Emmetropia and the Ametropias Scott P. Drexler OD University of Pittsburgh School of Medicine

 The direction and quality of that wave is changed as the wave transfers from one medium to another

 The boundary between two media with different indices nn’n n air water airglass

n 1 sin  1 = n 2 sin  2 n 1 = index of material before refraction n 2 = index of material after refraction  1 = incident angle   = refracted angle

 Light travelling from a less dense to a denser material will be refracted TOWARDS the normal.  Light travelling from a more dense to a less dense material will be refracted AWAY from the normal.

 In a media other than a vacuum, light waves slow down and the wavelength also decreases v=f  n= Speed of light in a vacuum (C) Speed of light in material  Note index of refraction varies with the frequency and wavelength of the light  Basically- How much light is bent by a material- the denser the material the greater the change

 Since c is always the greatest(speed of light in a vacuum), n is always greater than 1.  It is convention to treat the n air as 1.0  Vacuum =1  Air (nonpolluted) =1  Water= 1.33  PMMA =1.49  Crown glass =1.52  Diamond =2.417  Cornea =1.376  Zeiss hi-index =1.8  Crystalline lens= 1.42

 Refractive problems, such as nearsightedness, farsightedness, astigmatism, and presbyopia are the result of an inability of the cornea and the lens to focus light on the retina. Instead, light is focused either in front of or behind the retina.

 Two basic types of lenses are convex and concave. A convex lens, also known as a plus power lens, focuses light behind the lens; whereas, a concave lens, also known as a minus power lens, focuses light in front of the lens. The power of a lens is measured in Diopters (D) and reflects the focusing distance in meters of the lens- a + 10 D lens focuses an image at 10 cm= 1m/10D

Myopia Progression- 42% of young adults in US are myopic

Myopia Control Treatments  Eyeglass undercorrection  Bifocal Glasses  Bifocal Soft Contacts  Rigid Gas Permeable Contacts  Orthokeratology  Atropine  Outdoor exposure

 Convex or converging lenses  Different treatment in adults and children  Frequently treatment based on symptoms

Astigmatism

 Toric lenses- may be convex in one meridian and concave in another  Eyeglass lens or Contact lenses  Astigmatism has both magnitude and orientation so both glasses and contacts lenses must maintain the proper axis  X 060  Eyeglass lens is the better optical choice

 Loss of the accommodative ability of the lens that results in a difficulty focusing on near objects

 Soft Contact lenses contain the actual power of the needed lens and drape over the cornea to correct vision  RGP contact lenses create a tear lens that functions to correct vision so that the resulting lens power may not be the same as the power of the eyeglass lens needed to correct the vision

 Old technology made new again- from 1800’s  Bypasses irregular optics of the cornea by creating a new surface  Also used for eye surface diseases, cosmetic problems, and pain relief

Surgical Treatment  Hyperopic Lasik  Multifocal Lasik  Intacs  LTK  Myopic Lasik is the most common and predictable of the group  Limitations of Lasik are corneal thickness and curvature  Refractive lensectomy- cataract removal

Boston KPro

Thank You