The pupil is the mirror of various diseases. The various reflection of pupil shape, size and reaction represent the various disease. Many ocular diseases are diagnosed by the pupillary reaction and structure.
By the torch light examined we easily find lots of ocular problem.
This is how I discussed some various shape,size and reaction of the pupil .
The discussion topics are โโ
~ ๐๐ฉ๐ข๐ต ๐ช๐ด ๐๐ถ๐ฑ๐ช๐ญ
~ ๐๐ฐ๐ณ๐ฎ๐ข๐ญ ๐๐ถ๐ฑ๐ช๐ญ ๐ด๐ฉ๐ข๐ฑ๐ฆ & ๐ด๐ช๐ป๐ฆ
~ ๐๐ฉ๐ข๐ฏ๐จ๐ฆ ๐ฐ๐ง ๐๐ถ๐ฑ๐ช๐ญ ๐ด๐ช๐ป๐ฆ ๐ฅ๐ถ๐ฆ ๐ต๐ฐ ๐ท๐ข๐ณ๐ช๐ฐ๐ถ๐ด ๐ฅ๐ช๐ด๐ฆ๐ข๐ด๐ฆ๐ด ๐ข๐ฏ๐ฅ ๐ด๐ต๐ข๐ต๐ฆ
~ ๐๐ฉ๐ข๐ฏ๐จ๐ฆ ๐ฐ๐ง ๐๐ถ๐ฑ๐ช๐ญ ๐ด๐ฉ๐ข๐ฑ๐ฆ ๐ฅ๐ถ๐ฆ ๐ต๐ฐ ๐ท๐ข๐ณ๐ช๐ฐ๐ถ๐ด ๐ค๐ฐ๐ฏ๐ฅ๐ช๐ต๐ช๐ฐ๐ฏ & ๐ฅ๐ช๐ด๐ฆ๐ข๐ด๐ฆ๐ด
~ ๐๐ถ๐ฑ๐ช๐ญ๐ญ๐ข๐ณ๐บ ๐ญ๐ช๐จ๐ฉ๐ต ๐ณ๐ฆ๐ข๐ค๐ต๐ช๐ฐ๐ฏ
~ ๐๐ข๐ณ๐ช๐ฐ๐ถ๐ด ๐ค๐ฐ๐ญ๐ฐ๐ถ๐ณ ๐ฐ๐ง ๐ฑ๐ถ๐ฑ๐ช๐ญ๐ญ๐ข๐ณ๐บ ๐ณ๐ฆ๐ง๐ญ๐ฆ๐ค๐ต๐ช๐ฐ๐ฏ
~ ๐๐ถ๐ฑ๐ช๐ญ๐ญ๐ข๐ณ๐บ ๐ญ๐ช๐จ๐ฉ๐ต ๐ณ๐ฆ๐ง๐ญ๐ฆ๐น ๐ฑ๐ข๐ต๐ฉ๐ธ๐ข๐บ.
1) แดกสแดแด ษชs แดแดแดษชส?
Ans:- In the centre of the iris there is a round shape opening structure called pupil.
๐๐ช๐ป๐ฆ- Normally, it varies between 2-4 mm. It may be smaller ( ๐ฎ๐ช๐ฐ๐ด๐ช๐ด) or may be larger ( mydriasis).
For the refractive status size of the pupil is normally changed.
In ๐๐บ๐ฐ๐ฑ๐ช๐ค ๐ฑ๐ข๐ต๐ช๐ฆ๐ฏ๐ต, the size of the pupil > equal to 4 ๐ฎ๐ฎ ( Mydriasis).
In ๐๐บ๐ฑ๐ฆ๐ณ๐ฎ๐ฆ๐ต๐ณ๐ฐ๐ฑ๐ช๐ค ๐ฑ๐ข๐ต๐ช๐ฆ๐ฏ๐ต, the size of thr pupil < equal to 2 ๐ฎ๐ฎ ( ๐๐ช๐ฐ๐ด๐ช๐ด).
In ๐๐ฎ๐ฎ๐ฆ๐ต๐ณ๐ฐ๐ฑ๐ช๐ค ๐ฑ๐ข๐ต๐ช๐ฆ๐ฏ๐ต, the size of the pupil lying between (2 to 4 )mm.
