hello and welcome to Insight of thology this is Dr Amrit welcoming you to another lecture today we are talking about the topography and anatomy of the retina okay so the human retina basically measures about 32 mm from oraser of one side to the oraser of the other side along the horizontal Meridian okay now the total surface of the retina in each IE is about 1100 mm square and the average thickness of the retina although this varies basically from studies to studies is about 200 microm now the retina is thickest at the posterior pole near the optic nerve head and in the macula and as you move away from them it gets thinner and thinner right it gradually thins out at the oraser and at the fola right now if you look at this diagram I don't want you to really mug up all these values but remember that the retina is thickest at the optic nerve head and it is thinnest near the fola and the second place where it is thinner is the aura Sera okay so moving on in our video on the layers of the Rea we already talked about the 10 layers of the Rea and what really forms the 10 layers and how do we actually remember them easily and logically so the link is going to be there in the description box you can uh watch that video as well in this video we shall be focusing on the Topography of the RNA where we shall talk about what is meant by maula luua what is fobia what is fola what is is meant by the peripolia paraphobia region what is extra aial retina what is near Mid far periphery specifically we'll talk about the oraser and also some findings which we see in the peripheral area of the retina right now the first thing that we'll talk about is the maula lutea now the maula lutea is also known as the area centralis or the central retina it is about a 5 to 6 mm diameter circular zone of the retina as which is drawn here in the diagram and it is centered between these uh Superior and inferior temporal arcades and the optic nerve head okay now important Point regarding the macula lutetia is that it is predominantly um it predominantly has the cones right and also the gangon cell bodies are arranged in more than two or uh two or more layers within this area centralis so that is a very important point and more than about 50% of the total gangon cells that are present in the retina are actually present in this area Centras now now the area centralis or the MAA lutetia if you carefully observe it has this term which is known as lutetia now the reason is why is it called so uh this happens because of the presence of oxygenated carotenoid so lutetia basically means yellowish appearance so maula has this yellowish color to it because of the presence of carotenoids uh inside of it and these carotenoids are ltin zanine okay and they impart the yellowish color to the maula also they have a protective role because they will filter out all the short wavelength uh light which is basically composed of the UV radiation and therefore they also protect our eyeballs from the UV radiation all right now another important Point regarding this maula ltia is that it basically contributes to about 15° of the field of view right now mov moving on we have next is the fobia now the fobia is about 1.5 mm diameter area within the area centralis and as we all know that the size of the optic disc is also somewhat similar and therefore we can say that the fobia is about one dis diameter in size okay now again since the macula has only cones in it the uh since the macula has pre-dominantly cones in it the fobia region as a matter of fact is consisting of entirely cones there only cones and no rods in the four-wheel region and this accounts for the high spal visual Equity that we get over here and is also responsible for the great color vision that we enjoy okay now the fobia basically has a margin a slope and a floor to it okay so it's a three-dimensional structure as you can see in this OCD image drawn in yellow color is the fobia the fobia has a margin it has these sloping edges and it has this floor now the FIA size as I told you is about one disc diameter is equal to size of the optic disc and it actually accounts for about 5° on the visual field so maula is giving you 15° whereas the fobia accounts for about 5° of the visual field now I talked about the phobia now you can see something over here this is called the floor of the phobia now the floor of the phobia is known as the fola okay so fola is this 35 mm diameter area that you see within the phobia and this region that I drawn here can also be called as the floor of the phobia now Fula is smaller than the F vascular zone so we'll talk about the F vascular Zone and what is exactly meant by F vascular zone or F now what you should remember is that this Fula is entirely a vascular and it basically relies on the underlying choid and the Chio capillaries for its nourishment the fola is situated at a distance of about 4 mm from the center of the optic disc temporally and it is about 8 mm inferior to the center of the optic disc so that is the location of your fora very important point that is commonly asked in exams now I would like you to observe this OC image over here so what did I tell you that basically this point the floor of the fobia is formed by what is known