Uri S. Soiberman

Keratoconus is a potentially blinding condition characterized by progressive thinning and steepening of the cornea, leading to visual impairment due to irregular astigmatism and myopia. While the exact pathophysiology is still unknown, it is believed to involve genetic, environmental, and cellular factors. Treatment options for keratoconus have significantly expanded over the past few decades. Historically, glasses were the primary means of managing mild cases, whereas rigid gas permeable contact lenses were used in moderate to advanced diseases; yet the latter were rarely tolerated by patients with steep cones, in which full-thickness corneal transplantation was often performed. However, a variety of innovative treatments have been introduced in the past decades. Corneal collagen cross-linking (CXL) has revolutionized the field by halting the progression of keratoconus through creating new covalent bonds between individual corneal fibers. Custom, soft, and scleral contact lenses have improved visual outcomes for many patients. Additionally, surgical interventions such as intrastromal ring segments and Bowman layer transplantation have provided alternatives for visual restoration and postponing a potential keratoplasty. Furthermore, innovative cellular and pharmacological KCN treatments are on the horizon, awaiting clinical trials. This review article aims to provide a comprehensive overview of the current treatment options for keratoconus.

Purpose: To develop an ex vivo model for keratoconus that simulates eye rubbing, a hallmark characteristic of patients with this disease. Methods: Uniaxial stretch (3% strain, 6 h) was applied to human stromal caps placed in stretch chambers, followed by hematoxylin and eosin staining and evaluation of Bowman layer (BL) breaks in stretched corneas compared with unstretched controls. The impact of mechanical strain on corneal epithelium was also assessed by applying similar cyclical strain to mouse eyes, and changes in basal epithelium morphology were examined using F-actin immunostaining. In addition, Wnt10a and Col12a1 mRNA levels were analyzed in full-thickness epithelium. Results: Human corneas subjected to mechanical strain showed a significantly higher number of BL breaks compared with unstretched controls (2.0 ± 1 vs. 0.4 ± 0.53, P = 0.003). In mouse corneas, mechanical strain increased the basal epithelial cell width by 15% (7.16 ± 1.67 vs. 8.25 ± 1.82 μm, P < 0.001), while reducing the apical cell height by 8% (7.88 ± 1.93 vs. 7.30 ± 1.72, P = 0.025). Wnt10a and Col12a1 mRNA levels were reduced in stretched mouse epithelium compared with unstretched controls (67%, P = 0.0312; 65%, P = 0.0312, respectively). Conclusions: Eye rubbing is a well-known risk factor for the development and progression of keratoconus. By simulating eye rubbing using our ex vivo cyclical mechanical strain model reproduces changes that occur in early keratoconus. Specifically, this model recapitulates at least 3 elements of the keratoconus phenotype (BL breaks, enlargement of the basal epithelium, and reduction in transcript levels of Wnt10a and Col12a1), which makes it a valuable tool for the development of targeted drug therapies for progressive keratoconus.

Although mechanical injury to the cornea (e.g. chronic eye rubbing) is a known risk factor for keratoconus progression, how it contributes to loss of corneal integrity is not known. Here, we set out to determine how eye rubbing can influence keratoconus progression by exploring the expression of known disease markers in mechanically stressed corneal epithelial cells. To explore the effects of mechanical stress on the expression of genes implicated in keratoconus (e.g. WNT10A, COL12A1, and TGFB1), we measured their expression using an in vitro model that simulates eye rubbing by cyclic stretching of an immortalized human corneal epithelial cell line (hTCEpi) for 16 hours. We further examined the influence of WNT10A expression in hTCEpi cells using loss-of-function approaches. Mechanical strain led to a marked reduction in WNT10A mRNA and protein expression, as well as decreased collagen XII mRNA and protein expression, in hTCEpi cells. Reduced expression of WNT10A protein in WNT10A knockdown cells resulted in reduced protein expression of collagens I and XII, and reduced mRNA expression of MMP9 and TGFB1. Conversely, primary keratocytes treated with recombinant WNT10A protein increased TGFB1 mRNA expression. We provide a molecular explanation for how mechanical strain results in reduced expression of WNT10A in the corneal epithelium, which, in turn, leads to depletion of collagen type I and XII, and TGFβ1 expression. These results provide a molecular link among mechanical strain, WNT10A expression, and the biomechanical failure of the keratoconus cornea.

Objectives: This study aims to assess the presence of pathogenic microorganisms in the corneal epithelial layer of keratoconus patients. Methods: DNA was extracted from corneal epithelial samples procured from ten individual keratoconus eyes and three healthy controls. Metagenomic next-generation sequencing (mNGS) was performed to detect ocular microbiota using an agnostic approach. Results: Metagenomic sequencing revealed a low microbial read count in corneal epithelial samples derived from both keratoconus eyes (average: 530) and controls (average: 622) without a statistically significant difference (p = 0.29). Proteobacteria were the predominant phylum in both keratoconus and control samples (relative abundance: 72% versus 79%, respectively). Conclusions: The overall low microbial read count and the lack of difference in the relative abundance of different microbial species between keratoconus and control samples do not support the hypothesis that a chronic corneal infection is implicated in the pathogenesis of keratoconus. These findings do not rule out the possibility that an acute infection may be involved in the disease process as an initiating event.

