Histopathological and immunohistochemical studies of lenticules after epikeratoplasty for keratoconus

Post-LASIK Ectasia Versus Keratoconus: An In Vivo Confocal Microscopy Study

PURPOSE

To examine and compare corneal cellular and subbasal nerve (SBN) characteristics in post-laser-assisted in situ keratomileusis ectasia (PLE) corneas, normal post-laser-assisted in situ keratomileusis corneas (PLC), keratoconus (KC) corneas, and normal virgin corneas (NC).

METHODS

In this cross-sectional comparative study, 18 PLE eyes of 11 patients, 18 PLC of 15 cases, 32 KC eyes of 32 patients, and 29 NC of 29 subjects were assessed using in vivo confocal microscopy. The density of the basal epithelial cell (BEC), anterior keratocyte, posterior keratocyte, and endothelial cell layers, as well as the characteristics of SBN fibers, was compared between the 4 groups.

RESULTS

The density of the BEC and anterior and posterior keratocyte layers was significantly lower in KC compared with NC (-650 ± 190, P = 0.013; -181 ± 39, P < 0.001; and -36 ± 11, P = 0.021, respectively). However, there was no significant difference between PLE and PLC regarding these parameters (all Ps ≥ 0.6). Mean SBN parameters, including central corneal nerve branch density, nerve fiber length, total branch density, and nerve fiber area, were significantly lower in KC compared with NC and in PLE compared with PLC (all Ps ≤ 0.021).

CONCLUSIONS

The pathophysiology of PLE seems to differ from KC. Apparent changes in the BEC and anterior and posterior keratocytes associated with KC were not observed in PLE. However, SBNs seem to be involved in both conditions.

Dynamic corneal biomechanics in different cell layers: in keratoconus and normal eyes

PURPOSE

This study aimed to determine the relationship between corneal cellular structures and biomechanical deformation parameters in keratoconic (KC) and healthy eyes.

METHODS

In this prospective comparative study, 29 eyes of 29 KC patients were age- and gender-matched with 28 eyes of 28 healthy individuals using frequency matching. Corneal parameters examined included the density of basal epithelial cells, anterior keratocytes, posterior keratocytes and endothelial cells as assessed by in vivo corneal confocal microscopy (HRT III-RCM, Heidelberg Engineering, www.heidelbergengineering.com). Additionally, the coefficient of variation of endothelial cell size (CV) and the percentage of hexagonal endothelial cells (HEX%) were measured by specular microscopy (Konan NSP-9900, Konan Medical, www.konanmedical.com). Further, biomechanical deformation parameters were derived from Corvis Scheimpflug Technology (Corvis ST, Oculus, www.oculus.de). All cellular and biomechanical deformation parameters in KC and normal groups were compared, and the relationship between cellular and biomechanical parameters calculated.

RESULTS

In the KC group, the highest concavity (HC) delta arc length and maximum delta arc length were associated with endothelial cell density (Beta = -0.39, p = 0.03 and Beta = -0.60, p ˂ 0.001, respectively). Furthermore, there was a significant association between HC deflection length and HEX% (Beta = -0.67, p = 0.001). In the normal group, HC delta arc length and HC deflection length were significantly associated with endothelial cell density (Beta = 0.46, p = 0.02; and Beta = -0.51, p = 0.01, respectively). HC time, HC deformation amplitude and applanation 1 delta arc length were associated with CV (Beta = 0.50, p = 0.01; Beta = 0.27, p = 0.009; and Beta = -0.57, p = 0.002, respectively). Applanation 1 and applanation 2 deformation amplitudes were associated with HEX% (Beta = -0.49, p = 0.005; and Beta = -0.46, p = 0.02).

CONCLUSIONS

Biomechanical deformation parameters were significantly correlated with endothelial cell properties in both KC and normal groups, thereby indicating the importance of the integrity of endothelial cells to the biomechanical properties of both KC and normal corneas.

Femtosecond Laser-Assisted Allogenic Lenticule Implantation for Corneal Ectasia After LASIK: A 3-Year In Vivo Confocal Microscopic Investigation

PURPOSE

To investigate morphological changes in the cornea and the implanted lenticule in patients with corneal ectasia after laser in situ keratomileusis (LASIK) and implantation using a lenticule from small incision lenticule extraction (SMILE).

