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abstracts Edited by C. William Simcoe, M. D.

American Journal of Ophthalmology

Dailey RA, Samples JR, Van Buskirk EM: Reopening filtration fistulas with the neodymium-YAG laser. Am] Ophthalmol 102:491-495, 1986 The authors used the mode-locked Nd:YAG laser to reopen filtration fistulas in nine eyes in which the fistula had become occluded internally by a variably pigmented membrane, vitreous, or, in one case, cap­sular lens material. In five eyes filtration was suc­cessfully reestablished, reducing the intraocular pressure to less than 21 mm Hg (range 10 mm Hg to 20 mm Hg). The remaining four eyes had fistulas thought to be open internally after laser treatment; however, filtration was not established because of external subconjunctival scarring of the bleb. As with needling or argon laser fistular reopening, successful filtration followed Nd:YAG laser fistular surgery only when the fistula was occluded by an identifiable membrane and when the eye already had had a well-established bleb. The mode-locked Nd:YAG laser was used with a gonioprism to obliter­ate the occluding membrane and open the transcleral channel. An energy range of 0.7 mJ to 8.5 mJ was used with one to four pulses delivered at each firing.

Liesegang TJ, Bourne WM, Ilstrup DM: The use of hydroxypropyl methylcellulose in extracapsular cata­ract extraction with intraocular lens implantation. Am ] Ophthalmol 102:723-726, 1986

The authors conducted a prospective randomized clinical trial on the use of2% hydroxypropyl methyl­cellulose and 1 % sodium hyaluronate in the anterior chamber during anterior capsulotomy and nuclear expression in extracapsular cataract extraction with posterior chamber lens implantation in 70 patients. Both viscoelastic substances helped maintain the anterior chamber and facilitated the operation, although sodium hyaluronate was preferred. There was no excessive intraocular inflammation or toxicity noted with either agent. Patients given sodium hyaluronate had a larger increase in intraocular pres­sure during the early postoperative period (2.04 mm Hg) than did those given hydroxypropyl methylcellulose (1.1 mm Hg), but the difference was not significant. Nine weeks after surgery, the mean (± SD) central endothelial cell loss was 4.84% (± 7.26%) in the 17 eyes with sodium hyaluronate and 4.37% (±9.84%) in the 53 eyes with hydroxy­propyl methylcellulose. The intraocular pressure and corneal thickness were not significantly differ­ent before the operation and nine weeks after it. The chief advantage of hydroxy propyl methylcellulose is that it is readily available and should cost less than the naturally occurring organic molecules presently available.

J CATARACT REFRACT SURG-VOL 13, MARCH 1987

Mainster MA: The spectra, classification, and ratio­nale of ultraviolet-protective intraocular lenses. Am] Ophthalmoll02:727-732, 1986

Light can damage ocular tissues in three ways: through its ionizing effects, thermal effects, and photochemical effects. Ionizing effects are produced by Q-switched N d: YAG lasers with brief exposures, typically nanoseconds to picoseconds in duration. Thermal effects are produced with longer light exposures, typically between 0.1 and 0.5 seconds. They occur when a focused laser beam heats target tissues to a temperature high enough to produce a local inflammatory response. Photochemical effects are produced with even longer exposures, typically greater than 10 seconds in duration. They occur when light produces chemical reactions in target tissues, at light levels and temperature increases far below those needed for photocoagulation. Photo­chemical effects can be deliberate , as in laser exposure of tissues sensitized with a light-sensitive chromophore such as HpD derivative, or they can be inadvertent, as in photic retinopathy from solar observation, welding arc exposure, or operating microscope exposure. The authors measured the spectral transmittance of 16 implantable intraocular lenses (IOLs) from 12 manufacturers and examined the rationale for using ultraviolet-absorbing IOLs to protect pseudophakic individuals from photic retin­opathy. Each ultraviolet-protective lens was classi­fied by the wavelength at which its spectral transmit­tance fell to 10% in the blue or ultraviolet region of the spectrum. Current ultraviolet-protective IOLs differ in the effectiveness of their protection against photic retinopathy, and product descriptions may be misleading. Despite similar claims by manufac­turers, there is a wide disparity in the ultraviolet protection offered by ultraviolet-protective IOLs, ranging from excellent protection to poor protec­tion , to protection no better than clear poly­methylmethacrylate.

