hello and welcome to Insight of thermology this is Dr Amrit welcoming you to another lecture today we are studying about the witus embryology and its disorders the witus cavity is the largest cavity of the eye and it actually forms about 2/3 of the volume of the eye it is situated behind the lens and celery body uh anteriorly and the retina posteriorly its weight is about 4 G and the volume of the vitus cavity is about 4 CC in the video on velopment of eye we discuss in detail about the optical cycle and the development of the lens the link is going to be provided in the description box in that video we discuss how the neural tube and specifically the anterior part of the neural tube give rise to outpouchings which are going to develop into the future optic cup now as the before the optic cup develops we have the optic recycle and the optic stop now eventually what happens is that a vessel starts developing ventral to the optic stock and the optic recycle and this vessel will basically go inside and Supply the developing lens and this developing lens is known as the lens recycle and the vessel which is developed Here is known as the hyoid vessels now in order to give way to the hyoid vessels into the optic cup the optic Cup and the optic stock will start developing a Groove inferiorly and they will ultimately develop this Fisher over here and this Fisher is know known as the coral Fisher or the optic Fisher the purpose of the coral Fisher or the optic Fisher is basically to allow the hyoid vessels to grow inside the optic cup and reach the developing lens recycle okay so that is very important if you want to understand about the development of the vitus the following slide actually tells you about the same thing so we have the optic stop the optic cup and you can see this Fisher on the ventral aspect known as the coidal Fisher and the coral Fisher basically allows the heart yid artery and the hyoid veins to enter into the optic recycle and ultimately reach the lens recycle and Supply the lens Okay the reason this is important is because we should know that embryologically there are basically three types of Vitus we have a primary Vitus we have a secondary Vitus and we have a tertiary Vitus now the primary Vitus is formed first the primary Vitus is then replaced by the secondary Vitus and then we have the ter Vitus which is formed out of the periphery out of the peripheral area of the secondary witus now the first type of Vitus that we are going to discuss about is the primary vus the hyoid artery which has basically entered through the coral fissure and which has basically reached the optic vyle and ultimately the lens recycle is responsible for the formation of the primary Vitus as a matter of fact it would be not wrong to say that the primary Vitus is predominantly formed by the hyoid artery and its branches es the hyoid artery branches are also known as the Vasa hyoid propria or the vascular Meeny okay so at about fifth week of gestation the space between the lens and the retina gets occupied by this primary vascular witus which is basically formed by the hyoid artery and its branches so as the hyoid artery is basically Meen kimal in origin and since it's coming into the coral fissure and reaching the lens and ultimately forming the primary pitus it would not be wrong to say that the primitus is partially Meen kimal in origin it is partially Meen kimal because it also has some ectodermal elements from the first diagram you can see that here we have the surface ectoderm and the surface ectoderm thickens at a location where the optic bicycle approaches it and that forms a lens plod and ultimately the lens plod is going to form this lens pit and ultimately the lens recycle now as the lens recycle gets pinched off from the surface ectoderm some of the cells of the surface ectoderm will also get pinched off and they will move behind the lens and ultimately they will lead to the formation of the primary R Vitus and therefore we can say that the primary Vitus actually has a mixed origin it is partly ectodermal in origin and partly Meen kimal in origin so I hope that is clear but remember that primary Vitus is basically the vascular Vitus now as we discuss about the primary Vitus which is vascular Vitus it is important to discuss also about the Tunica vasculosa lentis that is the plexus of the vessels which are going to form around our lens to supply the lens during the embryon embryological period the Tunica vasculosa lendes starts developing at about fifth week of gestation and there are two arteries which are feeding the tuna vasculosa lenses we have the posterior sary artery supplying basically the anterior part of the lens up to the equator and the the branches of the posterior C artery will form what is known as the lamina Ido pilaris or the pupilary membrane it is called the lamina Ido pilaris because it is in throw association with the iris and the pupil now uh now the posterior component of the tuna vasculosa lentis that is beyond the equator and behind the lens is formed from the hyoid vessels and they are going to form the capsul vessels okay because they supplying the posterior part of the capsule at the equator and