The reaction of pupil in ๐๐บ๐ฐ๐ฑ๐ช๐ค ๐ฑ๐ข๐ต๐ช๐ฆ๐ฏ๐ต is good and fast and in ๐๐บ๐ฑ๐ฆ๐ณ๐ฎ๐ฆ๐ต๐ณ๐ฐ๐ฑ๐ช๐ค ๐ฑ๐ข๐ต๐ช๐ฆ๐ฏ๐ต is normal and slow.
๐๐ฉ๐ข๐ต ๐ข๐ณ๐ฆ ๐ต๐ฉ๐ฆ ๐ค๐ข๐ถ๐ด๐ฆ๐ด ๐ฐ๐ง ๐ฎ๐ช๐ฐ๐ด๐ช๐ด ๐๐ถ๐ฑ๐ช๐ญ?– small pupil
=Including thypermetropia there are lot of factor which are responsible for the miosis Pupil.these are —
(1) แดxแดสแดแดแด แดา แดษขแดs = In the older of size of pupil becomes gradually decreasing. For this recover in extreme of age the size of Pupil miosis.
(2) ษชษด สสษชษขสแด สษชษขสแด= sunlight or bright light the Pupil is constricteal for this recover Size of pupil become small.
(3) แดแดสแดสษชษดแด ษชษดsแดสแดแดแดษชแดษดs= morphine is a very story painkiller when is talles. By the reaction of it’s the size of the Pupil become miosis.
(4) แดแดษดแดษชษดแดแด สแดแดแดสแดษขแด=pontinue hemarage is a form of a intra cranial hemarage the most common cause of this problem is long standing poorly uncontrol chronic hypertension.
(5) แดแดแดแดแด ษชสษชแดษชs= iritis is intranation of the iris ,when the iritis develops suddenly,over .for the acute iritis pupil become miosis.
Acute Iritis – Iritis is the inflammation of the iris, when the Iritis develops suddenly , over hours and days is known as acute Iritis. For the acute Iritis pupil become miosis.
Use of Miotic drug- Use of Miotic drug the size of the pupil become smaller ( eg – Pilocarpine ).
2) แดกสแดแด แดสแด แดสแด แดแดแดsแด แดา แดสแด
สษชแดsษชs? (big pupil size>4mm)
Ans:- Including moderate high myopia there are lot of factors which are responsible for ๐ฑ๐ถ๐ฑ๐ช๐ญ ๐ฎ๐บ๐ฅ๐ณ๐ช๐ข๐ด๐ช๐ด, they are :
i) ๐๐ฑ๐ต๐ช๐ค ๐๐ต๐ณ๐ฐ๐ฑ๐ฉ๐บ – When the optic nerve gets damage anywhere along the path from retina to LGB(Lateral Geniculate Body), then ๐ฎ๐บ๐ฅ๐ณ๐ช๐ข๐ด๐ช๐ด takes place.
ii) ๐๐ค๐ถ๐ต๐ฆ ๐ข๐ต๐ต๐ข๐ค๐ฌ ๐ช๐ฏ ๐ข๐ฏ๐จ๐ญ๐ฆ ๐ค๐ญ๐ฐ๐ด๐ถ๐ณ๐ฆ ๐จ๐ญ๐ข๐ถ๐ค๐ฐ๐ฎ๐ข – It occurs when the iris bulges forward due to narrow or blockage in the drainage angle ,fluid can’t circulate through the eye and pressure increases resulting in ๐ฎ๐บ๐ฅ๐ณ๐ช๐ข๐ด๐ช๐ด.
iii) ๐๐ฃ๐ด๐ฐ๐ญ๐ถ๐ต๐ฆ ๐๐ญ๐ข๐ถ๐ค๐ฐ๐ฎ๐ข – It is the end stage in all types of glaucoma. The eye has no vision, there is totally absence of pupillary light reflex and pupillary response, due to this size of pupil increases.
iv) ๐๐ฐ๐ฎ๐ข๐ต๐ฐ๐ด๐ฆ ๐ฑ๐ข๐ต๐ช๐ฆ๐ฏ๐ต –
Coma is a state of prolonged unconsciousness with dilated pupil.
v) ๐๐ฆ๐ข๐ฅ ๐ช๐ฏ๐ซ๐ถ๐ณ๐บ – It sometimes results in ๐ฎ๐บ๐ฅ๐ณ๐ช๐ข๐ด๐ช๐ด.
