The lecture focuses on the pupillary mechanism, which controls the diameter of the pupil.
Pupillary mechanism is often misunderstood in comparison to accommodation.
Key Concepts
Accommodation: Involves the lens, suspensory ligaments, and ciliary muscles.
Pupillary Mechanism: Involves muscles in the iris and the pupil, controlling light entering the eye.
Pupillary Mechanism
The pupil's diameter is adjusted to control light entry based on brightness levels.
Bright Light Conditions
Radial Muscles: Relax.
Circular Muscles: Contract.
Result: Pupil constricts, reducing the diameter, allowing less light into the eye.
Dim Light Conditions
Radial Muscles: Contract.
Circular Muscles: Relax.
Result: Pupil dilates, increasing the diameter, allowing more light into the eye.
Muscle Associations
Radial Muscles: Associated with relaxation (R with R - radial with relax).
Circular Muscles: Associated with contraction (C with C - circular with contract).
In dim light, the associations reverse (R with C - radial with contract; C with R - circular with relax).
Effects of Light Conditions on Pupil
Bright Light: Pupil constricts (less light).
Small space for light passage.
Dim Light: Pupil dilates (more light).
Larger space for light passage.
Visual Representation
In diagrams, the pupil appears smaller in bright light and larger in dim light.
Conclusion
Understanding the differences in muscle actions during dim and bright light helps maintain constant light levels in the eye. The pupil adjusts to ensure optimal light entry.