Compressive mechanical properties of bovine cortical bone under varied loading rates.

Bone tissue functions in varied mechanical systems of the body under static and dynamic conditions. Therefore, it is essential to understand the mechanical responses of bone at varied loading rates, especially those at fast loading rates. This study has investigated the effect of loading rate on the compressive mechanical properties of bovine cortical bone. Bone specimens of 3.85 mm in diameter and 7.7 mm in length were compressed longitudinally with the loading rates of 2 to 2000 mm/s (corresponding strain rates of 0.26 to 260 s(-1)). As a result, bovine cortical bone showed high linear elasticity when the loading rate was slow, and exhibited three definite regions of linear elasticity, plastic deformation, and densification at faster loading rates. The elastic modulus showed no dependency on the loading rate. Compressive strength, strain at fracture, and toughness increased as the loading rate increased under the condition that the loading rates were slower than each critical loading rate of 1000, 100, and 1500 mm/s, respectively. However, all showed no significant changes when the loading rates were faster than the corresponding critical loading rates. In conclusion, as the loading rate increased, changes in the compressive mechanical parameters were different depending on the parameter and the loading rate range. Compressive mechanical behaviour of bovine cortical bone showed a brittle nature under high strain rates (strain rates > 13 s(-1)). These findings should be reflected in the biomimetic simulation of biomaterials for bone tissue repair and engineering.

Surgical outcomes of 25-gauge pars plana vitrectomy for diabetic tractional retinal detachment.

PURPOSE: To evaluate the outcomes and complications of 25-gauge (G) pars plana vitrectomy (PPV) for repair of diabetic tractional retinal detachment (TRD). METHODS: Retrospective review of consecutive, single-surgeon 25-G PPV cases between July 2007 and July 2014. Seventy eyes from 55 patients were operated on for diabetic TRD; all eyes were tamponaded with sulfur hexafluoride, octofluoropropane, silicone oil, or balanced salt solution. Mean age at surgery was 47.7 years (range 23-76 years), and mean length of follow-up was 713 days (range 90-2368 days; median 671 days). Primary outcomes included best-corrected visual acuity (BCVA), intraocular pressure (IOP), anatomic success, redetachment, and endophthalmitis. RESULTS: Preoperatively, 49 eyes (70%) had a concurrent rhegmatogenous component (8 of which also had proliferative vitreoretinopathy (PVR)). Mean BCVA improved from logarithm of the minimal angle of resolution 1.59 (20/800, SD 0.88) to 0.68 postoperatively (20/100, 0.77), P-value<0.001. Mean IOP increased from 15.9 to 20 mm Hg 1 day after surgery. Elevated postoperative IOP (≥ 22 mm Hg) occurred in 25 eyes, and low IOP (≤ 5 mm Hg) occurred in 2 eyes. Primary reattachment was achieved in 63 eyes (90%), and final anatomical success occurred in 69 eyes (99%). There were no cases of endophthalmitis. CONCLUSIONS: Twenty-five-G PPV repair was safe and effective in the repair of diabetic TRD, including eyes with a combined rhegmatogenous detachment or PVR. Gas, silicone oil, and balanced salt solution tamponading agents all proved to be efficacious in this surgical population.

Human scleral permeability. Effects of age, cryotherapy, transscleral diode laser, and surgical thinning.

PURPOSE: To determine the in vitro permeability of human sclera to compounds varying in molecular weight. To evaluate the effects of age, cryotherapy, transscleral diode laser, and surgical thinning on scleral permeability. METHODS: Scleral tissue from 97 human eye bank eyes was tested individually in a two-chamber Ussing apparatus with the following hydrophilic radiolabeled compounds on one side of the chamber: 5-fluorouracil, sucrose, dexamethasone, methotrexate, inulin, and three separate dextran polymers (MWt = 10,000, 40,000, and 70,000). Scleral hydration levels were obtained on 20 more scleral specimens. Additional groups of scleral specimens were treated with either a cryotherapy probe, a transscleral diode laser retinopexy probe, or partial thickness lamellar dissection, and specimens were mounted in the Ussing chambers for testing. Scleral tissue was digested to measure the amount of radioactivity present. Scleral sections were examined with electron microscopy. RESULTS: Scleral hydration was maintained during the perfusion. The mean scleral permeability (cm/second x 10(-6) +/- SD) was established for each of the above compounds. Age, cryotherapy, or diode laser treatment did not alter permeability or ultrastructure of the sclera. Surgical thinning significantly increased the scleral permeability to dexamethasone (P = 0.011) and methotrexate (P = 0.037). CONCLUSION: This study establishes baseline human scleral permeability to a series of hydrophilic compounds with various molecular weights. Age, cryotherapy, and diode laser treatment do not alter the permeability or ultrastructure of the sclera, whereas surgical thinning significantly increases permeability.