posterior D it right so that is a tunic vascular lindus so the the beginning of the primary Vitus is at about fifth week or 35 weeks of the station where you can see how the hyid vessel is actually entering and uh forming these branches known as the Vasa hyoid appropria and supplying the posterior part of the lens up to the equator and the anterior part of the lens is basically being supplied by the long posterior celer arteries which are coming like this and together they are for forming the Tunica vasculosa lenes in the anterior part of the eye and this hyoid artery which is present behind is going to take care of the posterior part of the vitus now together this is known as the primary Vitus right so primary Vitus is predominantly formed from your hyloid artery however not long that this primary Vitus is going to be now resolved by the appearance of specialized cells and these cells are known as the hyoc sites the cells of the vitus right now these hyoc sites are also Meen kimal in origin and these hydes actually have phagocytic properties that means they can eat up the primary Vitus and they start eating up your hyloid arterial system and now as they eat up the hyid arterial system they also start depositing the collagen fibrillary material within the vitus and now the vitus that is formed is known as the definitive Vitus or the IR vascular Vitus or the secondary Vitus and the time period during which it is formed is between 5.5 weeks to 12 weeks of gestation okay so I hope that is clear so that is your secondary Vitus now you should know that the adult Vitus basically is about 99% water apart from that we have collagen we have other soluble proteins and we have basically the extracellular Matrix formed of the glycosamino glycans and hyaluronic acid now all these constituents are major most of the hyaluronic acid and the collagen type 2 in the vitus gel is added after birth although most of the vitus the secondary Vitus or the definite vus is formed during the embryological period most of the hyaluronic acid and the collagen type 2 which forms the major type of collagen in the vitus will be formed after birth so I hope that is clear now that we know what is meant by the secondary Vitus you should know what is meant by tery Vitus as well now ter is the third Vitus so you can roughly remember that it comes at around the third month of gestation now basically what has starts happening is that the second rator starts condensing in the peripheral portion specifically in the area of the parts planner now from the anatomy of the sary body you would remember that we have the iris we have selary body we have two parts of sary selary body the anterior part is called the parts pet and we have the posterior smooth part called the par planner now the tertiary Vitus basically starts veloping these firm attachments with the epithelium of the parts planner and ultimately in adulthood or when it gets matured it is going to form what is known as the vitus base right so tertiary Vitus ultimately leads to formation of the vitous base okay now we discuss about the uh origin of the primary vus which is a mixed origin we discuss about the laying down of the secondary vus which is coming from the high L sides right and now we should also know what is forming the tertiary Vitus now it is believed that the non-pigmented selary epithelial cells in the region of the pars planner are actually responsible for the formation of the tertiary Vitus and they also give rise to the zonular fibers right so knowing about the origin of the vitus is very important you should know where is the primary Vitus coming from you should know where is the secondary Vitus coming from and you should also know the source of the tertiary Vitus so I hope that is clear having discussed about the embryology of the vitus now let's discuss about the abnormal development of the vitus okay so first let us talk about the disorders which are going to develop because of the abnormal atrophy of the Primitive structures now all the Primitive structures are supposed to involute so what I mean to say is initially we have the Primitive Vitus which is the primary Vitus that has to be replaced basically by what it has to be replaced by the secondary Vitus known as the definitive Vitus right so during the fourth month uh whatever remains of the primary Vitus are there they also begin to atrophy okay the vessels basically which are coming from behind and reaching the uh reaching the lens basically the course of these vessels through the vitus will be evident in the adult life as a very narrow Central fluid filled Canal so that narrow Central Canal is known as the clockit canal so the path that was taken by the hyoid vessel to reach the lens will be now replaced by by a small Canal without any hyoid vessel in it and that is known as the clockit canal or the hyoids canal okay now basically it is the macras which play a very important role in the regression of the primary Vitus I already discussed about that these macras are nothing but your Hyo sites right so that Central vitous um channel that you see over here is known as the clockit canal also known as the retrolental canal it extends from the