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Esben Nielsen, Jesper Hjortdal, Anders Ivarsen; Fuchs’ endothelial dystrophy: Hydration control. Invest. Ophthalmol. Vis. Sci. 2014;55(13):993.
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Corneal transparency relies partly on keeping a state of relative dehydration. The currently accepted theory of corneal hydration control is the “pump-leak” model, proposed by Maurice in 1972, which suggests that the endothelium actively pumps fluid out of the cornea and reduces “leakage” of fluid back into the cornea. We aimed to investigate the role of the corneal endothelium in hydration control by comparing a group of patients with Fuchs’ endothelial dystrophy (FED) to an age-matched group of cataract patients with normal corneas. This was done by first inducing corneal oedema and subsequently monitoring the reduction of oedema.
All patients gave informed consent and approval from the local Ethics committee was obtained. A group of 16 FED patients eligible for DSAEK surgery was compared to a group of 10 age-matched cataract patients with normal corneas. Endothelial cell density was measured in normal corneas by specular microscopy (Nidek CO.,ltd). This was not possible in the FED group. Corneal edema was induced by placing a contact lens (500 μm, Contaflex 38 %, Contamac, UK) and taping the eyelid for 2 hours. Corneal thickness was measured by Anterior OCT (Spectralis HRT, Heidelberg). We calculated percent of swelling induced (%SI). Values were compared between groups using Students’ t-tests. Deswelling curves were analysed and fitted using the least squares method, and curves were compared using the extra-sum-of-squares F-test.
All normal corneas had endothelial cell densities above 2.000 cells/mm2. %SI was similar between groups (p=0.20). The deswelling curves exhibited exponential decay properties for both groups. During the first hour after contact lens removal, the deswelling was similar between the groups (p=0.8), but after one hour there was a significantly slower recovery of corneal thickness in the FED group (p< 0.00001). At the end of the experiment, CCT in the normal corneas was -0.8 μm (±2 μm) from the baseline value, whereas CCT was 6.8 μm (±10 μm) from baseline in the FED group (p=0.02).
After one hour, deswelling became significantly slower in the FED group and did not return to baseline within the timeframe of the experiment. This is probably due to lower endothelial pump capacity. In the normal group, we noticed that CCT returned to baseline within 1 μm on average, indicating that corneal hydration is closely regulated under normal circumstances.
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