Pars plana vitrectomy (23-gauge) is associated with a low incidence of sclerotomy-related retinal breaks and postoperative retinal detachments. Eyes with breaks are more likely to be phakic and without a preoperative posterior vitreous detachment. The presence of vitreomacular traction may be a risk factor for the development of intraoperative sclerotomy-related breaks.

Purpose: To investigate the tensile and elastic properties of both commercially available and experimental human amniotic membrane preparations. Method: Nine preparations of human amniotic membrane were studied. The four dry preparations were untreated (nonirradiated, n = 20), and gamma (n = 25), low-dose (AmbioDry^®, Okto Ophtho Inc., Costa Mesa, Calif., USA, n = 20) and high-dose (n = 20) electron beam sterilized. The same dry membranes were moistened with balanced salt solution (n = 20, 34, 20 and 20, respectively). The ninth group consisted of thawed medium-frozen amniotic membrane (AmnioGraft^®, Bio-Tissue Inc., Miami, Fla., USA, n = 20). The membranes were cut into thin strips, loaded on a gram range load sensor, and stretched incrementally to the point of rupture. The modulus of elasticity, displacement until rupture and maximum tolerated stress were recorded and compared. Results: The dry preparations exhibited higher moduli of elasticity when compared with the moist samples, with the low-dose electron beam-irradiated samples having the greatest mean modulus of elasticity overall and maintaining a high modulus of elasticity as a moist sample (p < 0.05). Moist nonirradiated preparations and thawed medium-frozen preparations stretched the farthest before rupture and experienced the greatest mean stresses at the point of rupture. While 3 of 4 membranes had greater stretch when moistened as compared to their dry counterparts, there was no difference in the membrane stiffness between dry and moistened low-dose electron beam-irradiated samples (p > 0.8). Conclusions: Low-dose electron beam-irradiated amnion appeared to maintain desirable elastic characteristics in transition from a dry to rehydrated state and may thus provide an easy-to-manipulate transplant tissue for ocular surface reconstruction. Moist nonirradiated and thawed medium-frozen tissues, however, may provide surgical advantages as they required greater forces to rupture.

The objective of this study was to reproducibly measure corneal epithelial thickness centrally and at the limbus in the rabbit cornea using ultrahigh resolution optical coherence tomography (OCT). Twelve freshly enucleated New Zealand white rabbit eyes were kept in a moist chamber at 4 degrees C. An ultrahigh resolution OCT system with a spatial resolution of 1.3 microm was used to image the cornea and its component layers. The central and peripheral (limbal) regions of all the samples were scanned within 6 h of harvest in order to minimize the post-mortem degradation of the corneal epithelium. The thickness of the corneal epithelium was determined by measuring the pixel equivalents of the obtained image. Unpaired Student's t-test was used to evaluate differences. The epithelial thickness centrally was found to be 45.8 +/- 2.2 microm, and 37.6 +/- 1.4 microm at the limbus (P < 0.001). Rabbit corneal epithelium is thicker centrally than at the limbus when measured by ultrahigh resolution OCT. This technique will aid in delineating the pathophysiology of diseases of the anterior cornea.

Performing PPV from the temporal position seems to be advantageous in cases combining posterior and anterior segment surgery such as cataract extraction, pupillary membrane dissection, preservation of superior conjunctival blebs, and trimanual vitrectomy.