RGP Fitting in Extreme Keratoconus
This photo shows the left eye of a long-term patient of the Instituto de Olhos Dr. Saul Bastos. He has severe keratoconus OD and OS, and he came this year to be refit into a new pair of GP lenses. The patient is a cardiac surgeon who has worn contact lenses for more than 30 years. His keratoconus is severe in both eyes, with the right eye being considered advanced and the left eye extreme. We were able to refit the right eye with the first lens, but his left eye is always problematic. He also has flaccid palpebral tissues in his upper lids, which makes the evaluation extremely difficult.
The pictured corneal abrasions with fluorescein staining were caused by his last contact lens in his left eye, which had the following parameters: base curve (BC) 74mm x 48mm, overall diameter (OAD) 9.8mm, and optical zone diameter (OZD) 6.0mm. His visual acuity with this contact lens 20/40.
Figure 2 shows the sagittal curve map from corneal topography. Note how advanced the condition is.
It was not possible to fit a scleral lens in this case because the patient has a small palpebral fissure and because he has flaccid upper lid tissue. Figure 3 shows the Scheimpflug image from the left eye, which is not possible to obtain through slit lamp observation. Figure 4 shows the corneal thickness, indicating a more pronounced decrease in corneal thickness from the periphery to the center apex.
Extreme situations occasionally require extreme measures. We have tried to counsel this patient to undergo penetrating keratoplasty for more than five years. However, he states that he is satisfied with contact lens wear and with the 20/40 visual acuity.
After we examined the corneal abrasions, we instructed the patient to suspend contact lens wear for three days, and to instill Epitegel (Bausch + Lomb [B+L]) t.i.d., followed by a return to the office for a new fit. At his return visit, we observed no more fluorescein staining.
It is challenging to fit a case like this with contact lenses, but we have managed to design a specialty, extremely steep base curve that vaults the apex without touch and allows adequate tear flow. We redesigned his GP lens OS with the following parameters: BC 74mm x 50mm, OAD 10.4mm, OZD 6.5mm, power –31.25D.
We were able to fit the contact lens over the corneal apex. We steepened the secondary curve and increased the OAD and the central optical zone to increase the vault to avoid any contact with the corneal apex. Working with all of these variables together, we were able to design a lens that will provide a better fit and will also preserve comfort, the cornea’s physiological health, and optimize visual acuity.
Figures 5 and 6 show the new contact lens with an excessive amount of fluorescein. We plan to reduce the OAD to 10.2mm and flatten the peripheral curves in a subsequent contact lens that is being manufactured.
Dealing with Extreme Keratoconus
It is not easy to manage cases of extreme keratoconus in which scleral lenses are not an option and/or the patient is reluctant to undergo an invasive procedure such as a corneal transplant. There are patients who have severe keratoconus who can still benefit from corneal GP lenses. A successful keratoconus fit can help patients achieve great improvement in best-corrected vision as well as comfort and corneal physiological health.
It is also important to have a lab that is able to support high levels of customization when you need to adjust the contact lens parameter to achieve a reliable fit. Practitioners need to rely on an expert from their lab who also has knowledge of specialty lens fitting. In cases like this, both the practitioner and lab consultant must be able to converse with the same level of knowledge and experience. Digital imaging can also be helpful for consultancy1 in highly complex cases. Digital imaging is a healthy direction to go for a better practitioner-consultant relationship, especially when both are experienced.
- Bastos L. Digital Consulting for GP Lens Fitting. Contact Lens Spectrum. 2007 Nov. Available at http://www.clspectrum.com/issues/2007/november-2007/readers-forum . Accessed on Aug 28, 2017.
- Bastos L, Bittencourt M. Designing Lenses for Advanced Keratoconus. Contact Lens Spectrum. 2009 Jan. Available at http://www.clspectrum.com/issues/2009/january-2009/reader-and-industry-forum-(1) . Accessed on Aug 28, 2017.