visual acuity
ability of the lens of the eye to change shape to focus light rays on to the retina.
20/20 vision
20/20, the top number refers to the fact that it is standard to do this test 20 feet from the Snellen chart. The bottom number gives the distance in feet that a person with normal vision should recognize letters at 20 feet.
20/40 visionA person with a 20/40 vision rating recognizes from 20 feet what someone with normal vision can identify from 40 feet. This person has nearsightedness (myopia).
20/10 visionA person with a 20/10 vision rating recognizes from 20 feet what someone with normal vision can only identify from 10 feet. This person has excellent vision.
Where is the blind spot located in the visual field, and why does it occur?
Location: In the lateral (temporal) visual field of each eye.
Reason: The optic disc on the retina lacks photoreceptors, so light hitting this spot cannot be detected → creates a blind spot.
Additional info:
Each eye compensates for the other’s blind spot.
When using one eye, the brain fills in missing information from surrounding areas.
most common type of color blindness?
Most common is red-green color blindness.
Caused by deficiency in red or green cones.
More common in males (X-linked trait).
What causes astigmatism, and how does it affect vision?
people have blurred or distorted vision in a specific angle or direction.
Cause: Irregular curvature of the cornea (most common) or sometimes the lens.
Effect on vision: Light does not focus evenly on the retina, causing blurred or distorted vision at all distances.
