Sushruta described the Netra-sharira according to Nidan and Chikitsa into three distinct parts called Mandala, Patala & Sandhi. Mandalas are 5 in number and Patalas & Sandhis are 6 in number. The same division was adopted by Vagbhatta, Madhavakara and Bhavamishra also.
These are 5 in number from outer most to inner most layers and are as follows:
1) Pakshma mandala
2) Vartma mandala
3) Shweta mandala
4) Krushna mandala
5) Drushti mandala
1) Pakshma Mandala:
This is the first and outermost Mandala of the eye formed by the Pakshma or the eyelashes. This Mandala not appears as a circle when the eye is closed and it is apparently elliptical in shape when the eye is open.
2) Vartma Mandala:
Upper and Lower eyelids jointly form a circle in front of the eyeball, which is termed as Vartma Mandala. There are two Nimeshani Siras in the Vartmas which performs the functions of Nimesha and Unmeshana i.e. blinking. Pakshmashaya is also situated in this Mandala. Vartma Mandala is the seat of 21 diseases according to Sushruta and 24 diseases according to Vagbhatta. Upper and lower lids jointly form the two Vartma Patalas along with the orbital margins in front of the eyeball.
3) Shukla Mandala:
Shukla Mandala is the Mandala, which is present just inside the Vartma Mandala and beyond the black circle. This portion appears as whitish and therefore known as Shukla Mandala. Sushruta has described 11 clinical entities in Shukla Mandala, while according to Vagbhatta it is 13 in number. The Shukla Mandala can be correlated to the scleral part of the outer fibrous coat of the eyeball covered with conjunctiva.
4) Krishna Mandala:
The black portion of the eyeball is called as Krishna Mandala. The size of this Mandala is 1/3rd of the whole Netra. This Mandala can be compared with the cornea; and appears as blackish because of the iris below, even though it is transparent in nature. This Mandala encloses Drishti Mandala in it and is the seat of four diseases according to Sushruta and five diseases according to Vagbhatta. Also in Sushruta Samhita Sutrasthana chapter 35/12, Sushruta has used the word ‘Taaraka’ for one structure of Netra, which is also 1/3rd of the total Netra. According to Dalhana, it is the black part of the eye.
5) Drishti Mandala:
Last and innermost circular structure of the Netra is Drishti Mandala as it completes the function of Drishti (vision). Diameter of this Mandala is 1/7th of the Krishna Mandala in the opinion of Videha and Dalhana. Sushruta also expresses same thoughts. Again it is said to be equal to 1/9th part of the “Taaraka”. The size of the Drishti Mandala is equal to the cotyledon of Masura and is a hollow structure. Such structure which has its position inner to Krishna Mandala seems to be pupillary area which is circular in shape.
The pathologies either of cornea, or of iris are shared by both of them. Thus cornea and iris are considered as a unit for Krishna Mandala. Only then the meaning of this Mandala is justified.
C) Sandhi: These are 6 in numbers, and named as -
1) Pakshma – Vartmagata Sandhi:
The union line of Pakshma Mandala and Vartma Mandala is called as the Pakshma Vartmagata Sandhi and it is considered as the lid margin. Krimigranthi is a disease that occurs at this particular Sandhi.
2) Vartma – Shuklagata Sandhi:
The union line of Vartma and Shukla Mandala is called as Vartma Shuklagata Sandhi. The disease Parvani occurs at this Sandhi. Fornix of the eyeball where the palpebral conjunctiva is reflected on to the bulbar conjunctiva seems to be Vartma Shuklagata Sandhi.
3) Shukla – Krishnagata Sandhi:
The circular line joining between Shukla Mandala and Krishna Mandala is called as Shukla Krishnagata Sandhi. The disease Alaji is the one clinical problem among 9 diseases that occurs at Shukla-Krishnagata Sandhi and this junctional area can be considered as the sclero-corneal junction.
4) Krishna - Drishtigata Sandhi:
The union line of Krishna and Drishti Mandala is called as Krishna – Drishtigata Sandhi. By considering iris part in Krishna Mandala, this Sandhi can be explained and the central free margin of the iris, which rests on the anterior capsule of the lens, can be considered as the Krishna Drishtigata Sandhi. Otherwise there is no apparent union line between the cornea and pupil.