vi) 3๐ณ๐ฅ ๐ฏ๐ฆ๐ณ๐ท๐ฆ ๐ฑ๐ข๐ญ๐ด๐บ- The pupil becomes fixed and dilated due to paralysis of ๐ด๐ฑ๐ฉ๐ช๐ฏ๐ค๐ต๐ฆ๐ณ ๐ฑ๐ถ๐ฑ๐ช๐ญ๐ญ๐ข๐ฆ, pupil become larger.
vii) ๐๐ด๐ฆ ๐ฐ๐ง ๐ฎ๐บ๐ฅ๐ณ๐ช๐ข๐ต๐ช๐ค๐ด – Pupil gets dilated due to the use of drugs like atropine, homatropine, phenylphrine.
viii) ๐๐ฏ ๐ฅ๐ข๐ณ๐ฌ ๐ฑ๐ญ๐ข๐ค๐ฆ๐ด – The pupil gets larger in dark areas to allow more amount of light.
๐๐ฉ๐ฆ ๐ด๐ฉ๐ข๐ฑ๐ฆ ๐ฐ๐ง ๐ต๐ฉ๐ฆ ๐ฑ๐ถ๐ฑ๐ช๐ญ ๐ค๐ฉ๐ข๐ฏ๐จ๐ฆ๐ด ๐ฃ๐บ ๐ต๐ฉ๐ฆ ๐ท๐ข๐ณ๐ช๐ฐ๐ถ๐ด ๐ฐ๐ค๐ถ๐ญ๐ข๐ณ ๐ฅ๐ช๐ด๐ฆ๐ข๐ด๐ฆ๐ด. ๐๐ฆ๐ณ๐ฆ ๐ ๐ฅ๐ช๐ด๐ค๐ถ๐ด๐ด๐ฆ๐ฅ ๐ช๐ฏ ๐ท๐ฆ๐ณ๐บ ๐ด๐ฉ๐ฐ๐ณ๐ต๐ญ๐บ โโ
(๐) ษชสสแดษขแดสแดส ๐ดสแดแดแด :- ๐๐ฉ๐ฆ ๐ด๐ช๐ป๐ฆ ๐ฐ๐ง ๐ต๐ฉ๐ฆ ๐ฑ๐ถ๐ฑ๐ช๐ญ ๐ฃ๐ฆ๐ค๐ฐ๐ฎ๐ฆ ๐ช๐ณ๐ณ๐ฆ๐จ๐ถ๐ญ๐ข๐ณ ๐ข๐ง๐ต๐ฆ๐ณ ๐ต๐ฉ๐ฆ ๐ต๐ณ๐ข๐ถ๐ฎ๐ข ๐ฐ๐ณ ๐ช๐ณ๐ช๐ต๐ชs.
(๐) แด -๐ดสแดแดแดแด แดแดแดษชส :- ๐๐ฉ๐ฆ ๐ด๐ช๐ป๐ฆ ๐ฐ๐ง ๐ต๐ฉ๐ฆ ๐ฑ๐ถ๐ฑ๐ช๐ญ ๐ข๐ฑ๐ฑ๐ฆ๐ข๐ณ๐ด ๐ข๐ด ๐- ๐ด๐ฉ๐ข๐ฑ๐ฆ๐ฅ, ๐ธ๐ฉ๐ฆ๐ฏ ๐ช๐ณ๐ช๐ฅ๐ฐ๐ค๐บ๐ค๐ญ๐ช๐ต๐ช๐ด ๐ฑ๐ณ๐ฐ๐ฃ๐ญ๐ฆ๐ฎ ๐ข๐ณ๐ฆ ๐ฑ๐ณ๐ฆ๐ด๐ฆ๐ฏ๐ต.
(๐) สแดแดแด แดส สแดแดแดแดแดแด ๐ดสแดแดแดแด :- ๐๐ฉ๐ฆ๐ฏ ๐ท๐ช๐ต๐ณ๐ช๐ฐ๐ถ๐ด ๐ญ๐ฐ๐ด๐ด ๐ฅ๐ถ๐ณ๐ช๐ฏ๐จ ๐ค๐ข๐ต๐ข๐ณ๐ข๐ค๐ต ๐ด๐ถ๐ณ๐จ๐ฆ๐ณ๐บ, ๐ต๐ฉ๐ฆ๐ฏ ๐ต๐ฉ๐ฆ ๐ฑ๐ถ๐ฑ๐ช๐ญ ๐ฃ๐ฆ๐ค๐ฐ๐ฎ๐ฆ ๐๐ฐ๐ข๐ต ๐ฐ๐ณ ๐ฉ๐ข๐ฎ๐ฎ๐ฐ๐ค๐ฌ ๐ด๐ฉ๐ข๐ฑ๐ฆ๐ฅ.
