13C NMR studies of protein motional dynamics in bovine, human, rat, and chicken ocular lenses.

The motional dynamics of lens proteins were studied by two 13C nuclear magnetic resonance (NMR) techniques sensitive to molecular motion to define the effect of lens water content on the presence of solid-like protein domains in ocular lenses from bovine (juvenile and adult), human, rat, and chicken eyes. The solid state 13C NMR technique of proton dipolar decoupling was used to study slow (solid-like) motions (correlation time, tau o > or = 10 microseconds), whereas for intermediate (mobile) protein, rotational reorientational motion (tau o range of 1-500 nsec) the 13C off-resonance rotating frame spin-lattice relaxation technique was employed. 13C NMR studies of calf lens cortical and nuclear homogenates indicated a reversible loss of lens protein motional freedom with decreasing water content. Values of 6% and 63% solid-like protein contents were obtained for native cortical and nuclear calf lens homogenates, respectively. At equivalent total protein concentrations cortical and nuclear calf lens homogenates exhibited essentially the same solid-like (motionally restricted) protein content. Lens protein rotational correlation times determined by off-resonance rotating frame spin-lattice relaxation measurements were consistent with lens protein aggregation. The solid-like protein content of the bovine nuclear lens region was observed to increase with age, whereas no significant change was detected for the cortex. Across lens species an inverse correlation between the percentage of solid-like protein content and water content was observed. Very broad 13C NMR resonances, even in the presence of proton dipolar decoupling, were observed for the lens proteins present in the cataractous human lens, indicating the presence of highly aggregated protein species. The occurrence of solid-like protein domains in lens tissue has implications for the interpretation of proton nuclear magnetic resonance dispersion (NMRD) measurements of lens homogenates and for proton magnetization transfer contrast enhanced magnetic resonance imaging of lens. Solid-like protein domains may play a protective role in the maintenance of lens transparency by minimizing enhanced refractive index fluctuations created by protein packing defects resulting from post-translational modification.

A new inexpensive pump for vitreoretinal surgery.

An inexpensive and reliable fluid-gas exchange system has been developed for vitreous surgery. The system relies on a fish-tank air pump and was compared with the Grieshaber Air System in several laboratory and operating room situations. No significant differences were found between the two systems. Details of the Davis Ocular Air Pump are provided along with a cost analysis.

Nasolacrimal duct obstruction after endoscopic sinus surgery.

Intranasal endoscopic sinus surgery has several potential ocular complications, including visual loss, diplopia, retrobulbar hemorrhage, and epiphora. We treated eight patients with persistent nasolacrimal duct obstruction after endoscopic sinus surgery. All patients required dacryocystorhinostomy to achieve a patent lacrimal system drainage. To our knowledge, this is a previously unreported complication in the ophthalmologic literature. The relevant anatomy of the nasolacrimal duct is discussed in addition to surgical procedures for avoidance and treatment of iatrogenic injury to the system. Endoscopic sinus surgery is a highly successful procedure that is rapidly gaining popularity among otolaryngologists. As the number of patients undergoing this type of surgery increases, an increase in the relative number of ocular complications should be anticipated.

The effects of apraclonidine on conjunctival oxygen tension.

A prospective, randomized study evaluated the effects of unilateral, topical 1% apraclonidine hydrochloride on conjunctival oxygen tension in 10 normal volunteers using a conjunctival oxygen monitor. Conjunctival oxygen tension and intraocular pressure were measured prior to instillation of apraclonidine, then at 1, 3, and 5 hours. Apraclonidine was found to significantly decrease conjunctival oxygen tension 76% at 1 hour compared with baseline values. At 3 hours conjunctival oxygen tension was decreased to 56% and at 5 hours to 10% of baseline. Intraocular pressure was lowered maximally at 3 hours to 40% of baseline measurements in the treated eye. The contralateral eye had a small decrease in conjunctival oxygen tension and intraocular pressure that was not statistically significant. Lid retraction and conjunctival blanching were noted to occur maximally between 1 and 3 hours. Further study is needed to determine if the apraclonidine-induced conjunctival hypoxia noted in this study has clinical significance for ocular blood flow, particularly in patients with glaucoma.

Surface coil phosphorus-31 nuclear magnetic resonance studies of the intact eye.

The feasibility of employing the surface coil probe technique for the non-invasive study of ocular tissue metabolism by phosphorus-31 nuclear magnetic resonance spectroscopy (31P NMR) in enucleated bovine, rabbit, human and rat globes is demonstrated. An assessment of individual phosphorus-metabolite contributions from ocular tissues, including the cornea, lens and iris, to the overall 31P NMR spectrum (NMR spectral acquisition parameters optimized for the lens region of the globe) was accomplished through the combination of surgical ablation and difference spectroscopy. The NMR measurements also provided tissue pH values for the lens and cornea. The strengths and limitations of the surface coil NMR method, which is particularly appropriate for in vivo metabolic studies of ocular tissues such as the lens, are discussed.