Angiopoietin-1 upregulation by vascular endothelial growth factor in human retinal pigment epithelial cells.

PURPOSE: To determine whether vascular endothelial growth factor (VEGF) regulates angiopoietin (Ang)-1 and -2 expression in retinal pigment epithelial (RPE) cells. METHODS: Expression of VEGF, Ang1, and Ang2 in surgically removed human choroidal neovascular membranes (CNVMs) was analyzed by double-label confocal immunofluorescence microscopy. Total RNA was extracted from cultured human RPE cells treated with VEGF for mRNA analysis. Northern blot analysis was performed to examine the time course and dose response of Ang1 and Ang2 mRNA expression. mRNA stability and nuclear run-on analyses were performed. Secreted Ang1 and Ang2 protein levels in conditioned media from RPE cells were examined by Western blot analysis. RESULTS: Ang1 and Ang2 immunostaining colocalized with VEGF-positive stromal cells in human CNVMS: Ang1 and Ang2 mRNAs were expressed by cultured serum-starved RPE cells. VEGF upregulated Ang1 mRNA in a time- and dose-dependent manner without a significant change in Ang2 mRNA. Ang1 and Ang2 mRNAs in RPE cells were as stable as that of S18. VEGF stimulation further increased the half-life of Ang1 mRNA, but did not alter its transcription rate. VEGF increased the amount of Ang1, but not Ang2, protein secreted into the medium. CONCLUSIONS: The colocalization of Ang1 and Ang2 with VEGF in CNVM stromal cells and the upregulation of Ang1 expression by VEGF in cultured RPE cells suggest that VEGF may selectively modulate Ang expression during CNV.

Aminoglycoside toxicity in the treatment of endophthalmitis. The Aminoglycoside Toxicity Study Group.

OBJECTIVE AND METHODS: Intravitreous aminoglycosides are widely used for the treatment and prophylaxis of endophthalmitis. Because the toxicity of 0.4 mg of gentamicin sulfate is well documented, many surgeons now use amikacin sulfate or low-dose gentamicin to reduce the risk of macular infarction. A survey of retinal specialists has suggested that amikacin or low-dose gentamicin can also cause macular toxic side effects. To further investigate this issue, the critical details of the case histories, findings, and course of 13 patients who received intravitreous injections of 0.2 to 0.4 mg of amikacin sulfate or 0.1 to 0.2 mg of gentamicin sulfate for prophylaxis or treatment of endophthalmitis are summarized. For several patients, complete case histories and a fluorescein angiogram are provided. RESULTS: These cases suggest that amikacin and low-dose gentamicin, similar to gentamicin sulfate at a dose of 0.4 mg, can cause macular infarction. The causative dose cannot be ascertained in any of the cases, but doses were prepared by hospital pharmacists using typewritten protocols, a practice that helps to prevent dilution errors. Several of these cases differ from previously reported cases of aminoglycoside toxicity in that the involvement of the macula was quite discrete. Most of the patients suffered severe visual loss, but two patients, in whom most of the nonperfusion was adjacent to the macula and in whom some of the perifoveal capillaries were spared, recovered 20/50 visual acuity. CONCLUSIONS: These cases emphasize the potential hazards of the intravitreous use of aminoglycosides. A toxic reaction can occur even when injection of low doses is intended and precautions are made to avoid dilution errors. A localized increase in concentration in dependent areas of the retina may play a role in aminoglycoside toxicity. If some of the perifoveal capillaries are spared, retention of some central vision is possible. Consideration should be given to substituting ceftazidime for aminoglycosides for the treatment and prophylaxis of endophthalmitis.