(๐) แดแดแดส ๐ดสแดแดแดแด แดษดแด แดษดแด สแดแดกษด แดแดแดษชส :- ๐๐ฏ๐ค๐ข๐ณ๐ค๐ฆ๐ณ๐ข๐ต๐ช๐ฐ๐ฏ ๐ฐ๐ง ๐ช๐ณ๐ช๐ด ๐ธ๐ช๐ต๐ฉ ๐ค๐ฐ๐ณ๐ฏ๐ฆ๐ข๐ญ ๐ธ๐ฐ๐ถ๐ฏ๐ฅ.
(๐) าแด๐ดแดแดแดษดแดแด แดแดแดษชส :- ๐๐ณ๐ช๐ฅ๐ฐ๐ค๐บ๐ค๐ญ๐ช๐ต๐ช๐ด (๐ข๐ค๐ถ๐ต๐ฆ ๐ช๐ฏ๐ง๐ญ๐ข๐ฎ๐ข๐ต๐ช๐ฐ๐ฏ ๐ฐ๐ง ๐ต๐ฉ๐ฆ ๐๐ณ๐ช๐ด ๐ข๐ฏ๐ฅ ๐ค๐ช๐ญ๐ช๐ข๐ณ๐บ ๐ฃ๐ฐ๐ฅ๐บ) ๐ช๐ด ๐ต๐ฉ๐ฆ ๐ฎ๐ฐ๐ด๐ต ๐ค๐ฐ๐ฎ๐ฎ๐ฐ๐ฏ ๐ง๐ฆ๐ข๐ต๐ถ๐ณ๐ฆ๐ด ๐ฐ๐ง ๐ถ๐ท๐ฆ๐ช๐ต๐ช๐ด.
(๐) แดษชแด – แด ษชสแดแดแดแด & แดแด แดส แดแดแดษชส :- ๐๐ฐ๐ณ ๐ต๐ฉ๐ฆ ๐ข๐ฏ๐จ๐ญ๐ฆ ๐ค๐ญ๐ฐ๐ด๐ถ๐ณ๐ฆ ๐ฑ๐ข๐ต๐ช๐ฆ๐ฏ๐ต ๐จ๐ญ๐ข๐ถ๐ค๐ฐ๐ฎ๐ข ๐ฑ๐ข๐ต๐ช๐ฆ๐ฏ๐ต๐ด ๐ฑ๐ถ๐ฑ๐ช๐ญ .
(๐) แดษชแด แด ษชสแดแดแด แดแด แดส แดษดแด ษชษดาแดส๐ดแดษดแดส :- ๐๐ฉ๐ฆ๐ฏ ๐ต๐ฉ๐ฆ ๐ช๐ณ๐ช๐ด ๐ช๐ด ๐ข๐ฃ๐ด๐ฆ๐ฏ๐ต (๐ช๐ณ๐ช๐ด ๐ค๐ฐ๐ญ๐ฐ๐ฃ๐ฐ๐ฎ๐ข), ๐ต๐ฉ๐ฆ ๐ด๐ฉ๐ข๐ฑ๐ฆ ๐ฐ๐ง ๐ต๐ฉ๐ฆ ๐ฑ๐ถ๐ฑ๐ช๐ญ ๐ค๐ฉ๐ข๐ฏ๐จ๐ฆ ๐ข๐ฏ๐ฅ ๐ช๐ต ๐ค๐ฐ๐ฏ๐ท๐ฆ๐ณ๐ต ๐ช๐ฏ๐ต๐ฐ ๐ข ๐ฐ๐ท๐ฆ๐ณ ๐ด๐ฉ๐ข๐ฑ๐ฆ.
Key hole appeance- After optical iridectomy key hole apperance are seen in the pupil.
