IS EPITHELIAL thickness mapping (ETM) for orthokeratology (ortho-k) the new norm? Ortho-k is an established technology that provides myopic correction for patients looking for freedom from wearing contact lenses or glasses daily. Additionally, it is now being utilized to reduce the rate of myopia progression.
Ortho-k treatment often involves assessing the lens on eye to determine appropriate fitting characteristics, as well as ensuring appropriate over-refraction, pre- and posttreatment topographies, and assessment of refraction without the lens on assuring appropriate refractive correction.
The treatment effect of ortho-k is delivered through the pressure of the lens, which flattens and reshapes the cornea, providing the myopic correction that the eye needs (Bullimore and Johnson, 2020). Most of this remodeling occurs through changes in the corneal epithelium (González-Pérez et al, 2023).
Until relatively recently, practitioners haven’t been able to measure the ET. Eyecare providers now have access to technology that allows them to measure the ET through ETM software. Anterior segment optical coherence tomography (AS-OCT) provides the ability to metricize it.
In normal individuals, ET is expected to be between 53.4µm ± 4.6µm (Abtahi et al, 2024). For patients undergoing ortho-k, pre- and posttreatment ET can be assessed. Practitioners can expect to see that the ET is thinned centrally after ortho-k treatment. When comparing pretreatment and posttreatment measurements, it is clear where the treatment effect occurred, as evidenced by the area of epithelium that is thinned. Often, there is an associated region of epithelial thickening around the thinned treatment zone.
Ideally, the treatment zone will be centered on the cornea. This provides the best visual outcomes for the patient. This technology provides the opportunity to easily metricize this on patients. Contemporary AS-OCT systems now simultaneously also measure the topography of the anterior and posterior surfaces of the cornea as well.
To reference a specific case, a 13-year-old myopic male came to our office because he and his parents were interested in contact lenses. The patient was–3.00 DS 20/20 OD and–3.00 –1.00 x 146 20/20 OS. All ocular health findings were normal in both eyes.
We discussed options with the parents and the patient, and they decided to proceed with ortho-k. Next, ortho-k lenses with appropriate parameters were ordered.
The pre- and posttreatment epithelial thickness maps are shown in Figure 1. The right eye demonstrated appropriate alignment, but the treatment zone manifested in the left eye showed epithelial thinning inferiorly. The landing zone of the left eye was slightly loosened, which helped with the vertical positioning of the treatment zone.
If ETM is the new norm of ortho-k fitting, we are all in.
REFERENCES
1. Bullimore MA, Johnson LA. Overnight orthokeratology. Cont Lens Anterior Eye. 2020 Aug;43:322-332.
2. González-Pérez J, Sánchez-García A, Parafita MA. Epithelial and stromal thickness profile and lens decentration in myopic orthokeratology. J Optom. 2023 Oct 28;17:100485.
3. Abtahi MA, Beheshtnejad AH, Latifi G, et al. Corneal Epithelial Thickness Mapping: A Major Review. J Ophthalmol. 2024 Jan 2;2024:6674747.
