Guyton and Hall Physiology Chapter 50 - The Eye I. (Optics of Vision)
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Guyton and Hall Physiology Chapter 50 - The Eye I. (Optics of Vision)

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Questions and Answers

What is the characteristic of a cylindrical lens with a strength of +1 diopter?

  • It focuses parallel light rays to a line focus. (correct)
  • It diverges light rays.
  • It forms an image on both sides of the lens.
  • It has a focal point at infinity.

    • What effect do diverging light rays have on the focal length of a concave lens?

  • They have no effect on the focal length.
  • They lengthen the focal length.
  • They create a virtual focal point behind the lens. (correct)
  • They shorten the focal length.

    • If the axis of a cylindrical lens is vertical, what is its orientation in degrees?

  • 90 degrees (correct)
  • 180 degrees
  • 45 degrees
  • 0 degrees

    • What does a stronger lens imply about the location of its focal point?

    <p>The focal point is nearer to the lens.</p> Signup and view all the answers

    What is a key difference between convex and concave lenses?

    <p>Convex lenses always converge light; concave lenses diverge it.</p> Signup and view all the answers

    What happens when parallel rays enter a convex lens?

    <p>They focus at one point beyond the lens.</p> Signup and view all the answers

    How can a convex lens focus diverging rays?

    <p>By changing its curvature.</p> Signup and view all the answers

    What is the role of the center of a convex lens in image formation?

    <p>It does not refract light and allows rays to pass straight through.</p> Signup and view all the answers

    Which characteristic differentiates a convex lens from a concave lens?

    <p>Convex lenses focus light inward, while concave lenses disperse it.</p> Signup and view all the answers

    If an object is placed in front of a convex lens, the resulting image is a mosaic of point sources. What does this mean?

    <p>Each point source of light forms a distinct point focus at varying brightness.</p> Signup and view all the answers

    How does the curvature of a convex lens affect its focal length?

    <p>A more curved lens has a shorter focal length.</p> Signup and view all the answers

    What occurs to light rays generated by point sources when they pass through a convex lens?

    <p>They converge at one point along the axis.</p> Signup and view all the answers

    Which of the following statements is true regarding the function of a convex lens?

    <p>It can focus both parallel rays and diverging rays at the same distance.</p> Signup and view all the answers

    What happens to parallel light rays passing through a concave lens?

    <p>They diverge after passing through the lens.</p> Signup and view all the answers

    How does a convex cylindrical lens differ from a concave lens?

    <p>A convex cylindrical lens bends light rays in only one plane.</p> Signup and view all the answers

    What is the primary function of a convex lens?

    <p>To bend light rays to a single focal point.</p> Signup and view all the answers

    In which scenario do parallel light rays maintain their path when passing through a lens?

    <p>When hitting the lens's center perpendicularly.</p> Signup and view all the answers

    What is the result of using two crossed cylindrical lenses?

    <p>They combine to function like one spherical lens.</p> Signup and view all the answers

    What defines the focal point for a lens?

    <p>The point where parallel rays converge.</p> Signup and view all the answers

    What is the behavior of light rays at the edges of a concave lens?

    <p>They curve outward, causing divergence.</p> Signup and view all the answers

    Which statement is true regarding the behavior of a convex lens?

    <p>It bends light rays towards a single focal point.</p> Signup and view all the answers

    How does the curvature of a lens affect light rays?

    <p>Correct curvature converges rays to a single point.</p> Signup and view all the answers

    What characteristic distinguishes a concave lens from a convex lens?

    <p>Concave lenses can create virtual images.</p> Signup and view all the answers

    What is the distance known as where parallel rays converge to a common point when passing through a convex lens?

    <p>Focal length</p> Signup and view all the answers

    When light rays that are diverging enter a convex lens, how does their focal point relate to the lens compared to parallel rays?

    <p>It is farther from the lens than that of parallel rays.</p> Signup and view all the answers

    What type of lens converges light rays in one plane?

    <p>Convex cylindrical lens</p> Signup and view all the answers

    In the context of lens optics, what is a characteristic of concave cylindrical lenses?

    <p>They diverge light rays in only one plane.</p> Signup and view all the answers

    Which statement describes the behavior of light rays when using a cylindrical lens?

