hello and welcome to insight ophthalmology this is dr amrit and i welcome you to another lecture on pupillary pathways under this lecture we are going to study about what is direct and consensual light reflex what is the pathway of the light reflex what are the various pupillary muscles that is the sphincter pupillae and the dilator pupillae and finally we are going to talk about the nerve supply of these pupillary muscles that is the sympathetic and the parasympathetic supply of the pupillary muscles the pupils basically participate in several reflexes however three of them are of clinical significance to us the light reflects the near reflex and the psychosensory reflex starting with the light reflex the light reflex is nothing but whenever light enters an eye the pupil of that eye as well as the pupil of the other eye will constrict in reaction to this light this is called the light reflex whenever we look at an object from far to near there will be constriction of the pupil and this is called the near reflex coming to the psychosensory reflex it is nothing but it is a dilatation of the pupil that will occur on psychic and sensory stimulus so the light reflex and the near reflex we have constriction of the pupil and in psychosensory reflex we have dilatation of the pupil the light reflex is of particular importance to us and whenever testing for light reflects three points should be considered in our mind this is number one the illumination of the room should always be low number two the patient should be looking at the distance number three the light should be focused and bright light light reflex is of two types the direct pupillary light reflects and the consensual pupillary light reflex constriction of the pupil to which the light is shown is called the direct pupillary reflex however the constriction of the other's eye to which the light is not shown in response to the opposite eye in which the light is shown is called consensual pupillary reflex that means if we show light to this eye and this eye is also getting constricted along with this the response that we see in the counter lateral eye is called consensual pupillary reflex so what i mean to say is that if this is the right eye and this is the left eye and i have a torch with which i am showing light to the right eye the right eye will actually constrict in response to the direct light which is thrown inside it and this reflex is called the direct pupillary reflex of the right eye because i am throwing light directly in the right eye however the left eye also will constrict in response to the light which is thrown in the right eye and that response is called the left eye consensual pupillary reflex because it is consensually or indirectly responding to the light which is sent in the other eye now let us talk about the light reflex pathway at this point i want to clarify that the visual pathway is totally different from the light reflex pathway although they share certain similar structures in common the visual pathway video is already there on my channel and i will put the link in the description for you to follow that before so coming to the light reflex pathway they are specifically associated with the light reflex which we are getting from the pupil however visual pathway is associated with the various components of the vision the five components of vision okay so they're different the light reflex pathway also consists of an afferent a center and then an efferent so in our visual pathway what was happening was the temporal part of the retina which was carrying the nasal field was going into the optic nerve and then into the optic chiasm but in the optic chasm they were not crossing like the nasal fibers then they were they will go into the optic tract and then into the lateral geniculate body which was present at the end of the optic tract from there they were going into the optic radiations and finally they were reaching the visual cortex right similarly the nasal fibers what was happening to the nasal fiber the nasal fiber of the opposite side was coming into the optic nerve and then it was crossing in the optic chiasm and coming to this optic tract going into the lateral geniculate body optic radiation and finally the cortex the same thing was happening in the other eye also that is the nasal the nasal fibers were the one which were crossing and the temporal fibers were the one which will not cross and pass just like that traveling the optic nerve chiasm optic tract little geniculate body and finally reaching the visual cortex what happens differently in this light reflex is that few of the fibers from the optic tract they will take a d root and they will go to this structure in golden here present in the midbrain and this structure is called the pre-tectal nucleus right so both the fibers whether it is nasal fibers or it is a temporal fibers they are going to go and relay in the pre-tectal nucleus in the midbrain of the either side taking d root from the optic tract and they are not going to go to these lateral geniculate bodies to which the visual pathway was going right so this is the difference all the fibers are not going to go to the lateral geniculate body instead some of them are going to come out from the optic tracts and go to the pre-tectal nucleus present in the midbrain near the superior coliculus right the afferent part of the light reflex starts right from here that is from the retina and from the retina up to the pre-tectal nucleus of the either side so this will form the afferent part or the afferent limb of the light reflex the pretectal nucleus is connected with the structures present in the midbrain anterior to it and these structures are called the eddinger westfall nucleus okay and they are actually the main centers of relay in the light pathway now the pre tectal nucleus of both the sides will send the fibers to both the edinger vespal nuclear so there is a crossing so what happens is suppose this is a predicted nucleus it will send fiber to this adding a wasteful nucleus and also to this vespa nucleus similarly the other pre-tactile nucleus also will be sending fibers to both the edinger westball nucleus so these neurons which are going to both the ringer vespal nucleus they are called the international neurons