as a fola now FIA also consists of only cones and therefore the fola will also consist of only cones however there are some hystological differences over here the cones of the fola region are quite slender and elongated and densely packed compared to the cones of the other region of the fobia right so if you can see over here this uh black or hyp reflected region hyp reflected region that you see over here if you see in the region of fola it is slightly thicker compared to the rest of the retina right and this happens because the outer segment of the cones are quite longer and slender in this region and that is the reason why you see thicker outer segment layer just below the fola right apart from that if You observe carefully the inner retinal layers that means the you can see the gangon cell layer the inner plexiform layer and the inner nuclear layer they seem to be limited just till here okay they seem to be limited till this point and they're not really present within the forol region right and therefore we can say that the inner layers of the retina actually are slightly displaced and they basically stop at the region of fola and therefore the fola basically consist of only the outer layers of the retina like you can see the outer nuclear layer and of course the other outer layers of the retina the inner layers like the gangon cell layer the inner plexiform layer the inner nuclear lay they laterally displaced in the region of fola right so that is one important point that you must remember another important point is that it takes time for fola to develop it develops fully only at the age of 4 years right and this sloping border that I talked about um here the sloping border of the fobia where the fobia is meeting this floor and the floor is known as the fola this downward sloping border of the fobia where it meets the floor is known as the cus okay again another terminology that you you must know right now when we're talking about the visual field of the fora the visual field that the Fula represents is about 1° right so this is table of comparison so macula is about 5.5 mm in diameter FIA a region within the macula is 1.5 mm and Fiola is about. 35 mm now macula represents about 15° of the visual field FIA represents about 5° of the visual field and fola represents about 1° of the visual field now let us talk about another term and that is the UMO now within the fola region there is a tiny depression in the center and that is known as the UMO and it is seen of thalos scopically as a visible light reflex and that light reflex shiny reflex that you see just at the center of the macula is known as a fular reflex and it will be seen in every normal eye apart from that what you must know is the FZ so what is meant by FZ FZ is nothing but it is fovial avascular Zone it is a region within the phobia where the blood vessels are actually absent now the diameter of the FZ would be somewhere between 250 to 600 micromet it could be greater as well and it corresponds to a field area of about 1.5° now if you would remember fobia corresponds to about 5° of visual field whereas fola corresponds to about 1 degree of visual field and therefore we can say that the limits of the fourwheeler vascular Zone actually is somewhere between the ending of of the fobia and the Fiola right so as you can see over here this is actually a floresent Ang Geographic image you can see the central area where the blood vessels are basically absent this area over here and that area where the sorry that area where the blood vessels are actually absent is referred to as the fobal vascular Zone it's a very important Landmark that you see in the in the angiography okay now as you have understood what is meant by a four pit and what is meant by fob vascular Zone fobal pit is nothing but the the sloping edge of the fobia where it basically meets the fola okay that actually is forming a pit-like depression within the fobal region that is known as a fobal pit now embryologically what is seen is that the fal Pit and the fobal vascular Zone basically depend uh they develop together okay and if there's an abnormality in the fourwh pit usually there will be an abnormal normality in the fal vascular Zone as well okay now what did I tell you the fal development usually occurs uh is completed by the age of four years however in some individuals there will be incomplete development and in those individuals there will be absence of the fal pit and this condition is known as FAL hypoplasia okay now there are some diagnostic tests which actually tell you regarding the fourwh hyper placia so number one is on opthalmoscope you will see that the fourwh region because it is not developed properly you will see that there is no forhe reflex what did I tell you the forhe reflex is basically coming from the Amo or that extreme tip of the fal pit so therefore since the fal pit is not developed since there's fil hyperplasia there's going to be absence of the fal reflex apart from that the normal FAL pigmentation would also be absent on fluoresent angiography you will see that the F vascular zone is absent or the diameter of the F vascular Zone has basically decreased on OCD again you can see that the four-wheel pit is basically absent