Despite advances in eye care, the fundamental technique of subjective refraction in practice today is largely unchanged from the early 20th-century origins.1 Scleral lenses (SLs) are frequently prescribed for patients who have irregular astigmatism, most frequently keratoconus.2 The post-lens fluid reservoir is beneficial to enhance visual potential. Obtaining the precise refractive power is a critical component of SL fitting.
A study evaluated refraction, both with and without SLs, in individuals who had primary or secondary corneal irregularities.3 It specifically examined whether refraction and over-refraction values, along with the final visual acuity obtained using a semi-automatic refraction system, were comparable to results from conventional methods performed without SLs and over-refraction with SLs.
Variability in subjective refraction may be due to practitioner experience. In most conventional phoropters and diagnostic lens sets, adjustments are typically limited to 0.25 D increments.4 Recent technological advancements allow for finer and continuous adjustments in sphere and cylinder powers through electro-optical innovations guided by algorithms in modern semiautomated refractive systems.5
Automatic and semiautomatic phoropters streamline the refractive process to improve the accuracy of visual correction, especially in optimizing scleral lens fittings. By simplifying and accelerating refraction, these methods enable practitioners to focus on the SL fitting.
SL wear has unique factors, including midday fogging, variability in tear film reservoir thickness, and potential lens decentration, which can affect measurement accuracy, unlike customary refraction performed on healthy eyes without contact lenses.
Nineteen eyes from 10 subjects who have irregular corneas underwent non-cycloplegic refraction using 2 different methods. The first method was conventional refraction usingretinoscopy, followed by standard subjective refraction to determine the maximum visual acuity with the most positive prescription. The second method used an algorithm-assisted technique, starting with a Hartmann–Shack wavefront aberrometer, followed by refinement using a semiautomatic, algorithm-based phoropter.
Refraction measurements were performed with both techniques, without and with SLs. Primary outcomes included spherical equivalent (M), astigmatic components (J0 and J45), and monocular high and low-contrast visual acuity (HCVA and LCVA).
The algorithm-based refraction method yielded a more positive spherical equivalent than the conventional method refraction, while both methods demonstrated comparable HCVA and LCVA. These findings suggest that algorithm-based refraction may represent a viable alternative for over-refraction in patients with irregular corneas fitted with SLs.
References
1. Starynkevitch H, Marin G, Meslin D. Subjective refraction: a new vectorial method for determining the cylinder (1/3). Int Rev Ophthal Opt. 2020;1-8. optiqueduvillard.ch/images/blog/pdf/subjective_refraction_a_new_vectorial_method_for_determining_the_cylinder_part_1.pdf
2. Barnett M, Courey C, Fadel D, et al. CLEAR - Scleral lenses. Cont Lens Anterior Eye. 2021 Apr;44(2):270-288. doi: 10.1016/j.clae.2021.02.001
3. Alves-de-Carvalho RS, Macedo-de-Araújo RJ, González-Méijome JM. Optimizing scleral lens prescriptions: a comparison of algorithmic and conventional refraction and over-refraction in irregular corneas. Cont Lens Anterior Eye. 2025 Aug 10:102485. doi: 10.1016/j.clae.2025.102485
4. Marin G, Meslin D. Refraction: patients are sensitive to increments smaller than a Quarter Diopter! Int Rev Ophthal Opt. 2020;1-4. optiqueduvillard.ch/images/blog/pdf/refraction_patients_are_sensitive_to_increments_smaller_than_a_quarter_diopter.pdf
5. Longo A, Meslin D. A new approach to subjective refraction. Int Rev Ophthal Opt. 2020;1-5. https://www.essilorinstrumentsusa.com/wp-content/uploads/2021/05/General-Overview-a_new_approachto_subjective_refraction.pdf
This editorial content was supported via unrestricted sponsorship.