Physics of Lenses and Vision
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Questions and Answers

What is the focal length of a lens?

  • The distance that light travels before refracting
  • The distance at which light rays diverge
  • The distance beyond a convex lens at which parallel rays converge (correct)
  • The distance at which all light rays are blocked

    • Concave cylindrical lenses converge light rays in one plane.

    False

    What type of lens is demonstrated by an ordinary magnifying glass?

    Spherical lens

    When rays of light that are already diverging enter a convex lens, the distance of focus on the other side of the lens is farther than the focal length for __________ rays.

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

    What is the effect of cataracts on the lens of the eye?

    <p>They create cloudy or opaque areas</p> Signup and view all the answers

    Match the following lenses to their characteristics:

    <p>Convex lens = Converges rays of light Concave lens = Diverges rays of light Cylindrical lens = Focuses light from a point source Spherical lens = Used in magnifying glasses</p> Signup and view all the answers

    What happens when parallel rays pass through a convex lens?

    <p>They converge at a focal point</p> Signup and view all the answers

    The visual acuity of the human eye can distinguish two point sources of light separated by an angle of less than 25 seconds of arc.

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

    A cylindrical lens can focus light rays to a point.

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

    What happens to the proteins in lens fibers during the early stage of cataract formation?

    <p>They become denatured.</p> Signup and view all the answers

    Cataracts primarily occur in __________ people.

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

    The combination of two cylindrical lenses at right angles equals a __________ lens.

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

    Match the following terms related to the human eye with their descriptions:

    <p>Cataracts = Cloudy areas in the lens Visual acuity = Ability to distinguish point sources of light Fovea = Part of the eye that is less than 0.5 millimeter Denaturation = Process affecting lens proteins</p> Signup and view all the answers

    What happens to the image when a white sheet of paper is placed at the focus distance from the lens?

    <p>The image is upside down.</p> Signup and view all the answers

    The refractive power of a convex lens is measured in terms of yards.

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

    What is the formula to calculate the refractive power of a convex lens?

    <p>1 meter divided by its focal length.</p> Signup and view all the answers

    A lens that converges parallel light rays to a focal point 1 meter beyond it has a refractive power of ___ diopter.

    <p>+1</p> Signup and view all the answers

    If a lens has a power of +2 diopters, how far is the focal point from the lens?

    <p>0.5 meter</p> Signup and view all the answers

    Using two cylindrical convex lenses at right angles will give the same point focus as a single spherical convex lens.

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

    What effect does a lens with a greater refractive power have on light rays?

    <p>It bends light rays more.</p> Signup and view all the answers

    Match the following lens powers with their focal lengths:

    <p>+1 diopter = 1 meter +2 diopters = 0.5 meter +0.5 diopter = 2 meters +4 diopters = 0.25 meter</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 cm beyond it?

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

    Concave lenses have a positive refractive power.

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

    What is the dioptric strength of a concave lens that diverges light rays as much as a +10 diopter lens converges them?

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

    A concave lens that functions to diverge light at the same rate as a ___ converges will have a strength of -1 diopter.

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

    Match the following descriptions with the correct type of lens:

    <p>Convex lens = Converges light rays Concave lens = Diverges light rays Cylindrical lens = Used in astigmatism corrections Diopter = Unit of refractive power</p> Signup and view all the answers

    What is the effect of placing a 1-diopter concave lens in front of a 1-diopter convex lens?

    <p>Results in zero refractive power</p> Signup and view all the answers

    Cylindrical lens strengths are computed differently than spherical lens strengths.

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

    What do concave lenses do to the refractive power of convex lenses?

    <p>Neutralize it</p> Signup and view all the answers

    What happens to the lens of the eye as a person ages?

    <p>It grows larger and thicker</p> Signup and view all the answers

    The contraction of circular fibers in the ciliary muscle increases the diameter of ligament attachments.

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

    What is the condition called when the lens becomes nonaccommodating with age?

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

    As a person ages, the power of accommodation decreases from about 14 diopters in a child to less than ____ diopters by age 45 to 50.

    <p>2</p> Signup and view all the answers

    Match the following components with their corresponding functions:

    <p>Ciliary muscle = Controls lens tension Circular fibers = Decrease diameter during contraction Meridional fibers = Pull ligaments medially Presbyopia = Loss of accommodation ability</p> Signup and view all the answers

    Which type of muscle fibers is involved in relaxing the tension on the lens ligaments?

    <p>Both A and B</p> Signup and view all the answers

    Sympathetic stimulation has a strong role in the mechanism of accommodation.

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

    What effect does the contraction of smooth muscle fibers in the ciliary muscle have on the ligaments to the lens capsule?

    <p>It relaxes the ligaments.</p> Signup and view all the answers

    What effect does a small pupillary aperture have on depth of focus?

    <p>Increases depth of focus</p> Signup and view all the answers

    In hyperopia, light rays from distant objects focus in front of the retina.

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

    What is the term used for normal vision where parallel light rays focus sharply on the retina?

