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Ana
Hidalgo-Simón MD, PhD
At a meeting of cornea specialists, Gary S Schwartz MD presented the new staging system, beginning with a reminder that a healthy conjunctival layer, with enough secretion of mucin and aqueous humour, needs to be complemented by a structurally normal adnexa and a healthy cornea. “In a lot of cases, all the elements are there, and our task is limited to keep the cornea healthy. For that we need a healthy endothelium and a healthy epithelium, which is what concerned us and what led us to develop this staging of limbal cell deficiency. The goal is for the new system to help in clarifying the diagnosis and subsequent therapeutic decision,” he said. Dr Schwartz and colleagues have established a staging system that allows classification of the disease and treatment options to be specifically selected for each patient. The classification is based on two factors: the extent of the limbal stem cell deficiency and the status of the conjunctiva. With regard to cell deficiency, Dr Schwartz described two groups of patients. Stage I includes those who have lost less than half of their stem cell population, generally due to iatrogenic intervention, contact lens keratopathy or mild alkali injury. Stage II includes those patients with a loss greater than half of their stem cell population, generally associated with aniridia, severe S-J syndrome or severe alkali injury.  The
status of the conjunctiva is graded in three levels. Grade A represents
a normal conjunctiva, such as that of patients who have suffered
iatrogenic injury or who have aniridia. Grade B represents a quiet
though abnormal conjunctiva, without active inflammation, such as
can be seen after an old chemical injury that leaves a mild chronic
inflammation. Grade C represents an inflamed conjunctiva which can have an internal origin (autoimmune diseases such as S-J syndrome or ocular cicatricial pemphigoid) or an external source, such as a recent alkali injury. Both elements of this staging can be arranged in a table in which patients are allocated to a particular stage. This can be used to determine optimal therapy and prognosis. “The advantage of this classification system is that it allows us to compare like with like when evaluating the relative efficacy of various therapeutic procedures. “We see very different results with different treatments published in the literature, but the patients enrolled on different studies frequently vary considerable in aetiology and level of progression of the disease. With this benchmark we can compare results from comparable groups of patients,” Dr Schwartz said. In normal eyes, the repair mechanisms following a corneal abrasion do not come from the division of cells in the central section of the cornea, but from the limbal area in the periphery. There, the limbal cells are able to reproduce and replace the damaged epithelium. “Stem cells divide to originate transient amplifying cells which migrate centrally. In turn, those cells become post mitotic cells and finally terminally differentiated cells which constantly replace the healthy corneal epithelium,” he explained. A deficiency of stem cells will show itself as a combination of signs and symptoms including persistent epithelial defects on the cornea, injected conjunctiva, chronic irritation, neovascular pannus and eventually stromal scarring. “It is important to remember that epithelial disease can lead to stromal disease. It is only a question of time. If we catch — and treat — somebody with pure limbal stem cell deficiency early enough, they should not progress to stromal disease." he said. In the aetiology of stem cell deficiency, the alternatives are to have abnormal limbal stem cells or a decreased number of limbal cells. In most cases, Dr Schwartz said he finds a combination of both. “Abnormal
limbal stem cells are found in aniridia, in intraepithelial neoplasias
of the conjunctiva and in cases of contact lens keratopathy, where
cells are probably working in a hyperactive state,” he explained. Gary
S Schwartz MD |
