Optometry and the Art of Refraction

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17 min read
Refraction is such a critical skill within optometry. Here is what you need to know about refracting your optometry patients!

We all likely remember (despite how we try to forget...) the refraction we performed during optometry school practicals: A rote machination through confused retinoscopy, Jackson crossed-cylinder, Draconian plus-pushing, and probable contemplation of why we didn’t enter podiatry instead.
We also recall our horror on the first day of providing care to a real patient, when none of our well-rehearsed and unassailable tactics seemed to go anywhere positive: The answer to “Which is better, ‘1’ or ‘2’?” was returned a frustrating, “No.”
Throughout one’s optometry education, one hears the mystical and seemingly sagacious refrain of well-intentioned professors, that “Refraction is as much an art as it is a science”; and, for four years, this attractive but enigmatic notion receives little elucidation. In fact, we soon begin to realize, it is enormously difficult to explain certain aspects of this “art,” as a magnitude of it involves the unease of discovering one’s mistakes (which can be only scantly reified in the brief three-month excursions of clinical rotations), and of interpretations of human behavior.
Nevertheless, one finds certain trends might be sheltered within words, and in this article I shall seek to expound on some considerations I have found to be valuable in prescribing spectacles for my patients.


Although one occasionally will examine the fourteen-diopter myope who’s never worn eyeglasses, and has just happened to stumble into the optometry clinic for her first ever routine exam, overwhelmingly the patients one meets will have existing spectacle prescriptions (disclaimer: I don’t examine children). Accordingly, as one rightly learns that history is half the examination with respect to health and disease, so, too, is it imperative to talk with the patient about the current status of her vision.
Much of what I intend to prescribe is discovered before ever approaching the phoropter. A patient presenting in eyeglasses, expressing no vision symptoms, and reading the Snellen chart well, will rarely receive a dramatic change from me in spectacle prescription. As habit, I perform baseline refraction on all new patients (though this might be as simple as dry retinoscopy), and although it can be meritorious to discover that my asymptomatic patient in fact is over-minused by a diopter and a half, I would be hard-pressed to ameliorate all this away in the futile effort of refractive heroism.
Conversely, a patient with specific vision complaints — for example, difficulty reading road signs, despite comfort when staring at her computer screen all day at work — will guide me toward the changes I am likely to make, as well as to aspects of the prescription I will be cognizant to preserve (for instance, in this example, the equivalent ADD power).
In most circumstances, one will seldom bring about a positive situation by making dramatic modifications to the eyeglasses of a comfortable, functional person. Having an answer does not equal making a decision, and refraction is not synonymous with prescription.


Along the vein of the previous point, lensometry is indispensable in the spectacle prescription I make. Prior scripts may be helpful, but these can be troublesome when it turns out the patient’s habitual eyeglasses in fact are from a very different prescription. What is of import is not necessarily what a previous doctor found (though this occasionally is helpful to determine what did not work), but what the patient routinely wears on her face, and whether she experiences clarity and comfort in this.


In an age of fast, highly accurate auto-refractors, one wonders about the boons of retinoscopy within optometry. In my opinion, the latter not only can be immediately faster and cheaper (of course, the flow of every practice is distinct), but has the potential to save both subsequent time and sanity. As students, and early in our careers, I find we can become pinned under the duties of strictly regimented examination sequences, in which often refraction occurs early, and therefore in which it can last inordinately long. Retinoscopy can be a convenient indicator of how a particular patient encounter should move forward.
I would add, retinoscopy generally might take thirty to sixty seconds per eye. Unless I expect to prescribe from my findings, objective refraction helps me establish a starting point for subjective, and I disfavor nauseous inquisitions into whether the axis of one-half a diopter of cylinder rests along eighty-eight degrees or eighty-seven. Fine refinements, in my opinion, are tailored by subjective responses.
For instance, the retinoscopic reflex — or the absence thereof — suggests the likelihood that a poorly-seeing patient’s acuity is the manifestation of an optical problem, and that it is time to press forward with the examination rather than to travel twenty minutes into the abyss of a refraction that carries her from 20/200 to a fictitiously improved 20/100+1.
Finally, objective refraction offers a homing beacon of sorts to my refraction. Holding a mental (or written) note of where we began directs to me where I am likely to end up, and whether I have been led impossibly astray of this conclusion. If the patient’s subjective responses are vague or tremulous, or if she stretches the phoropter’s dials ponderous bounds from my retinoscopy (or auto-refraction) results (provided I have reasonable confidence in these), I find strong encouragement to halt the madness and to regain command of my refraction.