Meisler OM, Palestine AG, Vastine OW, Demartini DR, et al: Chronic Propionibacterium endophthal­mitis after extracapsular cataract extraction and intra­ocular lens implantation Am ] Ophthalmol 102: 733-739, 1986

The authors studied six cases of chronic, indolent intraocular inflammation that occurred after extra­capsular cataract extraction and posterior chamber intraocular lens implantation. The inflammation was characterized by a delayed onset and in three cases had the clinical appearance of a granulomatous iridocyclitis. Cultures of intraocular specimens ob­tained from six eyes yielded Propionibacterium; five yielded P. acnes. Pleomorphic gram-positive bacilli

consistent with Propionibacterium were identified in cytologic or histopathologic studies in four of the six culture-positive cases. After surgical and medical therapy, the inflammation resolved. Therapy consis­ted of surgical intervention, usually in combination with administration of intravitreal and systemic antibiotics. Surgical intervention included vitrec­tomy in all cases accompanied by removal of a portion or all of the posterior capsule in four. Removal of the intraocular lenses was unnecessary in four patients treated by pars plana vitrectomy. This would seem to be the preferred therapeutic approach. Propionibacterium acnes is sensitive to a wide spectrum of antibiotics, including penicillin and cephalosporins, which four of these patients received intraocularly. However, one patient re­ceived only gentamicin by intravitreal administra­tion, an antibiotic to which Propionibacterium may show resistance. Further, one patient was suc­cessfully treated without intraocular antibiotics. This suggests other mechanisms by which the infection is resolved: (1) systemically or locally administered antibiotics, (2) surgically reducing the intraocular infectious load, and (3) altering the infectious microenvironment of the Propionibac­terium. Postoperative Propionibacterium endoph­thalmitis may masquerade as a chronic iridocyclitis.

Insler MS, Zatzkis SM: Pigment dispersion syndrome in pseudophakic corneal transplants. Am ] Ophthal­mol 102:762-765, 1986

The authors observed the pigment dispersion syn­drome in two patients after keratoplasty with poste­rior chamber intraocular lenses. In addition to a heavily pigmented trabecular meshwork and iris trans illuminating defects, an inferior linear pig­mented endothelial line was seen in both patients. One patient developed glaucoma, which was well controlled with medication. These case reports are the first to document that fluctuation in intraocular pressure and transillumination defects (pigment dispersion syndrome) can occur after penetrating keratoplasty. Pigment precipitates on the graft en­dothelium and fine pigment cells in the anterior chamber should not be confused with an allograft reaction but should alert the transplant surgeon that a different process is occurring. Patients with intra­ocular lenses and corneal transplants should be examined periodically for iris transillumination de­fects and for increased pigmentation in the angle as well as wide variations in intraocular pressure , especially during the first year. Pigmented endo­theliallines in these patients appear in the inferior portion of the donor corneas, are linear, and are located close to the corneal wound margin.

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Archives of Ophthalmology

Tasman W: Are there any retinal contraindications to cataract extraction and posterior chamber lens im­plants? Arch Ophthalmol 104:1767-1768, 1986

Although extracapsular cataract surgery and poste­rior chamber intraocular lenses (IOLs) appear to have reduced the incidence of retinal detachment after cataract extraction, this apparently favorable effect has not been conclusively demonstrated and detachments do occur in pseudophakic eyes. Today's cataract surgeon must still individualize the therapy for each eye and must consider new and specific questions. Did this patient have a giant retinal tear in the other eye? Does he or she have a hereditary condition that predisposes to a malignant form of retinal detachment? Was there a penetrating injury involving the posterior segment of the eye? Can cortical material and the anterior lens capsule be adequately removed so that photocoagulation can be performed for branch vein occlusion, age-related macular degeneration, or diabetic retinopathy? This last question is particularly important in light of the results of recent collaborative studies, including the Early Treatment Diabetic Retinopathy Study, which reported a positive treatment effect with photo­coagulation for clinically evident macular edema. It is logical to predict that many more diabetics will receive photocoagulation. In summary, the retinal contraindication list has been considerably nar­rowed over the last few years, but it has not disappeared. While the treatment for each eye needs to be individualized, it is the author's opinion that anterior chamber lenses are contraindicated in eyes at high risk for retinal detachment, except for those in which vitreous loss has occurred if careful vitrectomy is performed. In addition, patients with untreated proliferative retinopathy due to diabetes, vein occlusion, or other causes; chronic or recurrent uveitis; Stickler's syndrome; a giant retinal break; and severe posterior penetrating trauma should presently be considered "offlimits" for an IOL, even if it were to be placed in the posterior chamber.

Stark WI, Whitney CE, Chandler }W, Worthen DM: Trends in intraocular lens implantation in the United States. Arch Ophthalmol 104:1769-1770, 1986

In light of recent government efforts at cost contain­ment and deficit reduction, the economic impor­tance of a large increase in the number of cataract operations is substantial. The overall number of cataract operations in the United States is difficult to assess precisely but some clues exist. Distributors and manufacturers of intraocular lenses (IOLs) are required to report the number and type of intraocu­lar lenses implanted to the Food and Drug Adminis-

tration; therefore, accurate data are available on lens implant usage. This communication presents the most recent statistics on IOLs implanted in the United States and presents data showing that the rapid growth in the number of operations per year may be reaching a plateau of approximately one million implantations per year. Changing indications for surgery resulted in a rapid increase in the number of patients receiving IOLs in the mid-1980s. With improved surgical technology and better reha­bilitation after IOL implantation, the indications for surgery have been liberalized. Patients are more likely to undergo surgery for symptoms of glare, with visual acuities measured by methods different from the usual Snellen visual acuity measurements. With depletion of the large reservoir of patients awaiting surgery under the old guidelines, the annual number of cataract operations appear to be adjusting to a new equilibrium rather than continu­ing the rapid increase of the first half of the decade. If the recent trend toward diminished growth in the number of surgeries per year persists, the number of lenses implanted per year should level off at just under one million.

