Comparison with shallow implants
“If you look at changes in refraction, patients with the shallow implants had an average shift of +0.45 D between 3 and 6 months after surgery, whereas the group with the deeper implants had no change in their spherical equivalent during the first 12 months for which we collected data,” Dr. Hoopes said. “Their prescription was very stable with deeper implantation.”
Distance uncorrected visual acuity was good in both groups, which is not surprising given the implant is labeled for individuals who have good uncorrected distance vision, he noted. The results were strikingly different for uncorrected near vision.
Before implantation, only 5% of patients were 20/25 or better and 40% were 20/40 or better. At 3 months after surgery, 34% of patients with shallow implants were 20/25 or better and 81% were 20/40 or better versus 45% and 90% of patients with deep implants. Fully 81% of shallow-pocket patients were J5 or better compared with 90% for deep-pocket patients.
By 6 months, the gap had opened to 22% versus 42% for 20/25 and 60% versus 84% for 20/40. Reflecting the shift in spherical equivalent, only 60% of shallow-pocket patients were J5 or better compared with 84% of deep-pocket patients.
At 12 months, the gap was 27% versus 59% for 20/25 and 77% versus 89% for 20/40.
“We saw a clear difference in visual performance at the greater implantation depth,” Dr. Hoopes said.
“The theory is that there are fewer keratocytes the deeper you go in the cornea, less cellular matrix to disrupt with surgery,” he said. “So you have less wound healing and less reactivity to the inlay within the cornea. The more shallow the implant, the more keratocytes and the greater the opportunity for inflammation, wound-healing complications, and other physiologic changes that can affect clinical outcomes.”