July 2020 myopia research update

Physiology

Axial length and reduced macular sensitivity before changes in acuity

Summary

Adult high myopes (6D or more) with axial length minimum of 25mm in at least one eye were evaluated for myopic macular degeneration (MMD) by the META-PM category system, and classified into ‘MMD absent’ (categories 0-1), ‘mild MMD’ (category 2) and ‘severe MMD’ (category 3). Macular sensitivity was assessed with microperimetry at 2, 4 and 6 degrees diameter of fixation. As expected, reduced sensitivity was correlated with more severe MMD. After adjusting for several factors, longer axial length was independently associated with worse macular sensitivity. Furthermore, while ‘absent’ and ‘mild’ MMD categories had similar best corrected visual acuity (BCVA), the ‘mild MMD’ category showed reduced macular sensitivity, indicating this microperimetry test could be a more sensitive marker of visual function in eyes with macular disease than BCVA.

Clinical relevance

The pervasive frequency of myopia in Singapore provides a volume of opportunity to understand the visual sequelae of high myopia. In this study, highly myopic adults with diffuse chorioretinal atrophy (META-PM Grade 2) showed reduced microperimetric macular sensitivity before any loss of BCVA, when compared to eyes without MMD. With an average age of 54 years and axial length of 28mm, these patients reflect people of working age likely to be seen in routine clinical practice and not just in tertiary retinal care. While longer axial length was associated with reduced macular sensitivity, although only 15-25% of the loss of sensitivity was explained by axial length indicating other factors can be at play. This underscores the importance of monitoring retinal health closely for any patients with longer eyes and high myopia, and points to use of microperimetry – more commonly used in retinal subspecialty tertiary eye care – as a more sensitive clinical tool than BCVA for monitoring the at-risk and compromised macula.

Limitations and future research

This was a video presentation of an ARVO abstract, so the full peer reviewed methodology is not available for critique. The authors themselves mentioned their small sample size and the repeatability of the microperimetry test as limitations, although noted that testing more points would take more time and could lead to more variability through fatigue. Future research cited by the authors includes investigating correlations between microperimetry results in different categories of MMD with choroidal and retinal thickness using OCT; as well as with retinal vascular parameters using OCT-A.

Binocular Vision

Accommodation training in multifocal contact lens wear

Summary

The accommodation response in multifocal contact lens (MFCL) wear could influence myopia control efficacy, and previous studies have shown that non-presbyopic MFCL wearers may relax their accommodation and use the ‘add’ at near, generating a larger lag of accommodation. This study used custom-developed photorefractor software to measure the lag and found it to be greater in young adult myopes wearing MFCL compared to single vision soft contact lenses (SCL) or trial spectacle lenses. They then undertook auditory biofeedback training for 200 seconds and found lag reduced in all three correction scenarios, but less so for the MFCL wearers. The authors concluded that while biofeedback training improved accommodative accuracy (reduced lag) in young myopes, it was less modifiable in MFCL wear and further training may be required.

Clinical relevance

There’s a building volume of research that MFCL wear reduces accommodative response (increases accommodative lag) in children and young adults, and that a reduced accommodative response may be correlated with a reduced myopia control effect. The auditory biofeedback training undertaken here improved accommodative response, but this improvement was less predictable in MFCL wear. It is not yet commercially available, but there are other clinical methods available to increase accommodative response. This research points to the value of assessing accommodation in young myopes – a normal accommodative response is important for visual comfort, and seems to be increasingly valuable in achieving myopia control efficacy. As we learn more about the interaction between MFCL and accommodation, it may be in future that we select a specific type of MFCL for the individual myope based on their accommodation, and/or we seek to improve accommodative responses through specific corrections or training, to optimize myopia control efficacy.

Limitations and future research

This was a video presentation of an ARVO abstract, so the full peer reviewed methodology is not available for critique. That being said, the methodology appears robust in this small study. The main limitation is while the single vision SCL and MFCL measures were repeated on the same participants, the trial spectacle lens wearers were a separate group – without baseline comparisons this makes the trial spectacle lens data less useful for further analysis. This study was undertaken on young myopic adults – longer periods of training and repetition of this study in myopic children, who are followed longitudinally, would allow further relevance to myopia control.

Myopia Progression

Predicting future myopia progression from prior myopia progression

Summary

Annual rate of myopia progression from an existing dataset is used to determine if rate of subsequent years of myopia progression can be reliably predicted, to reveal a statistically significant though only modest clinical relevance of myopia progression from one year to the next, with no improvement to the model from averaging up to three prior years of myopia progression measurement.

Clinical relevance

Reliance on prior annual rate of myopia progression alone is not a reliable enough predictor for subsequent years of progression. Consequently, myopia management strategy for a given individual should be determined based on multiple patient-specific factors including myopia progression in the previous year, higher initial SE, age of myopia onset and parental myopia.

Limitations and future research

  • Meeting abstract so not fully peer-reviewed
  • Dataset restricted to Singapore children - results don’t necessarily extrapolate to other nationalities / ethnicities
  • Gives promise of more accurate prediction models hopefully in the near future

Using growth charts to track progression of myopia – can they be used to predict success with MiSight?

Summary

Translating clinical trial results into clinical practice is made difficult by differences in participants vs patients and applying clinical trial analysis to a practice setting. The authors introduce the concept of using growth (centile) charts to monitor myopia progression and use these charts to assess the previously conducted MiSight 3-year data set to establish a good fit between the published outcomes from the clinical trial and representation on changes to centile chart tracking. This research establishes centile charts as a useful tool to use in clinical practice to determine successful outcome from a myopia control intervention.

Clinical relevance

Centile charts offer a simple way to monitor myopia development in an individual to determine whether they are likely to be slow or fast Progressors and whether a myopia control intervention is having an effect. However, while this provide promise, they are still at a relatively early stage of development.

Limitations and future research

  • Meeting abstract so not fully peer-reviewed
  • Growth charts and dataset restricted to European children - results don’t necessarily extrapolate to other nationalities / ethnicities
  • Gives promise of easy to use myopia progression charts to:
    • track progression of myopia in children
    • help explain to parents the predicted change to myopia progression and outcomes from myopia management intervention

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