Dean Psarakis, B.Optom, Senior Research Optometrist
Understanding what is to be expected in terms of visual quality reduction as a practitioner is critical in the guidance we can provide to our patients.
With a growing body of evidence supporting the effectiveness of optical devices in the management of myopia, the popularity of such interventions is on the rise. These devices include myopia management spectacle lenses, myopia management multifocal soft contact lenses, orthokeratology (OrthoK) lenses, and to a lesser extent, bifocal and progressive addition spectacles. Evidence on the efficacy of the above-mentioned interventions is extensive and ranges from approximately 30% to 60% (reduction in axial length elongation).1–5 However, the impact of these interventions on visual performance is less widely reported. Although it is generally regarded that optical strategies used to manage myopia impact visual performance, there is little guidance for practitioners on measuring and assessing visual quality with these devices.
Visual Quality with Devices Prescribed in Myopia ManagementCurrently, some research points to certain metrics that may be useful in measuring the loss of visual quality using myopia management devices.
High Contrast Visual Acuity (HCVA)When viewing through the portion of the spectacle lens with the myopia control features (for example, off-axis or peripheral gaze viewing through the lenslets), a reduction in high contrast visual acuity (HCVA) is expected with the use of myopia management lenses. This drop in HCVA ranges from three to five letters on the Snellen chart and depends on the specific design.6 A similar reduction in HCVA was also observed with the use of myopia management/multifocal contact lenses and found to be approximately a one-line reduction.7–9 In comparison, high contrast VA with OrthoK is thought to be comparable to that seen with single vision spectacles,10 with less than one letter reduction in VA observed over eight hours.11
Low Contrast Visual Acuity (LCVA)Compared to single vision lenses, a greater decrement in low contrast visual acuity (LCVA) is observed with myopia management lenses. LCVA is compromised in myopia management/multifocal contact lenses by a similar if not slightly higher magnitude of approximately five to six letters, or around one line.12–14 Unlike HCVA, LCVA is reduced in OrthoK, once again in the order of approximately one line, mainly due to the increase in higher order aberrations induced by the flattening of the cornea.15–17 It should be noted that lens designs that incorporate higher add power, greater variation in power profile across the optical zone, and decentered lenses may result in a greater decrement in visual performance. Furthermore, pupil variations (as occurs in low light conditions) also impact VA.
Contrast SensitivityContrast sensitivity has been shown to be reduced with myopia management spectacle lenses, particularly across higher spatial frequency ranges.6,18 Similarly, multifocal contact lenses have been shown to reduce contrast sensitivity compared to single focus contact lenses. Garcia-Marquez et al. found a reduction from 55 dB to 28 dB at the spatial frequency of 3 cpd.19OrthoK treatment has also been shown to reduce contrast sensitivity from 1.45 log units pre-treatment to 1.29 log units post-treatment in a study by Hiraoka et al.20
Subjective Assessment of Vision QualityObjective metrics such as visual acuity and contrast sensitivity have been shown to have little to no correlation with subjective visual satisfaction.13,21 This underscores the importance of exploring the quality of vision from the patient’s perspective and not relying on visual acuity alone as a predictor of satisfaction. Such questions may explore the overall comfort of vision, central vision, peripheral vision, daytime, and night vision.21
Guidance for Clinical PracticeUp until now, high contrast visual acuity alone has represented the extent of recommended assessment regarding visual quality in myopia management. Based on the evidence, additional measurements can add sensitivity and relevance in gauging the day-to-day quality of vision that patients may experience. The following table is a summary of a suggested list of measures that may inform the quality of vision patients can experience along with the approximate expected reduction according to the device used:
Suggested List of Measurements to Inform the Quality of Vision According to Myopia Management (MM) Device Used
Considerations at Follow-Up VisitsA six-month review is widely recognized as the gold standard for myopia management patients.22,23 The above measures should be reassessed regularly to monitor the quality of vision experienced by patients. It is important to keep in mind that changes in visual quality at subsequent follow-up visits may not solely be the result of the unwanted side effects of a particular myopia management device (particularly with multifocal spectacle and contact lenses), but they might be influenced by other factors, such as myopia progression, changes in binocular visual function, and even ocular health considerations, such as dry eye. Implementing the above assessments in routine assessments will help a more rapid diagnosis of the underlying reason for the decrement in visual performance. It will also help in educating the parents and/or the child on expected visual performance. When it comes to visual quality, it is also worth noting that some research suggests that the patient’s age may impact visual adaptation, with younger age groups demonstrating greater adaptive abilities.24,25 Therefore, closer monitoring and/or reinforcement of visual performance may be needed in older age groups.
Take-Home MessageUnderstanding what is to be expected in terms of visual quality reduction as a practitioner is critical in the guidance we can provide to our patients. Establishing what is to be anticipated and relaying this to our patients may improve compliance and ultimately result in better myopia management outcomes.
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