METHODS

Eight eyes of 8 patients with ectasia after LASIK from 2015 to 2018 at the Eye and ENT Hospital of Fudan Unversity were analyzed. For recipient eyes, lenticules were transferred with a mean cryopreserved time of 20 ± 21 days extracted from SMILE donors to the exposed stromal bed after lifting the flaps and the flap was repositioned. Uncorrected and corrected distance visual acuity, manifest refraction, and corneal topography were performed. Patients were followed up for 3 years. Changes in lenticules and recipient corneas were analyzed using in vivo confocal microscopy.

RESULTS

Activated keratocytes in the anterior and posterior stroma were observed near the lenticule at the first 6 months. Elongated, deformed keratocyte nuclei were found in the implanted lenticules in postoperative year 1. The anterior and posterior interfaces showed an absence or decrease of keratocytes and the presence of small particles of varying brightness. Nerve fibers in the implanted lenticules were detected in one case. No obvious difference was detected between cryopreserved and fresh lenticules.

CONCLUSIONS

The preliminary findings suggest that recipient keratocytes repopulate the lenticules and the keratocytes in lenticules gradually return to their normal morphology. [J Refract Surg. 2020;36(11):714-722.].

Peripheral Cornea Crosslinking Before Deep Anterior Lamellar Keratoplasty

Since Cornea crosslinking (CXL) has been proven to halt progression and biomechanically stabilize keratoconus, we hypothesized that CXL of the corneal periphery 3 months prior to corneal transplantation can reduce the incidence of recurrent ectasia by strengthening the peripheral corneal tissue and causing apoptosis of diseased peripheral host keratocytes. Thus, the aim of this case-report was to propose a novel peripheral CXL technique prior to keratoplasty and evaluate its safety. A 22-year-old woman was admitted with advanced right keratoconus and corrected distance visual acuities of 20/30 in the right eye and 20/200 in the left eye with a manifest refraction of -3.00D/ -8.00D × 36° and -17.00D/ -11.50D × 90°, respectively. The proposed treatment involved crosslinking of peripheral corneal tissue (6.5-9.5mm), sparing the central cornea and limbus, three months prior to corneal transplantation as a means of biomechanically strengthening the peripheral cornea tissue. This procedure was feasible and safe with repopulation of the peripheral cornea with keratocytes, no significant endothelial cell loss and a routine postoperative course following CXL and DALK. This method might reduce or eliminate the need for repeat corneal transplantation in patients with recurrent ectasia. Further studies are needed to confirm the results.

Tissue-Derived Biological Particles Restore Cornea Properties in an Enzyme-Mediated Corneal Ectatic Model

Purpose: To investigate the impact of tissue derived biological particles on enzyme-mediated weakened corneas. Methods: Rabbit corneas were treated with enzymes to create an ex vivo ectatic model that simulated representative characteristics of keratoconus (KC). Porcine cornea, cartilage, and lymph node tissues were processed to remove most cellular components and cryomilled into microparticles. The KC corneas were cultured in medium containing the tissue-derived biological particles (TDP) overnight. The mechanical, thermal, ultrastructural changes, and gene expressions of corneal stromal cells were characterized to evaluate the effects of the TDP treatment. Results: The enzyme treatment significantly reduced corneal mechanics and thermal stability, and also disrupted the extracellular matrix ultrastructure. After culturing with TDP medium, the Young’s modulus of the modeled KC corneas increased by ~50%, comparable to normal cornea controls. Similarly, the thermal denaturation temperature of the corneas was restored. These findings also corresponded to a significant increase in collagen fibril density after TDP treatment. Furthermore, corneas cultured in TDP medium significantly downregulated expression of the pro-inflammatory gene Tnfα, and restored the expression of the key keratocyte markers Aldh, keratocan, and biglycan. Conclusions: Tissue-derived biological particles reinforce mechanical and thermal properties of corneal tissue in an ex vivo model of KC. Through this study, we demonstrate and characterize the previously unexplored impact of tissue-derived biological scaffolds on corneal biomechanics, thermal stability, and gene expression, presenting a potential new therapy for ocular disease.

