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INTRODUCTION TO REFRACTION
Refraction is a multistep process that involves a combination of psychomotor skill and intellectual problem solving．The process allows the examiner to arrive at one individualized prescription，from a universe of approximately 200，000 possible prescriptions．
The goal of refraction is to render the retina conjugate with optical infinity through the application of lenses in front of the eye．However，refraction is done for people, not eyeballs，and the goal is restated here in functional terms：to identify the lenses which will allow the patient to achieve clear and comfortable vision．That is，to see everything he needs and wants to see and to use his eyes for as long as he desires without strain or discomfort．
The process of the routine refraction can be divided into three parts(see Figure 3-1)．In the first part，made of the starting points．the examiner collects preliminary information about the refractive status of the patient．Based on the information, the examiner makes predictions about the outcome of the refraction，and，in rare instances, can actually write a prescription．
The second part of the routine refraction is the refinement．In this phase，the predictions from the starting points are tested and refined．The principal tool of the refinement is the phoropter．The examiner makes changes in the targets or the phoropter lenses．The patient makes a response to indicate how each change affects what he sees．Because it relies heavily on patient response the refinement includes most of what is generally termed the routine subjective refraction．
The third part of the routine refraction is made of the endpoint techniques．These include the binocular balance and the demonstration or trial frame technique．The endpoint is not only technical, but is intellectual as this is when the patient’s refractive problems must be solved．To arrive at a single prescription that will provide the patient with clarity and comfort of visual function，the examiner must weigh all the available information, including the starting points，the results of the refinement, and the endpoint tests．The examiner must also factor in his knowledge of geometric and ophthalmic optics，his assessment of the patient’s ability to adapt to changes in the correction, and the patient’s lifestyle and attendant visual needs．Finally，exercising his professional judgment，the examiner chooses a prescription for the patient．But the intellectual process does not stop there．
Both health and visual function problems can manifest themselves as the apparent need for glasses or changes in the eyeglass prescription．Decisions about spectacles and contact lenses can have important implications for the patient’s safety, health，and visual function．Refractive problems must always be addressed within the context of both a health and a visual function analysis．The authors of this text subscribe to and agree completely with the resolution passed at the 1995 American Optometric Association Congress：“A refraction for the purposes of determining the need for corrective lenses is but one component of an eye health and vision eva luation．A refraction without a corresponding eye health eva luation can result in the failure to diagnose vision and life threatening diseases to the irreparable harm of the individual．”Although it is treated in the text as an isolated set of procedures, refraction should not be thought of as separate from the other processes that make the comprehensive ocular examination．
Chapter 3 includes a gro of problem-specific refractive tests．These side trips from the routine refraction allow the examiner to obtain additional refractive data about the patient and to refract the unusual or difficult patient．
Finally，readers should remember that refraction is a problemsolving，not merely a technical，exercise．The goal is not to perform certain steps and procedures, but to ascertain what lenses to prescribe to serve the best interests of the patient．By using all of the information available to him, the examiner can often determine an appropriate prescription without performing every one of the steps in the routine refraction． |