Pilot trial of transscleral diode laser retinopexy in retinal detachment surgery.

OBJECTIVE: To evaluate the safety and efficacy of the transscleral diode laser for retinopexy in rhegmatogenous retinal detachments. DESIGN: Ten consecutive patients with primary rhegmatogenous retinal detachments underwent scleral buckling surgery, using the transscleral diode laser for retinopexy. Patients were followed up for at least 6 months. STUDY PARTICIPANTS: Ten patients with primary rhegmatogenous retinal detachments were enrolled. Patients with chronic detachments, a retinal break greater than 90 degrees, history of uveitis or infectious retinopathy, or proliferative vitreoretinopathy were excluded. MAIN OUTCOME MEASURE: Retinal reattachment. Secondary measures: visual acuity and complications, including choroidal, retinal, and vitreous hemorrhage, inflammation, and scleral damage. RESULTS: By 6 months, nine of 10 retinas were successfully repaired following only one operation. The retina of the 10th patient redetached at 6 1/2 weeks owing to proliferative vitreoretinopathy. Following a vitrectomy and retinal reattachment procedure, the retina of the 10th patient has remained attached for 1 year. No significant complications were encountered with the laser retinopexy, although small presumed breaks in Bruch's membrane occurred in three eyes and a moderate scleral thermal effect occurred in two. Visual results in the postoperative course were comparable to those achieved previously with cryotherapy. CONCLUSION: In this pilot series, transscleral diode laser retinopexy served as a safe and effective means of obtaining chorioretinal adhesion in retinal detachment surgery.

Intraocular penetration of topical tissue plasminogen activator.

Fifty-eight eyes of 31 anesthetized rabbits received one drop of proparacaine hydrochloride, 0.05%, and two drops of tissue plasminogen activator (tPA) separated by 5 minutes. Four eyes of two additional rabbits had epithelial defects created before drug delivery. Tissue plasminogen activator in multiple doses was given to eight eyes of four other rabbits. We used this dosing regimen to investigate the effect of topical tPA on anterior chamber fibrin clots in three rabbits. A two-site enzyme-linked immunosorbent assay test was used to measure tPA levels in the aqueous samples, obtained by paracentesis in each eye. Of 53 eyes treated with the original dosing regimen, 21 (40%) had detectable tPA aqueous levels. Blood and aqueous from eyes of untreated control rabbits, contralateral control eyes of treated rabbits, and eyes with epithelial defects had nondetectable tPA. Multiple tPA drop dosing resulted in 75% of aqueous samples with detectable tPA and a higher average tPA concentration than the original dosing regimen. Eyes treated with tPA showed a significantly faster resolution of anterior chamber fibrin clots than did control eyes.

The role of gravity in gentamicin-induced toxic effects in a rabbit model.

OBJECTIVE: To define the role of gravity in gentamicin sulfate-induced retinal toxic effects by injecting the drug into vitrectomized rabbit eyes oriented in one of two positions. METHODS: Ten right eyes of New Zealand white rabbits underwent a two-port pars plana vitrectomy and were positioned with traction scleral sutures to rotate the medullary ray superiorly (five eyes) or nasally (five eyes). Six eyes received a pars plana intravitreal injection of 400 micrograms (0.1 mL) of gentamicin, and four eyes received 0.1 mL of balanced salt solution only. All eyes were kept in position for 30 minutes after the injection. Unoperated-on fellow eyes served as controls. Three or 5 days later, the eyes were enucleated and histopathologic examination was performed. RESULTS: Light and electron microscopy of gentamicin-treated eyes showed inner-retinal edema and disruption of the nerve-fiber and ganglion-cell layers within the more dependent retina vs sparing of the less dependent half of the retina. Eyes that received balanced salt solution showed rare inflammatory cells along the inner-retinal surface but essentially no inner-layer disruption. Examination of unoperated-on control eyes showed no inflammatory cells, edema, or necrosis. CONCLUSION: Gravitational effects and positioning contribute to the location of gentamicin-induced retinal toxic effects in vitrectomized eyes.