Don’t listen for just what you want to hear

Human beings have an odd tendency to confirm their biases, and in medicine — even beyond simply eye-care — this can taint our observations and our decisions. Too commonly one imagines success upon spending fifteen minutes on a refraction, and moving a patient from 20/25 to 20/20-2, with two new diopters of sphere and a thirty-five–degree shift in axis, not bothering to question whether the findings are reasonable.
Sometimes in optometry, we exacerbate the mess by neglecting that the patient, over this exhaustive orchestration, has been staring at the same lines of text, coincidently with our ever more incandescent pleas to take a guess at letters with which we were less concerned during entrance-acuity measurement than we have become at the end of our painstaking efforts. Before deciding on a prescription, it is crucial we verify whether our convictions in fact are sensible.

Check with trial lenses

I do not routinely perform trial-lens refraction, however when I want to confirm whether a change I’ve found will in fact help my patient, I find I am a bit fanatical about using trial lenses — not in
the trial frame (which is tedious and cumbersome, and seldom lines up on a face as do actual spectacles), but held over my patient’s existing eyeglasses (provided these are adjusted well and are in sufferable repair). Dipping a trial lens in front of a patient’s own glasses not only permits me to gauge her response to my intentions, but invites her to participate in the decision we shall make. In the happening of a lukewarm response to questionable modifications, I leave things as they are; inversely, a strong and consistent positive reaction confirms for me that a change should be issued, and it demonstrates to the patient, who is now explicitly involved in the process, that our alteration expects to improve her vision.
For this purpose, I also enjoy having plus-cylinder trial lenses on hand. There are times when I want to confirm whether an axis-shift is appropriate, and it is far more sensible that I neutralize and replace the present cylinder with plus- and minus-cyl. lenses respectively, than I engage in some serpentine mangling of the patient’s eyeglasses across her face and through her ears and nose.

Look at the habitual eyeglasses

There are instances in which the reason for someone’s visual complaints is not evident, as refraction yields the same result as lensometry, which matches the previous prescription. Existing eyeglasses should be checked for scratches and smudges, and it ought to be ascertained whether a frame sits properly on a person’s face. These quick and minor observations can help explain why one’s refraction is or isn’t consistent with the clinician’s expectations.

20/20 can suck (and, so can plus lenses and short exam lanes)

We are enslaved by the unfortunate relic of “20/20” visual acuity being regarded as the standard of good sight. I routinely take my patients down to 20/15 both during entrance-acuity measurement and after refraction, and the large majority, even in later years of life (provided good ocular health), read the line successfully. I, myself, in ideal conditions, can eek out ~20/6 vision on charts able to represent such small text.
The reason this matters is our enamorment with plus and inexplicable aversion to minus power. Before being convicted of optometric cardinal sin, I should note over-minusing is not desirable behavior, and one should be cognizant to avoid it given the repercussions of aesthenopia, and of premature presbyopia-symptoms. However, where over-minusing might cause a level of discomfort, over-plussing almost certainly will create annoyance (and return visits to the office).
If the previous doctor’s refraction has allowed a patient to read 20/15 or 20/10, then pushing so much plus that she can just barely guess at 20/20 print truly effects a legitimate depreciation of her vision. In addition to this, many examination lanes are only ten feet, and do not use a mirrored system to simulate optical infinity. Although text size can be calibrated to elicit “20/20-equivalent vision” at any distance, vergence is not negated simply by decreasing character-height, and refracting someone at a length of ten feet (~three meters) mathematically over-plusses her by slightly more than one-quarter of a diopter.
In combination, the 20/20 ideal, the tendency to suffocate prescriptions in convergent power, and the apparent preponderance of refractions conducted at distances substantially short of optical infinity, form a synergistic peril that can lead to headaches and re-makes.

