Physics · MU Sofia

27. Human eye as an optical system

Explains the human eye as an optical system, giving its optical power of roughly 59 to 71 dioptres with the cornea supplying about 40, and how accommodation adjusts the pupil to focus at different distances. It then covers spherical and chromatic aberrations, the image positions and corrections for myopia, hyperopia and astigmatism, a short note on strabismus, and laser correction such as LASIK. A picture accompanies the vision-problems section.

Inside: 1 section · 1 labelled picture · 9 flashcards · 2 min

Topic 28 of 42 in the MU Sofia syllabus for Physics (Dental Medicine, Year 1). The free AceMed note covers it in 1 section, about 328 words (2 min of reading), with 9 flashcards.

In this note

  1. Introduction

Introduction

Summary

  • The notes discuss the optical properties and common vision problems associated with the human eye, including its optical power, accommodation mechanism, and various aberrations such as spherical and chromatic. The human eye typically has an optical power between 59 and 71 diopters, with the cornea contributing about 40 diopters. Accommodation allows the eye to focus on objects at different distances by adjusting the pupil based on light intensity. Common vision errors such as myopia (nearsightedness), hyperopia (farsightedness), and astigmatism are noted, along with their corrections through lenses and laser surgery.

Optical Power and Accommodation of the Human Eye

  • Optical Power: Ranges from 59 to 71 diopters, with the cornea contributing approximately 40 diopters to this measurement.
  • Accommodation: The eye's ability to focus on objects at varying distances. This is achieved by the pupil adjusting its size based on the intensity of incoming light, converting light energy into electrical signals for the brain.

Aberrations in the Human Eye

  • Spherical Aberration: Occurs when light rays are focused at a point closer to the lens than the ideal focal point, leading to blurred vision.
  • Chromatic Aberration: Different colors of light focus at different points due to their wavelengths, resulting in color fringes around objects.

Common Vision Problems and Corrections

  • Myopia (Nearsightedness): The image is formed in front of the retina. Correction is typically made with diverging lenses or specific laser surgeries to flatten the cornea.
  • Hyperopia (Farsightedness): The image is formed behind the retina. Corrective measures include using converging lenses or laser procedures to steepen the cornea.
  • Astigmatism: Caused by an irregular curvature of the cornea or lens, leading to distorted or blurred vision. Corrected with cylindrical lenses or laser surgery to reshape the cornea.
  • Strabismus: Described as misalignment of the eyes, which can affect depth perception and coordination.

Laser Correction

  • Procedure: Laser surgery like LASIK is employed to correct refractive errors by reshaping the cornea, smoothing it to enhance focal points, which can address myopia, hyperopia, and astigmatism effectively.

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