posterior surface of the lens to the optic nerve head and it represents the remnants of the Lumen of the C uh of the course of hyoid artery during the embryogenesis now it's very important to know that this space is devoid of collagen fibral and it is about 1 to 2 mm in diameter and has an S shape uh shape from the anterior to the posterior end now as you can see over here the clocked Canal basically starts from the Pella fosa now if you would know if you would have seen our video on the anatomy of lens you would know what is meant by Pella fosa so Pella fosa is nothing but it is just an anterior depression in the Vitas where the lens basically sits right so this depression anteriorly is known as the patella fosa so our clocked Canal basically starts from the patella fosa as a very slight widening like this and then it takes this its s shaped course in the central Vitus and again it widens near the optic nerve head and this widening or the funnel shape widening is known as the space of marani okay so I hope you understood what is meant by space of marani next what we are going to talk about is the malformation of the vitus and the hyoid artery system so it's very important to revise the Primitive Vitus Anatomy or the primary Vitus Anatomy we know that it is majorly vascular and we have these hydroid artery and the long posterior celer artery which are actually going and supplying the lens now if you would carefully observe you can arbitrarily divide it into an anterior portion and a posterior portion the posterior portion is majorly formed by the hyoid artery and its branches whereas the anterior portion is actually being um supplied by the long posterior selary arteries now the long posterior celer arteries are actually forming the pupilary membrane whereas the hyoid artery is supplying the posterior aspect of the vitus here and the posterior aspect of the tuna vascular centis up to the equator and at the equator they are basically forming the capsul pupilary membrane okay now together the pupillary membrane and the pip membrane is known as the Tunica vasculosa lentis okay now normally the hyoid system of vessel will vanish completely however in some disorders the regression does not occur and these vessels will persist causing some problems now what happens is that whenever the vessels are persisting usually some amount of collagenous tissue will also persist along with them and such fibrovascular tissue are later going to cause contraction on the surrounding uh structures and traction sorry they're going to contract and cause traction on the surrounding structure leading to deformation of the normal tissues of the anterior and the posterior segment now if your anterior part or the vessels on the anterior part are basically persisting near the lens it is known as the persistent tuna vasculosa lentis and if the hyoid artery in the posterior aspect of the eye is persisting that is known as the persistent hyperplastic primary Vitus or the PHP V okay now let us see a few examples so here what you can see is the persistent pupilary membrane so here just the anterior part of the tuna vasculosa lentis is actually persistent here what we can see is fine Irish strands which are actually Bridging the pupil and they're also connected or they're also attached to the lens now in most of the cases the persistent pupilary membrane will arise or will be attached at the CATE of the iris okay so by this time I I assume that all of you know what is meant by Cate and if not you can actually visit our video on the anatomy of the iris okay now the persistent pupilary membrane they are usually asymptomatic and they um and they do not cause any functional disorders in the individuals who have this persistent pupillary membrane however in rare cases there might be really dense membrane and these dense membranes can persist and they can obscure the pupil and when they obscure the pupil they can actually cause what is known as amopa okay however in some portion of the pupilary membrane might be seen in normal individuals as well however in those people it is usually a symptomatic and does not cause any functional problem now if the posterior aspect of the hyoid system actually persists that is known as the persistent hyperplastic primary Vitus and here again we have two varieties the anterior persistent hyperplastic primary Vitus or the anterior phpv and we have the posterior phpv now in the an i ph phpv basically the part of the hydroid is supplying the posterior aspect of the lens up to the equator persist whereas in the posterior phpv it is the posterior part of the hydroid artery that basically persists so here you can see that this is a diagram depicting the anterior phpv you can see that here we have this persistent anterior fibrovascular membrane because of the Persistence of the anterior part of the hyoid artery which is forming the posterior part of the tunical vasculosa lentis so this is known as the persistent anterior primary Vitus you can see the posterior part of the stock is basically thinned out whereas the anterior part of the hyoid is persistent right so obviously here you will see the anterior fibrovascular tissue in the anterior