Quantified histopathology of the keratoconic cornea

PURPOSE

This study systematically investigated and quantified histopathological changes in a series of keratoconic (Kc) corneas using a physiologically formulated fixative to not further distort the already distorted diseased corneas.

METHODS

Twelve surgically removed Kc corneal buttons were immediately preserved and processed for light and transmission electron microscopy using an established corneal protocol. Measurements were taken from the central cone and peripheral regions of the host button. The sample size examined ranged in length from 390 to 2608 μm centrally and 439 to 2242 μm peripherally.

RESULTS

The average corneal thickness was 437 μm centrally and 559 μm peripherally. Epithelial thickness varied centrally from 14 to 92 μm and peripherally from 30 to 91 μm. A marked thickening of the epithelial basement membrane was noted in 58% of corneas. Centrally, anterior limiting lamina (ALL) was thinned or lost over 60% of the area examined, whereas peripheral cornea was also affected but to a lesser extent. Histopathologically, posterior cornea remained undisturbed by the disease. Anteriorly in the stroma, an increased number of cells and tissue debris were encountered, and some of these cells were clearly not keratocytes.

CONCLUSIONS

It is concluded that Kc pathology, at least initially, has a distinct anterior focus involving the epithelium, ALL, and anterior stroma. The epithelium had lost its cellular uniformity and was compromised by the loss or damage to the ALL. The activity of the hitherto unreported recruited stromal cells may be to break down and remove ALL and anterior stromal lamellae, leading to the overall thinning that accompanies this disease.

Histopathological study of 49 cases of keratoconus

AIMS

Keratoconus is a bilateral and asymmetrical corneal ectasia. The pathophysiology of this disorder has yet to be fully elucidated. The purpose of our study was to document the prevalence of the most common morphological features of keratoconic corneas.

METHODS

A retrospective analysis of 49 cases diagnosed as keratoconus between 2001 and 2006 was undertaken. Histopathological reports were reviewed to obtain data such as age and gender. Specimens were fixed in 10% buffered paraformaldehyde solution for 24 h, bisected through the centre of the button, and embedded in paraffin. Sections were stained with haematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) for light microscopic examination.

RESULTS

The studied group was composed of 29 men and 20 women. Age at the time of the penetrating keratoplasty was 39 +/- 14 years (mean +/- standard deviation). Forty of the 49 specimens (82%) presented with epithelial thinning. Other common features of keratoconus included breaks in Bowman's layer in 35 (71%), compaction of the stromal collagen fibres in 31 (63%), and folds in Descemet's membrane in 31 (63%) cases. Other less common histopathological findings were: presence of superficial iron deposits in 14 (29%), deep stromal scarring in 12 (24%), epithelial scarring in 11 (22%), endothelial cell loss in 11 (22%), and breaks in Descemet's membrane in nine (18%) cases.

CONCLUSIONS

Some of the histopathological findings associated with keratoconus are subtle. It is important to be aware of them in order to properly confirm the clinical diagnosis.

VSX1 gene variants are associated with keratoconus in unrelated Korean patients

Keratoconus is a bilateral ectatic disorder characterized by the central thinning of corneal tissue leading to visual impairment. To investigate the possibility of visual system homeobox 1 (VSXI) as a candidate susceptibility gene for Korean patients with keratoconus, we performed a mutation screening of the VSXI gene in 249 unrelated patients with keratoconus and 208 control subjects without the ocular disorder. We found two heterozygous novel missense mutations in exon 2: N151S and G160V. The G160V mutation was identified in 13 keratoconus patients (5.3%), and the N151S mutation was found in only one keratoconus patient (0.4%). We also detected three synonymous polymorphisms and four intragenic polymorphisms. The IVS1-11*a allele was associated with a significantly increased risk of keratoconus in Korean patients [3.6 vs. 0.5%, p = 0.001, odds ratio (OR) = 7.76, 95% confidence interval (CI) 1.989-30.241). Other polymorphisms did not show an association with keratoconus risk. Our data is the first reported VSX1 mutation screening in Korean keratoconus patients. We detected two novel missense mutations and one intragenic polymorphism in the VSX1 gene, which show a strong statistical association with unrelated keratoconus patients. Consequently, our study suggests that VSX1 gene variants seem to be significant genetic variants for keratoconus predisposition in unrelated Korean patients.