The refraction of light through the human eye
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The refraction of light through the human eye
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[post_date] => 2025-01-09 20:20:13
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[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Like a camera, the human eye focuses light to produce sharp images. Light rays reflecting from distant objects are focused on the retina after they passed through the cornea, aqueous humor, the lens, and finally the vitreous humor. A schematic of the eye is shown in Figure 1.
Figure 1: A Schematic of The Human Eye
As the light rays pass through these various mediums, they experience a physical phenomenon called refraction. Refraction is the change in direction of light rays as they transition between different mediums. Most of the refraction of light occurs when the difference in the refractive indices of abutting mediums is the greatest. Table 1 provides a list of refractive indices of the various components of the human eye.
Table 1: A list of Refractive Indices of Various Components of the Human Eye
Once the light rays are focused on the retina, the formed image is processed by millions of photoreceptor cells called rods and cones. These photoreceptors relay the signal to the brain via the optic nerve.
Emmetropia is the term used to describe an eye without any refractive errors. The axial length of the eye, the distance from the posterior cornea to the surface of the retina, is equal to the focal length of the eye. Two common refractive errors of the eye are myopia and hyperopia. Myopia, which is also known as nearsightedness, occurs when the eye can focus on nearby objects, but not on far away ones. The light rays reflecting from faraway objects is focused in front of the retina. Hyperopia or farsightedness occurs when the eye cannot focus on nearby objects. The light reflecting from a nearby object is focused behind the retina. Both of these refractive defects can be corrected with the use of compensating lenses.
Figure 2: Emmetropia, Myopia, and Hyperopia
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[quiz_unique_key] => 578908434
[question] => A distant object will form what type of image on the retina of an emmetropic eye?
[value] => Array
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[answer] => 2
[description] => Reason for the Correct Answer:
A real image is formed when light rays reflecting from a distant object converges as seen in the emmetropic eye in Figure 2.
Virtual images are upright.
Real images are inverted.
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[answers] => Array
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[0] => Array
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[each_answer] => A. An upright virtual image
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[each_answer] => B. An inverted real image
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[each_answer] => C. An inverted virtual image
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[each_answer] => D. An upright real image
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[quiz_unique_key] => 3873426850
[question] => Based on the indices of refractive provided in Table 1, where does most of the refraction of light occur in the eye?
[value] => Array
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[answer] => 3
[description] => Reason for the Correct Answer:
Most of the refraction of light occurs when the difference in the refractive indices of abutting mediums is the greatest.
Calculate the difference between the refractive indices of the abutting mediums provided in the answer choices.
Most of the refraction of light occurs when light rays passes from the air into the cornea.
Refractive index of the Cornea – Refractive index of Air = [1.376- 1.000 = 0.376]
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[answers] => Array
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[0] => Array
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[each_answer] => A. Aqueous Humor – Lens interface
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[each_answer] => B. Cornea – Aqueous Humor interface
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[each_answer] => C. Air – Cornea interface
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[each_answer] => D. Lens – Vitreous Humor interface
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[quiz_unique_key] => 83407773
[question] => Which of the following will NOT contribute to myopia?
[value] => Array
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[answer] => 3
[description] => Reason for the Correct Answer:
Myopia occurs when the focal length of the eye is less than its axial length. Anything that shortens the eye’s focal length or lengthens the eye’s axial length will cause myopia.
Increasing the curvature of the cornea and increasing the refractive index of the lens will shorten the eye’s focal length.
Increasing the pupil’s diameter will increase the the amount of light rays entering the eye. It does not affect the eye’s focal length or axial length.
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[answers] => Array
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[0] => Array
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[each_answer] => A. An increase in the eye’s axial length
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[1] => Array
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[each_answer] => B. An increase in the refractive index of the lens
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[2] => Array
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[each_answer] => C. An increase in the diameter of the pupil
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[each_answer] => D. An increase in the curvature of the cornea
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[3] => Array
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[quiz_unique_key] => 2377279144
[question] => Which of the following lenses can be used to correct for hyperopia?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
Hyperopia occurs when the focal length of the eye is greater than its the axial length.
Converging lenses refract light rays before it enters the eye, allows the ray of light to converge at the the retina.
Converging lenses are thicker at their centers than at their ends.
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[answers] => Array
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[each_answer] => A. 
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[each_answer] => B. 
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[each_answer] => C. 
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[each_answer] => D. 
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[question] => The optical power of the average human eye is 60 Diopters. Approximately, what is the height of the inverted image produced on the retina of a 1 meter tall child standing 10 meters away from a human eye?
[value] => Array
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[answer] => 3
[description] => Reason for the Correct Answer:
Solve for the distance of the image by using the thin lens equation.
Determine the magnification of the image by using the magnification equation.
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[answers] => Array
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[0] => Array
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[each_answer] => A. 6 meters
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[1] => Array
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[each_answer] => B. 1/ 60 meters
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[2] => Array
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[each_answer] => C. 1/600 meters
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[3] => Array
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[each_answer] => D. 1/6 meters
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