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Physiology and histology of deep sclerectomy
  1. S C Lin
  1. Department of Ophthalmology, University of California, San Francisco, 10 Kirkham Street, K-301, San Francisco, CA 94143-0730, USA; shanlitsa.ucsf.edu

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    Results from animal studies should be applied with caution to the human clinical situation

    The paper by Delarive et al in this month’s BJO (p 1340) studies the aqueous outflow characteristics and histology of deep sclerectomy (DS)—with (DSCI) and without collagen implant—in a rabbit model. This increasingly popular surgery has the advantage of fewer postoperative complications, as it is theoretically non-penetrating.1–3 The mechanism(s) by which DS and DSCI lower the IOP has been investigated non-invasively but not vigorously studied in an animal model with corresponding histology.

    Ultrasound biomicroscopy (UBM) studies in human eyes that underwent DS or DSCI have demonstrated formation of a subscleral lake and an overlying bleb.4,5 In half or more of the patients examined by UBM, a supraciliary hypoechoic area was identified.4,5 As a result, it has been postulated that aqueous flowing through the trabeculodescemetic membrane is absorbed into the subconjunctival space as well as the suprachoroidal space.

    Physiological and histological support for some of these UBM findings is provided in the present study. Formation of an intrascleral canal was observed. This structure corresponds to the subscleral lake seen on UBM. The use of cationised ferritin in the perfusate demonstrated the development of new vessels around the canal, which may possibly facilitate drainage into a suprachoroidal space. In eyes with the collagen implant, spindle cells were observed lining the canal. These cells may help maintain the long term viability of the canal, as suggested by the slightly higher outflow facility (OF) in DSCI eyes versus DS eyes (not statistically significant).

    The OF was significantly increased in both groups over the 9 months of study. This correlates well with clinical studies showing good long term IOP reduction.1–3 However, in the rabbit model, IOP reduction was maintained for only 2 months. This probably reflects, in part, the fact that the rabbits had a normal baseline IOP (not elevated, as in glaucoma patients). At the normal pressures there is probably less outflow and lower OF, thus avoiding hypotony. This also correlates well with clinical findings in which hypotony is rare and the maintained IOPs tend to be slightly higher than in trabeculectomies.1

    As always, results from animal studies should be applied with caution to the human clinical situation, particularly with respect to the rabbit model where inflammation and possibly vascular formation may be more vigorous. However, the authors should be congratulated for developing an excellent animal model of deep sclerectomy and providing physiological and histological evidence for the efficacy of this surgery. Future studies in primate eyes and cadaver specimens may further shed light on the mechanisms.

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    Results from animal studies should be applied with caution to the human clinical situation

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