Vision: Eye Anatomy and Basic Physiology - Anatomy and Physiology
- How do rods and cones differ in function?
- Rods are very sensitive and serve dim-light vision without color; cones need brighter light and provide color vision and sharp acuity.
- Which iris muscle constricts the pupil, and which autonomic division controls it?
- The sphincter pupillae, under parasympathetic control via the oculomotor nerve (CN III).
- Why does the optic disc create a blind spot?
- It is where the optic nerve leaves the eye and has no photoreceptors.
- A pituitary tumor compresses the optic chiasm. Which visual field defect results?
- Bitemporal hemianopia, loss of both outer (temporal) fields, because the crossing fibers from the nasal retinas are damaged.
- What happens to rhodopsin when light strikes a rod?
- Light converts 11-cis retinal to all-trans retinal, activating the pigment and causing the rod to hyperpolarize.
- What is the fovea centralis, and why is acuity highest there?
- A small pit in the retina containing only cones, densely packed, with overlying layers pushed aside.
- Where is aqueous humor produced, and where does it mainly drain?
- It is produced by the ciliary body and drains through the trabecular meshwork into the scleral venous sinus (canal of Schlemm).
- In what order does a visual signal pass through the neurons of the retina?
- Photoreceptors, then bipolar cells, then ganglion cells, whose axons form the optic nerve.
- What causes presbyopia?
- Age-related loss of lens elasticity, so the lens cannot round up enough for near vision.
- In myopia, where does the image focus, and what lens corrects it?
- In front of the retina; it is corrected with a concave (diverging) lens.
- How does the eye accommodate for near vision?
- The ciliary muscle contracts, the zonular fibers slacken, and the lens becomes rounder, increasing its refractive power.
- In hyperopia, where does the image focus, and what lens corrects it?
- Behind the retina; it is corrected with a convex (converging) lens.