and they are the ones which are responsible for our direct and consensual light reflex so what do i mean to say is that whenever we put light to one eye the other eye is also showing the light reflects why is the other eye showing light reflects the reason is because of the presence of these international neurons because of that when one light when one eye is also stimulated the information is going to go to the other eye also because of the crossing present at the level of input or because of the crossing which is present in between the pre-tectal and the edinger vespa nucleus finally we have the efferent limb of the light reflex the efferent pathway consists of basically the parasympathetic fibers which are arising from this edinger vespal nucleus of both the sides and these edinger the parasympathetic fibers which are coming from the ringer vespa nucleus they are present in close relation to the third cranial nerve okay and they are going to travel in one of the roots of the third cranial nerve and go up to the ganglion which is present on the either side of the eye and this ganglion is called the ciliary ganglion okay so now they're going to relay in the cedary ganglion and from the celery ganglion they will finally go and supply the sphincter pupillae using the short ciliary nerves so finally we have the short ciliary nerves which will go and supply the sphincter pupillae so this is what is meant by the efferent limb of the light reflex there are basically two pupillary muscles which are present in the pupil which are associated with the reactions of the pupil so the first pupillary muscle is a sphincter pupillae which is present in circular manner around the pupil okay and this sphincter pupil pupillae is under the control of our parasympathetic system however we have another muscle which is called the dilator pupillae and the dilator pupillae is under the control of our sympathetic system so the constrictor pupillae is actually present around the pupil in concentric circles and therefore bring about the constriction of the pupil whereas the dilator pupillae is actually arranged radially across the pupil so whenever this radial muscles are going to contract under the influence of the sympathetic system what happens is that the pupil will actually dilate and because of the dilatation action it is called dilator pupillae now another difference between the two papillary muscles is with respect to the ciliary nerves which are actually going to go and supply these muscle so the sphincter pupillae you can remember it as a mnemonic that it is supplied by the short ciliary nerves on the contrary the dilator pupillae which is supplied by the sympathetic system is getting its nerve supply from the long ciliary nerve okay so for the spring to pupila it is a short posterior ciliary nerve and for the dilator pupillae it is the long posterior ciliary nerve now let us talk about the parasympathetic supply of the pupil as i already told you that it is the sphincter pupillae which is supplied by the parasympathetic system so the sphincter is supplied by the cholinergic nerves of the parasympathetic system which is basically coming using the third cranial nerve so let me tell you how does it happen as i already mentioned that few of the fibers were coming out of the optic tract and they were going into the pretectal nucleus which was present in the midbrain the pre-tectal nucleus will send fibers into both the edinger westpal nucleus as a dingo vespa nucleus of both the site the edinger vespel nucleus is present near the aqueduct of silvius as and also is in very close relationship with the third nerve nucleus therefore these fibers coming from the edinger vespal nucleus will now be traveling inside the optic inside the oculomotor nerve which is the third cranial nerve when these fibers will reach the cavernous sinus the division of the third cranial nerve will take place the third cranial nerve will again be dividing into the superior division and the inferior division now we know that the superior division of the oculomotor nerve will go and supply the superior rectus muscle and the levator palpable superioris however the inferior division of the third cranial nerve will go and supply the lat the medial rectus the inferior rectus and the inferior oblique muscle now the fibers which are coming from the edinga vespal nucleus are going into the third cranial nerve and then they are going to travel in the inferior division of the third cranial nerve especially to the part which is going and supplying the inferior oblique muscle okay traveling to the inferior oblique muscle branch from this side they are going to go and relay in an important ganglion which is present lateral to the eyeball between the eyeball and the lateral rectus muscle and this ganglion is called the ciliary ganglion and this pathway till the level of ciliary ganglion is called the preganglionic parasympathetic pathway for the light reflex after reeling in the ciliary ganglion the postganglionic fibers will start from the ciliary ganglion and now they are going to exit through the short root of the ciliary ganglion and as they exit out of the short route of the ciliary ganglion now they will be called the short ciliary nurse so these short ciliary nerves are going to go towards the eyeball and pierce this clearer near the optic nerve and travel between the sclera and the choroid and now they're going to travel forward now the short ciliary nerves are actually about 8 to 10 in number which will further subdivide and form almost about 20 in numbers so 20 short posterior ciliary nerves can actually be present and the short ciliary nerves will now go traveling between the sclera and the choroid and will be supplying two basic muscles number one is the cd muscle and number two is the splinter pupillae which will cause constriction of the pupil now at this point it is very important to know that almost out of these 20 ciliary nerves which are present almost 95 percent will be supplying the ciliary muscle okay and only five percent of these uh short ciliary nerves will go and supply the sphincter pupillae so this was about the parasympathetic supply of the pupil which is coming mainly from the edinger west palm nucleus traveling in the inferior division