By Dr Raghuram Y.S. MD (Ay) & Dr Manasa, B.A.M.S
Netra Krishnagata Rogas are the set of disorders which occur in the black portion of the eye i.e. cornea.
Cornea is a transparent shield located in front of iris, the part of the second / middle tunic (layer) of the eye. Through cornea the colour of the iris can be seen, just like as in a mirror. Generally the iris is black in colour; therefore the same colour is seen through the cornea.
Read – Eye Diseases Causes, Pathogenesis, Symptoms, Treatment, Herbs
Iris may have some other color too; those colors are depicted through cornea. Thus, cornea is actually not the black portion of the eye but is a transparent part through which the color of iris is seen. But Ayurveda has mentioned cornea as Krishna bhaga i.e. black portion on the basis of color of iris seen through it.
The cornea covers the iris, pupil and anterior chamber of the eye. Likewise, cornea along with the anterior chamber and lens refracts light. Cornea accounts to approximately two thirds of the eye’s total optical power.
For convenience of study and seeing the description in the Ayurveda texts, we shall consider krishnabhaga of the eye to be cornea with iris in its backdrop.
Read – Netra Shuklagata Rogas – Disorders Affecting Sclera
Element predominance in the black of the eye
Krishna Bhaaga i.e. black portion of the eye including iris and cornea is created from Vata Mahabhoota i.e. air element.
Measurement of black of the eye
Krishna Mandala measures one third (1/3) of the measurement of Netra Budbuda (eyeball).
Read – Anatomy of Eye: Netra Rachana: Ayurveda Perspective
Cornea, iris – Krishna Mandala
Cornea / iris contributes to the Krishna Mandala
Mandala means circles. Krishna Mandala is the circle made up of iris or black of the eye (the middle tunic / layer of the eye) and corneal circle. Seen from outside, the cornea along with the iris in its backdrop looks like a circle.
Cornea, along with iris in its backdrop contribute to two sandhis i.e. joints of the eyes
Shukla Krishna Gata Sandhi – This is the meeting place of Shukla Bhaga i.e. Sclera / white of the eye along with the conjunctiva covering it and Krishna Bhaga i.e. black of the eye / cornea along with iris in its backdrop. This junction can also be correlated with the Sclero-Corneal Junction, also called Limbus. But since cornea is transparent, it is wise to take Iris as Krishna Bhaga. But since sclera doesn’t form a junction with iris, shukla-krishna gata sandhi should be taken as limbus. It should in textual language be taken as a place where the white of the eye apparently appears to meet with the black of the eye, though not in strict sense.
Krishna Drushti Gata Sandhi – This is the junction between Krishna Bhaga i.e. black of the eye or Iris and Drushti i.e. slit of the Iris. This Sandhi represents the margins of the Pupil. Pupil is a small opening at the centre of the Iris.
Read – Classification of Eye Diseases As Per Ayurveda
The cornea and iris contribute to form the prathama and dwitiya patala (first and second layers / tunics according to Ayurveda anatomy)
According to Ayurveda anatomy, cornea contributes in the formation of first layer whereas iris forms the second layer of the eye. Since we consider cornea and iris as Krishna bhaga i.e. black of the eye, the black portion of the eye involves both first and second tunics.
Read – Relation Between Doshas, Sense Organs And Perception
Prathama Patala (first layer) – It is also called as Tejo Jala Aashrita Patala since it is related to Teja (fire element) and Jala (water element). Thus, this layer is formed by the predominance of fire and water elements. According to Dalhana, commentator of Sushruta Samhita, the first layer is the seat of Alochaka Pitta, a sub-type of Pitta. This pitta helps in perception of objects of vision. It is the first part of the eye which receives the light. The first layer can be correlated with Cornea and Aqueous Humour.
Read – Alochaka Pitta – Location, Functions, Imbalance, Disorders, Treatment
Dwiteeya Patala (second layer) – It is also called Mamsa Aashrita Patala. This layer is located in the Mamsa Dhatu (muscle tissue) of the eye. This layer can be correlated with Iris and Ciliary body of the eye.
Krishnagata Rogas – Diseases of the black of the eye
Number and names of disorders of cornea / iris with probable modern correlation
Diseases of cornea / iris are four in number. They are –
- Savrana Shukra / Savrana Shukla – Ulcerative Keratitis / Corneal ulcer
- Avrana Shukra / Avrana Shukla – Opacity of cornea
- Akshipakatyaya – Hypopyon / Keratomalacia
- Ajakajata – Anterior Staphyloma
Read – Stye – Causes, Symptoms, Remedies, Treatment
Dosha Relation in causation of disorders of cornea / iris and their prognosis
Tridoshaja Asadhya – Akshipakatyaya is caused by simultaneous vitiation of all three doshas and is said to be incurable.
Raktaja Asadhya – Savrana Shukra and Ajakajata are caused due to vitiation of blood and are said to be incurable.
Raktaja Sadhya – Avrana Shukra is caused due to vitiation of blood and is said to be curable.
Read – Blepharitis: Inflamed Eyelids Ayurvedic Treatment, Remedies
Treatment of disorders of iris and cornea
Three out of four diseases occurring in the iris and cornea are said to be incurable. Avrana Shukra / Shukla can be treated.