Corneal Stromal Regeneration: A Review of Human Clinical Studies in Keratoconus Treatment

Abstract

The use of advanced therapies with stem cells to reconstruct the complex tissue of corneal stroma has gained interest in recent years. Besides, collagen-based scaffolds bioengineering has been offered as another alternative over the last decade. The outcomes of the first clinical experience with stem cells therapy on corneal stroma regeneration in patients with advanced keratoconus were recently reported. Patients were distributed into three experimental groups: Group 1 (G-1) patients underwent implantation of autologous adipose-derived adult stem cells (ADASCs) alone, Group 2 (G-2) received a 120 μm decellularized donor corneal stromal laminas, and Group 3 (G-3) received a 120 μm recellularized donor laminas with ADASCs. A follow up of 36 months of clinical data, and 12 months of confocal microscopy study was performed, the authors found significant clinical improvement in almost all studied mean values of primary and secondary outcomes. Corneal confocal microscopy demonstrated an increase in cell density in the host stroma, as well as in the implanted tissue. Using different approaches, allogenic small incision lenticule extraction (SMILE) implantation was applied in cases with advanced keratoconus. Some authors reported the implantation of SMILE intrastromal lenticules combined with accelerated collagen cross-linking. Others performed intrastromal implantation of negative meniscus-shaped corneal stroma lenticules. Others have compared the outcomes of penetrating keratoplasty (PKP) vs. small-incision Intralase femtosecond (IFS) intracorneal concave lenticule implantation (SFII). Femtosecond laser-assisted small incision sutureless intrasotromal lamellar keratoplasty (SILK) has been also investigated. The published evidence shows that the implantation of autologous ADASCs, decellularized or recellularized human corneal stroma, allogenic SMILE lenticules corneal inlay, and recombinant cross-linked collagen have shown initially to be potentially effective for the treatment of advanced keratoconus. In light of the present evidence available, it can be said that the era of corneal stromal regeneration therapy has been already started.

Keywords: autologous adipose-derived adult stem cells; corneal bioengineering; corneal stem cell therapy; corneal surgery; cross-linked collagen; keratoconus; regenerative medicine; stem cells.

Figure 1

Cornea Visante optical coherence tomography images and pachymetric maps. (A) Preoperative OCT in case 1, G-1. (B) OCT at 12 months post-op of the same patient, notice the transparency of the cornea. (C) OCT at 36 months post-op with case 2, G-1. Observe the transparency of the cornea, the (yellow arrows) demonstrate the limit of the flap. (D) Preoperative OCT in case 7, G-2, Notice the highly reflective area in the corneal stroma (red arrow). (E,F) OCT at 12 months and 36 postoperative in case 7. The improvement of the reflective band of neo-collagen in the periphery of the implanted lamina (yellow arrows) can be seen. The reflectance of the neo-collagen band (red arrow) is higher at 12 months in the center of the implanted lamina. (G) Preoperative OCT in case 13, G-3. The reflective paracentral scars can be noticed (yellow arrow). (H,I) OCT at 12 and 36 months post-op. The high reflectance of the neo-collagen band (red arrow) can be seen more evident at 36 months with this patient in the center of the lamina. Notice the improvement of the preoperative paracentral scars at 36 months post-op (yellow arrows). (J) OCT in Case9, G-2, and (K) in Case 12, G-3 at 36 months post-op. (yellow arrows) shows the limits of the laminas.

Figure 2

Biomicroscopic changes between the preoperative up to 36 months post-operative. (A) G-1, case 4, OS, shows the transparency of the cornea in the preoperative. (B) G-1, case 4, shows the transparency of the cornea. The presence of a peripheral surgical scar (red arrow) at 1month post-op can be noticed. (C) G-1, case 4, shows the stability of the peripheral scaring (red arrow) in the cornea at 12 months post-op. (D) G-1, case 4, shows the transparency of the cornea at 36 months post-op. (E) G-2, case 9, OD, shows the presence of a slight paracentral scar( red arrows) at the pre-operative. (F) G-2, case 9, 12 months post-op, observe the improvement in the transparency of the implanted lamina, (red arrow) represent the periphery of the lamina. (G) G-2, case 9, 36 months post-op, notice the marked improvement in the transparency of the lamina, the periphery of the sheet becomes not very marked (red arrow). (H) G-3, case 12, OD, shows the transparency of the cornea in the preoperative. (I) G-3, case 12, 12 months post-op. The (red arrow) indicates the implanted recellularized lamina. (J) G-3, case 12, 36 months post-op. The (red arrow) indicates the periphery of the recellularized lamina. Notice the improvement of the transparency of the implanted tissue.