and normally what happens is that the inner layers are laterally displaced at the fobia and it is just the outer layers which are present there and over here in for hypoplasia that lateral displacement fails to occur and therefore there will be Persistence of the inner layers through the expected area of the phobia again on the OCTA that is your Optical coherence tomography Ang angiography you will see that the the FZ is absent both in The Superficial capillary plexus and also in the Deep capillary plexus now over here you can see that do you find any uh shiny reflexs in the fourwh region no that is absent right and similarly over here if you do an OCD scan you can see there's no FAL pit normally it should be like this and moreover the internal layers or the inner layers of the retina are continuous in the region of the fobia okay so there's no fobal pit formation as well the next terminology that we'll talk about is the paraphobia so what is meant by paraphobia now till now we discussed about area centralis or maula and within the maula we discussed about this small circle of 1.5 mm D diameter of course this image is again not to scale otherwise this is this is known as fobia and the fobia is almost equal in size to that of the optic disc right and within the phobia this blue color thing is your Fiola and within that you will have a small Depression known as the Amo okay now outside the phobia if you draw another ring of about5 mm in uh5 mm thickness around the phobia that is known as the parap fobi region okay so what did I tell you this if this is your phobia if this is your phola and this is the Amo around the fobia if you again draw a circle of about5 mm thickness around the fobia that region is going to be called as the parap fobal region now another important nugget regarding the paraph fobal region is that in the paraph fobal region the gangon cell layer the inner nuclear cell layer and the outer plexiform layers also known as the Henley fiber layer is actually the thickest okay so if you if I have to show you those layers in this image so eny's fiber layer is nothing but it is the outer plexiform layer okay so as you can see over here this is the outer plexiform layer so these sloping fibers of the outer Plex form layer in the re out in the region outside the fora is known as the Henley's layer so you can see over here these are the Henley layer fibers and then above the Henley layer fibers what do you have you will have the inner nuclear layer the inner plexiform layer and then finally you will have inside the gangon cell layer so in the region of the paraphobia all these layers are going to be thicker okay so in this region and in this region so that is one important clinical nugget that you must remember now the area of the maula which is outside that parap forhe region is ultimately called as the peroia okay so this is what has been labeled in green color right so again if you have to label this is macula this is the ring which was demarcating your paraphobia this is the phobia then you have Fiola okay and inside that you will have Amo right now the region outside the paraphobia and the beginning of the maula or the boundary of the maula is known as the peripodial region right so periphal region is surrounding the zone of paraphobia and it is about 1.5 mm in width and therefore we can say that the Amo basically forms the center of the maula and the periphery of the peripolia will form the margin or the outer part of the maula so now let us try to revise so in the retina at the center of the retina what do we have we have a 5.5 mm Zone and that zone is known as the macula okay so this green circle is the maula now within the maula we have a 1.5 mm zone or we can also call it as one dis diameter because it is equal to the size of disc and this is known as the phobia now within the phobia again we have a 35 mm circular Zone and that is known as the fola and right at the center of the fola we have a tiny depression which is known as the Amo now don't forget that in between the fola and the F uh fobia we have a Zone which is known as the fal a vascular Zone all right now if you draw a circle of about5 mm in thickness on or around the FIA now that zone is known as the the parap fobal region and the remaining part of the retina which is outside the paraphobia region is known as the perip phobia right so what can we say we can say that the macula basically has three zones it has one what is known as the paraphobia the paraphobia is about5 MM thickness and it has a perip phobia around it which is about 1.5 mm thickness okay so if you actually do the math it actually uh comes to about 5.5 mm okay so let us see how so here you can see that this zone is our fobia and what did I tell you the fobal diameter is about 1.5 mm right then around the fobia what do you have you have paraphobia which has thickness of about 0.5 mm on the all around right so that comes to about 1 mm so add to 1.5 and then you have the perip phobia which is about 1. 