Progressive power lenses (PPLs) are a cornerstone in the correction of presbyopia, offering a seamless transition between multiple focal points for near, intermediate, and distance vision. These lenses are particularly valuable for individuals over the age of 40, who often experience diminished near vision due to presbyopia. However, not all progressive lenses are created equal. Variations in lens design, such as those emphasizing near or distance vision, influence visual quality and adaptation, but understanding these differences requires more than traditional visual acuity (VA) measurements.

A novel approach to assessing progressive lens performance involves analyzing gaze patterns—fixations and saccades—using eye-tracking technology. This study investigated how different progressive lens designs affect gaze efficiency during high-contrast visual acuity tasks at varying distances. The results shed light on how lens-specific designs influence visual performance and may guide optometrists in recommending the most suitable lens for individual needs.

Traditional measures of visual acuity assess clarity of vision by testing the ability to discern fine details on an eye chart. However, this metric often overlooks other important aspects of visual perception, such as gaze efficiency. Efficient gaze patterns, characterized by shorter fixation times, fewer fixations, and smaller saccade amplitudes, indicate the ease with which the eyes interact with visual stimuli.
Gaze inefficiency in progressive lenses can arise from design limitations, such as peripheral distortions or insufficient optimization of focal zones. Eye-tracking technology provides a powerful tool to quantify these subtleties, offering insights beyond what static VA measurements can capture. This study focuses on evaluating three PPL designs:

• PPL-Balance: A balanced lens for general-purpose use.
• PPL-Distance: A distance-specialized lens with a wider field of view for far vision.
• PPL-Near: A near-specialized lens optimized for reading and close work.

Figure 1. (A) Eye movement gaze pattern more efficient. Characterized by a lower fixation time, lower number of fixations and saccades, shorter saccade time, and smaller total saccade amplitude. (B) Eye movement gaze pattern less efficient. Characterized by a greater fixation time higher number of fixations and saccades, longer saccade time, and higher total saccade amplitude.

The study involved 27 experienced progressive lens wearers aged 54 ± 6 years. Participants included individuals with myopia, hyperopia, and emmetropia, with an average refractive error of -0.8 ± 2.6 D. All participants met strict inclusion criteria, such as:

• A minimum monocular visual acuity of 0.1 logMAR,
• Binocular visual acuity of 0 logMAR,
• Refractions between -6.0 D and +4.5 D,
• Cylindrical errors below 2.50 D.

The study compared three progressive lens designs manufactured using free-form technology:

• PPL-Balance: A general-purpose design providing equal weight to near and distance tasks.
• PPL-Distance: Specially designed for enhanced distance vision, with a wider distance zone.
• PPL-Near: Tailored for near tasks, offering a broader near zone.

Participants underwent high-contrast VA testing at two distances:

• Distance VA Task: 5.25 meters.
• Near VA Task: 0.37 meters.

Eye-tracking data was recorded using the Tobii Pro 3 Glasses, which monitored pupil positions at a frequency of 50 Hz. Gaze efficiency metrics—such as fixation count, saccade amplitude, and duration—were measured. Each participant wore all three lens types, with the order randomized to eliminate bias.

Figure 2.  Mean power map and cylinder map for the designs (A) PPL-Balance (B) PPL-Distance (distance-specialized design, with a wide distance area) and (C) PPL-Near (near-specialized design, with a wide near area) .

A randomized complete block test was employed to determine statistical differences in gaze efficiency across lens designs. A p-value <0.05 was considered significant.

Figure 3.  Area of the lens used for distance and near vision for the designs PPL-Balance, PPL-Distance, and PPL-Near .

Visual efficiency during tasks like reading or observing distant objects depends on how well our eyes move and process visual stimuli. Efficient gaze patterns are characterized by:

• Fixation Time: The duration spent focusing on a single point.
• Saccade Time: The time taken for rapid eye movements between fixation points.
• Fixation Count: The number of times the eyes pause to focus.
• Saccade Amplitude: The size of the eye movements between fixations.

Rather than any single metric driving performance, it is the interaction of these variables that determines the effectiveness of a lens design. Task-specific progressive lens designs leverage this understanding to optimize gaze efficiency for distinct visual activities, such as distance viewing or near work.

Figure 4. Comparison in the performance of each design for the duration of the fixations, nº of fixations and amplitude of the saccades, for the (A) distance VA task and (B) near VA task.

The PPL-Distance design demonstrated superior gaze efficiency for distance-focused tasks. Participants exhibited smoother and more stable eye movements, which facilitated quicker visual processing and enhanced stability. The interaction of reduced fixation time, fewer fixations, shorter saccade times, and smaller saccade amplitudes underscored the PPL-Distance design’s task-specific optimization for activities requiring clear and stable distance vision, such as driving or viewing distant objects.

The PPL-Near design excelled in near-vision tasks, such as reading or close-range work. By optimizing the interaction of gaze metrics, this design allowed participants to navigate near visual fields with ease. Reduced fixation time, fewer fixations, shorter saccades, and smaller amplitudes contributed to a comfortable and efficient viewing experience, making the PPL-Near design ideal for tasks requiring stability and clarity in the near zone.

The PPL-Balance design performed adequately across both distance and near tasks, showcasing its versatility for mixed-distance activities. However, it did not achieve the same level of efficiency as the task-specific designs. While suitable for general use, the PPL-Balance design lacked the specialized optimization of the PPL-Distance and PPL-Near lenses, resulting in less efficient gaze patterns during distance- or near-specific tasks.

The study’s findings have significant implications for both optometrists and progressive lens wearers:

1. Task-Specific Optimization: PPL-Distance and PPL-Near lenses are superior for distance and near tasks, respectively, highlighting the importance of tailoring lens recommendations to the wearer’s primary activities.
2. Gaze Efficiency as a Metric: Eye-tracking data provides valuable insights into lens performance, offering an objective complement to subjective wearer satisfaction surveys.
3. Adapting to Needs: While PPL-Balance lenses remain a versatile option for general-purpose use, they may not deliver the same efficiency for specific tasks as specialized designs.

For wearers, this means that selecting the right progressive lens design can significantly improve comfort, efficiency, and overall satisfaction during daily tasks.

Learn more: Single Vision vs. Progressive Lenses: Understanding the Differences

This study demonstrates the potential of eye-tracking technology to revolutionize how progressive lenses are evaluated. By analyzing gaze efficiency, researchers can gain a deeper understanding of how lens designs influence visual performance. The results confirm that task-specific lenses—like PPL-Distance for far vision and PPL-Near for close work—offer superior performance compared to general-purpose designs.

For optometrists, integrating eye-tracking insights into clinical practice could enhance the precision of lens recommendations, ensuring that each wearer receives a product tailored to their unique visual needs. As progressive lens technology evolves, leveraging tools like eye-tracking will be essential to refining designs and improving wearer satisfaction.

In summary, the study highlights the importance of considering both objective measures, such as gaze patterns, and subjective feedback when evaluating progressive lenses. By aligning lens choice with the wearer’s primary tasks, optometrists can provide enhanced visual comfort and functionality, ultimately improving the quality of life for presbyopic individuals.