vitous phas or behind the lens you can see over here the lens is normal and behind the lens you see that whitish membrane and that whitish membrane also shows certain vessels in it so for telling you that there is this is actually a fibrovascular membrane and actually it is a persisting anterior fibrovascular tissue from the posterior tuna vasculosa lendes right now what happens is that as I told you that wherever there is a vascular component there's also a fibrous component and that fibrous component goes and attaches to the surrounding cedary body uh processes right so as they attached to the celery processes they will also draw those celery process internally so basically what I mean to say is that this fibrovascular tissue will connect or will attach to the cery processes and as the fibrovascular tissue is going to contract it's going to pull inwards the cery processes making them visible through a dilated pupil examination so normally through a dileted pupular examination we usually do not see the cery processes however in a case of anterior phpv because of that fibrovascular tissue sitting behind the lens that is going to cause traction on the CER processes making them qu prominent right lens obviously will be opaque in the anterior phpv and this happens because this fibrovascular Mass can actually erode the posterior lens capsule and also penetrate the lens cortex right and obviously there will be appearance of a whitish pupil this is known as lucco Cora and anterior phpv is a very uh common differential of lucco Cora and sometimes it can be mistaken for retinoblastoma as well now what about posterior phpv in this diagram you can see that the lens is pretty clear there is no uh just the stock is connected here but there's no fibrovascular proliferation behind the lens and here you can see that the posterior part of the hyoid artery is actually persisting and you can see here the retina is basically wrapping around that stock of the persistent hyoid artery right and this is known as the posterior phpv so Persistence of the posterior part of the hyid artery is known as the posterior phpv now usually you're going to see this vascular structure or fibrovascular structure projecting from the optic disc to the adjacent retina okay and this will also cause distortion on the dis by the prepapillary and preretinal fibrous membr so what did I tell you wherever there's a vessel which is U wherever there's a vessel which is enormous there will also be a fibrous component associated with that vessel and there will be contraction and because of that contraction of the fibrovascular structure there will be traction on the adjacent structures which are present there and in this case it is the disk and therefore the dis will be distorted in case of posterior phpv apart from that the retina also might be dysplastic and there will be some radial forms uh radial folds or falciform folds which can be seen on the retina so fform folds are nothing but they are the sickle shaped folds that you can see on the retina now here again is a picture of the phpv now phpv is also known as the persistent fetal vascul and you can see over here the dis is also not normal so you can see this band which is actually extending anteriorly this band can actually extend right up to the posterior aspect of the lens and the dis over here is dismorphic so this is an example of posterior phpv right so we already discussed what is meant by the space of marani so space of marani is nothing it is a funnel shaped dilation of the clockit canal basically near the optic disc so that is important and why we discuss about uh the space of marani is that because sometimes you can find just a flake of Gile tissue projecting from the optic disc now this is also a remnant of the hyd artery system it's just that you will just find that Gile tissue sitting over there and not the vessel and this is quite smaller compared to the posterior phpv right so this G tissue sitting at the optic disc is known as the bergm papill okay so this Burg Mis Pap is situated in the space of Marti and it's a flake of Gile tissue projecting from the optic disc as you can see over here similarly you might find a very small Remnant or at the anterior end of the hyoid artery attached to the posterior lens capsule and that is known as the mid-end off dot okay now this dot might actually be responsible for the development of the posterior polar cataract so that is one clinical Point associated with it right so in this video we talked about the embryology and the development of the primary secondary and the tertiary Vitus with special Focus to to their Origins because that forms a very important high yield question apart from that we also discuss about the various disorders uh developmental disorders of the vitus that can arise because of the Persistence of the hyoid arterial system so we discussed about the persistent pupilary membrane we discussed about the persistent fetal vasculature also known as the persistent hyperplastic primary Vitus or phpv and we ended by discussing what is meant by Berg Mr Pap and the mitt of dot okay so that's all for today I hope that was useful thank you and have a nice day