Glasser DB, Matsuda M, Edelhauser HF: A compari­son of the efficacy and toxicity of and intraocular pressure response to viscous solutions in the anterior chamber. Arch Ophthalmol104:1819-1824, 1986

An intraocular lens abrasion test, vital dye staining, and scanning electron microscopy were used for an in vitro (fresh corneal buttons obtained from rabbits) comparison of endothelial protection offered by four viscous solutions of 1% sodium hyaluronate (Healon®), 3% sodium hyaluronate (AmVisc®), 4% chondroitin sulfate (Viscoat@J), and 2% methyl­cellulose. Wide-field specular microscopy with anal­ysis of endothelial cell density and morphologic evaluation, pachymetry, and intraocular pressure measurements were also used to study the toxicity of the viscous solutions in an in vivo cat model with and without anterior chamber washout. All four solu­tions provided complete endothelial protection from mechanical trauma. Endothelial cell density and morphologic nature were unaffected during the in vivo toxicity study. A mild increase in intraocular inflammation occurred at one and two days after intraocular injection with all four viscous solutions. Intraocular pressure elevations peaked within four hours after instillation of the viscous solutions and were significantly reduced by anterior chamber washout.

N anevicz TM, Prince MR, Gawande AA, Puliafito CA: Excimer laser ablation of the lens. Arch Ophthalmol 104:1825-1829, 1986

220 J CATARACT REFRACT SURG-VOL 13. MARCH 1987

Ablation of the bovine crystalline lens was studied using radiation from an excimer at four ultraviolet wavelengths as follows: 193 nm (argon fluoride), 248 nm (krypton fluoride), 308 nm (xenon chloride), and 351 nm (xenon fluoride). The ablation process was quantitated by measuring mass ablated with an electronic balance and characterized by examining ablation craters with scanning electron microscopy. The highest ablation rate was observed at 248 nm with lower rates at 193 nm and 308 nm. No ablation was observed at 351 nm. Scanning electron micros­copy revealed the smoothest craters at 193 nm while at 248 nm there was vacuolization in the crater walls and greater disruption of surrounding tissue. The craters made at 308 nm did not have as smooth a contour as the 193 nm lesions. The spectral absor­bance of the bovine lens was calculated at the wavelengths used for ablation and correlated with ablation rates and thresholds. High peak-power, pulsed ultraviolet laser radiation may have a role in surgical removal of the lens. In reviewing the results of this study, it is important to recognize that the spectral absorbance of the noncataractous human lens is known to be different from that of the normal bovine lens. Moreover, the spectral absorbance of the human lens changes with age, with an increase in pigmentation and corresponding increase in absor­bance in the 310-nm to 400-nm region. Further studies using cataractous human lenses as ablation targets are necessary. Nevertheless, this investiga­tion provides a framework within which future studies of the use of high-intensity ultraviolet laser radiation for removing human lens tissue can be pursued.

Ophthalmology

Shamsuddin AKM, Nirankari VS, Purnell DM, Chang SH: Is the corneal posterior cell layer truly endothelial? Ophthalmology 93:1298-1303, 1986

The posterior cell layer of the normal human cornea or "endothelium" was investigated by electron mi­croscopy and immunocytochemistry. Ultrastruc­turally, the cells lacked the characteristic marker for endothelial cells (Weibel-Palade body). Immu­noperoxidase studies demonstrated these cells to be negative for factor VIII antigen, but strongly posi­tive for keratine, vimentin, S-lOO protein, and neuron-specific enolase. The anterior epithelial cell layer showed identical immunoreactivity. These studies strongly suggest that (1) the posterior cell layer of the cornea lacks ultrastructural and immu­nocytochemical markers of endothelial cells and (2) both the anterior and posterior cell layers share similar cell markers. The presence of keratin, vi­mentin, neuron-specific enolase, and S-lOO protein in both the anterior and the posterior cell layers and the absence of factor VIII in both suggest that the cell layers may have similar origin. It has been shown elsewhere that both the anterior and poste­rior cell layer of avian cornea are of neural crest origin. The stromal cells of the cornea are also of neural crest origin. Furthermore, the neural crest is the delamination of the surface ectoderm. Thus, embryologically, both the anterior and posterior layers are similar in origin, but they may not be neural in origin. The authors propose that these cells be called the "posterior cell layer" because they have no resemblance to endothelial cells.

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