A new syndrome of myelinated nerve fibers, vitreoretinopathy, and skeletal malformations.

OBJECTIVE: To report a new vitreoretinopathy with high myopia, myelinated nerve fibers, and skeletal abnormalities. PATIENTS: A mother and daughter with a previously undescribed constellation of severe vitreoretinal degeneration with high myopia and extensive myelination of the retinal nerve fiber layer, and in addition, the daughter has limb reduction deformities. Vision was severely impaired in both patients and results of electroretinography indicated the presence of cone and rod dysfunction. CONCLUSION: This is a previously undescribed autosomal dominant vitreoretinopathy with congenital poor vision, vitreoretinal degeneration, myelinated nerve fibers, and skeletal deformities.

Penetrating ocular injury from contaminated eating utensils.

Although the rate of infectious endophthalmitis following penetrating ocular injury is generally less than 10%, certain settings may carry a greater risk of infection. One such setting is penetrating injury resulting from eating utensils contaminated with oral flora. We reviewed six of these injuries. Culture-positive bacterial endophthalmitis developed in four of the six eyes; only one of the eyes retained reading visual acuity (greater than 20/50) and two eyes lost light perception. The potential for infection and limited visual outcome in this series warrants aggressive prophylaxis and treatment. The unexpected isolation of Haemophilus influenzae in two of the four infections suggests that broad-spectrum antibiotic treatment should be considered in all such injuries since less common organisms may be encountered.

Assessment of intraocular pressure in vitrectomized gas-containing eyes. A clinical and manometric comparison of the Tono-Pen to the pneumotonometer.

Elevation of intraocular pressure (IOP) in gas-containing eyes occurs not infrequently, and applanation tonometry in eyes with epithelial irregularities is not accurate. The pneumotonometer and TonoPen (Oculab, La Jolla, Calif) are alternative tonometers for use in these eyes, yet the accuracy of determining IOP with the Tono-Pen has not been determined manometrically. We performed a clinical and manometric study comparing the Tono-Pen with the pneumotonometer in gasfilled vitrectomized eyes. In our clinical study, we measured IOP in 50 eyes of 50 patients with corneal irregularities following vitrectomy and air/gas-fluid exchange. Tono-Pen measurements were highly correlated with those of the pneumotonometer. However, there was a mean difference of 1.4 mm Hg between Tono-Pen and pneumotonometer IOP readings. A larger percentage of Tono-Pen readings were lower than those of the pneumotonometer as IOP levels increased. To assess the accuracy of these tonometers, we compared manometric readings via an indwelling catheter with Tono-Pen and pneumotonometer IOP readings in 11 eye bank eyes following a lensectomy, vitrectomy, and air-fluid exchange. Overall, Tono-Pen and pneumotonometer readings were highly correlated with those of the manometer. However, both machines showed a significant underestimation of IOP at pressures greater than or equal to 30 mm Hg; pneumotonometer and Tono-Pen readings averaged 10.2 and 12.1 mm Hg lower, respectively, than those of the manometer. We conclude that both the pneumotonometer and the Tono-Pen underestimate IOP at pressures greater than or equal to 30 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Iatrogenic choroidal neovascularization.

Iatrogenic choroidal neovascularization is an uncommon complication of laser photocoagulation and other ocular surgical procedures. It appears to be the result of a number of conditions, including damaged Bruch's membrane and/or retinal pigment epithelium, whose reparative processes trigger the release of angiogenic factors. Inflammatory cells and choroidal ischemia may also play a role. The prognosis varies depending on the underlying disease and the type of choroidal neovascularization (subretinal, chorioretinal, or choriovitreal). Minimizing the amount of laser energy used during laser procedures, avoiding repeat laser treatment to the same retinal area, and minimizing direct mechanical trauma to the retinal pigment epithelium and choroid decrease the chance of inducing iatrogenic choroidal neovascularization.

What to tell the patient with optic neuritis about multiple sclerosis.

If the ophthalmologist tells the patient with an initial isolated attack of optic neuritis that multiple sclerosis may develop, will he/she worry the patient needlessly or provide useful information that the patient is rightfully entitled to have? In this set of articles, the philosophies and individual circumstances that should influence the ophthalmologist in deciding what information to supply are discussed.

