VISUAL PROCESS AND VISUAL PATHWAY

VISUAL PROCESS AND VISUAL PATHWAY

The process of vision involves the reception of light by the eye, conversion of light into electrical signals, and interpretation of those signals in the brain. In Ayurveda, this function is governed by Alochaka Pitta, mainly located in the Netra and Hridaya. In modern physiology, the visual system comprises the eye, optic nerve, visual pathways, and the visual cortex in the occipital lobe of the brain.

AYURVEDIC CONCEPT OF VISUAL FUNCTION

ALOCHAKA PITTA

• Alochaka Pitta is one of the five types of Panchapitta mentioned in Ayurvedic physiology.

• It is responsible for the perception of light and vision.

• It is divided into two parts:

  • Chakshur Alochaka Pitta – located in the eye; responsible for receiving visual stimuli.

  • Buddhi Alochaka Pitta – located in the Hridaya (heart/mind); responsible for interpretation.

REFERENCE FROM CLASSICAL TEXTS

• chakshurindriyam alochakakhyam pittam prakashayati – (Ashtanga Hridaya, Sutrasthana)

• alochaka iti pitta dve chakshushi hridi ca sthite – (Charaka Samhita)

MODERN PHYSIOLOGY OF VISION (BASED ON SEMBULINGAM)

STRUCTURE OF THE EYE

• The eye consists of three layers:

  • Fibrous layer: Sclera and Cornea

  • Vascular layer: Choroid, Ciliary body, and Iris

  • Nervous layer: Retina

• The retina contains photoreceptors:

  • Rods – Responsible for vision in dim light (scotopic vision)

  • Cones – Responsible for color and daylight vision (photopic vision)

PROCESS OF VISION

• Light enters the eye through the cornea → aqueous humor → lens → vitreous humor → reaches the retina.

• Photoreceptor cells (rods and cones) convert light into electrical impulses (phototransduction).

• These impulses are carried by bipolar and ganglion cells to form the optic nerve.

• The optic nerve carries the signal to the brain for interpretation.

PHOTOTRANSDUCTION PROCESS

• In rods, the pigment rhodopsin undergoes bleaching in presence of light.

• This activates a series of events leading to hyperpolarization of the photoreceptor cell, decreasing the release of glutamate.

• Resulting changes in the bipolar cells initiate nerve impulses that are passed to the ganglion cells.

VISUAL PATHWAY

• Begins at retinal ganglion cells.

• Axons of ganglion cells form the optic nerve.

• At the optic chiasma, fibers from nasal half of each retina cross over.

• The optic tract then continues to the lateral geniculate body (LGB) of the thalamus.

• From the LGB, optic radiations (geniculocalcarine tract) project to the primary visual cortex (area 17) in the occipital lobe.

COMPONENTS OF VISUAL PATHWAY

• Retina

• Optic nerve

• Optic chiasma

• Optic tract

• Lateral geniculate body (LGB)

• Optic radiations

• Visual cortex (Occipital lobe)

VISUAL FIELD REPRESENTATION

• Each half of the visual field is represented in the opposite occipital cortex.

  • Right visual field → Left occipital lobe

  • Left visual field → Right occipital lobe

CLINICAL CORRELATION (MODERN VIEW)

• Lesion in Optic nerve: Monocular blindness

• Lesion at Optic chiasma: Bitemporal hemianopia

• Lesion in Optic tract: Homonymous hemianopia

• Lesion in Visual cortex: Cortical blindness or visual agnosia

INTEGRATION OF AYURVEDA AND MODERN UNDERSTANDING

• Alochaka Pitta can be correlated with the retinal photoreceptors and neural pathway responsible for vision.

• Chakshurendriya corresponds to the eye as a sensory organ, and its connectivity with the mind (Manas) and brain (Buddhi Alochaka Pitta) signifies the interpretation centers of the brain like the visual cortex.

• Hridaya as the seat of cognition (Chetana) aligns with cortical processing of visual input.