    <p>They can create additional focal lines for diverging rays.</p> Signup and view all the answers

    What happens when a cylindrical lens is used to focus light from a point source?

    <p>It focuses the rays into a line focus.</p> Signup and view all the answers

    Which lens type causes light rays to diverge?

    <p>Concave lens</p> Signup and view all the answers

    Which lens would be used to demonstrate the focusing of parallel light rays in a simple experiment?

    <p>Convex lens</p> Signup and view all the answers

    What characterizes the focal distance for light sources that are not far away when using a convex lens?

    <p>The distance is shorter than for parallel rays.</p> Signup and view all the answers

    What is the result of using two cylindrical lenses at right angles to each other?

    <p>They create the equivalent effect of a spherical lens.</p> Signup and view all the answers

    What is the refractive power of a lens that converges parallel light rays to a focal point 10 centimeters beyond the lens?

    <p>+10 diopters</p> Signup and view all the answers

    Which statement describes the refractive power of concave lenses?

    <p>Concave lenses cannot be measured by focal distance beyond the lens.</p> Signup and view all the answers

    If a concave lens diverges light rays as much as a +10-diopter lens converges them, what is its dioptric strength?

    <p>-10 diopters</p> Signup and view all the answers

    What results from placing a 1-diopter concave lens immediately in front of a 1-diopter convex lens?

    <p>A lens system with zero refractive power</p> Signup and view all the answers

    How is the strength of cylindrical lenses computed in comparison to spherical lenses?

    <p>Cylindrical lenses require stating the axis along with strength.</p> Signup and view all the answers

    What happens to light rays when they pass through a convex lens?

    <p>They converge to a point.</p> Signup and view all the answers

    What is the dioptric strength of a concave lens that diverges light rays at the same rate as a 1-diopter convex lens converges them?

    <p>-1 diopter</p> Signup and view all the answers

    In which scenario would the refractive power of a lens be considered neutral?

    <p>A concave lens placed in front of a convex lens of equal strength.</p> Signup and view all the answers

    What is the effect of placing a +10 diopter lens in combination with a -10 diopter lens?

    <p>They produce a neutral effect.</p> Signup and view all the answers

    If a concave lens has a strength of -5 diopters, how does it affect incoming parallel light rays?

    <p>They diverge from a point.</p> Signup and view all the answers

    What is the significance of light rays passing through the center of a convex lens?

    <p>They do not change direction.</p> Signup and view all the answers

    How do variations in the convexity of a lens affect the focusing of light rays?

    <p>It allows both parallel and diverging rays to focus at the same distance.</p> Signup and view all the answers

    What happens to point sources of light in front of a convex lens?

    <p>They create a distinct point focus on the opposite side.</p> Signup and view all the answers

    What is the result of focusing light from multiple point sources through a convex lens?

    <p>A range of color variations is displayed.</p> Signup and view all the answers

    What determines the distinct point focus created by each point source in front of a convex lens?

    <p>The alignment of the sources with the lens center.</p> Signup and view all the answers

    What determines the refractive index of a substance?

    <p>The velocity of light in the solid compared to air</p> Signup and view all the answers

    What occurs to light rays that strike the center of a convex lens?

    <p>They pass through without being refracted</p> Signup and view all the answers

    What phenomenon occurs at the edges of a convex lens when light rays are entering?

    <p>The rays bend increasingly toward the center</p> Signup and view all the answers

    When light travels through a transparent substance with a refractive index of 1.50, how does its speed compare to the speed of light in air?

    <p>It travels slower than in air</p> Signup and view all the answers

    What is the effect of the angle at which light rays strike a lens's surface?

    <p>It influences the degree of refraction of the rays</p> Signup and view all the answers

    What occurs to the lens shape when the ciliary muscle relaxes?

    <p>The lens assumes a more spherical shape.</p> Signup and view all the answers

    What is presbyopia?

    <p>A condition where the lens can no longer accommodate for near and far vision.</p> Signup and view all the answers

    How does the amount of light entering the eye through the pupil relate to its diameter?

    <p>It increases with the square of the diameter of the pupil.</p> Signup and view all the answers

    What role does parasympathetic nerve stimulation play in vision?

