New Connecting Kids to Coverage Outreach Video. Learn about Las Vegas, Nevada's Foundation for Positively Kids outreach efforts using their network of community-based, school-based, and specialty health care clinics.
Young adults with 20/20 vision can often focus at 4 to 6 inches. At 6 inches, they can see detail at 600 pixels per inch or 300 line pairs per inch. As you age, your lenses become less resilient and the focus distance increases. At about 50 years, the average minimum focus distance is about a foot corresponding to 150 line pairs per inch or 300 pixels per inch. These numbers reflect good light and high contrast scenes. Generally, under more typical conditions, people don't see this well. --.
The young human eye can change focus from distance (infinity) to 6.7 cm from the eye in 350 milliseconds. This dramatic change in focal power of the eye of approximately 15 dioptres (the reciprocal of focal length in metres) occurs as a consequence of a reduction in zonular tension induced by ciliary muscle contraction. The amplitude of accommodation declines with age.