5 mm on the um either side so that will be about 3 mm so if you add all of this what you get is about 5.5 mm okay so that was about the central retina area andralis or the macula next we are going to talk about the area of retina which is outside the macular area now this retinal area outside the macular area is known as the extra aial periphery of the retina and an important fact fact about this part of the retina is that it is rich in rods so when we were talking about the maula we said that the maula area basically has cones in plenty whereas here in the extra aial periphery we have rods in abundance and also the periphery has just one single layer of the gangon cell bodies okay and the anterior end of the periphery of the retina or we can say that the uh anteriormost part of the retina is basically formed by the AAS Sera so we are going to talk about what is meant by oras Sera but know that the distance of the oras Sera from the center of the disk on the nasal side is about 18.5 mm average and on the temporal side it is about 23 to 24 mm from the center of the disk all right now just like we divided the central rtina we can also divide the peripheral retina now we know that the macular area is about 5 . 5 mm in diameter now if you draw a circle of width about 1.5 mm thickness all around the macular area now that is known as your neop periphery again if you draw another circle of thickness about 3 mm around the near peripheral Zone that will be known as your mid peripheral Zone okay this is your mid periphery this one is your near periphery now beyond that whatever you see is known as the far peripheral area of the retina now this far peripheral area of the retina is about 16 mm from the center of the disc on the N nasal side and it is about 9 to 10 mm on the temporal side from the center of the disc okay so I hope that is clear so this is one way of classifying near periphery mid periphery and far periphery okay apart from that some textbooks actually uh give this term far periphery uh using the equator as a reference okay now if you would have seen our video on the blood supply of the eye in that I mentioned about the vortex veins ampula right now the ampula of the vortex veins they basically situated at a distance of about 8 to 9 mm from the oras Sera and remember the outermost border of the retina is actually the auras Sera or we can also call it as the anteriormost limit of the retina okay why am I calling it as the anteriormost limit is because the retina or the eyeball as such we know is not a straight plane uh it is actually a curved it is a curved structure like this so the retina is also curved here you have your cornea so the part of retina which is going to be anterior to the equator is called as the anterior retina and then posterior to the is the posterior retina right so over here the part of the retina which is near the uh cornea celery body Iris and the lens that is called the anterior retina right and this anteriormost part or the anteriormost limit of the retina near the sary body is known as the oraser okay now coming back to the topic so here the ampula of the vortex veins as you can see over here they are about at a distance of 8 to 9 mm from that anterior limit or the oraser right and these ampul are visible on indirect opthalmoscope now if you draw an imaginary Circle uh at the Vex ve ampul then what you are drawing is basically the equator okay now some textbooks like Forester they basically classify the peripheral retina based on this Equator the textbook says that the retina which is posterior to this equator is known as the mid periphery or the peripheral retina and the retina which is anterior to the equator will be known as the far retina okay or the far periphery okay now there's another way of talking about the anatomical equator and that is from using the limbus as a reference so the anatomical limbus is situated at a distance of about 14 to 15 mm from the limbus okay another high he point that you can remember now this was the video I was talking about the blood supply of the eye and the link is going to be uh there in the description box so now we are going to talk about the oraser in detail okay so as I explained to you the anterior limit of the retinal tissue is formed by the aura Sera now we know anterior to the retina or anterior to the oraser what is present it is a celer body now the celer body has two parts an anterior part which has the processes coming out of it which is known as the par pator and the posterior smooth part of the CER body which is known as the parts planner now at this point if you're not aware about if you're not very confident about the anatomy of sary body we do have a video on that as well okay so the oraser basically forms that boundary between part plan and the neurosensory retina at the oras Serita you can say that the neurosensory retina basically becomes continuous with the cinar non-pigmented epithelium of the parts planner now if you can see this diagram over here the imaginary Circle drawn at the ampula of the vortex veins basically is the equator and then you can see drawn in orange color is your oraser now if you would carefully observe the oraser actually is situated at a distance of about 18 to 19 mm on the nasal side from the optic disc whereas on the temporal side the oras Sera is situated at a distance of about 23 to 24 mm now again if you carefully observe the oras Sera actually has this more scalloping Edge on the nasal side