๐๐ข๐ณ๐ช๐ฐ๐ถ๐ด ๐ค๐ฐ๐ญ๐ฐ๐ถ๐ณ ๐ณ๐ฆ๐ง๐ญ๐ฆ๐น ๐ฐ๐ง ๐ต๐ฉ๐ฆ ๐๐ถ๐ฑ๐ช๐ญ๐ญ๐ข๐ณ๐บ ๐ข๐ณ๐ฆ๐ข
(1) แดแดแด สสแดแดแด แดแดแดษชสสแดสส สแดาสแดx :- For the aphakic eye the reflection of the pupil is jet black colour.
(2) แดกสษชแดแด แดแดแดษชสสแดสส สแดาสแดx :- White pupillary reflex are seen in the cataract eye.
(3) ษขสแดsส แดแดแดษชสสแดสส สแดาสแดx :- For pseudophekic eye glasy pupillary reflex are visible.
(4) แดแดแดแดสแดแดษชแด แดแดแด’s แดสแด สแดาสแดx :- If the Retiono blastoma, eongenital cataract, PHPV, Endopthalmitis, coloboma of Choroid like these type of problem present then the Amauratic cat’s eye reflex are visible.
๐๐๐๐๐๐๐ผ๐๐ ๐๐๐๐๐ ๐๐๐๐๐๐
In this topic, I will dicsuss —
~~Pupillary Light Reflex Pathway.
~~How To Localize The Site Of Lesion In Cases Of Abnormal Pupillary Reflex.
So I will start with the very basics.
This is the diagram of the eye. This circular brown structure is the Iris and this round gap in the center of the Iris is known as the Pupil.
The normal size of the Pupil ranges from 2-4 mm in diameter. Light enters our eye through the Pupil.
Now, when bright light is shone on the Pupil, the Pupil responds by decreasing in size. This is known as “Constriction of the Pupil” and this constriction of the Pupil in response to light stimulus is known as “Pupillary light reflex”.
Pupillary light reflex can be a Direct light reflex or it can be an Indirect light reflex which is also known as Consensual light reflex.
๐๐๐๐๐๐ ๐๐๐๐๐ ๐๐๐๐๐๐
Direct light reflex is when constriction of the Pupil is seen in response to light shone in the ๐๐ข๐ฎ๐ฆ ๐ฆ๐บ๐ฆ, that is the Ipsilateral eye.
For example, if this the right eye of the patient and we shine light in this right eye & in response we see the Pupil of the right eye constricting, it is known as Direct light reflex because the response is occurring in the same eye that is receiving the stimulus.
๐๐๐๐๐๐๐๐๐๐ / ๐๐๐๐๐๐๐๐ ๐๐๐๐๐ ๐๐๐๐๐๐
The other reflex is the consensual light ๐ณ๐ฆ๐ง๐ญ๐ฆ๐น. Consensual light reflex when the light stimulus is given to one eye but the response to that stimulus is seen in the opposite eye that is the Contralateral eye.
So, again in this patient, when we show light in the right eye, we will see constriction of the Pupil in the opposite eye that is the left eye. So this constriction of Pupil that occurs in response to light stimulus given in the contralateral eye is known as Consensual light reflex.
Both of these responses that is the direct light reflex as well as the consensual light reflex they occur simultaneously that is they occur together at the same time. So, if we shine light in the right eye, we will see both pupils constricting together, which means that the right eye will show direct light reflex and the left eye will show consensual light reflex and both of these reflexes are seen in response to the same light stimulus that was given in the right eye.
แดสแดแดแดแด แดสแด
So how do you perform pupillary light reflex test?
First of all, it should be done in a semi dark room. ‘Semi dark’ so that you are able to observe the response in the contralateral eye. So we ask the patient to fixate on a distant object . If the patient fixate on a near object, the near reflex pathway will get activated which will cause pupillary constriction.
So we want to eliminate any cause of pupillary constriction when we are checking the pupillary light reflex pathway.
So we first observe the position, size and shape of the pupil in each eye. Then we shine the torch in one eye and we observe the response of the pupil in the same eye. This is the Direct light reflex. Then again we shine light in the same eye but this time we observe the response in the opposite eye. That is the contralateral eye & this is the consensual light reflex. And then we repeat the procedure on the other eye to check the direct & the consensual light reflex to light stimulus given on the opposite side.
ษดแดแดแดษดแดสแดแดแดสแด
Before proceeding further, we need to be absolutely clear about certain terminologies. Suppose in a patient, light is shone in the left eye and both pupils constrict, we document it as left direct light reflex present and light consensual light reflex present. So the nomenclature is with respect to the eye which is responding to the stimulus and not with respect to the eye which is receiving the stimulus.
