Reading glasses provide magnification to help the eye focus on close-up objects. The strength is quantified in units called diopters, always indicated with a plus sign (e.g., +1.50). This magnification compensates for presbyopia, a common age-related condition where the eye’s natural lens hardens and loses the flexibility needed for near vision. Presbyopia affects nearly everyone, typically beginning around age 40, making close-range tasks difficult without optical assistance.
Identifying the Signs of Presbyopia
The first indications that you may require reading glasses are often behavioral and occur during everyday tasks. A noticeable symptom is needing to hold books, menus, or your smartphone farther away from your face to bring the text into focus. This action compensates for the lens’s reduced ability to accommodate at close range.
You may also find yourself seeking out the brightest available light to read fine print, as increased illumination can help sharpen a blurred image. Extended periods of close work, such as reading or needlework, often result in eye strain, leading to soreness or fatigue. This prolonged strain can also trigger mild frontal headaches, signaling that your eye muscles are overworking.
Performing the At-Home Power Test
The most common method for determining diopter strength involves using a printable reading chart, which can be easily found online. This chart presents lines of text in progressively smaller sizes, each corresponding to a specific magnification power. For an accurate result, the chart must be held at a standard reading distance, typically 14 to 16 inches from your eyes.
Start by trying to read the smallest print without glasses, then systematically move down the lines until you find the smallest print that is completely clear. The magnification strength listed next to that line is your starting diopter power. Over-the-counter reading glasses are sold in positive (+) strengths, usually starting at +1.00 and increasing in increments of +0.25 diopters.
The goal of this test is to find the lowest power that allows you to see the text clearly without squinting or straining. If you are unsure between two strengths, selecting the weaker one is advisable, as overcorrection can lead to discomfort.
Fine-Tuning Your Strength Selection
After performing the initial test, cross-reference the result with general guidelines correlating strength to age, though individual needs vary. Individuals between 40 and 45 typically require +1.00 to +1.50 diopters. Those in the 50-55 age range commonly need +1.75 to +2.25, while people 55 and older may require +2.50 diopters or higher.
Consider the specific distance of the task you are performing. A power perfect for reading a book at 14 inches may be too strong for a computer monitor, which is usually viewed at an intermediate distance (20 to 30 inches). For computer work, you may require a power that is one-half to one full diopter weaker than your primary reading glasses.
To confirm the ideal power, wear the selected strength for a sustained period, such as 15 minutes, while performing a close-up task. If the glasses cause dizziness, visual distortion, or eye strain, the power may be too strong. Always aim for the minimum magnification that provides crisp, comfortable vision.
When Over-the-Counter Glasses Aren’t Enough
Generic over-the-counter reading glasses are manufactured with the same power in both lenses and the optical center aligned for an average person. They only correct simple presbyopia and cannot account for complex vision issues like astigmatism or anisometropia (a difference in power between your two eyes). Using non-customized lenses when these conditions exist can result in headaches and visual discomfort.
A comprehensive eye examination is necessary to rule out more serious conditions, such as glaucoma, cataracts, or macular degeneration. Relying solely on OTC readers may delay the diagnosis and treatment of these progressive diseases. Schedule an appointment with an eye care professional immediately if you experience a sudden change in vision, double vision, eye pain, or if you require a magnification stronger than +3.00 diopters.