compared to the temporal side so we can say the AA cator is more saturated on the nasal side compared to that of the temporal side all right so it has a scalloped appearance it is more serated nasally and also uh something else also happens nely that the orac serator is situated much more anteriorly compared uh Nas compared to the temporal part so uh distance from the limbus of the oraser on the nasal side is going to be about 6 mm and distance from the limbus on the temporal side is about 7 mm okay so this proves that the oraser is situated more on the nasal side of the eyeball all right now why do we see that saturated margins of the orac serator why does it have that scalloped appearance okay and that happens because of these projections over here this is the reer and this is your iris this is as if you're looking from inside as if you have uh you know cut cut open an eyeball and you're standing within the eyeball and you're looking straight from inside so this is your pupil this is the iris and this part here with The Ridges is your par ply and this brown color things is the par planum and here these whitish processes you can see right so these are the processes which are coming from your oraser this part is the oraser right so oraser as it merges with the p Plana it actually sends these tooth like projections into the P planner and these are known as the dentate process es okay you can see over here these are the the pointed ones are the dented processes okay and these rounded tips of the parts plan are known as the oral base okay so these hemic circular uh things are known as the oral base so I hope that is clear what is meant by dented process and the oral base okay now let us see a few diagrams and try to understand so this is your Rea and this part will be your past planner okay and again you can see that the retina is actually uh the oras serata region of the retina is is projecting these tooth likee processes which are known as the dented processes okay so these tooth likee processes will be dented processes and in between the dented processes the part of the oral the part of the past planner is known as the oral base right again on an ultra wide field Imaging again you can see these ones here marked by the arrow are the dented processes and in between that what you see is the oral base okay now Mark with asteris here is a meridional fold so we're going to talk about it again in a while now sometimes what happens is that the dented processes will actually move like this and they are going to meet the other dented process the adjacent dented process and in this process and in this um meeting up with the adjacent process what they do is that they will enclose a part of the past planner within itself and that is known as an enclosed oral Bay so it's an oral Bay which has been enclosed by two adjacent dented processes right so there's an island of P plan enclosed within the retinal tissue so you know that this dented process is the retinal tissue which is coming from the oraser right now if you can see this diagram over here uh this picture over here from retina this is actually from retina image Bank okay so here you can see this part this is the retinal tissue no sorry this is the P plan tis tisue and the P Plana has actually been a part of it has been enclosed by the retina so this is the retinal tissue this is p planner tissue and over here is the P planner again so importance of enclosed oral Bay is that they might mimic a retinal hole okay so that is one thing that you should remember again over here one more image showing that these dented processes are actually enlarged and they are basically enclosing an oral base this is again an example of enclosed oral Bay so if you look carefully you can see these drusens like structures okay so these drusen like structures over here okay they are known as the oral pearls or the pars Plana pearls right these D like structure basically appear at the junction of the retina and the celery epithelium and mostly they are along the rented process and histologically they are basically formed under the RP e and near the BRX membrane okay that's the reason why I'm calling them drusen like right so these oral pearls are actually present in about 20% of the eyes don't have any sex or age predilection right so again another image which is showing these small pearls you can call them past planner pearls or you can call them oral pearls as well another finding that sometimes you might find is known as the meridional fold right so sometimes you will see these full thickness uh radially oriented folds of the retina so normally the retina is like this flat but sometimes it might get folded on itself and get thicken like this now these are when this happens it forms a fold and this fold is called meridional fold this meridional fold is actually oriented 90° to the orasa so you can see over here this is a meridional fold in the diagrammatic representation and this is again a meridional fold now this thickened retinal tissue actually extends into the parts planner region right now this is also present in about 26% of the population and they can actually be bilaterally present as well and the most common quadrant where you find these meral