Expansion of long-acting gas bubbles for intraocular use. Principles and practice.

Expansion of long-acting gas bubbles used in vitreoretinal surgery may lead to increased intraocular pressure and central retinal artery occlusion. To further understand the principles controlling the expansion of long-acting gases, we compared the expansion of perfluoropropane gas bubbles with that of sulfur hexafluoride gas bubbles in an in vitro model, as well as in rabbits. We found that perfluoropropane bubbles expand more rapidly and to a greater extent than do sulfur hexafluoride bubbles in the first 24 hours. The early rate of expansion of a long-acting gas is largely dependent on convection of the surrounding fluid and is independent of the type of long-acting gas. Early postoperative monitoring of intraocular pressure is, therefore, equally important when using any long-acting gas.

Effect of silicone oil viscosity on emulsification.

Emulsification of intravitreal silicone oil has been observed as a late complication after its use as a retinal tamponade. We compared the emulsification potential of silicone oil of different viscosities (100 centistokes [cs], 1000 cs, and 12,500 cs) and molecular composition in an in vitro model using a commercial detergent (benzalkonium chloride) and physiologic surface-active agents (human serum and lysed red blood cells). We found that silicone oils that have low-molecular-weight contents emulsify more readily than those that do not. Moreover, the extent and susceptibility to emulsification increases with decreasing viscosity or with an increase in the proportion of low-molecular-weight constituents. Hence, higher-molecular-weight (viscosity) oils or removal of low-molecular-weight components from medical grade fluid may lessen the emulsification observed clinically.

Exudative retinal detachment after photodynamic injury.

Exudative retinal detachments occur in a variety of retinal and choroidal diseases. We created serous retinal detachment in the cat eye by means of photodynamic injury produced by activation of intravascular rose bengal using filtered, focused light (550 nm). Fluorescein angiography later revealed focal retinal and choroidal vascular occlusion surrounded by a larger area of leakage through the pigment epithelium. Serous retinal detachments occurred rapidly, gradually enlarged over the next 3 days, and resolved in all eyes after 14 to 21 days. Histopathologic and ultrastructural features of early lesions included the accumulation of proteinaceous fluid in the subretinal space, pigment epithelial cell damage, and localized occlusion of retinal vessels and the choriocapillaris. Later changes consisted of limited regeneration of the retina and portions of the tapetum. In several respects, these experimental detachments resemble the serous retinal detachments associated with choroidal ischemia in humans, and may serve as a useful model in the study of choroidal microvascular hypoperfusion.

Controlled aspiration of subretinal fluid in the diagnosis of carcinoma metastatic to the choroid.

Carcinoma metastatic to the choroid was diagnosed in three patients by cytopathologic examination of subretinal fluid. The specimen was obtained using a scleral depressor modified to allow controlled aspiration of subretinal fluid through a sharp, angled, 30-gauge needle. This new method provides a useful tool for accurate diagnosis of carcinoma metastatic to the choroid in cases where the diagnosis is in question.

Photochemical initiation of thrombosis. Fluorescein angiographic, histologic, and ultrastructural alterations in the choroid, retinal pigment epithelium, and retina.

A new method of producing vascular occlusion, photochemical activation of intravenously injected rose bengal, was used to produce experimental thrombosis of the preretinal and choroidal blood vessels in rabbit eyes. Fluorescein angiography and light and electron microscopy were used to describe the resultant pathologic alterations over time. As early as one hour after treatment, the endothelium of both preretinal and choroidal blood vessels was severely damaged or completely obliterated, and platelet aggregates occluded the vascular lumina. Occlusion of the preretinal and choroidal blood vessels persisted for up to three days; however, endothelial regeneration and reperfusion had occurred in both vascular beds by seven days. In addition, the retinal pigment epithelium and myelin wings suffered ischemic damage. The retinal pigment epithelium began to recover by seven days, but the myelin wings appeared to be irreversibly damaged.

A new method for vascular occlusion. Photochemical initiation of thrombosis.

A new photochemical method has been used to produce focal thrombosis and occlusion of the blood vessels on the surface of the myelin wings of rabbit retinas. Following intravenous injection of rose bengal, the vessels next to the disc on the nasal wing were exposed to filtered light (550 nm, the absorption maximum of rose bengal) for four minutes. As a control, the vessels on the temporal wing of each rabbit eye were exposed to filtered light for four minutes before the injection of rose bengal. Complete vascular occlusion was produced on the nasal wing in all eyes, with no visible alterations on the temporal wing. Progressive reopening of the arteries on the nasal wing was observed at three days, with reopening of the veins visible by seven days. Reperfusion of capillaries had occurred by 21 days. Light and electron microscopic examination of blood vessels on the nasal wing after light exposure with rose bengal showed disrupted endothelial cells in all exposed blood vessels and platelet aggregates in the arteries and arterioles. No morphologic abnormalities were observed in the temporal wings. This method should be useful in studying the effects of vascular occlusion in the retina and could lead to a new treatment modality for subretinal, iris, or corneal neovascularization.

Interferon-associated retinopathy.

Interferon alfa is used to treat various systemic disorders and recently has been suggested as a possible treatment for choroidal neovascularization. We report 10 cases of retinal ischemia associated with the use of interferon alfa for various illnesses. The retinal findings include cotton-wool spot formation, capillary nonperfusion, arteriolar occlusion, and hemorrhage. The retinal complications may sometimes be reversible when treatment is stopped. Our findings emphasize the need to have patients who are receiving interferon alfa therapy monitored for these retinal complications, which may rarely be associated with permanent loss of vision secondary to closure of retinal capillaries.