Figure 3

Shows statistical mean results after 3 years follow-up in G-1, G-2, and G-3, respectively (A) Shows an amelioration in CDVA (corrected distance visual acuity) (decimal), mean values in the pre-operatives were (0.40, 0.22, 0.21), at 12 months post-operatives mean values were (0.60, 0.42, 041) and (0.58, 0.40, 0.40) at 36 months post-operative. Desviation Standard = 0.151. (B) Shows an upgraded in CLDVA (decimal equivalent to logMar scale) from the pre-operative (0.61, 0.39, 0.52) until reach a maximum mean values at 36 months post-operative (0.84, 0.62, 0.75). Desviation Standard = 0.180. (C) Presents Visante CCT (central corneal thickness) (μm) mean values in the pre-operative (410, 454, 487) (μm), at 12 months post-operative, these values reached a maximum average (469, 513, 546) (μm), then at 36 months post-operative, they were established with the following average values (440, 484, 517) (μm). Desviation Standard = 62.940. (D) Presents the Scheimpflug corneal topography thinnest point (μm) mean values in the preop (385, 435, 449) (μm), there were an increase in the topographic mean values till 12 months post-operative (433, 484, 498) (μm), than at 36 months post-operative, a small decrease was obtained with this mean values (416, 466, 480) (μm). Desviation Standard = 67.966. (E) Observe the amelioration in RMS HOA (high order aberration in μm) in mean values at the pre-operative values (15.01, 10.11, 12.23), at 36 months post-operative (13.15, 8.25, 10.37). Desviation Standard = 4.530. (F) Observe Kmax , the pre-operative mean values (68, 68, 66), there was a mean values of 2 diopters more flatter at 12 months post-operative (66, 66, 64) regarding the preoperative, followed by another mean value of 1 diopter of flattening till 36 months post-operative (65, 65, 63). Desviation Standard = 8.250.

Figure 4

Corneal topography (Pentacam) comparison between preoperative, 12 and 36 months post-op. (A) Comparative paquimetric examinations (right side) among the preoperative (middle) and 12 months post-op (left side) in case 1, G-1. Observe the modest improvement of the corneal thickness (B) Preoperative (middle) and 12 months post-op (left side) sagittal curvature comparative exams (right side), in case 1, G-1. Notice the modest improvement in the keratometric parameters of the cornea. (C) Comparative paquimetric examinations (right side) among the preoperative (middle) and 12 months post-op (left side) in case 6, G-2. Observe the improvement of the corneal thickness. (D) Preoperative (middle) and 36 months post-op (left side) sagittal curvature comparative exam (right side), in case 6, G-2. Notice the improvement in the keratometric parameters of the cornea. (E) Sagittal curvature comparative exam (right side) among the preoperative (middle) and almost 3 years post-op (left side) in case 12, G-3. Enhancement of the keratometric parameters can be observed. (F) Comparison pachymetric exam (right side) among the preoperative (middle) and 3 years post-op (left side) in case 12, G-3. The markable enhancement of the paquimetric parameters can be noticed.

Figure 5

Corneal Aberrometry with case 5, G-2. (A,B) (Pentacam) Third-order aberration RMS 3rd order RMS (μm). Observe the improvement in mean values from the preoperative (10.356) (μm) till (7.924) (μm) at 36 months post-op. (C,D) (Pentacam) high order aberration RMS HOA RMS (μm). Notice the amelioration between the preoperative mean values (12.339) (μm) and 36 months post-op (8.451) (μm).

Figure 6

Confocal microscopy study with HRT3 RCM (Heidelberg). (A) Confocal microscopy of the anterior corneal stroma with case 1, G-1. Notice the few nuclear corneal cell density. (B) Nuclear cell density in the anterior stroma with case 1 at 12 months post-operative. Notice the increment of the cell density. (C) Acellular implanted lamina with case 5, G-2 at 1 month post-operative. (D) Recellularization of the anterior surface of the implanted decellularized lamina in the same case 5 at 12 months postoperative. (E) The posterior surface of the recellularized lamina with case 13, G-3 at 1 month after the operation: the presence of few ADASCs with similar morphology of keratocytes. (F) The posterior surface of the recellularized lamina with case 13 at 12 months after surgery: Observe the abundant number of stromal cells.