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

    Myopia is also known as ________ vision.

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

    Match the eye condition with its description:

    <p>Emmetropia = Normal vision Hyperopia = Focusing behind the retina Myopia = Focusing in front of the retina Depth of focus = Range of focus before blurring occurs</p> Signup and view all the answers

    How does the size of the blur circle change when the retina is moved back in the lower eye?

    <p>The blur circle increases in size</p> Signup and view all the answers

    When the ciliary muscle is completely relaxed, the emmetropic eye can see objects at all distances clearly.

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

    What occurs when the pupillary aperture is extremely small?

    <p>Greatest depth of focus</p> Signup and view all the answers

    Study Notes

    The Eye: Optics of Vision

    • Understanding the eye's optical system requires knowledge of light refraction, focusing, and depth of focus.
    • Refractive index of a substance is the ratio of light's velocity in air to its velocity in that substance. Air's refractive index is 1.00.
    • Light travels slower through transparent mediums than air, affecting its velocity and wavelength.
    • Refraction is the bending of light at an interface between two mediums with different refractive indices. The degree of bending depends on the refractive index ratio and angle between the interface and incident light.
    • Convex lenses converge parallel light rays to a focal point. Light passing through the center of the lens doesn't refract.
    • Concave lenses diverge parallel light rays, the rays spreading out. Light through the center of the lens doesn't refract.
    • Cylindrical lenses refract light in only one plane, focusing light to a line instead of a point.
    • Focal length of a convex lens is the distance beyond it where parallel rays converge to a common point.
    • A convex lens focuses diverging light rays further from the lens than its focal length for parallel rays.
    • The eye's lens system has four refractive interfaces: air/cornea, cornea/aqueous humor, aqueous humor/lens, and lens/vitreous humor.
    • The eye's refractive power is measured in diopters.
    • One diopter is equal to 1 meter divided by the focal length of a convex lens.
    • Concave lenses are measured by their ability to diverge light; a strength of -1 diverges light as a +1 convex lens converges it.
    • Concave lenses neutralize convex lenses.
    • Parallel to the other lenses, the eye's normal refractive power is 59 diopters.
    • The refractive power of the cornea (air/cornea interface) accounts for most of the eye's refractive power.

    Accommodation

    • Accommodation is the eye's ability to change the shape of its lens to focus on objects at various distances.
    • Children have a greater range of accommodation, from 20-34 diopters.
    • The ligaments attached to the lens maintain its form via tension; the ciliary muscle adjusts this by relaxing or contracting the ligaments.
    • Contraction of meridional and circular fibers in the ciliary muscle relaxes the suspensory ligaments allowing the lens to become more rounded, increasing its refractive power.
    • This process uses the sympathetic nervous system fibers and parasympathetic nerve signaling from the brain.
    • Presbyopia is the loss of accommodation as the lens loses elasticity with age, reducing its ability to change shape. Accommodation reduces to virtually zero in old age.

    Errors of Refraction

    • Emmetropia (normal vision): Parallel light rays focus correctly on the retina with the ciliary muscle relaxed.
    • Hyperopia (farsightedness): Parallel light rays focus behind the retina with the ciliary muscle relaxed. Accommodation helps focus near-objects.
    • Myopia (nearsightedness): Parallel light rays focus in front of the retina with the ciliary muscle relaxed. Distant objects are blurry. Accommodation doesn't help focus distant objects.

    Depth Perception

    • Depth perception is the ability to perceive 3D space.
    • Three main means of depth perception:
    • size of retinal images of known objects
    • parallax (relative movement of images on the retina when head/eyes move, useful for close objects)
    • stereopsis (binocular vision; images of nearby objects on each retina are slightly different, better for close distances)

    Fluid System of the Eye

    • Aqueous humor is the fluid in front of the lens.
    • Vitreous humor is the fluid behind the lens.
    • The fluid fills and maintains pressure in the eye. Maintain constant pressure and resist flow, especially for outflow.
    • Aqueous humor formation occurs in the ciliary body; flow out occurs through the trabecular meshwork, aqueous veins, and the canal of Schlemm.
    • Intraocular pressure (IOP) is measured using a tonometer; normal range is 12-20 mm Hg.
    • High IOP can damage the optic nerve and lead to glaucoma.

    Visual Acuity

    • Visual acuity describes the sharpness of vision.
    • Optimal vision allows for the distinction of two or more light points.
    • Visual acuity is tested by presenting letters of varying sizes at a fixed distance.
    • Normal visual acuity is 20/20; 20/200 vision means the person sees at 20 feet what a person with normal vision sees at 200 feet.
    • Visual acuity decreases with age due to many factors, including lens thickness changing, curvature of lens, and presbyopia.

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    Guyton Physiology 14th Edition PDF - Chapter 50

    Description

    Explore the fascinating world of optics with this quiz focused on the properties and functions of different types of lenses. Test your knowledge about focal lengths, the effects of cataracts, and how the human eye perceives light. Perfect for students studying optics and vision science.

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