The process of getting an updated prescription for glasses or contact lenses can sometimes feel confusing due to the different terms used by eye care professionals and insurance providers. The specific tests performed during the visit determine the vision correction needed. Understanding the terminology and procedures involved is important for ensuring you receive the best vision correction possible. This examination is a necessary step before purchasing new corrective lenses.
Defining the Exam: The Terminology for Corrective Lenses
The core procedure for determining an eyeglass prescription is technically called a refraction. Refraction is the process of precisely measuring how light bends as it enters the eye to focus on the retina. An eye that does not focus light correctly has a refractive error, such as nearsightedness, farsightedness, or astigmatism, necessitating corrective lenses.
While “refraction” is the clinical term for the measurement, the entire appointment is frequently referred to as a Routine Vision Exam or a Comprehensive Eye Exam. This appointment focuses on assessing visual acuity and determining the exact lens power required to achieve 20/20 vision, or the best-corrected visual acuity possible. The goal of obtaining a prescription is the defining factor for a vision exam.
Key Steps in Determining Your Prescription
The determination of your precise prescription begins with a visual acuity test, which involves reading letters of decreasing size from a standardized Snellen chart. This provides a baseline measurement of current uncorrected vision. The eye doctor may then use an autorefractor, a computerized instrument that provides an objective estimate of the necessary prescription. This initial estimate is refined using a manual process known as subjective refraction.
The subjective refraction is performed using a device called a phoropter, which holds multiple lenses positioned in front of the eyes. During this test, the doctor rapidly switches between different lens combinations, asking the patient, “Which one is clearer, one or two?” This interactive process fine-tunes the sphere (nearsighted/farsighted correction) and cylinder/axis (astigmatism correction) measurements until the sharpest possible vision is achieved. A final measurement, the pupillary distance (PD), is also taken to ensure the corrective lenses are centered correctly in the eyeglass frames.
Vision Exam vs. Medical Eye Exam: Understanding Scope and Coverage
The distinction between a Vision Exam and a Medical Eye Exam is significant, particularly concerning insurance coverage. A Vision Exam is generally considered routine care, focusing on determining a prescription and checking for refractive errors. The entire refraction procedure is billed as a component of this routine visit and is typically covered by vision insurance plans.
A Medical Eye Exam, conversely, focuses on the health of the physical eye and is necessitated by a medical condition, such as glaucoma, cataracts, or diabetic retinopathy, or symptoms like an eye infection or injury. This type of exam is covered by standard medical insurance. The specific refraction test—the process of determining the glasses prescription—is often not covered under medical insurance, even if performed during a medical eye exam, and may result in a separate out-of-pocket fee.