Having two different eye prescriptions is a common occurrence, and it is helpful to understand why this happens and what it means for your vision. An eye prescription quantifies the specific optical power needed to correct refractive errors, which are conditions that prevent light from focusing properly on the retina. These errors include nearsightedness (myopia), farsightedness (hyperopia), and astigmatism, where the cornea or lens has an irregular curvature. The numbers on a prescription indicate the lens strength in diopters, with negative values for nearsightedness and positive values for farsightedness.
Is It Common to Have Different Prescriptions?
It is common for individuals to have different prescriptions for each eye. This condition is medically termed anisometropia, which means unequal refractive power between the two eyes. While a slight difference in vision between eyes is normal and often unnoticeable, a significant disparity can interfere with clear, binocular vision. It is estimated that approximately 6% of children between six and eighteen years old experience anisometropia. Even those with naturally clear vision can have a small percentage difference in the refractive power of each eye without experiencing issues.
When the difference in prescription between the eyes is greater than one diopter, it is generally classified as anisometropia. This difference is not unusual, as each eye is a distinct organ with its own unique shape, size, and focusing power. The brain typically compensates for minor variations, but when the difference becomes more pronounced, it can lead to noticeable visual challenges. The presence of differing prescriptions is a natural outcome of individual eye development and characteristics.
Why Prescriptions Can Differ Between Eyes
The eyes are complex organs, and several factors contribute to why their prescriptions might vary. Natural variations in eye development mean that each eye can have a slightly different shape or size. The cornea, the clear front surface of the eye, and the overall length of the eyeball are two main determinants of a person’s prescription. Even minor differences in these structures can lead to noticeable disparities in vision.
During childhood, eyes grow and develop, and these growth rates can differ between the two eyes. For instance, one eye might become more nearsighted or farsighted than the other as it develops. Astigmatism, which results from an irregularly shaped cornea or lens, can also affect each eye differently, requiring distinct corrections. One eye might have more or less astigmatism, or the direction of the astigmatism might vary, leading to different cylindrical values on a prescription.
Certain eye conditions can also cause a difference in prescription between eyes. Cataracts, which involve clouding of the eye’s natural lens, can progress at different rates in each eye, leading to unequal vision. Other conditions, such as presbyopia, an age-related loss of near focusing ability, can also manifest differently in each eye as individuals age. Previous eye surgery or an eye injury can also alter the refractive properties of one eye, creating a disparity with the other.
How Unequal Prescriptions Affect Vision and What Helps
Significant differences in eye prescriptions can lead to various visual impacts. Individuals may experience blurred vision in one eye, eye strain, or headaches as the brain attempts to reconcile the two dissimilar images received from each eye. Other symptoms can include poor depth perception, dizziness, nausea, or sensitivity to light. The brain often tries to suppress the blurrier image, favoring the clearer one, which can lead to difficulties with binocular vision.
In children, a significant unequal prescription can be particularly concerning because it may lead to amblyopia, commonly known as “lazy eye.” Amblyopia occurs when the brain consistently favors the stronger eye, causing the weaker eye’s vision to not develop properly and potentially become permanently impaired if left untreated. Early detection and treatment are important to prevent long-term vision problems in children.
Eye care professionals manage unequal prescriptions with several correction options. Eyeglasses can be prescribed with different strength lenses for each eye to correct refractive errors. However, for very large differences in prescription, eyeglasses might create a noticeable difference in image size between the eyes, which can sometimes cause discomfort or interfere with proper binocular vision. Contact lenses are often a preferred solution for more substantial differences because they sit directly on the eye, minimizing image size disparities and providing a more balanced visual experience. For adults, refractive surgery, such as LASIK, can be a potential long-term solution to correct the underlying refractive errors and reduce or eliminate the need for glasses or contact lenses.