Basic Structure of the Human Eye

Basic Structure of the Human Eye

• The human eye is a complex optical system that converts light energy into neural signals, enabling vision.
• The transparent refracting media of the eye brings images of external objects into focus on the retina, a light-sensitive membrane.
• The eye acts as a transducer.

Main Structures

• Cornea: Transparent tissue covering the front of the eye, containing no blood vessels, and having nerves.
• Iris: A circular band of muscles controlling pupil size; pigmented.
• Lens: Transparent tissue bending light passing through the eye to focus light, and changing shape to focus light.
• Pupil: An aperture in the center of the eye, letting light pass through.
• Aqueous Humor: Clear, watery fluid in the anterior chamber of the eye.
• Choroid: Layer of blood vessels nourishing the eye, acting as a light-absorbing layer due to its high melanocyte content.
• Sclera: Protective coating around the posterior 5/6ths of the eyeball.
• Vitreous Humor: Clear, jelly-like fluid in the back portion of the eye, maintaining its shape.
• Retina: Tissue layer at the back of the eye, containing photoreceptors (rods and cones).
• Rods: Photoreceptors responsive in low light conditions.
• Cones: Photoreceptors responsive to color and bright conditions.
• Eyeball: The overall structure of the eye, with three main coats:
  • Outer Fibrous Tunic: Comprised of sclera and cornea to maintain intraocular pressure.
  • Middle Pigmented Vascular Coat (Uvea): Includes the choroid, ciliary body, and iris.
  • Inner Retina: Posterior part is photosensitive.
• Anterior Chamber: Contains aqueous humor; bounded by the cornea and iris.
• Posterior Chamber: Lies between the iris and ciliary body, and the lens.
• Vitreous Chamber: Contains vitreous humor.
• Crystalline Lens: Optically clear, biconvex structure that adjusts focus from distance to near.
• Ciliary Body: Consisting of two regions: outer ciliary ring, and inner ciliary crown with ciliary processes, to support crystalline lens.

Optic Disc and Nerve

• Optic Disc: Region at the back of the eye's inner surface where the optic nerve exits the eye, and the retina thins abruptly (Ora Serrata).
• Optic Nerve: Leaves the eyeball, passing through the optic canal, and connected to the posterior part of the medial orbital wall.

Measuring and Recording Visual Acuity

• Visual Acuity: Smallest detail that can be seen, with or without correction.
• VA (Visual Acuity): measured with instruments like Snellen chart, Teller acuity cards, or Kay picture cards.
• Levels of Visual Function:
  • Light Perception: Can the patient detect light?
  • Detection/Discrimination: Can the patient detect differences in contrast?
  • Resolution: Can the patient distinguish fine details?
  • Recognition: Can the patient identify forms or shapes?
  • Relative Position: Can the patient perceive the relative position of objects or lines?
• Vernier Acuity: Techniques measuring integration across retinal images for tasks like stereopsis.

Explore the intricate anatomy of the human eye with this quiz. Learn about key components such as the cornea, iris, and lens, and understand how these structures work together to facilitate vision. Test your knowledge of the optical system that allows us to see the world around us.