Adhere Donor In Abnormally Structured Eyes In DSAEK

Jing Hong

Department of Ophthalmology,Third Hospital of Peking University,Beijing,China

Bubbling is a common method for normal structured eyes, but is insufficient for those with iris-lens diaphragm defect and/or liquid vitreous eyes.The most important reason is that the air bubble can not remain stable within the AC. Tsai consider that migration of air bubble into the vitreous cavity is due to the intraocular pressure (IOP) at the AC is higher than that in the posterior chamber (PC). They lower the AC pressure by releasing fluid or air, and then slowly inject more air into the AC with scleral indentation. It has been our experience that in a closed aphakic or iris defected eye, the pressure between anterior and posterior chamber is equal. D.M. Silver et al. have proposed a hypothesis that differential pressure between the anterior and posterior chambers arises from the dynamics of aqueous flow across the iris-lens channel.They concluded that pressure difference between anterior and posterior chamber approximate to zero when lens-iris distance above 5 to 9 μm and pupil diameter over 5 mm. So in Tsai's procedure, releasing of fluid or air in AC can indeed decrease the IOP of the whole globule, but not only of the AC. We consider the pressure difference between anterior and posterior chamber exists only during bubbling. It is generated by and dependent on the injection of air manually.

When surgeons perform sclera indentation with cotton swabs, the IOP has to elevate in accordance with scleral stress generated by scleral elastic moduli and curvature changes. Once sclera indentation is stopped, the vitreous cavity would rebound to previous curvature and stress, and its pressure will reduce to previous. So the bubble in AC still tends to bulge backward into the vitreous cavity. In eyes with axial iris-lens diaphragm defect and strengthy iris with dilated but not distorted pupil, the iris can bear the bubble even with equal strength. In eyes with floppy and partially defected iris plus a malpositioned and distorted pupil, air can easily bulge into vitreous cavity following the pressure gradient.

In eyes with large superior iris defect, the air bubble may easily migrate into the vitreous cavity from superior iris defect post operation when patient changed position from supine to HUT( head-up tilt). For These patients, the bubble still has a risk of migrating into vitreous cavity post operation, in spite of good position we observed intra operation.

Recently we routinely apply a vitreous irrigation for post-vitrectomy eyes during bubbling, to maintain vitreous pressure equal to that of AC. It is effective for patients with dilated pupil and intact iris, and air bubble is enough to support the graft. While we still apply viscoelastics to aid graft position in floppy and superiorly defect iris. In subsequent cases, a few patients underwent IOP elevation periods because of excessive amount of the viscoelastic. However, after 4 hours' supine position, we would release the viscoelastic from the AC by paracentesis. The IOP maintained normal through long term observation.

In conclusion, for patients with dilated pupil and intact iris, air bubble provides good support to the graft, while for those with malformationed pupil and defect iris, viscoelastics is an effective aid for graft position.