Comparison of the Challenger digital applanation tonometer and the Goldmann applanation tonometer.

We compared the Challenger electronic tonometer to the Goldmann applanation tonometer in 70 eyes without corneal abnormalities. There was a good overall correlation between the two machines. Correlations between interobserver readings were excellent, demonstrating that obtaining reproducible measurements is possible with either machine. However, the scattergrams indicated that the Challenger tonometer gave consistently lower readings and showed more variability than the Goldmann tonometer. Additionally, the mean underestimation of intraocular pressure increased as the intraocular pressure increased above 20 mm Hg. Therefore, the Challenger electronic tonometer as presently calibrated is not accurate enough for clinical use in the detection and management of glaucoma.

Foveomacular dystrophy.

We reviewed the clinical records of 47 patients (92 eyes) at the Wilmer Institute in whom foveomacular dystrophy had been diagnosed between 1977 and 1990 to determine reasons for initial examination, long-term visual prognosis, and the factors associated with visual loss. From each clinical record, we obtained the patient's age at the time first seen, symptoms, initial and final visual acuity, lesion size and appearance, and results of fluorescein angiography, electroretinography, and electro-oculography. The most common reasons for examination were decreased visual acuity in 25 of the 47 patients (53%), metamorphopsia in six (13%), referral for diagnosis in seven (15%), and misdiagnosis of age-related macular degeneration in seven (15%). Over an average follow-up period of 5.0 years, in 29 patients (56 eyes), visual acuity changed less than two lines in 41 eyes and decreased greater than or equal to two lines in 15 eyes. In most patients with foveomacular dystrophy, visual acuity appears to remain relatively stable.

Indocyanine green angiography-guided photocoagulation of choroidal neovascularization associated with retinal pigment epithelial detachment.

PURPOSE: To determine visual acuity outcome after indocyanine green angiography-guided laser photocoagulation of choroidal neovascularization associated with pigment epithelial detachment in eyes with age-related macular degeneration. METHODS: We retrospectively reviewed pretreatment and posttreatment visual acuity after laser photocoagulation to well-demarcated hyperfluorescent areas seen with indocyanine green angiography adjacent to or within pigment epithelial detachments in 20 eyes of 20 patients with age-related macular degeneration and suspected choroidal neovascularization. RESULTS: Visual acuity before and after laser photocoagulation was followed up for 3 to 24 months (median, 9 months). At 3 months after laser photocoagulation, visual acuity had improved 2 or more Snellen lines in two eyes (10%), worsened by 2 or more lines in 10 (50%), and remained unchanged in eight of 20 (40%). By 6 months after laser photocoagulation, visual acuity had improved by 2 or more lines in two eyes (12%), worsened by 2 or more lines in nine (53%), and remained unchanged in six of 17 (35%). At 9 months after laser photocoagulation, visual acuity had improved by 2 or more lines in one eye (9%), worsened by 2 or more lines in nine (82%), and remained unchanged in one of 11 (9%). CONCLUSIONS: Indocyanine green angiography-guided laser photocoagulation may temporarily stabilize visual acuity in some eyes with choroidal neovascularization associated with pigment epithelial detachments, but final visual acuity decreases with time.

Multiple evanescent white dot syndrome in older patients.

PURPOSE: To report two patients in their seventh decade who exhibited findings consistent with multiple evanescent white dot syndrome. METHODS: Case reports of two patients referred for evaluation of decreased vision, visual field loss, and retinal white spots. RESULTS: A 60-year-old man and a 67-year-old woman had photopsia, visual field loss, and decreased central visual acuity. Examination disclosed numerous white retinal spots, ranging from 50 to 400 microm, with eventual foveal granularity. Visual field testing showed an enlarged blind spot and peripheral field defects. Fluorescein angiography, electroretinography, and electrooculography results were consistent with multiple evanescent white dot syndrome. Eventually, the retinal lesions resolved in both patients and baseline visual acuity was recovered. CONCLUSION: A diagnosis of multiple evanescent white dot syndrome should be considered in patients with retinal findings typical of multiple evanescent white dot syndrome, regardless of age.