    <p>It contracts the ciliary muscle, allowing the lens to thicken.</p> Signup and view all the answers

    At what diameter can the human pupil vary?

    <p>From 1.5 mm to 8 mm.</p> Signup and view all the answers

    Why might older individuals require bifocal glasses?

    <p>To accommodate for both near and far vision due to presbyopia.</p> Signup and view all the answers

    What happens as a distant object moves closer to the eye?

    <p>Parasympathetic impulses to the ciliary muscle must increase.</p> Signup and view all the answers

    Which of the following describes the primary function of the iris?

    <p>To control the amount of light entering the eye.</p> Signup and view all the answers

    What is a primary characteristic of the ciliary muscle's control?

    <p>It is controlled by parasympathetic nerves.</p> Signup and view all the answers

    What determines the fixed focus distance experienced by a presbyopic person?

    <p>The physical characteristics of each person's eyes.</p> Signup and view all the answers

    The refractive index of a transparent substance is determined by the ratio of the velocity of light in the substance to the velocity of light in air.

    <p>False</p> Signup and view all the answers

    A convex lens causes light rays to diverge towards the edges.

    <p>False</p> Signup and view all the answers

    Light rays travel slower in transparent solids and liquids than in air.

    <p>True</p> Signup and view all the answers

    The outer light rays striking a convex lens bend toward the center due to a phenomenon called divergence.

    <p>False</p> Signup and view all the answers

    The refractive index of air is 1.00, meaning light travels at its maximum speed in air.

    <p>True</p> Signup and view all the answers

    When light rays enter a medium at a perpendicular interface, they change their velocity but do not bend.

    <p>True</p> Signup and view all the answers

    In a medium with a refractive index of 1.50, light travels at a speed of 300,000 km/sec.

    <p>False</p> Signup and view all the answers

    The degree of refraction increases with the difference in refractive indices of two media.

    <p>True</p> Signup and view all the answers

    Refraction occurs at interfaces only when light rays travel from a slower medium to a faster medium.

    <p>False</p> Signup and view all the answers

    The wave front of light rays bending at an angulated interface will always remain vertical.

    <p>False</p> Signup and view all the answers

    A camera lens focuses images on film by reversing the image upside down.

    <p>True</p> Signup and view all the answers

    A lens with a strength of +2 diopters bends parallel light rays twice as much as a lens with a strength of +1 diopter.

    <p>True</p> Signup and view all the answers

    The refractive power of a lens is generally measured in terms of feet.

    <p>False</p> Signup and view all the answers

    A convex lens creates a focal point 0.5 meters beyond the lens if it has a refractive power of +2 diopters.

    <p>True</p> Signup and view all the answers

    A lens that diverges light rays has a positive refractive power.

    <p>False</p> Signup and view all the answers

    Using two convex cylindrical lenses at right angles creates a common point focus.

    <p>True</p> Signup and view all the answers

    The refractive power of a lens is determined by its physical length.

    <p>False</p> Signup and view all the answers

    Light rays that pass through the center of a convex lens are affected by the curvature of the lens.

    <p>False</p> Signup and view all the answers

    An image formed by a convex lens placed at its focus distance is upright.

    <p>False</p> Signup and view all the answers

    A lens that converges parallel rays to a focal point 10 centimeters beyond it has a refractive power of +10 diopters.

    <p>False</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Refraction = Bending of light rays at an angulated interface Wave fronts = Surfaces connecting points of equal phase in a wave Refractive index = A measure of how much light slows down in a medium Focal length = The distance from a lens at which parallel rays converge</p> Signup and view all the answers

    Match the following materials with their respective refractive indices:

    <p>Air = 1.00 Glass = 1.50 Water = 1.33 Diamond = 2.42</p> Signup and view all the answers

    Match the descriptions with the corresponding light ray behavior:

    <p>Light rays entering perpendicular to the surface = No deviation from their course Light rays entering at an angle = Rays bend due to different refractive indices Wave front traveling in air = Moves at 300,000 km/sec Wave front traveling in glass = Moves at 200,000 km/sec</p> Signup and view all the answers

    Match the following concepts with their relevant figures:

