LECTURE 18 HUMAN EYE 19.2 The human eye How do corrective eye glasses work? Focusing and accommodation Vision defects and their correction Learning objectives

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 Apply thin-lens equation to human eyes and corrective lenses.

 Identify whether converging or diverging corrective lenses are needed and calculate the power of corrective lenses for a give eye problem. 19.2 The human eye

 Incoming light rays are refracted (mostly at the air-cornea Vitreous boundary) to produce a real inverted image on the retina. humor  For a cataract, the lens is removed, and the cornea alone 푛vh = 1.34 provides a marginal level of vision. 푛l = 1.40 푛ah = 1.33  Rods and cones on the retina convert the light into 푛 = 1.00 electrical impulses, which travel down the optic nerve to air the brain.

 The brain adjusts the image in order for it to appear upright. 푛c = 1.38

 The iris determines how much light enters the eye through the pupil. 19.2 Focusing and accommodation

 Accommodation is the process of changing the lens shape as the eye focuses at different distances.

 https://www.youtube.com/watch?v=p_xLO7yxgOk

 https://www.youtube.com/watch?v=1yIpyitm6eE

 The near point (NP) is the closest point on which the eye can focus.

 The far point (FP) is the most distant point on which the relaxed eye can focus. Quiz: 19.2-1 through 19.2-7

5 19.2 Vision defects and their correction

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 Presbyopia, hyperopia and myopia can be corrected with corrective lenses.

 When corrective lens is used in combination with the eye’s lens, the image produced by the corrective lens acts as the object for the eye’s lens.

 This is true regardless of whether the image produced by the first lens is real of virtual, or whether it is in front of or behind the eye’s lens.

 Refractive power in diopter D:

1 푃 = 푓 Quiz: 19.2-8 through 19.2-10 & Group discussion 19.2