Validity of Bowman layer transplantation for keratoconus: visual performance at 5–7 years

Advanced keratoconus (KC) has historically been treated by penetrating keratoplasty (PK) or deep anterior lamellar keratoplasty (DALK) (Parker et al. 2015). As these patients may be ineligible for UV-cross-linking or intracorneal ring segments (ICRS), we recently introduced isolated Bowman layer (BL) transplantation as an alternative treatment option, to redress and stabilize the corneal curvature to (again) allow normal daily contact lens wear, potentially postponing PK or DALK (van Dijk et al. 2014). We previously reported on technical feasibility and initial outcomes, documenting a corneal flattening of approximately 8 dioptres (D) within the first postoperative month and stabilization up to 1–2 years (van Dijk et al. 2015). For BL transplantation to attain widespread acceptance, it may be important to determine its long-term validity, that is, to evaluate if daily visual performance is stable in time. We therefore evaluated the midterm best-corrected visual acuity with contact lenses (BCLVA) for our cohort of 20 BL eyes that reached 5–7 years of follow-up. These 20 eyes (17 patients; eight men/ nine women; mean age 31 (±12) years) underwent BL transplantation for progressive KC stages III to IV according to the Amsler–Krumeich criteria (progression was defined as ≥1D increase in simulated keratometry values and/or ≥2D increase in maximum keratometry (Kmax) during the year prior to surgery). All eyes presented with acceptable BCLVA – but variable degrees of tolerance – and were considered ineligible for UV-cross-linking or ICRS implantation. Therefore, halting progression and reducing corneal steepness to allow continued daily contact lens wear and preserve the present BCLVA was considered the main treatment objective. All patients signed an IRB-approved informed consent prior to surgery; the study was conducted according to the Declaration of Helsinki. Of the 20 eyes that underwent successful BL transplantation, two were lost to follow-up and one underwent routine cataract surgery (unrelated to BL transplantation) at 3 years. Hence, ≥5 year BCLVA data were available for 17 eyes. 16/17 (94%) eyes were fitted with a scleral lens and 1/17 (6%) eyes with a hybrid contact lens (Visser et al. 2007). After surgery, the lenses were well tolerated allowing full daily wear. Mean BCLVA did not change from preoperative up to the latest follow-up time-point (p > 0.07). At 5–7 years postoperatively, 14/17 (82%) of eyes had a BCLVA of ≥20/50 (≥0.4), 10/17 (59%) had ≥20/40 (≥0.5) and (2/17) (12%) had ≥20/25 (≥0.8); approximately equal to those preoperatively (Figure 1). Mean Kmax showed a topographic flattening from 77.2 (±−5.8) D preoperatively to 69.5 (±5.3) D (n = 16) at 5–7 years postoperatively (p < 0.001). Mean Kmax initially flattened within the first postoperative month (p < 0.001) and stabilized thereafter (p = 0.87). Keratometry readings showed an ongoing increase in two patients: one with a preoperative thinnest point pachymetry of 236 μm and the other with a self-reported tendency towards continued eye rubbing. Three other eyes of two patients with a history of (severe) eye rubbing and atopy developed an acute corneal hydrops at 4.5, 6 and 6.5 years postoperatively despite no evidence of ongoing steepening or thinning. No postoperative complications were observed in the other cases. Our report shows that BL transplantation may allow for preservation and/or recovery of the preoperative BCLVA in patients with advanced KC. Most often, these patients are satisfied with the BCLVA, but the progression of ectasia would cause relative contact lens intolerance, which results in a dramatic drop in functional visual acuity (because the spectacle-corrected visual acuity is often below 20/200 (0.1)). So far, such eyes would be managed with either PK or DALK, which may both impose a relatively high postoperative follow-up burden and entail the risk of significant complications. As BL transplantation induces significant and durable corneal flattening, it may preserve or restore comfortable contact lens wear, and therefore normal daily visual performance.