Evaluation of the relationship between corneal diameter and lens diameter.

PURPOSE: To investigate the relationship between corneal diameter (white to white) (WTW) and the dimensions of the crystalline lens. SETTING: Private practice, Cincinnati, Ohio, USA. METHODS: Human cadaver eyes were oriented to allow caliper measurements of the horizontal and vertical corneal diameters (WTW). Globes were sectioned and reoriented so the horizontal and vertical measurements of the crystalline lens were recorded and statistically analyzed. RESULTS: The mean horizontal corneal diameter was 11.46 mm, approximately 0.8 mm greater than the mean vertical corneal diameter of 10.63 mm. The mean horizontal crystalline lens diameter was 9.28 mm, nearly identical to the mean vertical diameter of 9.30 mm. The correlation between the mean corneal diameter and mean lens diameter was weak, although it was significant. There was no correlation between horizontal dimensions. CONCLUSION: It was not possible to predict the dimensions of the human crystalline lens using calipers to measure the WTW corneal diameter.

Development of an in vitro model to assess posterior capsule safety during phacoemulsification with ultrasound or AquaLase handpieces.

PURPOSE: To develop a cadaver eye model that would assess posterior capsule (PC) vulnerability when different cataract removal technologies were evaluated and use the model to evaluate the relative amplitude levels required to rupture the human PC with the AquaLase handpiece (Alcon) compared with an ultrasound (US) handpiece. SETTING: Private practice, Cincinnati, Ohio, USA. METHODS: In part 1 of the study, 26 phakic human cadaver eyes were sectioned in the anteroposterior meridian. The anterior portion of the globe was placed cornea side down, and the vitreous was gently cleared from the posterior surface of the lens capsule. Ultrasound was applied directly to the central capsule after achieving a vacuum of 100 mm Hg. The power was incremented until rupture was observed. In part 2 of the study, the same procedure was repeated with 50 eye pairs. For each pair, US was randomly applied to 1 eye and AquaLase to the other. The 50 pairs were divided into 3 groups based on vacuum level: 100, 300, or 500 mm Hg. RESULTS: Part 1 results show that at 100 mm Hg, the mean power needed to break the PC with US was 19% +/- 6% (SD). There was no correlation between time from harvest to test and rupture power (R(2) = 0.04) or between donor age and rupture power (R(2) = 0.2). When the same procedure was repeated in part 2, on average, US power ruptured the capsule at a lower power than the AquaLase magnitude at each vacuum setting. The respective means were 18.5% +/- 6.7% and 61.0% +/- 23.3% for 100 mm Hg, 15.2% +/- 5.4% and 47.1% +/- 14.5% for 300 mm Hg, and 11.8% +/- 6.5% and 20.0% +/- 9.4% for 500 mm Hg. The difference between the groups and the values within each group decreased as vacuum levels increased. CONCLUSION: This new experimental model in a cadaver eye provides a useful method for comparing factors and techniques that contribute to PC rupture.

Surgical options in the face of positive pressure.

Positive pressure during cataract surgery can adversely affect the clinical outcome if the surgeon is unprepared. A variety of surgical maneuvers are described, including dry insertion of the phacoemulsification needle, capsule protection with the second instrument, dry cortical aspiration in an ophthalmic viscosurgical device (OVD) environment, intraocular lens restraint with an injection cannula at the end of OVD removal, aspiration or vitrectomy through the pars plana, a technique of OVD clearance to manage extreme cases of positive pressure, and intraoperative ophthalmoscopy using a lens designed to function with the operative microscope. Mastery of these important surgical maneuvers will help the surgeon manage challenging cases of positive pressure.

Intraocular pressure during phacoemulsification.

PURPOSE: To assess changes in intraocular pressure (IOP) during standard coaxial or bimanual microincision phacoemulsification. SETTING: Oregon Eye Center, Eugene, Oregon, USA. METHODS: Bimanual microincision phacoemulsification (microphaco) was performed in 3 cadaver eyes, and standard coaxial phacoemulsification was performed in 1 cadaver eye. A pressure transducer placed in the vitreous cavity recorded IOP at 100 readings per second. The phacoemulsification procedure was broken down into 8 stages, and mean IOP was calculated across each stage. Intraocular pressure was measured during bimanual microphaco through 2 different incision sizes and with and without the Cruise Control (Staar Surgical) connected to the aspiration line. RESULTS: Intraocular pressure exceeded 60 mm Hg (retinal perfusion pressure) during both standard coaxial and bimanual microphaco procedures. The highest IOP occurred during hydrodissection, ophthalmic viscosurgical device injection, and intraocular lens insertion. For the 8 stages of the phacoemulsification procedure delineated in this study, IOP was lower for at least 1 of the bimanual microphaco eyes compared with the standard coaxial phaco eye in 4 of the stages (hydro steps, nuclear disassembly, irritation/aspiration, anterior chamber reformation). CONCLUSION: There was no consistent difference in IOP between the bimanual microphaco eyes and the eye that had standard coaxial phacoemulsification. Bimanual microincision phacoemulsification appears to be as safe as standard small incision phacoemulsification with regard to IOP.

Iris reconstruction with a multipiece endocapsular prosthesis in iridocorneal endothelial syndrome.

Iris reconstruction in cases of iridocorneal endothelial (ICE) syndrome is extremely challenging because of the nature of the iris tissue, which is typically friable and poorly suited to suture repair. Reconstruction in such cases often requires artificial iris implantation. This report illustrates cataract extraction and iris reconstruction with a multipiece endocapsular iris prosthesis that can be inserted through a small incision. Maintenance of a small incision size is a distinct advantage when glaucoma is coexistent in patients with ICE syndrome. It also demonstrates the presence of an ICE membrane over the anterior capsule and the importance of recognizing this membrane rather than confusing it with the anterior capsule when performing the capsulorhexis.