ics Optics Shoreline Ophthalmology 2005

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 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