HOW TO FIT SOFT CONTACT LENSES USING SAGITTAL HEIGHT

Introduction

The dropout rate in soft contact lens wear remains a persistent challenge. It is now clear that the one-size-fits-all approach does not work for every eye, and patients with ocular parameters outside the average range have limited soft lens options available. Fitting soft contact lenses based on ocular sagittal height (OC-SAG) has emerged as an alternative strategy to achieve better lens alignment and improved outcomes. However, there is little information regarding the ideal relationship between the sagittal depth of the contact lens (CL-SAG) and the OC-SAG, which is referred to as δ-sag.

Shifting the Paradigm in Soft Contact Lens Fitting

In the Department of Optics at the University of Granada, Razvan Ghinea and I jointly lead research activities focused on soft contact lens fitting based on sagittal height. In one of our recent studies,¹ we evaluated eight pairs of daily disposable soft contact lenses from different manufacturers, all with known CL-SAG values.²

The study included 30 subjects who were tested with each of the eight lens pairs. Fifteen minutes after application, the typical sequence of eye movements was recorded to assess lens behavior. These videos were later analyzed in two ways: (a) Objectively, using digital image processing software (ImageJ) to measure centration and movement speed following the push-up test and (b) Subjectively, by two experienced evaluators who assessed lens centration and movement. They followed traditional clinical criteria, using a numerical rating scale (1 to 5) in which 3 represented an ideal fit, values < 3 indicated decentration or limited movement, and values > 3 indicated decentration or excessive movement.

The results showed that for most eyes, the δ-sag values ranged between 200µm and 600µm. Interestingly, not all δ-sag values were positive in about 12% of cases, the lenses appeared flatter than the flat meridian of the cornea. Comfort at 15 minutes was generally good across all lenses, although it would be valuable to assess this factor after longer periods of wear.

Correlation analyses and regression models examining the relationship between δ-sag and both objective and subjective evaluations indicated that δ-sag is an important parameter influencing fitting outcomes. A δ-sag range between 120µm and 280µm may result in an optimal fit according to the regression model derived from subjective assessment data (Figure 1), which is in line with previous findings.³

Figure 1. Subjective lens assessment results from two independent expert evaluators by δ-sag groups, including all eyes and contact lenses tested in the study.

Conclusions and Future Directions

The results suggest that δ-sag could serve as a key reference parameter for fitting soft contact lenses, though it should not be the only factor considered. The extensive data collected in this study revealed significant variability. Neither objective nor subjective evaluations of lens centration and movement consistently demonstrated a clear pattern of lens behavior relative to δ-sag across all cases.

This raises the question of whether the traditional methodology used to assess soft lens fitting should be reconsidered. Further research is needed to identify better markers for evaluating fit. What might these markers be? Patient-reported symptoms? Objective, quantifiable changes in the ocular surface or tear film quality following lens wear? Or perhaps a combination of these factors?

Future studies will help provide answers. What is certain, however, is that not all eyes are the same, and many avenues remain to be explored to improve soft contact lens fitting.

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