CONTINUING EDUCATION, 1 CE Credit – $9.99, 1 Hour, General Knowledge, Level 1, Release date: October 2007, Expiration date: October 31, 2012

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OD PERSPECTIVE

Refraction Revisited

In an article by Warren G. McDonald, PhD on Refraction/Refractometry that was published in the December 2009 edition of this magazine, I was impressed with the details that Dr. McDonald offered in his article. I wanted to add my perspective on refraction as an optometrist that will hopefully compliment Dr. McDonald’s excellent article on the same subject.

In the textbook that first-year optometry students used at the New England College of Optometry, “Clinical Procedures for Ocular Examination”, Dr. Carlson, Dr. Kurtz, Dr. Heath, and Dr. Hines state, “we refract for people, not eyeballs and therefore prefer to state the goal in functional terms: to identify the lenses that will allow the patient to achieve clear and comfortable vision; that is, to see everything he or she needs and wants to see and to use his or her eyes for as long as desired without strain or discomfort” (1990. P.43). What held true in 1990 still holds true in 2010.

One of the leading educators and greatest minds in optometry, Dr. Irvin Borish wrote a 1500 page book on “Clinical Refraction” which he regularly updates. Dr. Borish first wrote this scholarly textbook in 1949, and it became the Bible for thousands of optometry students. This book emphasizes the fact that there are many aspects to vision analysis and that refraction is one component of a very complex process.

In respect to an optometrist’s eye and vision examination and refraction, there are many pieces of information that are evaluated subjectively and objectively in order to provide a medically and legally approved prescription for a patient. This holds true whether this is a prescription for eyeglasses or for contact lenses. The refraction is a big part of this analysis but there are other pieces of information that need to be evaluated in order to be a good “detective” and to solve the patient’s vision problem. Refractions are a complex, many-step process that involves problem solving skills, education, practice, and experience. It is often said that refraction is simultaneously both a science and an art.

There are always clues during an examination that will help to determine the best refractive outcome. Every patient who completes a history or questionnaire is asked: What is the chief complaint? What brings you in for this examination? If their vision is blurry in the distance, this may be a myopia or astigmatism problem. If it is blurry only up close, this may be a hyperopia or presbyopia problem. Is it blurry in the distance and close, also? There may be combination of refractive problems and they may be different in each eye. Is it blurry to the same degree out of each eye? One eye may be nearsighted and one eye may be farsighted. Is there a significant anisometropia or antimetropia between the two eyes? Are there some unknown, underlying medical conditions that have not been diagnosed that any refraction may not improve such as advanced cataracts, macular degeneration, corneal dystrophies, diabetic retinopathy, hypertensive retinopathy, or glaucoma?

A patient’s visual acuities and their age will provide the clinician with further insight as to what the vision problem may be. An auto-refractor-keratometer can be used on every patient in order to provide some idea as to what the prescription may be. With statistical analysis included with every measurement, the measurements provide statistical validity. With corneal problems, cataracts, or non-cooperative patients the auto-refractor-keratometer measurements are sometimes not accurate. In lieu of an auto-refractor-keratometer, retinoscopy can be used as an objective source of information on the patient’s refractive status. A simple spectacle neutralization can also provide valuable clues.

A keratometer should be used on every patient in order to confirm the auto-refractor-keratometer measurements. It provides another source of information and will indicate if any astigmatism found during the refraction is confirmed again. Does the patient have a pair of glasses that they were wearing? Lensometry will provide more clues as to what a correct prescription should be.

Retinoscopy is something that is done with every patient and is a skill that definitely takes a great deal of practice. Using a retinoscope allows the clinician to determine a patient’s refractive error and prescription. It is extremely important for children, un-cooperative patients, or non-communicative patients.

Every clinician must be a good observer of their patients. Look at the patient’s eyes even before they sit in the exam chair. If a patient has a turned eye or a head tilt, there may be a need as a component of a refraction to incorporate prismatic lenses to improve a patient’s vision. The head tilt or turn is often indicative of a muscle imbalance associated with strabismus. Prisms can be used after other tests confirm the diagnosis that will help the visual problem. These other vision tests include phoria testing, vergence testing, NRA/PRA testing, Maddox Rod testing, and Hirschberg testing.

Refractions can be done using a phoropter or a trial frame. A trial frame refraction may simulate wearing a pair of glasses more closely than a phoropter. Both methods are accurate and reliable. Some practitioners will utilize both methods. The phoropter to do the clinical refraction and the trial frame to show the patient what the final prescription will look and feel like. The patient must be given an opportunity to determine which spherical and/or astigmatic lenses will best correct their refractive error. This requires patience and gives the patient time to make decisions about their own eyes. One eye is occluded while the other eye is tested and then the first eye is occluded while the second eye is tested. When the clinician is satisfied that the proper prescription is found, the refraction in the distance is continued by doing a “binocular balance.” This involves being sure that the patient determines that each eye has the same comfortable and balanced visual acuity. A near refraction will then be done to be sure that the patient’s visual acuity at near, at a comfortable reading distance, or at a computer terminal, is also clear.

For those presbyopic patients, an add prescription will be necessary. The clinician should always check each patient’s visual acuity monocularly, right eye and left eye for near vision. Some patients require unequal adds or “split adds.” Age-related adds are useful as a guide but it is always necessary to check the patient’s reading distance, posture, and near demands to be sure that they will be comfortable with what is prescribed.

Cycloplegic refractions using eyedrops may be necessary in order for the clinician to determine the amount of total, absolute, facultative or latent hyperopia present. Other factors that may affect a patient’s refraction, their prescription, or to achieve an accurate visual outcome is the health of the eye. Trying to have a patient see 20/20 or 20/15 may be predetermined by medical complications of the eye. A few of these complications may include the following: Are there preexisting eye muscle problems or the presence of a strabismus? Are the eyelids in a normal position or is there the presence of a ptosis? Are there corneal irregularities such as keratoconus or high or irregular astigmatism? Are there iris anomalies or pupillary problems such as anisocoria? Are there cataracts present? Are there floaters in the vitreous or a problem such as asteroid hyalosis? Are there retinal problems such as hypertensive or diabetic retinopathy, macular degeneration, or glaucoma?

The vision of an elderly, aging eye may not permit 20/20 vision. The practitioner can utilize a pinhole occluder to determine if the patient’s vision can be improved further with lenses. Every health aspect of the visual system must be evaluated in order to appropriately evaluate the proper visual outcome. This should include other testing such as visual field analysis and dilation.

It is very important to discuss all findings with every patient. The extra time that is spent with a patient is time worth educating and informing a patient or the parent/guardian. Every clinician may have some unique technique or skill that will help them with their refractions. Every patient presents with differing vision problems that may require further vision testing that cannot be covered in this brief analysis. In order to provide an accurate evaluation of this complex topic, only the genius of Dr. Borish’s textbooks and articles or the many authors who have written on this subject would provide greater details. This would also provide the reader with the understanding of the complex neurological connection between vision, seeing, psychology, the eyes, and the brain.

Jason Smith
OD, MS

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