As the eye naturally changes with age, typically starting around 40, the crystalline lens inside the eye becomes less flexible—a condition known as presbyopia. This loss of elasticity impairs the eye’s ability to focus on close objects, making reading and near tasks increasingly difficult. Multifocal contact lenses address this common issue by correcting both distance vision and the required near vision within a single lens. These lenses require a specialized designation on the prescription to indicate the degree of near correction needed.
Understanding Addition Power (ADD)
The term “ADD” on a contact lens prescription is an abbreviation for “Addition Power,” which quantifies the extra magnifying strength required for comfortable near vision. This power is always a positive value, measured in diopters (D), and is layered on top of the wearer’s distance prescription. It compensates for the diminished ability of the eye to accommodate, or change focus, which is the hallmark of presbyopia. The required ADD power increases progressively as the crystalline lens continues to harden with age.
The total range of ADD power typically falls between +0.50 D and +3.00 D. The specific number is determined by the patient’s visual needs and the severity of their presbyopia.
Decoding the “MAX” Designation
The “MAX ADD,” or sometimes “HIGH ADD,” designation is a simplified grading system used by contact lens manufacturers instead of a precise diopter value. Manufacturers group the continuous range of ADD powers into broad categories, typically low, medium (MED), and high (MAX), to simplify the fitting process. “MAX ADD” indicates the strongest level of near correction available within that brand’s multifocal product line.
This maximum strength generally corresponds to a diopter range of approximately +2.00 D to +2.50 D or higher, though the exact range varies between different brands. This designation allows the eye care professional to quickly select the appropriate lens for patients with advanced presbyopia who require the greatest amount of near magnification.
How Multifocal Lenses Utilize ADD Power
Multifocal lenses incorporate the prescribed ADD power using a simultaneous vision system. This means both the distance and near prescriptions are present in the lens at all times, and the brain selects the clear image needed for the current task. Two common designs achieve this dual focus: concentric rings and aspheric optics.
Concentric Designs
The concentric design features alternating rings of near and distance power, similar to a target. The near or distance correction is typically positioned centrally.
Aspheric Designs
Aspheric designs function more like progressive eyeglasses, with the power gradually transitioning across the lens surface. These designs allow the wearer’s pupil to utilize the correct power zone without the lens having to move.
Modern lenses often incorporate a Pupil Optimized Design. This feature tailors the optical zones to the individual’s pupil size variations, ensuring the ADD power is delivered effectively regardless of lighting conditions.