Drop ’em (or, ...don’t)

It is difficult to predict whether refraction after dilation will facilitate or hinder the exercise. On one hand, with respect to retinoscopy, the wide pupil allows greater appreciation of the light reflex; on the other, peripheral aberrations of the reflection can stymie its interpretation. Concerning subjective refraction, a miotic patient may have a broader range of clear vision per expanded depth of focus, leading to less precise refraction, whereas the aberrations yielded upon mydriasis may challenge her ability to resolve small letters, and thus itself force inaccurate refraction.
Given such uncertainties, my approach is to attempt to refract in the undilated state, and, if not met with success, to revisit the procedure upon mydriasis.

Respect “20/happy

It is necessary to determine what level of detail the eye is able to resolve, as this helps guide whether further investigation must be conducted into the presence of pathology. However, a patient whose uncorrected distance vision is 20/25-2, and who has no difficulty accomplishing her daily tasks, is not necessarily in need of spectacle correction; inversely, someone seeing 20/20-1, with the potential for 20/15+2, and a lifestyle that benefits from such high visual resolution, very well may benefit from prescription lenses. Once it has been determined what a person can see, it is important to realize that our job is not to force maximum clarity upon people, but to create a situation in which their eyes aid the activities of their life.

Bum your patient out a little

Setting the patient’s expectations appropriately is necessary to preventing failure of her trust in the doctor, and is requisite to having respect for the human being who has allowed us to participate in caring for her health and vision. Although I work toward achieving the best vision I can provide for my patient (a combination of clarity and comfort), I err against inflating expectations to a level from which they only can collapse.
When large changes are made, or a new type of lens is chosen (such as progressives rather than lined bifocals), this ought to be explained, and the patient needs to be cautioned that a period of adaptation (I say as long as two weeks) can be required for the new prescription to feel comfortable. Further, I tell her that, after this stage, if she remains uneasy in the prescribed spectacles, she is encouraged to return for re-evaluation. It is unfortunate to find a patient has worn her old lenses since her previous exam because the new set did not work well for her, but she sought not to “be a bother about it.”
At the other end of the spectrum, I aim to be forthright when no substantial change in prescription has occurred. This is not an essay on the ethical or pecuniary concerns of providing medical care, however it is intuitive to a practitioner when his motivations are founded upon finances rather than clinical outcomes. A person in search of a new pair of eyeglasses for cosmetic reasons or any other is welcome to purchase these, however it is the responsibility of the doctor to disclose when a prescription is identical to or negligibly different from existing correction. With respect to entrepreneurialism as well as to morality, there lie untenable tribulations in misleading a patient to believing a new pair of eyeglasses will help her see better when in fact this is not so.

Don’t refract everyone

I feel the inclination to activate my flame-shield at this time, but I truly do not believe every routine examination of an established patient requires refraction. As stated above, an asymptomatic patient who is seeing well is not expected to have substantial changes in refractive status. I find we are sometimes driven to bracket plus and minus quarter-diopter spheres, and maybe wiggle the J.C.C. in place for a few seconds, from an inexplicable mental compulsion rather than as a matter of good practice. Going through the motions of this obsessive chore does not improve the outcome for patients, as we either find minor changes that will likely be of no consistent difference to a person’s vision, else large shifts that make no sense and leave us contemplating whether to prescribe them (which, usually, we should not).
In conclusion, the art of refraction is important for the vast majority of optometrists to master, and with time most probably will do so.
I hope the above observations may aid in navigating some of the hurdles one encounters in this journey, while circumventing the ills of learning them upon personal folly.
My own conceptions and approach continue to evolve, and I do humbly wonder, if revisiting this essay some time in the future, just how much nodding or head-shaking I might resume.
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