Malapposition of graft-host interface after penetrating keratoplasty (PK) and deep anterior lamellar keratoplasty (DALK): an optical coherence tomography study

BACKGROUD: Previous studies of internal graft-host malappositions have not dealt with the precise ways in which each malapposition affected post-penetrating keratoplasty (post-PK) visual outcomes. In this study, we reviewed our post-PK and post-deep anterior lamellar keratoplasty (post-DALK) keratoconic patients and used anterior segment optical coherence tomography (AS-OCT) to evaluate the associations between graft-host interface (GHI) characteristics and visual outcomes. METHODS: Novel GHI metrics included: mean graft-host touch (GHT), total prevalence of malapposition proportion (Pm), frequency of apposition (F), size of malapposition (Sm), junctional graft thickness (Tg), junctional host thickness (Th) and the absolute value of difference between Tg and Th (|Tg-Th|). We connected the external and internal junction points of GHI (GHT) and drew a straight line through the central point, perpendicular to both sides of the cornea. Tg and Th were the thicknesses at cross-points 1 mm away from the meeting point on the external side of the graft and host, respectively. Linear regression analysis was used to describe associations between GHI metrics and postsurgical visual outcomes [logarithm of minimum angle of resolution best-corrected visual acuity (logMAR BCVA), spherical equivalent diopter (SE), diopter of spherical power (DS), diopter of cylindrical power (DC) and keratometric astigmatism (Astig value)]. RESULTS: We enrolled 22 post-PK and 23 post-DALK keratoconic patients. Compared with the regular-apposition results, GHT was decreased in step and gape patterns, and increased in hill and tag patterns. SE increased averagely by 6.851, 5.428 and 5.164 diopter per 1% increase in: F (step) [β = 6.851; 95% Confidence interval (CI) = 2.975–10.727; P = 0.001]; F (graft step) [β = 5.428; 95% CI = 1.685–9.171; P = 0.005]; and Pm [β = 5.164; 95%CI = 0.913–9.146; P = 0.018], respectively. SE increased averagely by 0.31 diopter per 10-μm increment in |Tg-Th| [β = 0.031; 95% CI = 0.009–0.054; P = 0.007]. LogMAR BCVA increased (on average) by 0.01 per 10-μm increment in both GHT [β = 0.001; 95% CI = 0–0.002; P = 0.030]. and Tg [β = 0.001; 95% CI = 0.001–0.002; P = 0.001]. Astig value increased on average by 0.17 diopter per 10-μm increment in Sm [β = 0.017; 95% CI = 0–0.033; P = 0.047]. CONCLUSION: This investigation of GHI characteristics suggests explanations for varied ametropia in keratoconic eyes and has potential significance as a reference for promoting pre-surgical planning and technology for corneal transplantation.