Purpose: The objective of this study is to perform a histological analysis of Bowman layer (BL) grafts. Methods: BL grafts were procured from 13 human cadaver corneal tissues using 3 different donor preparation techniques. Subsequently, the grafts were fixed in 10% buffered formalin phosphate and embedded in paraffin. Hematoxylin and eosin sections of BL grafts were obtained and analyzed under a light microscope. BL and full graft thickness were measured using an image-processing software. Results: All 13 BL grafts contained residual anterior stromal tissue. BL stripping using Kelman-McPherson and Moorfield forceps (technique 3) achieved the thinnest graft thickness with a mean full graft thickness of 18.7 μm (95% confidence interval [CI], −9.8 to 47.2) at the thinnest point of the graft, whereas BL procurement using the Melles lamellar dissector (technique 2) led to the highest mean full graft thickness of 279.9 μm (95% CI, 251.4–308.5) even at the thinnest area of the graft. By contrast, BL dissection using a blunt dissector (technique 1) provided a mean full graft thickness of 70.2 μm (95% CI, 40.4–100.1) at the graft's thinnest point. Although peripheral graft tears occurred in 50%, 50%, and 100% of techniques 1, 2, and 3, respectively, intact 6.25-mm diameter BL grafts could be secured in 50%, 100%, and 80% of techniques 1, 2, and 3, respectively. Conclusions: None of the techniques used led to the procurement of pure BL grafts devoid of the anterior stroma. Peripheral scoring with a thin needle and tissue manipulation with Kelman-McPherson and Moorfield forceps led to the thinnest grafts in this study.

Purpose: Corneal biomechanical failure is the hallmark of keratoconus (KC); however, the cause of this failure remains elusive. Collagen type XII (COL12A1), which localises to Bowman’s layer (BL), is thought to function in stress-bearing areas, such as BL. Given the putative protective role ofCOL12A1in biomechanical stability, this study aims to characteriseCOL12A1expression in all corneal layers involved in KC.Methods: TaqMan quantitative PCR was performed on 31 corneal epithelium samples of progressive KC and myopic control eyes. Tissue microarrays were constructed using full-thickness corneas from 61 KC cases during keratoplasty and 18 non-KC autopsy eyes and stained with an antibody specific to COL12A1. Additionally,COL12A1was knocked out in vitro in immortalised HEK293 cells.Results: COL12A1expression was reduced at transcript levels in KC epithelium compared with controls (ratio: 0.58, pCOL12A1is thought to have in stress bearing areas, suggests thatCOL12A1may play a role in the pathogenesis of KC. Further studies are necessary to investigate the mechanisms that lead toCOL12A1dysregulation in KC.

Purpose: The aim of the current research was to measure the thickness of the residual central corneal bed after performing the manual “Groove and Peel” deep anterior lamellar keratoplasty (GP-DALK) technique on human cadaveric eyes. Methods: The manual GP-DALK technique was performed on 6 human cadaver eyes by an experienced corneal surgeon. After surgery, the eye globes were fixed in 10% buffered formalin and embedded in paraffin. For each eye, 4-μm-thick hematoxylin and eosin sections involving the pupillary axis were obtained and examined. Using an image-processing software, 2 observers measured the corneal thickness of the residual central corneal bed and the peripheral corneal rims. Results: The overall mean central corneal bed thickness was 35.5 ± 12.9 μm, whereas the mean right and left peripheral rim thicknesses were 993.0 ± 141.1 and 989.3 ± 147.1 μm, respectively (P = 0.0006). In most corneas, the level of dissection reached almost to the pre-Descemetic collagen (Dua) layer. Conclusions: The GP-DALK technique is effective in removing most of the corneal stroma and may be non-inferior to “big-bubble” deep anterior lamellar keratoplasty in some cases.

Purpose. To evaluate whether unilateral crosslinking (CXL) and conservative follow-up of the fellow eye is an acceptable management strategy in patients with keratoconus (KC). Methods. Seventy-nine fellow eyes of KC subjects that initially underwent unilateral CXL were included. Thirty fellow eyes ultimately received CXL (group 1) whereas 49 fellow eyes were followed (group 2). Best spectacle corrected visual acuity (BSCVA) and corneal tomographic parameters were collected in all eyes preoperatively and at the last follow-up. Results. Subjects who received CXL in the fellow eye (group 1) were younger than subjects who did not (group 2, ). Group 1 eyes had higher baseline K1 ( ), K2 ( ), Km ( ), and Kmax ( ) compared to group 2 eyes. Amongst the 49 naïve fellow eyes (group 2), 19 eyes showed evidence of progression. Progressing naïve eyes had higher baseline K1, K2, Km, and Kmax ( ); progressors also had thinner pachymetry at the pupil, apex, and thinnest point ( ). Baseline values of K1 ≥ 43.5 Diopter (D), K2 > 45.1D, Km > 44.3D, K_max > 47.9D, astigmatism > 1.4D, pachymetry at the pupil μm, and thinnest pachymetry μm were tentative predictors of progression in the naïve fellow eye. Conclusions. Unilateral CXL with vigilant follow up of the fellow eye may be an acceptable management strategy in a subset of KC eyes.