EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/87458
48 EW CATARACT October 2012 Complicated cataract cases Cataract surgery in the setting of nanophthalmos by Hart Moss, M.D., and Douglas D. Koch, M.D. N E yes at the extremes of axial length can be challenging to operate on. Very large and highly myopic eyes usually have deep anterior chambers and are subject to trampolining of the lens-iris diaphragm, high perceived intraocular pres- sure at relatively low infusion bottle height, and lens power calculation inaccuracy. Nanophthalmic and highly hyperopic eyes often sit in deep-set orbits and are subject to shallow anterior chambers, a propensity for iris prolapse and chafing, scleral thickening that can result in uveal effusion, higher than normal posterior pressure, and lens power calculation inaccuracy. In this month's column, Hart Moss, M.D., and Douglas D. Koch, M.D., define what constitutes a nanophthalmic eye and describe some of the associated conditions that are seen in nanophthalmos. They review some of the important considerations when working in an eye with a shallow anterior chamber. They discuss management strate- gies for handling high posterior pressure de- pending on the specific anatomic situation. They also discuss the issues surrounding lens power calculation and selection in highly hyperopic eyes. Patients with nanophthalmos do not come around very often. When they do, however, they can be a surgical challenge. This article may prove to be a useful reference for that occasional patient. Kevin M. Miller, M.D., Complicated cataract cases editor anophthalmos can be defined in various ways, including an axial length of two standard devia- tions below average or as an extremely short eye with a shal- low anterior chamber. It presents an array of challenges even to seasoned cataract surgeons. Pre-op, short eyes raise uncertainty with IOL power calculation. Intraoperatively, a shal- low anterior chamber, small corneal diameter, and positive posterior pressure can conspire to make maneuvers within the anterior segment difficult and hazardous to the endothelium, iris, and posterior capsule. Extreme axial hyperopia, with high dioptric IOL require- ments, may complicate lens implan- tation. Associated ocular conditions, such as increased scleral thickness, pseudoexfoliation syndrome, angle-closure glaucoma, and retinal pathology, can also affect manage- ment. Amblyopia is more common in nanophthalmic eyes, and reason- able patient expectations should be ensured prior to proceeding. How- ever, with appropriate measures, one can achieve good visual results and even improve angle configuration. Shallow anterior chamber These eyes have very small and crowded anterior segments, often with anterior chamber depths of less than 2 mm. This may lead to diffi- culty with capsulorhexis, iris pro- lapse, endothelial cell loss, and posterior capsular rupture. Meticu- lous wound construction and small incision sizes with appropriate sleeves are standard means to pro- vide a stable and formed anterior segment. A viscoadaptive agent (Healon 5, Abbott Medical Optics, AMO, Santa Ana, Calif.) can be instrumental in sufficiently deepen- ing the anterior chamber for capsu- lorhexis and phacoemulsification, while minimizing progressive loss of viscoelastic during the surgery. Be- cause the capsulorhexis is prone to tear toward the periphery, extra at- tention must be taken and the ante- rior chamber should be refilled with viscoelastic as necessary. Iris hooks or other expansion devices should be kept handy given the propensity for poor dilation and iris prolapse. During phacoemulsification, raising the bottle height can help to main- tain an adequately formed anterior chamber. Of course, care must be taken to direct phaco energy and lens fragments away from the corneal endothelium, while phaco settings should be optimized to min- imize energy output. As with capsu- lorhexis, periodically refilling the eye with a dispersive or viscoadap- tive viscoelastic may be helpful. This can be done through the paracente- sis while the phaco handpiece is still in the eye, to avoid repeated anterior chamber shallowing and transient hypotony. Posterior pressure The increased scleral thickness seen in nanophthalmic eyes may lead to uveal effusions and marked intraop- erative posterior pressure, which can compound an already shallow ante- rior chamber. Mechanical compres- sion with one's palm or a Honan balloon may help decompress the vitreous body; intravenous mannitol (20%, 1-2 ml/kg) can also be used to dehydrate the vitreous and should be given 15-30 minutes prior to the incision. If surgery is delayed, make sure to give the patient access to a bathroom. To minimize positive pressure, a peribulbar block or topi- cal anesthesia may be preferable to a retrobulbar block. There are two types of situations in which sur- geons encounter problems with chamber depth, and they require completely different approaches for management: 1. If the chamber is excessively shallow at the beginning of the surgery, this suggests that the problem is the thickened sclera and inherent posterior pressure. If the above-noted measures are not adequate and if one is comfortable with the procedure, a limited pars plana vitrectomy is a definitive means to reduce posterior pressure and deepen the anterior chamber when otherwise impossible. The incision should be placed around 3.25-3.5 mm posterior to the limbus (less if an extremely short eye). Because the lens volume is still normal in these otherwise very small eyes, care must be taken to always direct instruments toward the optic nerve and away from the lens. Vitrectomy should be done with the highest cut rate available to limit vitreous traction; Injection of a viscoadaptive OVD in a nanophthalmic 15.5 mm eye with a slit anterior chamber. Following removal of the cataract and insertion of the 40 D IOL, there was no room for the 12 D piggyback IOL that was planned. Because of the anterior position of the single IOL, the post-op refractive error was only +3.00, and the post-op course was complicated by formation of posterior synechiae and secondary glaucoma Scleral cutdown to drain choroidal effusion that developed intraoperatively (performed by Peter T. Chang, M.D., assisting the author in this procedure) Injection of the 14 D piggyback IOL into the ciliary sulcus in front of the 40 D IOL in the capsular bag Source (all): Douglas D. Koch, M.D. newer 25-gauge systems can now be used transconjunctivally as well. 2. If posterior pressure develops during the procedure after the chamber was initially of sufficient depth, this indicates a choroidal effusion until proven otherwise. Unfortunately, this can be hard to