of the third cranial nerve going up to the ciliary ganglion and from the ciliary ganglion traveling in the short ciliary nerves and finally going into the sphincter pupillary muscle now let us talk about the sympathetic nerve supply of the pupil as i already told you that it is the dilator pupillae which is supplied by the sympathetic nerve supply and it is happening via the long ciliary nerves the center of the sympathetic nerve supply starts from the hypothalamic center the hypothalamic center will give inhibitory impulses to the eddango westpal nucleus now i already told you that the edinger vespa nucleus is mainly associated with the parasympathetic nerve supply that means supply of the sphincter pupillae okay which is associated with the constriction of the pupil therefore the hypothalamic center what does it do first is that it will cause inhibition of the edinger vespa nucleus now from this hypothalamic centers the fibers are going to go and pass up to the serious spinal center of the budge it is also called celio spinal center of budge which is basically formed by the c8 t1 t2 t3 and t4 however as it reaches from the hypothalamus to the center of budge there will be a decussation which will occur at the level of the midbrain so that the hypothalamic center of one side will be giving the impulses to both the serious central spinal of budge that means there will be a bilateral innovation in the sympathetic system also now the fibers are going to leave through these ventral lamia ventral rami of cat1 t2 t3 t4 that means they are leaving now from the cell spinal center of budge and they will now be traveling in the cervical chain that is a sympathetic chain which is present in our neck that's why it is called cervical change chain now they're going to travel without reeling through the inferior cervical ganglia middle cervical ganglion and finally they are going to reach a point of relay and this point of relay is the superior cervical ganglion right so the preganglionic sympathetic fibers are going to relay where in the superior cervical ganglion now from this level the post ganglionic fibers will start okay so now after they emerge from the superior cervical ganglion they are going to now enter the skull okay now as they enter the skull they are going to come across the internal carotid artery and they are going to coil around the carotid artery now this is called the carotid plexus okay now from here they are going to go up to the cavernous sinus [Music] let us imagine this box to be actually the cavernous sinus okay so what happens is as they are coming out of the superior cervical ganglion as the postganglionic nerve fibers sympathetic nerve fibers they will go and coil around the internal carotid artery okay which is now coming uh which will enter which is actually entering now the cavernous sinus right now in the lateral ward of the cavernous sinus there are three nerves which are traveling that is the third cranial nerve the fourth cranial nerve and we also have the first division of the fifth cranial nerve that is the ophthalmic ophthalmic division of the fifth cranial nerve so what happens is from this carotid plexus now these fibers are going to come in close contact with the v1 division of the fifth cranial nerve and now they are going to start passing through this now i have tried to represent the same thing in this diagram so the structure over here which is drawn in yellow is nothing but the trigeminal ganglion which is also called the gasserian ganglion okay so now the trigeminal ganglion basically has three three divisions that is the v1 division which is the ophthalmic division the v2 division which is the maxillary division and the v3 division which is the mandibular division the ophthalmic division is associated basically with the eye which travels in the cavernous sinus so our fibers are going to go and pass over this ganglion okay so they are not relaying in this glycerin ganglion don't get confused the sympathetic fibers are reeling where they are reeling in the superior cervical ganglion so they are going to just pass like that near the gassarian ganglion and finally they are going to enter where in the v1 division in the cavernous sinus that means in the ophthalmic division now from the ophthalmic division where will they pass so for that you need to know that the ophthalmic division is again dividing into various branches okay so it is dividing into the lacrimal branch which will go supply the lacrimal gland and again subdivide and one is the frontal branch and then we have a nasoceliary branch also which is again going to subdivide into further branches right but there is one important branch of the nasal celery that we must remember is and that is the long series nerve okay so now what happens is from the gaserian ganglion traveling above the basarian ganglion it will enter the v1 division that is the ophthalmic division and from the ophthalmic division these nerves will decide to go in the nasociliary branch and from the nasocelery branch they will enter the long ciliary nerves okay so after going into the long celery nerves these nerves will actually pierce this clearer and travel between the sclera and the choroid and finally supply our dilator pupillae and cause dilatation of the pupil so now if you see carefully tillery ganglion is present over here but what is happening the long ciliary nerves have almost no relationship with this ciliary ganglion okay so our sympathetic nerve supply of the pupil the sympathetic nerves are not going into the ciliary ganglion it was the parasympathetic nerves that is the short cylinders which were coming out of the ciliary ganglion the long sillery nerves carrying the sympathetic system will not go into the ciliary ganglion so i so this was about the sympathetic supply of the pupil okay so starting from the hypothalamus so hypothalamus spinal tract going to the cellular spinal center of budge from there going to the superior cervical ganglion going to the carotid plexus from there going to the v1 division that is the ophthalmic division of the trigeminal going into the nasoc dairy finally from the nasocelery the long cillary nerve going to supply the dilator pupillae so i hope this was clear and useful thank you and have a nice day