    <p>Figure 50-1A = Light rays entering a glass surface perpendicular Figure 50-1B = Light rays striking an angulated glass surface Figure 50-2 = Bending of light rays at a convex lens Wave fronts in glass = Shorter distances between wave fronts</p> Signup and view all the answers

    Match the following actions with their outcomes in light behavior:

    <p>Passing through an angulated interface = Light rays bend Entering two different media = Change in velocity and wavelength Striking the center of a lens = Minimal deviation Focusing parallel rays = Convergence at a focal point</p> Signup and view all the answers

    Match the following characteristics of a convex lens with their descriptions:

    <p>Convergence of light rays = Brings light rays to a point focus Passing through the center = Light rays are not refracted Image formation = Mosaic of point sources in an object Effect of convexity = Changes how light is focused</p> Signup and view all the answers

    Match the following scenarios with their outcomes when using a convex lens:

    <p>Parallel rays entering the lens = Focused at the same distance Diverging rays entering the lens = Also focused at a point Point source of light = Creates distinct point focus Object in front of lens = Appears as a mosaic of light</p> Signup and view all the answers

    Match the following terms related to convex lenses with their meanings:

    <p>Focal point = Distance where light rays converge Optical center = Point where light passes without refraction Convexity = Curvature affecting how light is focused Light mosaic = Collection of bright and weak light points</p> Signup and view all the answers

    Match the types of light rays with their behaviors through a convex lens:

    <p>Diverging rays = Focused by the lens to a point Parallel rays = Converged to a common focal point Point sources = Each creates its own point focus Light rays at edges = May behave differently than center rays</p> Signup and view all the answers

    Match the following aspects of light behavior through a convex lens:

    <p>Image from point source = Appears directly in line with the source and lens center Center passage of rays = No refraction occurs Collection of light points = Forms the image seen Lens type overall = Can change how incoming rays are focused</p> Signup and view all the answers

    Study Notes

    Lens and Light

    • Convex Lens: Converges parallel light rays at a focal point.
    • Concave Lens: Diverges parallel light rays.
    • Cylindrical Lens: Bends light rays in only one plane, creating a line focus.
    • Two Cylindrical Lenses: Crossed at right angles, have the same function as a spherical lens.

    Focal Length

    • Focal length: Distance at which parallel rays converge to a focal point.
    • Diverging Rays: Focal distance is farther from the lens than the focal length for parallel rays.

    Refractive Power

    • Refractive Power: Measured in diopters.
    • +10 diopters: Lens focuses parallel light rays 10 cm beyond the lens.
    • Concave Lenses: Diverge light, have negative dioptric strengths.
    • Concave and Convex Lens Combination: Can neutralize each other's refractive power.

    The Eye as a Camera

    • Eye's Refractive Power: Approx. 59 diopters.
    • Eye's Components: Cornea, aqueous humor, lens, vitreous humor.
    • Each component has different refractive power: Cornea (1 diopter), lens (10 diopters), aqueous humor (2 diopters), vitreous humor (1 diopter) and Air (1 diopter).

    Refraction of Light

    • The refractive index of a substance is the ratio of the speed of light in air to the speed of light in that substance.
    • Light bends when it passes from one medium to another with a different refractive index. This bending is called refraction.
    • The amount of bending depends on the difference in refractive indices and the angle of incidence.
    • A convex lens converges light rays, focusing parallel light rays at a point called the focal point.

    Accommodation for Near Vision

    • The lens of the eye can change shape to focus on objects at different distances, a process called accommodation.
    • The ciliary muscle contracts, relaxing the ligaments attached to the lens capsule. This allows the lens to become more spherical, increasing its refractive power.
    • Accommodation is controlled by parasympathetic nerves.
    • As a person ages, the lens loses elasticity, making it harder to accommodate for near vision. This condition is called presbyopia.

    Pupillary Diameter

    • The iris controls the amount of light entering the eye by changing the size of the pupil.
    • The pupil can range in diameter from 1.5mm to 8mm.
    • A smaller pupil increases the depth of focus, meaning the retina can be displaced from the focal plane without causing blurring.

