Overview
This lesson covers the pathway of light through the eye, detailing the structure and function of each part involved in forming and processing an image for vision.
Pathway of Light Through the Eye
- Light first enters the eye through the cornea, the transparent outermost layer that protects and bends light.
- It then passes through the aqueous humor, a fluid-filled cavity behind the cornea.
- Light continues through the pupil, an opening controlled by the iris, which adjusts its size based on light intensity.
- The iris is a circular muscle that controls the amount of light that enters by altering the pupil size.
- The lens, held by ciliary muscles and ligaments, further focuses light for near or distant vision.
- After the lens, light travels through the vitreous humor, another fluid-filled cavity.
- Finally, light reaches the retina, the eye’s neural layer containing photoreceptors.
Image Formation and Processing
- The retina contains rods and cones (photoreceptors) that convert light into chemical signals.
- The fovea (yellow spot) is the area of the retina with the sharpest vision.
- Light must pass through several cell layers in the retina before reaching the pigmented epithelial layer.
- Photoreceptors generate an impulse based on light, which is passed to other neurons in the retina.
- The optic nerve carries these impulses to the brain’s occipital lobe (part of the cerebral cortex) for interpretation.
- The eyes detect stimuli, but actual vision occurs in the brain where images are interpreted and oriented correctly.
Key Terms & Definitions
- Cornea — transparent outer layer of the eye that protects and bends incoming light.
- Aqueous humor — liquid filling the space between cornea and lens.
- Iris — colored, circular muscle controlling pupil size and light entry.
- Pupil — adjustable opening in the iris through which light enters the eye.
- Lens — transparent structure that fine-tunes light focus onto the retina.
- Vitreous humor — gel-like fluid filling the main cavity of the eyeball.
- Retina — neural layer at the back of the eye containing photoreceptors (rods and cones).
- Fovea (yellow spot) — central retina area with highest visual acuity.
- Photoreceptors — rods (sensitive to dim light) and cones (detect color and detail).
- Optic nerve — nerve transmitting visual impulses from the retina to the brain.
Action Items / Next Steps
- Create a flow diagram showing the path of light through each eye structure as described.