With range of keratoconus refractive options, is there role for PTK?

In eyes with keratoconus undergoing corneal crosslinking (CXL), topography-guided photorefractive keratectomy (TG-PRK) provides superior refractive and functional outcomes compared with transepithelial phototherapeutic keratectomy (TE-PTK).

Yet, there remains a role for PTK, said Simon P. Holland, MD, at the 2018 ASCRS Symposium.

He reported results from a retrospective study that found TE-PTK provided no useful improvement in astigmatism or vision, whereas significant gains were achieved after TG-PRK.

Dr. Holland noted, however, that TE-PTK had the advantage of limiting stromal ablation, which can be important considering that it may decrease the likelihood of keratoconus progression and recognizing that some eyes with keratoconus have very thin corneas.

“Our results provide a case for both techniques in the refractive management of keratoconus with CXL,” said Dr. Holland, private practice, Pacific Eye Laser Centre, Vancouver, BC, and clinical associate professor of ophthalmology and visual sciences, University of British Columbia, Vancouver.

Existing knowledge base

In a previous retrospective statistically case-matched cohort study that included 18 eyes, Dr. Holland and colleagues found statistically significant cylinder reduction using both TG-PRK (-2.55 D) and PTK (-0.91 D) with no statistically significant difference between groups.

Both groups also had statistically significant improvement in UDVA and CDVA, but TG-PRK was associated with a significantly greater mean gain in UDVA compared with PTK CXL, 7 vs 2 lines, respectively.

Larger series

To further compare the two techniques, Dr. Holland and colleagues undertook a retrospective study that included 31 eyes that had TE-PTK CXL and 305 eyes that had TG-PRK CXL. Both treatments were performed with the Amaris 1050 excimer laser (Schwind). The PTK removed 55 microns of epithelium. TG-PRK was performed using SmartSurfACE treatment, which was prepared with the SCHWIND custom ablation manager. Follow-up was to 1 year.

Dr. Holland reported that in the TE-PTK group, mean spherical equivalent was reduced from -2.19 D preoperatively to -1.72 D. With TG PRK, mean spherical equivalent was reduced from -2.79 D to -0.62 D. Mean astigmatism was reduced from 3.24 to 2.08 D after PTK and from 3.13 D to 1.57 D after TG-PRK.

The analyses of visual acuity outcomes showed that almost 61% of TG-PRK eyes achieved 20/40 UDVA compared with only 11.5% of eyes in the PTK group. CDVA was unchanged or improved in 78% of TG-PRK eyes compared with 58% of eyes in the PTK group.

Improvement of 2 or more lines of CDVA was achieved by 18% of TG-PRK eyes and 13% of PTK eyes, while 13% of PTK eyes and only 6% of TG-PRK eyes lost 2 or more lines of CDVA.