    Errors of Refraction

    • Emmetropia is normal vision where parallel light rays focus on the retina when the ciliary muscle is relaxed.
    • Hyperopia (farsightedness) occurs when parallel light rays focus behind the retina. This is corrected by convex lenses.
    • Myopia (nearsightedness) occurs when parallel light rays focus in front of the retina. This is corrected by concave lenses.
    • Astigmatism occurs when the cornea has an uneven curvature, causing light to focus at different points on the retina. This is corrected by cylindrical lenses.

    Cataracts

    • Cataracts occur when the lens of the eye becomes cloudy, impairing vision.
    • This clouding can be caused by aging, injury, or disease.
    • Cataracts can be removed surgically, which involves replacing the lens with an artificial lens.

    Refraction of Light

    • The refractive index of a transparent substance is the ratio of the speed of light in air to the speed of light in the substance.
    • Light rays bend when entering a medium with a different refractive index.
    • The degree of bending (refraction) increases with a greater difference in refractive indices between the two media and with a greater angulation between the interface and the entering wave front.

    Convex Lens Focuses Light Rays

    • Convex lenses converge parallel light rays to a point called a focal point (focus).
    • The focal length is the distance between the lens and the focal point.
    • The refractive power of a lens is measured in diopters, where 1 diopter = 1 meter / focal length.

    Depth of Focus

    • The depth of focus is the range of distances in front of the lens over which objects appear to be clearly focused.
    • Objects closer than the near point are not in focus.
    • Objects farther than the far point are not in focus.

    Accommodation

    • Accommodation is the process of adjusting the shape of the lens to focus objects at different distances.
    • This is achieved by the ciliary muscles contracting/relaxing, changing the tension on the suspensory ligaments that hold the lens.
    • Near vision requires a thicker, rounder lens.
    • Far vision requires a thinner, flatter lens.

    Myopia (Nearsightedness)

    • Occurs when the eye is too long or the lens has too much refractive power.
    • Light rays are focused in front of the retina, causing blurry vision for distant objects.
    • Corrected with concave lenses.

    Hyperopia (Farsightedness)

    • Occurs when the eye is too short or the lens has too little refractive power.
    • Light rays are focused behind the retina, causing blurry vision for near objects.
    • Corrected with convex lenses.

    Astigmatism

    • Occurs when the cornea has a different curvature in one plane compared to the other.
    • Vision is blurred at all distances.
    • Corrected with cylindrical lenses.

    Cataracts

    • Occurs from clouding of the eye's lens, interfering with light passage.
    • Can be corrected by surgically removing the clouded lens and inserting a clear artificial lens.

    Light Travel and Refraction

    • Light rays travel in a beam and strike an interface. If the interface is perpendicular to the beam, they travel through with decreased velocity and shorter wavelength.
    • If the interface is angulated, the rays bend, the degree of refraction increases with the difference in refractive index of the two mediums.
    • Light travels perpendicular to the plane of the wave front, bending downward.

    Convex Lenses

    • Bending of light rays at the surface of a convex lens focuses parallel light rays to a focal point.
    • Convex lens can focus both parallel and diverging rays at the same distance.
    • A point source of light is focused, by a convex lens, on the opposite side of the lens, directly in line with the point source.
    • Objects in front of the lens are a mosaic of point sources of light, each focused at a separate point on the opposite side of the lens in line with the lens center.

    Eye Focusing

    • Lens accommodation is the ability of the eye to focus on objects at varying distances
    • The lens is held in place by ligaments attached to the ciliary muscle
    • Contraction of the ciliary muscle relaxes the ligaments, allowing the lens to become more spherical and increase refractive power.

    Presbyopia

    • With age, the lens loses elasticity and becomes less accommodating.
    • Presbyopia: lens changes shape, becoming less spherical.

    Pupillary Diameter

    • Iris controls the amount of light entering the eye by adjusting the pupil size.
    • Pupil diameter can vary from 1.5 to 8 millimeters.

    Astigmatism

    • Astigmatism is caused by uneven curvature of the cornea or lens, causing light rays to not focus at a single point.
    • Light rays focus at different distances in different planes.
    • A cylindrical lens is used to correct astigmatism.

    Cataracts

    • Cataracts are clouding of the lens.
    • Cataracts obstruct light transmission, leading to blurry vision.
    • Surgical removal of the lens corrects cataracts.

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