One of the most common questions asked during an eye exam is “has my prescription changed?” but less frequently requested is, “how stable is my prescription?”. The eye has natural mechanisms in place that aid in keeping the prescription (refraction) from fluctuating. A spectacle prescription is based on eye features including corneal curvature, anterior chamber depth, lens thickness, and the axial length of the globe (whole eye). During early developmental years, the prescription is least stable, due to rapid growth causing changes in these eye features. Starting in early adulthood, refractive changes usually slow but this depends on the type of refractive error (myopia, hyperopia, etc.) and age of onset. In later adult life, refraction changes primarily result from changes in the lens of the eye.
However, some health conditions can induce refractive error instability by altering one or more eye features, for instance:
During pregnancy, various changes occur throughout the body including the eye. Ocular changes affecting the prescription of expectant mothers are most often related to alterations of the corneal curvature due to the corneal thickness from swelling or a change in the tear film. These changes usually appear in the second and third trimester, are transient but occasionally, may be permanent. Refractive surgery requires a stable refractive status. Therefore, the current recommendations during pregnancy are to delay surgery and wait until the refraction is once again stable. This precaution also applies to getting new glasses unless the refractive change significantly impairs vision.
Hyperglycemia (elevated blood glucose) is a significant cause of temporary refractive changes in diabetic patients. Newly diagnosed individuals beginning treatment can experience fluctuation in vision from refractive instability. Once blood glucose levels normalize, the prescription typically stabilizes. Although the precise mechanism for the refractive change is not clear, lens abnormalities appear to be the likely cause. The general recommendation is to wait for at least 4-weeks before prescribing new glasses to allow for stabilization of the prescription.
Dry Eye Syndrome
Dry eye syndrome (DES) is characterized by a deficiency in the amount and quality of tears, an unstable tear film and resulting ocular surface changes. Consequently, vision can fluctuate during the day depending on the severity. Refractive instability leads to challenges in daily tasks including reading, computer work, and driving. Left unmonitored and untreated, DES can progress causing permanent changes in vision. Instability in the prescription decreases with appropriate dry eye therapy and close monitoring.
Between 2-4 million people in the U.S. have glaucoma, which can cause blindness by damaging the optic nerve. Trabeculectomy, a surgical procedure to lower intraocular pressure, is typically reserved for patients with severe glaucoma who no longer respond to treatment with standard medication or laser therapy. Vision changes/instability accompany this procedure in over half of the cases but are usually temporary. Recent studies have shown that after the surgery the axial length of the eye changes due to choroidal thickening, which can lead to temporary and possibly permanent changes in an individual’s vision.
Keratoconus is a noninflammatory corneal bulging or ectasia with onset typically in puberty and progresses until about forty years of age. Alterations of the front surface of the cornea lead to irregular astigmatism. The stability of the prescription during this time may vary depending on the severity of the disorder, however, once keratoconus progression stops the refractive status stabilizes.
About The Author: Dr. Careen Caputo
Dr. Careen Caputo graduated with her Doctor of Optometry degree from the Southern California College of Optometry (SCCO) in Fullerton, California,
after completing a BS in Visual Science. Dr. Caputo received specialized training in low vision at the Center for the Partially Sighted in Santa Monica as well as rotations in ocular diseases. Dr. Caputo will complete her Master’s in Public Health in Global Health Leadership at the Keck School of Medicine of the University of Southern California in 2017, where she conducted research in an underserved community to inform and develop educational materials to increase awareness of diabetic retinopathy in a Latino population with diabetes. Dr. Caputo was awarded the Delta Omega Honorary Society in Public Health. She volunteers her time at community clinics giving eye exams to the underserved, working to increase access to quality affordable eye care. Her aspiration is to reduce the burden of vision loss through increasing awareness and access to timely, acceptable and quality eye care to vulnerable populations both locally and globally.
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