folds is in the superior nasal quadrant now this is an ultra wild Field image okay so here also you can see that uh these one these thickening are the meral folds and on high magnification again you can see these are the meridional folds now these meridional folds actually have not been significantly associated with any peripheral retinal pathology although sometimes it has been suggested that you might find some small retinal holes near the meral folds because of the termination of the vitus over there and because of some of the vital traction component right now before we go to other findings let me uh tell you one more important clinical point and that is why do you see most the degenerations uh at the oraser region right now that happens because the oraser region actually acts as a watershed zone between the anterior and the posterior circulation okay and therefore this region actually has just single layer of the blood vessel and moreover the thickness of the region is also very very less and that is the reason why the degenerations are more common within the aura Sera so we talked about the meridional for and now let's talk about what is meant by meridional complex okay so complex means that there will be multiple components okay a meridional complex is formed basically by an enlarged dented process as you can see over here and if this dented process aligns with the cery process which is here like this and it aligns with the meridional fold like this so all these three structures together will form what is known as a meridional force okay so a meral fold is formed by an abnormal alignment between the dentate process which is usually enlarged and that dented process is continuous with an enlarged cery process and a meridional fold right now whenever they are present it also leads to actually retinal excavation in the corresponding meridian so this Meridian will have retinal excavation okay and these meridional complexes are found in about uh you know 16% of the population and they can be about they can also be seen bilaterally right again the most common site where you find them is in the superior nasal quadrant another structure that uh that another findings that you can see in the periphery is the presence of a cyst in the parts planner region now they are quite different from the pearls that we saw okay now these cyst can be small cyst or they can be really large cyst they are basically these Bullis elevations that you can see over here and they they're looking clear because they filled up with the hyaluronic acid right and these are formed by the separation between the non-pigmented and the pigmented Cedar epithelia okay so that is one thing that you must remember this this picture is actually from Rea bank and here you can see the SP plan cyst and this the cyst were actually found uh during the vitrectomy surgery for regenus retinal detachment okay so there has been a peripheral indentation that has been applied so you can see over here these are your CER processes and this is the PPL region then again the oraser and then you have the retina so in the PPL region you can see this cyst okay now many times you might actually uh be confused sometimes people get confused between retinal detachment retinoschisis and the pass plan assis and a very easy way to differentiate them is by observing the blood vessels so normally in a retinal detachment the blood vessels are going to be uh you know they're going to follow the counter of your Detachment they're going to be moving with the attachment whereas here the blood vessels will be found underneath this cyst okay so if you trace this this is how the blood vessel is and here also the blood vessel is like this okay I I know the picture is not very clear but um in a retinal detachment you might not be able to find the blood vessels below the Detachment whereas in case of pastan assis you will be easily able to track uh track the pathway of the blood vessels right and how can we not discuss about the nerves and the veins that are seen um in the peripheral retina so this is seen usually in the wi field Imaging so you can see over here these are the ampul of the vortex veins and this horizontal line that you see here is basically the long celery nerves and these ones the radially oriented ones are the short posterior selary nerves right again here you can see this one is a long posterior celer nerve now sometimes what happens is that there might be in some cases a normal variation of the RP distribution that means the RP might be densely uh present near the central retina and the mid peripheral retina and in the far in the far periphery the RP um the pigment might not be distributed as densely right so this leads to this variation in the uh in the color of the retina and that might actually uh you know might be falsely diagnosed as retinal detachment or retinoschisis right so that is one point that I want to tell you about the variable RP distribution okay so that was regarding the Topography of the peripheral retna and Central RNA as well I hope you found it useful and if you did kindly like and uh hit that subscribe button that really makes a difference for the channel and that's all for today thank you and have a nice day