Enzyme-assisted deep anterior lamellar keratoplasty-a new method of lamellar dissection-a wetlab-based pilot study

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

"Groove and Peel" Deep Anterior Lamellar Keratoplasty: How Deep Can You Go?

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.

Intrastromal Injection of Hyaluronidase Alters the Structural and Biomechanical Properties of the Corneal Stroma

Purpose

Glycosaminoglycans (GAGs) are important components of the corneal stroma, and their spatiotemporal arrangement regulates the organization of collagen fibrils and maintains corneal transparency. This study was undertaken to determine the consequences of hyaluronidase (HAse) injected into the corneal stroma on stromal stiffness and ultrastructure.

Methods

Equal volumes of HAse or balanced salt solution (vehicle) were injected intrastromally into the corneas of New Zealand white rabbits. Ophthalmic examination and multimodal imaging techniques, including Fourier-domain optical coherence tomography and in vivo confocal microscopy (IVCM), were performed at multiple time points to evaluate the impact of HAse treatment in vivo. Atomic force microscopy and transmission electron microscopy (TEM) were used to measure corneal stiffness and collagen's interfibrillar spacing, respectively.

Results

Central corneal thickness progressively decreased after HAse injection, reaching its lowest value at day 7, and then returned to normal by day 42. The HAse did not impact the corneal endothelium but transiently altered keratocyte morphology at days 1 and 7, as measured by IVCM. HAse-injected corneas became stiffer by day 1 postinjection, were stiffest at day 7, and returned to preinjection values by day 90. Changes in stromal stiffness correlated with decreased interfibrillar spacing as measured by TEM.

Conclusions

Degradation of GAGs by HAse decreases the corneal thickness and increases stromal stiffness through increased packing of the collagen fibrils in a time-dependent manner.

Translational Relevance

Intrastromal HAse injection appears relatively safe in the normal cornea, but its impact on corneal biomechanics and structure under pathologic conditions requires further study.

A year of cornea in review: 2013

PURPOSE

The goal of this study was to provide an update of significant corneal literature published in 2013.

DESIGN

This study is a systematic literature review.

METHODS

We conducted a systematic review of the English-language literature published from January 1, 2013, to December 31, 2013, using the following PubMed search and Medical Subject Headings terms: cornea transplantation, keratoplasty, Descemet membrane endothelial keratoplasty, Descemet stripping endothelial keratoplasty, cross linking, pre-Descemet's layer, Rho-associated kinase, keratoprosthesis, infectious keratitis, corneal dystrophy, corneal astigmatism, and keratoconus.

RESULTS

This review summarizes relevant and innovative original articles, review articles, and novel techniques from the following journals: American Journal of Ophthalmology, British Journal of Ophthalmology, Cornea, Graefe's Archive for Clinical and Experimental Ophthalmology, Investigative Ophthalmology & Visual Science, JAMA Ophthalmology, Journal of Cataract and Refractive Surgery, Journal of Refractive Surgery, and Ophthalmology. Case reports, abstracts, letters to the Editor, and unpublished work were excluded, as well as articles e-published ahead of print in 2012 that were discussed in the previous review. One hundred twenty-seven articles met the criteria for this review.

CONCLUSIONS

This review summarizes significant cornea-related literature from 2013.

Deep anterior lamellar keratoplasty with a manual spatula: anatomical and functional results

Objective:

Evaluate the anatomical, refractive, and functional results of an innovative technique of deep anterior lamellar keratoplasty with a manual spatula.

Materials and Methods:

We evaluated the results and examinations of 16 eyes from 14 patients who underwent deep anterior lamellar keratoplasty using the technique described by Ferrara. Residual bed thickness after keratoplasty was evaluated postoperatively using Visante. The measurement was performed using a technique similar to that used to measure flap thickness after laser in situ keratomileusis refractive surgery. The measurements were performed at the center of the cornea in an area comprising the central 3-mm in the 45° and 135° meridians.

Results:

Best-corrected visual acuity was 0.34 ± 0.18 LogMar (0.09 to 0.60 LogMar), the spherical equivalent was -4.31 ± 3.38 D (+0.25 to -9.50 diopters), and keratometry was 45.75 ± 2.77 D (41.11 to 52.48 diopters) postoperatively. Corneal astigmatism was 3.19 ± 2.78 D (0.18 to 11.81 diopters). Residual stromal bed thickness measured by optical coherence tomography showed values of 67.1 ± 24.3 μm (30 to 109 μm). The statistical correlation by Spearman's test between the best-corrected visual acuity and the residual stromal bed thickness was 0.11 (P = 0.67).

Conclusion:

Deep anterior lamellar keratoplasty, in which manual dissection was performed using an instrument similar to that used to implant corneal rings, provided good visual and anatomical results.

Indications of optical coherence tomography in keratoplasties: literature review

Optical coherence tomography (OCT) of the anterior segment, in particular corneal OCT, has become a reliable tool for the cornea specialist, as it provides the acquisition of digital images at high resolution with a noncontact technology. In penetrating or lamellar keratoplasties, OCT can be used to assess central corneal thickness and pachymetry maps, as well as precise measurements of deep stromal opacities, thereby guiding the surgeon to choose the best treatment option. OCT has also been used to evaluate the keratoplasty postoperative period, for early identification of possible complications, such as secondary glaucoma or donor disc detachments in endothelial keratoplasties. Intraoperatively, OCT can be used to assess stromal bed regularity and transparency in anterior lamellar surgeries, especially for those techniques in which a bare Descemet's membrane is the goal. The purpose of this paper is to review and discuss the role of OCT as a diagnostic tool in various types of keratoplasties.