James S. Tiedeman

Pneumatic retinopexy : a two-year follow-up study of the multicenter clinical trial comparing pneumatic retinopexy with scleral buckling

The authors report 2-year follow-up information on 179 of 198 eyes (90%) enrolled in a previously published multicenter, randomized, controlled clinical trial comparing pneumatic retinopexy (PR) with scleral buckling (SB) for the management of selected retinal detachments. Scleral buckling was compared with PR with regard to redetachment after the initial 6-month follow-up period (1% versus 1%), overall attachment (98% versus 99%), subsequent cataract surgery (18% versus 4%; P less than 0.05), preoperative visual acuity (no significant difference), and final visual acuity of 20/50 or better in eyes with macular detachment for a period of 14 days or less (67% versus 89%; P less than or equal to 0.05). Reoperations after a failed PR attempt did not adversely affect visual outcome. After 2 years, PR continues to compare favorably with SB.

Epstein-Barr Viral Antibodies in Multifocal Choroiditis and Panuveitis

A syndrome of multifocal choroiditis, pigment epithelial disturbance, and inflammatory vitreous cells was found to be associated with Epstein-Barr virus specific antibodies. The ten patients in this series had positive viral capsid antigen IgM or Epstein-Barr early antigen antibody titers. Patients with this syndrome were generally healthy and had no history of a clinical episode of infectious mononucleosis. No patient from the control group with other ocular diseases had positive viral capsid antigen IgM or early antibody titers. All patients in the study group and most of the control patients had viral capsid antigen IgG and Epstein-Barr nuclear antigen antibodies, indicating a previous exposure to the virus as expected in an adult population.

Intraocular tamponade and surface tension

Surface tension is an important property of substances used as intraocular tamponades. The physical properties of currently available intraocular tamponades (gases, silicone oil and Healon) are compared with emphasis on surface tension. The gas/water interface surface tension is the greatest and therefore is the most effective in closing retinal breaks (70 erg/cm2). This is followed by silicone oil/water interface surface tension (50 erg/cm2). Healon is a 1% solution of water and therefore has no surface tension. Practical and theoretical considerations of various tamponades are described. Some properties of an ideal tamponade are suggested.

Classification of Proliferative Vitreoretinopathy Used in the Silicone Study

The Silicone Study is a multicenter randomized clinical trial that compares a long-acting gas with silicone oil for the surgical treatment of proliferative vitreoretinopathy (PVR). As part of the study, a topographic classification of PVR has been developed that is based on the characteristic patterns of retinal distortion produced by the contraction of proliferative membranes on the retina or within the vitreous base. This classification is used to document the extent and anatomic distribution of PVR present preoperatively and to help standardize the surgical treatment. Experience has shown that this classification facilitates the identification of these membranes and their systematic dissection, and the authors therefore suggest that it be used to augment the Retina Society classification of PVR.

A Physical Analysis of the Factors That Determine the Contour of the Iris

By solving equations that result from the application of basic newtonian physical principles, I developed a model that can predict the profile of the iris by using only the pupil radius, the iris root radius, and the anterior displacement of the pupil from the iris root. The model requires some theoretically and clinically reasonable assumptions regarding the relative importance of forces acting on the iris. Former analyses made false assumptions about contact between the lens and the iris, as well as inappropriate substitution of the physical concept of force for tension. The validity of the new model and its inherent assumptions can now be tested with biometric measurements made in normal eyes and eyes with shallow anterior chambers.

