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.
