Presentation on theme: "Ics Optics Shoreline Ophthalmology 2005. ptics Optics Optics deals with the properties of light and vision The two principal areas that most concern."— Presentation transcript:
ptics Optics Optics deals with the properties of light and vision The two principal areas that most concern ophthalmology are physical and geometric optics
Optics What is commonly referred to as light is the small visible portion of a wide spectrum of electromagnetic radiation One way of differentiating the types of electromagnetic energy is by wavelength
Wavelength The wavelengths of light visible to the human eye range from about 400-750 billionths of a meter These wavelengths comprise light with the colors violet, blue, green, yellow, orange, and red Violet has the shortest wavelength and Red has the longest
Light Light can travel through certain substances but may be blocked by others. Substances that completely block light are called opaque. Substances that significantly interfere with the transmission of light are called translucent. Substances that allow the passage of light without significant interference are called transparent.
Refraction Light rays are refracted when they pass at an angle from one transparent medium, such as air to another transparent medium, such as water or glass They are refracted once again when they exit the second medium This occurs due to the differences in the speed at which light travels through various substances
Refractive Index The ratio of the speed of light in a vacuum to its speed in a specific substance is called the refractive index The more dense the substance, the slower the speed of light and the higher the refractive index.
Prism Prism – triangular piece of glass or plastic with plane flat sides, an apex, and a base When a light ray passes through a prism, the emerging light ray bends toward the base of the prism
Prisms and refractive properties of lenses If two prisms are placed together base to base, light rays passing through will be refracted to converge or come together Prisms placed together apex to apex will diverge or spread apart light rays that pass through
Prisms and refractive properties of lenses The prisms placed together base to base, with the sharp angles shaped into curves becomes a convex lens The prisms placed together apex to apex, with the sharp angles shaped into curves becomes a concave lens with the sharp angles shaped into curves becomes a concave lens
Lenses The two basic forms of lenses are Convex – converges light Concave – diverges light The power of a lens is a measure of its ability to converge or diverge light rays
Properties and Uses of Corrective Lenses Sphere – Concave – Myopia (-) Sphere – Convex – Hyperopia (+) Cylinder – Spherocylinder – Astigmatism (+ or -) Prism – Plane with at least two non-parallel surfaces – Double Vision
Refractive States The two basic refractive states are Emmetropia – the ability to focus correctly Ametropia – an inability to focus correctly due to refractive errors The power of a lens is a measure of its ability to converge or diverge light rays
Refractive States Myopia – condition in which the cornea and lens of the non-accommodating eye have too much plus power for the length of the eye Hyperopia – condition in which the cornea and the lens have too little plus power for the length of the non- accommodating eye
Refractive States Astigmatism- a condition occurring when the cornea is not uniform resulting in different levels of myopia or hyperopia in different optical planes Cylindrical lenses focus light rays to a focal line rather than a point
Refractive States Presbyopia – is a progressive loss of the accommodative ability of the crystalline lens
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