REFRACTIVE CHANGES FROM USE OF SILICONE OIL IN VITREOUS SURGERY

When silicone oil fills the vitreous cavity of the phakic eye or the entire aphakic eye, the refractive correction can be expected to change by 5-9 diopters and sometimes as much as 14 diopters. Aphakic eyes become less hyperopic when filled with silicone oil, whereas phakic eyes become more hyperopic when the vitreous cavity is filled with silicone oil. Previously emmetropic aphakic eyes that are filled with silicone oil have only 4-6 diopters of hyperopia, whereas the same eyes have 10-12 diopters of hyperopia before insertion or after removal of silicone oil. Phakic eyes develop 5-7 diopters of hyperopia when the vitreous cavity is filled with silicone oil, and this puts them in the same range as the silicone oil filled aphakic eyes. High myopia, incomplete silicone oil filling, and several other factors influence the final optical outcome. The vitreoretinal surgeon must anticipate significant changes in refractive error when silicone is introduced into an eye or removed from the eye. Careful retinoscopy and refraction is essential for obtaining optimal vision in these patients.

Accuracy of topographic measurements with the optic nerve head analyzer

We used a plastic model of the human eye to study the accuracy with which the Optic Nerve Head Analyzer estimates the surface contour and two-dimensional size of the optic nerve head. Computer-generated contour lines were similar to the actual cross-sectional contour of plastic cups as photographed by scanning electron microscopy. The magnification error of computer-measured cup diameters was inversely related to the axial length of the model. The slope of this relationship was reduced with the use of either refraction or axial length as a correction factor for magnification error. Of the two correction factors, the former provided the closest estimation of the known diameters in the phakic model, while the latter performed better in the aphakic model.

Optics of the eye with air or silicone oil.

Replacement of intraocular contents with gas or silicone oil changes the optical characteristics of the eye. This affects the surgeons view of the fundus and the patients vision. Gullstrands schematic eye was used to calculate the refractive properties of eyes with air or silicone oil in the vitreous cavity or anterior chamber in phakia, aphakia, and pseudophakia. The article gives a general solution of the optical characteristics of the eye with any substance filling the eye or the vitreous cavity. Criteria are shown for selection of appropriate corneal contact lenses for visualization of the fundus during and after vitreous surgery.

Effect of Synthetic Cannabinoids on Elevated Intraocular Pressure

Two chemical derivatives of delta-1-tetrahydrocannabinol were evaluated in a randomized, double-masked study, administered as a single oral dose to a group of ocular hypertensive patients. One of the compounds (BW146Y) was found to have a significant intraocular pressure lowering effect that was independent of orthostatic blood pressure changes, although such changes did occur in some patients. The other compound (BW29Y) was ineffective in lowering intraocular pressure at the doses tested. Psychological and performance parameters were measured, and except for a time production test among the BW29Y group, these parameters were not significantly affected by the test drugs. Patients receiving both drugs experienced mild subjective side effects.

Aspects of rate-related hyperpolarization in feline Purkinje fibers.

We studied rate-related hyperpolarization (RRH) in feline Purkinje fibers by standard microelectrode techniques. Restrictions to ionic diffusion are shown to be less in this preparation than in canine preparations. The maximal hyperpolarization (VH) and time constant (T) for the exponentially decaying hyperpolarization following cessation of rapid drive were used as aggregate indices for the underlying rate of sodium pumping, the coupling ratio, and membrane resistance. Changes in VH and T in response to varying stimulation frequencies and durations of rapid drive, to cooling and addition of ouabain, and to changes in [K+]o and addition of cesium were used to assess the effects on RRH of sodium loading, pump inhibition, and short-circuiting potassium current, respectively. Steady state hyperpolarization was a linear function of stimulation frequency. Increased sodium loading led to an increase in VH, but no change in r. Onset and decay of RRH were symmetrical processes. The Qios of T and VH were 1.57 and 2.00, respectively. For a time after exposure to ouabain, T and VH were unchanged; later, T increased and VH decreased, both linearly with time. Relative membrane resistance decreased with rapid drive and increased with an exponentially decaying time course following cessation of rapid drive. Cesium immediately increased VH and decreased T, and led to progressive deterioration of the fibers. From the steady state equation for RRH, we show that one need not invoke a change in coupling ratio to account for the observed steady state hyperpolarizations. From the nonsteady state equation, we show that the Qit for VH is consistent with the Qio for Na*, K*-ATPase. Ore Reg 44: 813-634, 1979