As scleral contact lenses continue to gain in popularity for both irregular and regular corneas, the demand for multifocal optics in this modality is on the rise. The combination of multifocal scleral lens benefits can entice patients to invest in a lens that corrects their refractive error, provides great comfort, and now decreases their dependency on reading glasses.
The process of fitting a scleral lens can be complex, and adding multifocal optics on top of it may be enough to push some practitioners away from attempting these fittings. Thankfully, there are some simple and straight-forward techniques that we can use to optimize visual outcomes with scleral multifocal lenses.
Specific Corneal Vaults
When fitting scleral lenses, manufacturers have a recommended vault range for their designs, which maintains a maximum vault over the corneal apex. These recommendations help maintain appropriate oxygenation of the cornea and limit debris buildup in the post-lens tear layer. During a multifocal scleral lens fitting, the distance from the cornea to the posterior lens surface needs to be even more exact, as the scleral lens optics are designed to work with a specific range of corneal clearances to optimize the visual performance of the aspheric or concentric optics.
Each multifocal scleral design will require a slightly different vault depth, so be sure to consult with the laboratory. If a lens is fit with too much vault, the line of sight may not be able to take full advantage of what the multifocal optics can provide; too little vault could compromise the corneal surface after lens settling. Utilizing an anterior segment optical coherence tomographer and allowing time for the lens to settle will streamline this important fitting step.
Centering the Optics
Much like soft multifocal contact lens fittings, centering the optics of the multifocal scleral lens with a patient’s line of sight is important. The combination of gravity and the shape of the ocular surface may push the lens to an inferior-temporal placement, causing patients to look through the midperiphery of the lens optics.
Consider adding toric lens haptics or decreasing the lens diameter to encourage the lens to center as much as possible. Decreasing the corneal vault to the lower end of the recommended range may also improve lens centration. Lastly, topography over the lens surface while on eye can help measure the distance and direction of the misalignment between the optics of the lens and a patient’s line of sight. While a perfectly centered contact lens is not always achievable, this information can help with adjusting zone sizes or powers to attain the best optics possible.
Power Determination Tips
Determining the power of any multifocal lens can be difficult, and strategies are similar in most aspheric multifocal lens designs. When working with a multifocal scleral lens, patience is the first and most important step. Because every lens takes about a week to be delivered, we want to make sure that any power adjustments are accurate and are not due to a lack of adaptation.
Keep in mind that most patients will appreciate the contrast provided by a small amount of extra minus in the over-refraction, but that doesn’t mean it should be prescribed in the lens. In fact, patients may accept plus at distance if given time to adapt to their lenses, especially in the nondominant eye. If needed, add minus in small steps with loose lenses, and consider adding it to the dominant eye only. CLS