Suppose in a patient’s case sheet it written that right direct light reflex and right consensual light reflex is present, it means that the right eye constricts to light stimulus given to the right eye which is the direct reflex and it also constricts to light stimulus given in the left eye which is the consensual reflex. So, right consensual reflex doesn’t mean that light stimulus is given in the right eye. It means that the pupillary response to light stimulus is seen in the right eye.
I hope this is clear for you now.
ษชสษชs แดแดsแดแดสแดแดแดสแด
Now the storma of the iris has 2 muscles. The “Sphincter pupillae” and the “Dilator pupillae”.
sแดสษชษดแดแดแดส แดแดแดษชสสแดแด
Sphincter pupillae muscle is circulary arranged at the border of the pupil. So when the sphincter pupillae contracts it leads to constriction of the pupil & this occurs via the parasympathetic pathway. This constriction of the pupil is known as Miosis.
แด ษชสแดแดแดส แดแดแดษชสสแดแด
The dilator pupillae muscle is inserted at the root of the iris and from there it extends radially to 2 mm from the pupillary margin. So, the dilator pupillae muscle gets activated by the dark reflex pathway which is a Sympathetic pathway and this results in dilatation of the pupil & dilatation of the pupil is known as Mydriasis.
Now the diameter of the pupil the result of the balance between these two antagonistic muscles of the iris that is the sphincter pupillae and the dilator pupillae of the iris.
Since in this topic I am talking about the light reflex pathway I will be restricting ourselves to only parasympathetic pathway that results in constriction of the pupil via the sphincter pupillae muscle.
แดแดแดษชสสแดสส สษชษขสแด สแดาสแดx
So, Pupillary light reflex pathway is a parasympathetic pathway with an afferent limb and an efferent limb.
“Afferent limb” means that Sensory stimulus is carried to the brain via this route.
“Efferent limb” means that this route carries signals from the brain to the effector organ, that is the sphincter pupillae muscle in this case.
แดแดแดษชสสแดสส สษชษขสแด สแดาสแดx แดแดแดสแดกแดส
As we all know, Light enters the eye through pupil. Then it falls on the Retina of the eye. From the retinal gangionic cells, the information is carried by the the optic nerve. Optic nerve is the second cranial nerve. Optic nerve carries impulses from the nasal half of the retina and the temporal half of the retina. So the fibers here that are arranged laterally represent the temporal fibers and the fibers that are present medially represent the nasal fibers. Then the optic nerve reaches the optic chiasma. Optic chiasma is located just above the Pituitary gland. At the optic chiasma, decussation of these nerve fibers takes place. Now what is the meaning of decussation?
~ Decussation means that the nerve fibers from one side cross over to the opposite side. So the fibers that were carrying signals from the nasal half of Retina on the right side cross over to the left side but the fibers that were carrying from the temporal half of the Retina do not cross. They continue to travel along the same side that is along the right side. It is seen that the ratio of crossed to uncrossed fibers is approx 53:47 which means that more fibers cross over than those that stay on the same side. This decussation occurs on both the sides. So nasal fibers of the right eye cross over to the left side and then they continue with the temporal fibers of the left eye. While the nasal fibers of the left eye cross over to the right side and then they continue with the temporal fibers of the right eye. They continue as optic tracts. Thus each optic tract contains ipsilateral temporal fibers and contralateral nasal fibers. Now the pathway that we are discussing here is the pupillary light reflex pathway. But we also know that it is the same optic nerve that carries signals to the optical cortex of the brain via the visual pathway and this is how image processing takes place and I am able to see things. This means that the optic nerve carries afferents for vision as well as for pupillary constriction. Now how are these two pathways separate from each other?
So most of the nerve fibers that are carried by the optic tracts synapse in the lateral geniculate body. Lateral geniculate body is located in the thalamus and from the lateral geniculate body, the signals are carried to the visual centre which is located in the occipital lobe of the brain. So this is the visual pathway in brief. However a small number of these fibers- they don’t go to the lateral geniculate body. They exit from the optic tract and instead of going to the lateral geniculate body, they go to the pretectal nucleus. Pretectal nucleus is located in the midbrain at the level of the superior colliculus.