Hemeralopia in an older adult.

An elderly male was referred for evaluation of hemeralopia when cataract extraction did not alleviate his symptom of difficulty seeing in bright illumination. Visual acuity was 20/40 OU. Funduscopic examination revealed marked arteriolar attenuation, disc pallor, and retinal pigment epithelial changes. Visual fields demonstrated relative paracentral scotomata. An ERG was consistent with widespread photoreceptor degeneration. A diagnosis of visual paraneoplastic syndrome was made and an extensive systemic evaluation revealed a squamous cell carcinoma of the lung. The presentation and evaluation of acquired photoreceptor dysfunction in adulthood is discussed.

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.

Oximetry of retinal vessels by dual-wavelength imaging: calibration and influence of pigmentation.

A method for noninvasive measurement of Hb O2 saturation (SO2) in retinal blood vessels by digital imaging was developed and tested. Images of vessels were recorded at O2-sensitive and O2-insensitive wavelengths (600 and 569 nm, respectively) by using a modified fundus camera with an image splitter coupled to an 18-bit digital camera. Retinal arterial SO2 was varied experimentally by having subjects breathe mixtures of O2 and N2 while systemic arterial SO2 was monitored with a pulse oximeter. Optical densities (ODs) of vascular segments were determined using a computer algorithm to track the path of reflected light intensity along vessels. During graded hypoxia the OD ratio (ODR = OD600/OD569) bore an inverse linear relationship to systemic SO2. Compensation for the influence of choroidal pigmentation significantly reduced variation in the arterial SO2 measurements among subjects. An O2 sensitivity of 0.00504 +/- 0.00029 (SE) ODR units/%SO2 was determined. Retinal venous SO2 at normoxia was 55 +/- 3.38% (SE). Breathing 100% O2 increased venous SO2 by 19.2 +/- 2.9%. This technique, when combined with blood flow studies in human subjects, will enable the study of retinal O2 utilization under experimental and various disease conditions.

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.

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.

Computer-assisted composition and reproduction of ophthalmic documentation.

We use computer software graphics (MacPaint) to create individualized drawings that can be reproduced as high-resolution printouts, kept in disk storage, or transmitted via telephone lines.

Computerized scoring and graphing of the Farnsworth-Munsell 100-hue color vision test.

The Farnsworth-Munsell 100-hue test is a sensitive and accurate test of color discrimination. A major disadvantage of the test is the laborious and time-consuming calculation needed to score the results and plot them on a chart for interpretation. We present a computer program, written in Microsoft's BASIC language, that performs the calculation and reports both the individual color cap error scores (from which the graph is plotted) and the total error score. If used with an IBM personal computer (or compatible) capable of graphics, the program plots a graph in a modified polar coordinate format that can be printed on a dot-matrix printer.

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.

Autologous marrow injection for delayed unions of the tibia: a preliminary report.

Over a 3-year period, we have treated 10 delayed unions of the tibia by using percutaneous marrow injection rather than standard operative bone grafting. Nine of the 10 fractures responded by forming callus in the area where the marrow was injected. This relatively simple technique avoided potential problems associated with operative grafting methods that have been standard for at least 50 years. Most importantly, it encourages early treatment of fractures when healing problems are anticipated or are becoming evident.

A 10-year-old girl with a left little-finger deformity.

The following case is presented to illustrate the roentgenographic and clinical findings of a condition of interest to orthopedic surgeons. The initial history, results of the physical examination, and roentgenographic findings are presented on this and the next page. The clinical and roentgenographic diagnoses follow.

Functional distal interphalangeal joint splinting for trigger finger in laborers: a review and cadaver investigation.

This two-part study evaluates the efficacy of functional distal interphalangeal joint (DIP) splinting for the treatment of trigger finger. Thirty-one fingers from 21 meat packing plant workers were treated with DIP splinting. A single corticosteroid injection was offered if triggering was stage 4 or greater. All workers returned to work immediately. Eighty-one percent of the digits were treated successfully (mean follow-up: 1 year). Treatment failure correlated with duration of symptoms and stage of triggering but did not correlate with age, race, sex, disease in multiple digits, or prior treatment. For the second part of the study, the effect of DIP splinting on flexor digitorum profundus (FDP) tendon excursion was studied in 16 fingers from 4 fresh cadavers. Excursion decreased 4.8 mm for the Stax splint and 4.2 mm for the dorsal Alumafoam splint. We conclude that DIP splinting provides a reliable and functional means of treating work-related trigger finger without lost time from work. Our cadaver investigation supports our theory that DIP splinting significantly decreases FDP excursion.

The role of a composite, demineralized bone matrix and bone marrow in the treatment of osseous defects.

The efficacy of demineralized bone matrix (DBM) used alone and with bone marrow as a graft material in the treatment of osseous defects was evaluated in 48 patients. Of these 48 patients, 39 were available to follow up and review. Follow up averaged 19 months for all patients. In the entire series, 30 of 39 patients demonstrated osseous union for a 77% success rate. Patients with fracture nonunion represented the most recalcitrant group clinically, with union achieved in only 61% of these cases. Overall, the 39 patients grafted with DBM demonstrated healing that was comparable to results achieved with standard iliac crest bone graft. The results indicate the DBM and marrow composite grafting is a suitable alternative to autologous iliac crest bone graft for use in certain clinical situations, such as bone defects in children, comminuted fractures with associated bone loss, nonunited fractures, or to augment an intended arthrodesis site.