When fitting soft contact lenses, the initial evaluation seems relatively straightforward; this is due to the flexibility and forgiving nature of modern soft lenses that generally fit a wide range of corneal profiles and that provide adequate limbal coverage, movement on blink, and comfort.

However, when critically analyzing the position of a soft lens on eye and the relative position of the optics within the lens compared to the underlying cornea, pupil, and visual axis, the task becomes more difficult. After a cursory glance with the slit lamp, the lens may appear centered; however, careful analysis may reveal subtle differences in lens centration nasal versus temporal and/or superior versus inferior. When a soft lens decenters along the horizontal meridian, it is commonly in the temporal direction (Ramdass et al, 2018; Zheng et al, 2016). Additionally, as the decentration of a soft multifocal contact lens takes its optical center away from the visual axis, the visual quality and performance of the lens degrades (Ramdass et al, 2018; Zheng et al, 2016).

In one analysis of scleral shape, Ritzmann et al (2018) described the temporal sclera as steeper and lower relative to the nasal sclera, thereby contributing to the temporal decentration of lenses that fit over the sclera. The authors additionally noted that this effect became greater the farther away from the cornea and the farther out onto the sclera that the lens extends.

The Connection

But, how does this relate to soft contact lens fitting? The answer: 1) The farther that a soft lens extends beyond the limbus, the more that it has a chance to interact with the asymmetric sclera and to potentially decenter more in the temporal direction; and 2) The shallower the lens’ sagittal depth is in relation to the sagittal height of the eye, the greater the chance that the lens will additionally decenter temporally and superiorly.

Using Sagittal Depth

Until recently, the sagittal depths of lenses were not widely known. Van der Worp et al (2021) described the variation in sagittal depth values of commercially available soft lenses. They noted that by knowing these sag values and the on-eye performance of the lenses, practitioners are better able to align with the ocular surface and provide patients with the necessary centration for optimal visual performance.

Significant amounts of lateral decentration can indicate that a lens has an inadequate sagittal depth (fitting too loose); therefore, the lens will need to be deepened to provide better centration (Figure 1). Using the sagittal height charts provided by van der Worp et al, practitioners are better able to find a lens that provides better centration and better visual performance. CLS

For references, please visit www.clspectrum.com/references and click on document #312.