis then we have a zonular plexus okay then we have a fork and that fork is dividing basically into the limbs so that is important now here I would like to mention just for the sake of completion two important canals which are associated with these only fibers so we have a canal of Hanover and a canal of Petit the canal of Hanover as you can see it's a space between the pre-equatorial and the post equatorial zones okay so this was the pre-equatorial and the post equatorial that is called the canal of Hanover the canal of Petit is a small space behind the post equatorial zonules and the highlights on it so basically hyalodon nothing but some zonules will become through association with the vitrus so that those are called the haloids onions so if you find a small space between those hyloid zonules and the post equator Zone use that is called the canal of pet now the diagram actually explains to you about the three types of Zone limbs that we saw okay so what did I tell you about the anterior Zone limb the anterioration limb means that it is inserted anterior to the equator and it is inserted 1.5 millimeters anterior to the equator but where are they coming from they are coming from the parse planner they are coming from behind right and getting inserted anteriorly now the posterior limb is actually getting inserted posterior to the equator how much posterior 1.25 millimeters posterior to the equator but where are they coming from they're coming I'm from anterior part that means from the parts glycata and then of course you have an equatorial limb which is directly coming from the parts placate and getting inserted at the Equator so you can see and appreciate this crisscrossing of the zonular fibers finally we have the surgical anatomy of the lens now some surgery textbooks and for the purpose of cataract surgery the lens is divided again into a central hard nucleus okay and then above that you have a variable thickness of epineuclear plate then we have a layer of Cortex and then we have a capsule right now this is important to understand the concepts of hydro dissection and hydrodelineation so this is an important clinical nugget for you so what is the difference between hydrosection and hydrogenation these basically are these two are basically steps of the cataract surgery in Hydro dissection we are basically trying to put fluid in very simple terms we are trying to push fluid between the capsule and the cortex in such a way that the cortex will get separated from the capsule and therefore the man the manipulation of the lens during cataract surgery will become easier okay so if you would know that in cataract surgery what do we do we actually open the capsule we remove the lens out and we leave the capsule there right so in order to nicely separate the lens from the capsule we need to separate it using the technique of hydro dissection first now sometimes you might want to remove the nucleus first and then go ahead and remove the capsicle the cortex okay so in such conditions what we can use is a process of hydrodelineation in hydrodelineation we will actually push fluid between the layers of the layers of the nucleus I think we are actually trying to separate the nucleus from the from the epinucleus okay so if you separate the nucleus from the epinucleus that is called Hydro delegation and if you separate the cortex from the capsule that is called Hydro dissection then the lens can be actually classified just based on its hardness and this was actually an old classification of course but still it is relevant just based on the color of the lens you can tell how hard the lens is so if you see a lens which is slightly transparent grayish or maybe very less greenish in color that is called a grade one lens okay if you see a lens turning more into amber color greenish yellow that is called a grade 2 lens if it becomes more yellowish in color that's called grade three if it now starts becoming more brownish that means the hardness is increasing and that is called a brown cataract grade 4 or Bruna said sometimes the hardness increases so much that the lens will now look black which is called cataract okay so that is called a grade 5 cataract however what we follow now is the lens opacity classification three okay so what is this loc classification 3 in loc classification three we are going to basically compare what you are seeing on the slit lamp to this set of pictures right so under this loc3 system 3 basically we have six pictures for the nuclear color and opelism so we have this no1 nc1 you can see it's almost clear then NO2 and C2 it has started to get opacified slightly at whitish color coming up NO3 nc3 slum some sort of greenish color coming no4 nc4 here what do you see it is becoming more yellowish here it has become more yellowish and then going towards the brownish okay so like that you have six images from no one nc1 to no6 nc6 and o means nuclear Opelousas and c means color right then you come do a retro elimination and you have basically two diagrams under the Retro elimination right so for first we will actually staging the cortical cataract okay so in that C1 is almost nothing you can see under elimination in C2 you can see some amount of a pacification has started in the periphery c3s that has started to grow eccentrically C4 is when it starts to reach the center so this wedge-shaped corticulopacification which has started to reach the center and C5 is it actually crosses the center right then again the third set of pictures are for the grading of the posterior subcapsular cataracts so in P1 you have the small spec P to a slightly bigger P3 is more bigger P4 and then P5 right so you can actually compare your what uh you are seeing clinically to this locks three pictures so that's all for today I hope it was useful thank you and have a nice day