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HomeMyopia ResourcesMyopia In FocusHE SAID: Instruments for use in a myopia management practice

HE SAID: Instruments for use in a myopia management practice

Daniel Tilia, BOptom (Hons), MOptom, GradCertOcTher, FBCLA, FAAO
PhD candidate, Brien Holden Vision Institute

Many of the instruments required by the eye care professional in managing myopia should be already available in most, if not all, practices.

These include:

  • Phoropter
  • Trial lenses and trial frame
  • Retinoscope
  • Visual acuity chart
  • Auto-refractor
  • Slit-lamp biomicroscope
  • Binocular indirect ophthalmoscope
    • Mydriatic / cycloplegic agent
    • Appropriate fundoscopy lenses

Myopia-management is typically performed on children of various ages and so a computer-driven acuity chart is recommended due to the myriad of choices available in terms of letters, symbols and other functions. These can be especially useful when measuring visual acuity in young children.

These instruments are available in many different designs from a variety of manufacturers and most are inter-changeable between each other, irrespective of manufacturer. However, some consideration should be given to specific instruments for myopia-management.

Myopia-management is typically performed on children of various ages and so a computer-driven acuity chart is recommended due to the myriad of choices available in terms of letters, symbols and other functions. These can be especially useful when measuring visual acuity in young children.

Auto-refraction has the advantage of being an objective measure not subject to the bias of subjective refraction. As such, it is ideally suited to monitor refractive changes in patients undergoing myopia-management. An open-field auto-refractor is less susceptible to residual myopia and instrument myopia than closed auto-refractors, and so are better suited to monitor refractive changes.1

Cycloplegic refraction is an essential indicator as to when to initiate myopia-management2,3 and for monitoring refractive myopia progression.

Cycloplegia can be adequately achieved with either 1% cyclopentolate or 1% tropicamide,4 but the latter has a shorter duration and so is the preferred agent.1

Ideally, the eye-care professional performing myopia-management should also have access to instruments which image the posterior segment, perform corneal topography and measure axial length.

Myopia is associated with various structural changes to the posterior segment,5,6 and so imaging of the posterior segment is recommended to more easily detect these subtle changes. Optical coherence tomography (OCT) is becoming more common in modern practice, and is ideally suited to monitor myopic changes.1

A retinal camera can also be used to monitor myopic changes and has the advantage of being cheaper and more commonly used in practice compared to OCT. However, a retinal camera cannot compete with the detail provided with OCT.1

Instruments that measure axial length are currently rarely used in optometric practice. This is an issue with monitoring myopia progression with orthokeratology as refractive changes cannot be easily measured. It is also an issue with low-concentration atropine due to the mismatch between refractive error and axial length changes.8,9

A corneal topographer is an essential instrument for eye-care professionals using orthokeratology in myopia-management. Corneal topography can also be used to diagnose corneal conditions such as keratoconus,7 which will affect planned myopia-management.

Instruments that measure axial length are currently rarely used in optometric practice. This is an issue with monitoring myopia progression with orthokeratology as refractive changes cannot be easily measured. It is also an issue with low-concentration atropine due to the mismatch between refractive error and axial length changes.8,9

Optical biometry is the method of choice for measuring axial length. Examples of instruments employing ocular biometry are the IOL Master (Carl Zeiss Meditech, Germany) and the Lenstar (Haag-Streit, Switzerland). Compared to ultrasound, optical biometry does not touch the cornea, is easier to use, and has increased resolution and precision.1 While not common in optometric practice, optical biometry is routinely performed prior to cataract surgery for calculating the required power of the intra-ocular lens.

Modern practice has seen optometry and ophthalmology work closely together for the mutual benefit of patients. If a practice is unable to purchase an ocular biometer, perhaps an arrangement can be made with the local cataract surgeon for yearly axial length measurements on myopic patients. Instrument manufacturers are also exploring the possibility of making axial length measurement more accessible to optometric practice.

In summary, most of the instruments required for myopia-management are already found in a modern optometric practice. Instruments to image the posterior segment and perform corneal topography are also becoming more common in optometric practice.

Axial length measurements will become more common in myopia-management, either with the purchase of an optical biometer, referral for axial length measurement or with the development of other methods to measure axial length.

References

  1. Wolffsohn JS, Kollbaum PS, Berntsen DA, et al. Imi – Clinical Myopia Control Trials and Instrumentation Report. Investigative ophthalmology & visual science 2019;60:M132-m60.
  2. World Health Organization – Brien Holden Vision Institute. The Impact of Myopia. In: The Impact of Myopia and High Myopia. Report of the Joint World Health Organization – Brien Holden Vision Institute Global Scientific Meeting on Myopia. Available at: https://www.who.int/blindness/causes/MyopiaReportforWeb.pdf. Accessed: 18 April 2019.
  3. Flitcroft DI, He M, Jonas JB, et al. Imi – Defining and Classifying Myopia: A Proposed Set of Standards for Clinical and Epidemiologic Studies. Investigative ophthalmology & visual science 2019;60:M20-m30.
  4. Egashira SM, Kish LL, Twelker JD, et al. Comparison of Cyclopentolate Versus Tropicamide Cycloplegia in Children. Optometry and vision science : official publication of the American Academy of Optometry 1993;70:1019-26.
  5. Read SA, Alonso-Caneiro D, Vincent SJ. Longitudinal Changes in Macular Retinal Layer Thickness in Pediatric Populations: Myopic Vs Non-Myopic Eyes. PloS one 2017;12:e0180462.
  6. Samarawickrama C, Mitchell P, Tong L, et al. Myopia-Related Optic Disc and Retinal Changes in Adolescent Children from Singapore. Ophthalmology 2011;118:2050-7.
  7. Tummanapalli SS, Maseedupally V, Mandathara P, et al. Evaluation of Corneal Elevation and Thickness Indices in Pellucid Marginal Degeneration and Keratoconus. Journal of cataract and refractive surgery 2013;39:56-65.
  8. Chia A, Chua WH, Cheung YB, et al. Atropine for the Treatment of Childhood Myopia: Safety and Efficacy of 0.5%, 0.1%, and 0.01% Doses (Atropine for the Treatment of Myopia 2). Ophthalmology 2012;119:347-54.
  9. Yam JC, Jiang Y, Tang SM, et al. Low-Concentration Atropine for Myopia Progression (Lamp) Study: A Randomized, Double-Blinded, Placebo-Controlled Trial of 0.05%, 0.025%, and 0.01% Atropine Eye Drops in Myopia Control. Ophthalmology 2019;126:113-24.