5) Kaneenika Sandhi:
Sushruta has not given any explanation regarding the anatomical position of this Sandhi, but Dalhana describes this Sandhi as ‘Nasasameepasthita Sandhi’. So it can be considered as the inner or nasal canthus of the eye. The lacrimal passages are situated in this Sandhi. The diseases of this Sandhi include four types of Srava and Puyalasa.
6) Apanga Sandhi:
Dalhana describes Apanga Sandhi as “Bhrupuchhantah Sthita Sandhi”, and so it can be considered as the outer canthus of the eye.
There are 6 Patalas in the eyeball – 2 Vartma Patalas and 4 Akshi Patalas. There are two outer patals which are considered as external layers of the eye. One upper and one lower eyelid are the two external patals. Drishtigata roga can not happens in these two Vartma patals.
The outermost first patala is supported by Tejas & Jala; the second one consists of muscles, the third Patala is described as ‘Medoashrita’ and the fourth Patala is ‘Asthyashrita’. Their thickness is equal to one-fifth of the Drishti.
The first or outermost Patala is described as “Tejojalashrita”. According to Dalhana, the word Teja means Alochaka Pitta and so Siragata Rakta can be taken as Teja Jala, according to him implies Rasa Dhatu. So it can be considered that the first Patala is the Ashraya for Rasa and Rakta Dhatus.
According to some scholars, the Prathama Patalas can be taken as Cornea and Aqueous humour; as they are the seat of Tejas and Jala. The 2nd Patala, which is Mamsashrita, can be taken as Iris and Ciliary body. Both iris and ciliary body are mesodermal in origin and contain muscles tissue. The 3rd Patala or Medoashrita Patala can be taken as Lens & Vitreous humour, as lens is explained as 3rd patala for its position next to uvea & vitreous is a jelly like structure which resembles medas (fat). The 4th Patala or Asthyashrita Patala can be taken as Retina, as it is the seat for Linganasha. Their opinion can be summarized as follows:
Name & Anatomical Structure
1st Patala - Cornea & Aqueous humour
2nd Patala - Iris and Ciliary body
3rd Patala - Lens & Vitreous humour
4th Patala - Retina
Relative Posiition of Each Patala:
First Patala, among the four Akshi Patalas, is known as Bahya or outer; this means that the other three are relatively inner to the former. According to Sushruta, the disease Timir vitiates the first Patala, followed by second, third and fourth Patalas. Therefore the first Patala is considered as the outermost and the fourth Patala is considered as the innermost Patala according to Sushruta. But the commentary given by Dalhana did not correspond to it and he has reversed the relative position of each Patala.
Dalhana describes ‘Kalakasthi Ashrita’ Patala as the first Patala and considers it as innermost. According to him, the second Patala is Medoashrita, third Patala is Mamsashrita and the fourth Patala is Tejojalashrita. This description can be considered as a misinterpretation from Dalhana. Actually he had misunderstood the word ‘Abhyantara’ given by Sushruta in the description of Prathama Patalagata Timir and considered the first Patala as the Abhyantara (innermost) Patala.
According to some other scholars, the Patalas can be taken as the layers of the cornea. They quote Vagbhatta to justify their opinion. While describing the prognosis of the disease ‘Kshata Shukla’, it has been said that the disease is Kricchra Sadhya when it occurs in the first Patala. There the word ‘Twak’ is used for Patala. When the disease involves the second Patala, it becomes Yapya and Asadhya when it involves the third Patala. As the disease ‘Kshata Shukla’ is limited to the cornea only, these Patalas can be taken as successive layers of the cornea.
According to some other views, the Patalas can be taken as different layers of retina. There is third Patala involvement for the diseases Pittavidagdha Drishti and Kaphavidagdha Drishti. These are the diseases where patients complain of day blindness and night blindness respectively. As these diseases occur due to degeneration of rods and cones. The Patalas can be taken as different layers of retina. But, by taking the retina as Patalas, we cannot explain the clinical entity Timir.