CLSA Eye Witness Spring 2011 - (Page 28)

cause the travel in power from one meridian to the next. The change from +7.62 D to +5.25 is 2.37D) The optical cross should always be utilized for bitoric and front toric gas permeable lenses as well as for all soft toric contact lenses. The calculation of the vertex distance is an important step when choosing the correct contact lens; however, it may not always represent the final power needed by the patient. This is especially relevant when fitting aphakic patients or determining the final power needed for refractive surgery. For many aphakic patients, the elimination of the space between a spectacle lens and the cornea through the use of contact lenses is important and may be necessary to reduce or eliminate distortion. In higher refractions, the amount of correction for vertex distance will be greater in plus powers (for example, a +19.00 will vertex up over 5 diopters to a +24.75 while a –19.00 will vertex down over 3 diopters to a –15.50). The greater the spectacle lens power, the more important it becomes to know the actual vertex distance of the refraction in order to make an accurate vertex adjustment for a contact lens. Because of this, some fitters of aphakic lenses will not even consider vertex distance and prefer aspheric front surface brings all light rays to a precise focal point spherical aberration Figure 6 to use a diagnostic lens of known power and then over refract, largely eliminating the need for vertex correction. It is also very important to note that if the over refraction is greater than ±4.00D, then the over-refraction itself will need to be vertexed before a new diagnostic contact lens is ordered. If a contact lens is placed onto the eye and yields poor vision, a number of factors may be involved. These factors may include but may not be limited to: optical clarity, fit, or a problem with the optical system. Some soft contact lenses may be labeled such that correcting for vertex will not result in the correct power. Spherical and aspheric lenses provide a good example. While an aspheric lens may provide a fairly consistent power across the optical surface, a spherical design may actually provide more or less power than labeled as you progress from the center of the lens across the optical surface (Figure 6). For instance, if a lens is labeled –7.00 but is really more like a –7.50, you may question your vertex correction if an over-refraction yields a resultant of +0.50. Sometimes if a toric prescription is not fully vertexed and results in the patient being over-corrected, an over refraction may result in a higher cylindrical over-refraction which can confuse the fitter and complicate the fitting process. Most fitters agree the best results come from placing a lens on the eye and over-refracting; however, accurately vertexing a prescription in the beginning should always provide a good starting point and help you come to a final Rx more quickly and efficiently. As the contact lens industry continues to introduce new materials and designs, the options for choosing a lens will only continue to improve. Remembering to vertex the contact lens prescription will improve efficiency in the practice and provide greater success for the contact lens fitter. 28 w w w. c l s a . i n f o | c o n ta c t l e n s s o c i e t y o f a m e r i c a | EyEWitnEss spring 2011 http://www.clsa.info http://WWW.CLSA.INFO

Table of Contents for the Digital Edition of CLSA Eye Witness Spring 2011

CLSA Eye Witness Spring 2011

CLSA Eye Witness Spring 2011 - (Page Cover1)
CLSA Eye Witness Spring 2011 - (Page Cover2)
CLSA Eye Witness Spring 2011 - (Page 1)
CLSA Eye Witness Spring 2011 - (Page 2)
CLSA Eye Witness Spring 2011 - (Page 3)
CLSA Eye Witness Spring 2011 - (Page 4)
CLSA Eye Witness Spring 2011 - (Page 5)
CLSA Eye Witness Spring 2011 - (Page 6)
CLSA Eye Witness Spring 2011 - (Page 7)
CLSA Eye Witness Spring 2011 - (Page 8)
CLSA Eye Witness Spring 2011 - (Page 9)
CLSA Eye Witness Spring 2011 - (Page 10)
CLSA Eye Witness Spring 2011 - (Page 11)
CLSA Eye Witness Spring 2011 - (Page 12)
CLSA Eye Witness Spring 2011 - (Page 13)
CLSA Eye Witness Spring 2011 - (Page 14)
CLSA Eye Witness Spring 2011 - (Page 15)
CLSA Eye Witness Spring 2011 - (Page 16)
CLSA Eye Witness Spring 2011 - (Page 17)
CLSA Eye Witness Spring 2011 - (Page 18)
CLSA Eye Witness Spring 2011 - (Page 19)
CLSA Eye Witness Spring 2011 - (Page 20)
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CLSA Eye Witness Spring 2011 - (Page 22)
CLSA Eye Witness Spring 2011 - (Page 23)
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CLSA Eye Witness Spring 2011 - (Page 25)
CLSA Eye Witness Spring 2011 - (Page 26)
CLSA Eye Witness Spring 2011 - (Page 27)
CLSA Eye Witness Spring 2011 - (Page 28)
CLSA Eye Witness Spring 2011 - (Page 29)
CLSA Eye Witness Spring 2011 - (Page 30)
CLSA Eye Witness Spring 2011 - (Page 31)
CLSA Eye Witness Spring 2011 - (Page 32)
CLSA Eye Witness Spring 2011 - (Page 33)
CLSA Eye Witness Spring 2011 - (Page 34)
CLSA Eye Witness Spring 2011 - (Page 35)
CLSA Eye Witness Spring 2011 - (Page 36)
CLSA Eye Witness Spring 2011 - (Page Cover3)
CLSA Eye Witness Spring 2011 - (Page Cover4)
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