Selective use of indocyanine green angiography for occult choroidal neovascularization.

PURPOSE: Indocyanine green angiography is useful in situations where fluorescein angiography shows occult choroidal neovascularization or pigment epithelial detachment. We sought to determine how often the selective application of indocyanine green angiography results in useful information for eyes with occult choroidal neovascularization. METHODS: We reviewed 153 consecutive indocyanine green angiograms and identified 77 in which corresponding fluorescein angiograms showed occult choroidal neovascularization or pigment epithelial detachment. We examined the indocyanine green angiograms to detect areas of hyperfluorescence and to classify the margins of hyperfluorescence as well demarcated or poorly demarcated. RESULTS: Of 77 eyes, 42 (55%) eyes had occult choroidal neovascularization by fluorescein angiography, seven (9%) eyes had both classic and occult choroidal neovascularization by fluorescein angiography, and 28 (36%) eyes had pigment epithelial detachments. Of 42 eyes with occult choroidal neovascularization by fluorescein angiography, 21 (50%) had well-demarcated margins, 13 (31%) had poorly demarcated margins, and eight (19%) had no detectable hyperfluorescence by indocyanine green angiography. Of seven eyes with both classic and occult choroidal neovascularization by fluorescein angiography, two had both poorly demarcated and well-demarcated borders, two had only poorly demarcated borders, and three had well-demarcated borders by indocyanine green. The indocyanine green angiogram showed 23 (82%) of 28 pigment epithelial detachments to have well-demarcated borders of hyperfluorescence; 13 (57%) of 23 were treated. CONCLUSION: Indocyanine green angiography adds clinically useful information to fluorescein angiography by demonstrating well-demarcated areas of hyperfluorescence in 50% of eyes selected because of diagnosis of occult choroidal neovascularization and in 82% of eyes selected because of pigment epithelial detachment.

Postoperative hypopyon after intravitreal bovine thrombin for macular hole surgery.

PURPOSE: We used intravitreal autologous fibrinogen with bovine thrombin for the surgical closure of macular holes in 60 cases. METHODS: Pars plana vitrectomy with separation of the posterior cortical vitreous was performed after air/fluid exchange. One to two drops each of autologous fibrinogen and bovine thrombin (20 to 80 U) were instilled in each patient. RESULTS: Five (8%) of 60 patients developed a hypopyon without unusual pain on the first postoperative day. Inflammation responded to frequent topical corticosteroids within 48 to 72 hours. CONCLUSION: Postvitrectomy hypopyon after the use of bovine thrombin may represent an immune reaction that must be differentiated from endophthalmitis. We recommend careful observation and frequent topical corticosteroids.

Laser treatment of choroidal neovascularization in patients with angioid streaks.

The benefit of laser photocoagulation to choroidal neovascularization secondary to angioid streaks remains controversial. To further expand our knowledge, we reviewed the records of 20 patients (24 eyes) with classic (well-defined) choroidal neovascularization secondary to angioid streaks, who were treated with laser between 1982 and 1991 at the Retinal Vascular Center of the Wilmer Institute. The choroidal neovascularization was extrafoveal in 18 (75%), juxtafoveal in two, subfoveal in three, and indeterminate in one eye. Seventeen of the 24 fellow eyes (71%) had a disciform scar or choroidal neovascularization, or both. Follow-up ranged from three months to nine years (mean, 3.5 years; median, two years). Lines of visual acuity change averaged -2.5 at three, -2.6 at six, -2.4 at 12, and -4.8 lines at 24 months. Choroidal neovascularization persisted in five of 24 eyes and recurred in nine of the remaining 19 eyes at risk. When the fellow eye had choroidal neovascularization, scar, or both, at the time of treatment, the rate of persistence or recurrence was 65% vs 33% if the fellow eye had no choroidal neovascularization, scar, or both. An average of four lines of visual acuity was lost when fellow eyes had choroidal neovascularization, scar, or both, vs one line when the fellow eye had no choroidal neovascularization or scar. Laser photocoagulation of choroidal neovascularization in patients with angioid streaks can result in closure of the choroidal neovascularization and stabilization of visual acuity.