While fitting corneal GPs is more time-consuming compared to most soft lenses, the rewards can be great for patients. Although some of us may fit fewer corneal designs compared to sclerals these days, there are still cases for which corneal lenses are the best option. Here are some helpful strategies when fitting these lenses.
1) Start with the Right Design
Using the correct lens design is key. While keratometry values are useful, they aren’t as valuable as corneal topography data is. For example, knowing the amount of corneal toricity and elevation differences will help you choose a spherical or toric base curve. If the elevation difference between meridians along an 8mm chord is more than about 60 microns (Figure 1), a toric base curve is likely needed (in orthokeratology lenses, as little as 30 microns could require a toric periphery). Topography also shows whether the astigmatism is regular or irregular, which also impacts lens design selection.
2) Use Anesthetic
For corneal GP lenses, I typically use an anesthetic drop to make the experience more comfortable for patients. This also reduces reflex tearing, which makes viewing the fluorescein pattern much easier.
If you are concerned about giving patients an unrealistic experience of the lens sensation, remember that corneal GP lenses generally start to feel more comfortable after the first 20 minutes or so; by then, the anesthetic drop is starting to wear off.
3) Fit Empirically If You Can
When possible, I prefer to order lenses empirically based on the refraction and keratometry readings or based on topography data. This way, the first lens that patients have on their eye is close to the correct fit, and vision is optimal from the start (remember that excellent vision is a great benefit of wearing GP lenses).
I do like to apply an ortho-k lens to children’s eyes before ordering their lenses to confirm that they will be able to tolerate lens wear, though kids are often better corneal GP patients than adults are! I also don’t empirically order contact lenses for irregular corneas; I prefer to trial fit these patients.
4) Careful Edge Inspection
Most of the sensation from a corneal GP design is from the lid/lens edge interaction. A carefully formed and polished edge is critical to GP lens success. While time-consuming, checking the lens edges with the slit lamp prior to dispensing can prevent issues with lens discomfort. Problems with lens edges are rare, but I do occasionally need to polish edges prior to dispensing.
When in Doubt
I hope that these tips will help to get you off to a great start with your corneal GP lens fits. As always, your GP lab consultants are great resources for helping you choose the best lenses for your patients and for providing tips for GP fitting success. CLS