Changes In Corneal Stroma Research Articles

Corneal Optical Coherence Tomography Speckle in Crosslinked and Untreated Rabbit Eyes in Response to Elevated Intraocular Pressure

PurposeTo ascertain the influence of intraocular pressure (IOP) on corneal optical coherence tomography (OCT) speckle in untreated and ultraviolet A–riboflavin induced corneal collagen crosslinked rabbit eyes.MethodsLeft corneas of eight rabbits were de-epithelialized and crosslinked by applying riboflavin and 30-minute ultraviolet A light exposure. After enucleation (6 months after treatment), each eyeball (treated and untreated) was mounted in a measurement setup, in which IOP was increased from 15 to 45 mm Hg in steps of 5 mm Hg. At each IOP value, single B-scans of the central cornea were acquired three times with the spectral-domain OCT Copernicus-HR. Then, three regions of interest, including the anterior, posterior, and entire corneal stroma, were automatically extracted. Five different probability distributions were used as a model for the corneal speckle and the one with the best goodness of fit was chosen for further analysis.ResultsThe generalized gamma distribution achieved the best goodness of fit and its scale (a) and shape (v) parameters statistically significantly changed with increasing IOP in the three regions of analysis (two-way repeated measures analysis of variance, all P < 0.05). The statistically significant difference between untreated and crosslinked eyes was observed for the shape parameters of the posterior and entire corneal stroma.ConclusionsCorneal OCT speckle is influenced by IOP and shows to be significantly different in untreated and crosslinked eyes. Corneal OCT speckle analysis has the potential to be indirectly used for assessing changes in corneal stroma in ex vivo and in vivo studies.Translational RelevanceInvestigation of corneal OCT speckle statistics can offer additional diagnostic biomarkers related to changes in the corneal stroma after ocular surgeries.

Metabolomic Analysis in Corneal Lenticules From Contact Lens Wearers.

To investigate the mechanisms of pathological changes in corneal stroma and the wearing time of soft contact lenses using the metabolomic method. Laser scanning confocal microscopy was used to evaluate the pathological changes of corneal stroma between wearing time groups before small incision lenticule extraction. After small incision lenticule extraction, 190 corneal stroma samples were obtained, and a metabolomic method using high performance liquid chromatography coupled with time of flight mass spectrometry was established to analyze the changes in metabolites between wearing time groups. Laser scanning confocal microscope results demonstrated that the corneal nerve fiber length, the number of corneal anterior stromal cells, and the number of corneal posterior stromal cells were reduced gradually with increasing wearing time. The metabolomic study demonstrated that 11 biomarkers were identified between patients who did and did not wear soft contact lenses and 6 biomarkers were identified between less than 5 years and more than 5 years of wearing time. These biomarkers participate in energy metabolism, lipid metabolism, inflammatory reactions, and neuroprotecton processes, and partially lead to the pathology of dry eyes, eye inflammation, and corneal nerve fiber length decrease. Five biomarkers in the citrate cycle metabolism pathway were found demonstrating that energy metabolism was seriously disturbed. This study systematically revealed the metabolite mechanism for eye discomfort and related disease after wearing soft contact lenses. The identified biomarkers and related physiology pathways supply a new direction for avoiding the side effects of wearing soft contact lenses. [J Refract Surg. 2020;36(5):317-325.].

Age-related changes of the corneal speckle by Optical Coherence Tomography.

Ageing of the population has several consequences for the human visual system. The corneal tissue which is responsible for two thirds of the total optical power is not an exception, suffering structural and anatomical changes with the age. In this study, we have explored the usefulness of Optical Coherence Tomography (OCT) speckle to study the age-related changes in corneal stroma. The Generalized Gamma distribution has been suggested as a model for OCT corneal speckle and was used here to investigate OCT envelope statistics in three different age groups (65 subjects in total). The scaling and the two shape parameters have shown significant statistical differences (p <; 0.05) among the age groups, showing the possibility to track the corneal changes using envelope statistics. This study shows that Generalized Gamma distribution has a great potential to fit the corneal speckle and could be a helpful complement to evaluate the structure and elastic properties of the cornea in vivo.

Modifications in stromal extracellular matrix of aged corneas can be induced by ultraviolet A irradiation.

With age, structural and functional changes can be observed in human cornea. Some studies have shown a loss of corneal transparency and an increase in turbidity associated with aging. These changes are caused by modifications in the composition and arrangement of extracellular matrix in the corneal stroma. In human skin, it is well documented that exposure to solar radiation, and mainly to the UVA wavelengths, leads to phenotypes of photoaging characterized by alteration in extracellular matrix of the dermis. Although the cornea is also exposed to solar radiation, the extracellular matrix modifications observed in aging corneas have been mainly attributed to chronological aging and not to solar exposure. To ascertain the real implication of UVA exposure in extracellular matrix changes observed with age in human cornea, we have developed a model of photoaging by chronically exposing corneal stroma keratocytes with a precise UVA irradiation protocol. Using this model, we have analyzed UVA-induced transcriptomic and proteomic changes in corneal stroma. Our results show that cumulative UVA exposure causes changes in extracellular matrix that are found in corneal stromas of aged individuals, suggesting that solar exposure catalyzes corneal aging. Indeed, we observe a downregulation of collagen and proteoglycan gene expression and a reduction in proteoglycan production and secretion in response to cumulative UVA exposure. This study provides the first evidence that chronic ocular exposure to sunlight affects extracellular matrix composition and thus plays a role in corneal changes observed with age.

The impact of common classes of topical antiglaucoma medications on central corneal thickness

Abstract Purpose Recent studies have shown that prostaglandin analogs (PGA) may induce biochemical (via FP receptor and MMP‐2 activation) and morphological (via collagen type I contraction) changes in corneal stroma thus affecting central corneal thickness (CCT). Beta‐blockers (BB) and topical carbonic anhydrase inhibitors (CAI) were found to have rather no effect on CCT. To investigate the influence of common classes of topical antiglaucoma medications used either in monotherapy or combined therapy on CCT. Methods In a retrospective study 487 eyes from consecutive 260 patients (148F/112M) with open angle glaucoma were examined. Depending on the topical treatment they were classified into 7 groups: A/ PGA (n = 212), B/ BB (n = 54), C/ CAI (n = 36), D/ PGA + CAI (n = 25) E/ PGA + BB (n = 23) F/ BB + CAI (n = 54), G/ non‐treated (n = 83). The CCT was measured using ultrasound pachymetry Tomey AL‐2000. The central corneal power was measured with the Topcon keratometer. ANOVA analyses were used for statistical analysis. Results There were no statistically significant differences between CCT of all groups (F=1,06, p=0,3931); the lowest values were in the eyes treated with PGA + BB (535,9 nm SD 31,4) and the highest in the eyes treated with PGA + CAI (571,3 nm SD 46,3). The mean CCT in group A was 550,4 (SD 40,8), group B 552,5 (SD 34,7), group C 562,6 (SD 40,2), group D 571,3 (SD 46,3), group E 535,9 (SD 31,4), group F 559,5 (SD 32,5), group F 557,5 (SD 42,2) nm. Conclusion In this study CCT appears not to differ in eyes treated with different classes of antiglaucoma medications either in monotherapy or combined therapy. CCT of treated glaucoma eyes does not differ from CCT of untreated glaucoma eyes.