I recently sat in on a heated debate between colleagues arguing over whether anterior segment optical coherence tomography (AS-OCT) or profilometry (scleral shape topography) provided greater value during scleral lens fitting. It was difficult to declare ultimate superiority of either type of technology.

Failure to Launch? Profilometry

Most patients exhibit rotationally asymmetric scleras and would benefit from back-surface landing zone customizations beyond traditional toric designs (DeNaeyer et al, 2017). The traditional fitting process, which often starts with a spherical diagnostic scleral lens, is entirely reliant on practitioners relaying accurate findings to manufacturers.

The road to finalizing an adequate scleral lens is inefficient and can be challenging, especially if there are conjunctival obstacles such as blebs or other scleral shape asymmetries. Directly transmitting accurate scleral shape information for lens fabrication can greatly decrease chair time; however, limitations do exist.

Patients who have photophobia, deep-set orbits, small palpebral apertures, or recent scleral lens wear may display unreliable or incomplete data sets. Furthermore, scleral topographers do not consider dynamic conditions such as eyelid interactions.

Rocky Road? AS-OCT

Anterior chamber height measurements of various chord diameters from AS-OCT can refine initial scleral lens sagittal depth considerations. Based on clinical experience, adding the desired pre-settling tear reservoir thickness to the anterior chamber height should provide a decent starting point if the chord diameter and scleral lens overall diameter are similar.

Careful biomicroscopy is mandatory when fitting scleral lenses, but minute findings can evade even the most astute clinicians. AS-OCT can clarify post-settling areas of concern. Lens clearances of 50 microns or less are difficult to observe behind the slit lamp and can be confused with lens touch (Figure 1). Lens awareness can also be difficult to solve (Figure 2). AS-OCT over uncomfortable areas in both primary and extreme gaze can identify whether edge lift, impingement, or poor lens design is to blame (Figure 3).

When a lens does not perform as expected, I find myself turning to the AS-OCT rather than revisiting profilometry.

Symbiosis at Its Finest

I cannot choose one over the other. Profilometry can take you to a near-final lens, while AS-OCT can help troubleshoot unexpected obstacles. Technology can help greatly ease the scleral fitting process. CLS

For references, please visit www.clspectrum.com/references and click on document #315.