溶解性角膜溃疡

Aseven-year-oldmixedbreeddogwaspresentedwithadeepmeltingstromalcornealulcer.Themedicaltermfor‘melting’iskeratomalacia.Whatisthemechanismforthe‘melting’process,andhowisitmanifestclinically?

7岁混血犬由于深度基质溶解性角膜溃疡就诊。“溶解”是角膜软化的医疗术语。“溶解”过程的机制是什么?在临床上是如何表现?

Keratomalacia,or‘melting’,iscornealstromalcollagendissolutionandliquefactionundertheinfluenceofelevatedlevelsoftissue,microbial,andtearfilmproteases.Thekeratomalaciagivesagrayish-gelatinousliquefiedappearancetotheulcerandtheulcermargin.Meltingstromaintheearlystagesmaybedifficulttodistinguishfromcornealedema.Thiscatastrophiccornealdegenerativeconditionmaydeterioraterapidlyandleadtocornealperforationandirisprolapseinasfewas12–48hours.Proteolyticenzymes(proteases)performimportantphysiologicfunctionsinthenormallyslowturnoverandremodelingofthecornealstroma.Naturalproteaseinhibitorsarealsopresentintheprecornealtearfilmandinthecornea.Thesenormallypreventexcessivedegradationofnormalhealthytissue.Meltingcornealdisordersoccurwhenthereisanimbalancebetweenproteasesandproteaseinhibitorsinfavoroftheproteases,thereforecausingpathologicdegradationofstromalcollagenandproteoglycansinthecornea.

角膜软化或“溶解”，是角膜基质胶原组织微生物和泪膜蛋白酶水平升高的影响下发生溶解。角膜软化使溃疡和溃疡缘呈现灰白色凝胶状液化外观。早期基质溶解可能难以与角膜水肿区分。这种毁灭性的角膜退化可能迅速恶化，并在短短12-48小时内导致角膜穿孔和虹膜脱垂出。蛋白水解酶(蛋白酶)在正常角膜基质的缓慢更新和重建中发挥重要的生理功能，天然的蛋白酶抑制剂存在于泪膜和角膜中，可防止正常健康组织的过度退化，当蛋白酶和蛋白酶抑制剂之间失衡时，就会发生角膜溶解，从而导致角膜基质胶原和蛋白多糖的发生病理性降解。