Innovations in the design of rigid corneal lenses and scleral lenses have delayed the use of or eliminated the need for keratoplasty.
Reviewed by Dr Deborah S. Jacobs.
Patients with keratoconus can generally undergo a successful corneal transplant surgery but nevertheless be unsatisfied with the outcomes because of high astigmatism. “The improvement in visual function does not correlate with the postoperative acuity in the grafted eye. The improvement … is inversely associated with visual acuity in the better-seeing eye (i.e., the good eye rules when the bad eye undergoes surgery),” said Dr Deborah Jacobs, associate professor of ophthalmology, Harvard Medical School, Boston, Massachusetts, United States.
In addition, despite good visual outcomes following penetrating keratoplasty, the vision-related quality of life is impaired in patients who have undergone bilateral procedures with resulting good vision in the better eye. Dr Jacobs theorised that the patients are dissatisfied because they are comparing the outcomes with the eye that is less affected or they anticipated vision at the same level that they achieved with rigid gas-permeable contact lenses.
“The truth is that the rate of astigmatism is high, in that it averages 4 D, and up to 40% of patients are contact lens-dependent,” she said. “In addition, performing Descemet anterior lamellar keratoplasty is not advantageous regarding achieving decreases in postoperative astigmatism despite high expectations. Keratoplasty should only rarely be performed.”
In her practice, Dr Jacobs refers all patients with keratoconus who are not satisfied with spectacle or soft lens vision for scleral lenses. She explained that once rigid gas-permeable scleral lenses were developed in the 1990s, she did not perform keratoplasty without first giving the patient the opportunity to have a trial with scleral lenses with innovator Dr Perry Rosenthal, in Boston, MA.
However, Dr Jacobs noted that her effort to enlighten surgeons about the benefits of scleral lenses was an uphill battle, with surgeons maintaining that the lenses were a “boutique technology” (i.e., expensive, labour-intensive and not readily available). Surgeons also argued that high K values would prevent fitting of the lenses, or that the presence of an axial scar would limit vision in a scleral lens. Patients went along with the idea of surgery, expecting that a transplant meant a cure.
Meanwhile, Dr Jacobs and her colleagues in Boston, as well as groups at Mayo Clinic in Rochester, Minnesota, US, and University of California Davis, US, were achieving excellent outcomes in visual function and visual acuity in patients with keratoconus fitted with scleral lenses. Because of this work, interest in these lenses increased markedly.
“The technology is no longer considered a boutique technology; many lenses are now widely commercially available due to industry involvement, trial sets are widely available, custom options are available for eyes requiring a larger diameter and a higher vault, and clinical education is available,” she said. Dr Jacobs added that there are now optometrists who study for an extra year in their cornea and contact lens residencies and are trained in scleral lens fitting.
Ophthalmologists ultimately realised that no cornea is too steep, and the outcomes are better than those achieved with keratoplasty.1-4 As Dr Jacobs noted, researchers in Michigan recently found that the use of scleral lenses or gas-permeable corneal lenses reduced the risk of keratoplasty by 80% and that the need for keratoplasty was not associated with the maximum K.5 A high K value does not mean that rehabilitation with contact lenses is impossible—which had been true before the introduction of scleral lenses.
Another previously held belief was that the presence of an axial scar required keratoplasty. Dr Jacobs does not believe this to be true. “Good vision can be achieved despite an axial opacity. Even with a scar, it is worthwhile to assess the patient in a scleral lens before choosing surgery.”
Dr Jacobs provided an example of a patient aged 35 years, with keratoconus with atopy, who achieved 20/25 vision in a scleral lens despite a dense vascularised inferior scar extending over much of the pupillary zone; the vision, vascularisation and scar have been stable for more than 10 years of scleral lens wear. The patient is at high risk for rejection and failure with keratoplasty because of the atopy and stromal vessels.
An important consideration is that reduced vision in an eye with a scar may be optical in nature and related to irregular cylinder, not the opacity. Dr Jacobs likes to remind surgeons that the entire cornea is involved in image formation and the presence of opacity over part of the pupil does not disrupt the vision.
Another advantage of scleral lenses is that they facilitate remodelling of the cornea over time when previously worn corneal lenses have hurt the cornea. Dr Jacobs described a patient for whom a keratoplasty seemed inevitable; however, scleral lenses allowed for remodelling to take place after the patient had worn poorly fitting corneal lenses for decades.
Although corneal cross-linking is commonly credited with reducing the rate of penetrating keratoplasties performed, the use of hybrid lenses, rigid corneal lenses and scleral lenses have delayed the use of or eliminated the need for the graft procedure.
Dr Jacobs pointed to the innovations in scleral lens design and manufacturing related to moulding, image-guided fitting of the lenses and surface profiling. In addition, it is possible to add wave-front optics to the lenses to improve the best-corrected vision and provide super vision in healthy eyes. “Given all of these advancements, one should not perform keratoplasty for keratoconus without first performing a scleral lens trial,” Dr Jacobs concluded.