An eyeglass prescription (Rx) uses a standardized, technical language of abbreviations and numbers to detail the precise lens power needed to correct a patient’s vision. For those unfamiliar with the terminology, this document can appear confusing. This article will break down the meaning of Spherical Power (SPH) and Plano as they appear on your prescription, clarifying the concept of “SPH Plano.”
Understanding Spherical Power (SPH)
The abbreviation SPH stands for Sphere, representing the primary lens power required to correct nearsightedness or farsightedness. This measurement is given in diopters (D) and indicates the degree to which the lens needs to bend light to achieve clear focus on the retina. A minus sign preceding the number signifies correction for nearsightedness (myopia), meaning light is focused in front of the retina. Conversely, a plus sign indicates correction for farsightedness (hyperopia), where light rays focus behind the retina. The term “spherical” is used because this correction is uniform across the entire surface of the lens. The further the numerical value is from zero, regardless of the sign, the stronger the vision correction required for that eye.
What Plano Means on a Prescription
The term Plano is derived from the Latin word meaning “flat.” In the context of an eye prescription, Plano indicates a lens with zero refractive power. When Plano appears in a prescription column, it means the eye requires no spherical correction for either nearsightedness or farsightedness. Plano is equivalent to a value of “0.00” diopters, sometimes abbreviated as “PL” or simply left blank. A Plano lens is optically neutral, acting as a simple window pane without any curve designed to adjust the light path.
Interpreting “SPH Plano”
When your prescription shows “Plano” or “PL” in the SPH column for one or both eyes, it means you do not have any measurable spherical refractive error. This reading confirms that overall distance vision is excellent, requiring no corrective power to bring distant objects into focus. This finding is noted in the rows designated for the right eye (OD) and the left eye (OS) under the SPH column. The SPH Plano designation signifies that the eye’s natural focusing components, the cornea and the lens, are successfully directing light rays to converge correctly on the retina. This means the lens prescribed for that part of your vision will be non-corrective.
Why You Might Still Need Glasses
Seeing SPH Plano on your prescription does not mean your vision is perfect or that you do not need glasses at all. A patient can have no nearsightedness or farsightedness but still require vision correction for other issues. The primary reason for needing glasses with an SPH Plano finding is the presence of astigmatism.
Astigmatism is a condition where the cornea or lens is irregularly shaped, more like a football than a basketball, causing light to focus unevenly. This is corrected by the CYL (Cylinder) and AXIS measurements on the prescription, which provide power to specific meridians of the lens to compensate for the irregular curvature. Even with SPH Plano, a significant CYL value indicates a need for glasses. Furthermore, older adults may have SPH Plano for their distance vision but still require an ADD (Addition) power to correct presbyopia, the age-related loss of near focusing ability.