Midvitreous Cavity Research Articles

A new approach to stage 3 macular holes

Purpose The purpose of this article is to demonstrate the feasibility of a surgical approach that might be possible in an office setting for idiopathic stage 3 macular holes. The posterior hyaloid of the vitreous and perihole tissue is enzymatically manipulated to create an atraumatic posterior vitreous separation and may stimulate cell proliferation to close macular holes. Design Prospective noncomparative interventional case series. Participants Nine eyes of eight patients with idiopathic stage 3 macular holes were treated. Methods The patients were treated with an injection of 0.4 IU of autologous plasmin enzyme into the midvitreous cavity and lavage of the vitreous cavity with an infusion light pipe and vitreous cutter followed by filling 70% to 80% of the vitreous cavity with 14% C3F8 and head-down positioning. Main outcome measures Posterior vitreous detachment, macular hole closure, and vision improvement. Results Eight of nine eyes showed a spontaneous posterior vitreous detachment. One eye required minimal suction of less than 50 mmHg to elevate the posterior hyaloid off the retinal surface. Eyes were followed for a minimum of 6 months. All holes closed, and there was an average visual acuity improvement of four lines. The average surgical time for this procedure was 20 minutes. Conclusions Autologous plasmin enzyme–assisted vitreous surgery techniques can reduce operative time, expense, and patient inconvenience while maintaining excellent surgical results, which may allow office-based vitreous surgery for idiopathic stage 3 macular holes.

PHARMACOKINETICS OF THE FLUOCINOLONE/5-FLUOROURACIL CODRUG IN THE GAS-FILLED EYE

Purpose: To determine the effect of intraocular gas tamponade on drug levels achieved with the intravitreal sustained-release fluocinolone (FL)/5-fluorouracil (5-FU) codrug pellet. Methods: After insertion of a 10-mg codrug pellet into the right eyes of 43 New Zealand white rabbits, perfluoropropane (0.4 mL of 100% C3F8) or a control sham was then injected into the midvitreous cavity. On postoperative days 2, 4, 7, 21, and 42, aqueous samples were collected, the rabbits were killed, and the right eyes were enucleated. The vitreous and remaining codrug pellet were then isolated. Pellet and intravitreal drug levels were determined by high-pressure liquid chromatography. Results: No measurable drug levels were detected in any of the aqueous samples. Maximal gas expansion occurred by day 4 and partial resorption was observed by days 14 to 21. Vitreous FL and 5-FU levels during C3F8 expansion (day 2) were statistically significantly higher in the gas-filled eyes. On postoperative days 4, 7, 21, and 42, there were no statistically significant differences between FL and 5-FU drug levels in eyes containing C3F8 as compared with control eyes. Pellet codrug, FL, and 5-FU levels over time were similar in gas-filled and control eyes. Conclusions: Intraocular gas tamponade does not significantly affect the sustained intravitreal drug levels achieved with the FL/5-FU codrug. If clinically efficacious, the FL/5-FU codrug formulation does not need to be altered to treat proliferative vitreoretinopathy in the presence of intraocular gas.

Retinal toxicity of commercial intravitreal tissue plasminogen activator solution in cat eyes.

We previously reported retinal toxic reactions in rabbit eyes receiving intravitreal injections of commercial tissue plasminogen activator (tPA) in concentrations greater than or equal to 50 microg/0.1 mL, and recent clinical experience suggests that intravitreal tPA solution may produce toxic effects in human eyes. We therefore investigated the dose-dependent retinal toxicity of intravitreal commercial recombinant tPA solution in cat eyes, which have a vascularized inner retina and vitreous volume similar to that of human eyes. Commercial tPA in L-arginine solution was injected into the mid vitreous cavity of normal cat eyes in doses of 25, 50, 75, and 100 microg/0.1 mL and 200 microg/0.2 mL. Control (fellow) eyes received an equal volume of sterile saline solution. After injection, eyes were evaluated by ophthalmoscopy and electroretinography for 14 days and then enucleated for histopathological evaluation. Fundus pigmentary alterations were observed in eyes receiving doses greater than or equal to 50 microg/0.1 mL. Changes were centered in the area around the injection site, and the area's size increased in proportion to the dosage. Mean electroretinography B-wave amplitude measured at 14 days was significantly reduced in eyes receiving greater than or equal to 50 microg of tPA in a dose-dependent fashion. Light microscopy of the involved areas showed loss of photoreceptor elements with necrosis and proliferation of the retinal pigment epithelium. Intravitreal injection of commercial tPA solution results in dose-dependent retinal toxicity in cat eyes. Because cat eyes are similar to human eyes regarding retinal vascularity and vitreous volume, intravitreal injections of commercial tPA (with L-arginine vehicle) in concentrations greater than 25 microg/0.1 mL are potentially unsafe in human eyes.

INTRAVITREAL INJECTION OF HYALURONIDASE CANNOT INDUCE POSTERIOR VITREOUS DETACHMENT IN THE RABBIT

To investigate whether intravitreal injection of hyaluronidase can induce posterior vitreous detachment (PVD) in the rabbit. One eye each of 12 New Zealand white rabbits received intravitreal injection via the pars plana of 20 IU of hyaluronidase (0.1 mL reconstituted in sterile balanced salt solution [BSS]) into the midvitreous cavity. The fellow eye of each rabbit received a vitreous injection of 0.1 mL of BSS. At 3 and 6 months after intravitreal injection, four and eight rabbits were killed, respectively, and the eyes were enucleated. After fixation, scanning electron microscopy was performed to study the vitreoretinal interface. At 3 and 6 months after injection, scanning electron microscopy showed that the retinal surfaces in eyes that received either hyaluronidase or BSS were covered with vitreous collagen fibers. No eyes, even those that received hyaluronidase over a period of 6 months, had the smooth retinal surface consistent with a bare internal limiting lamina that suggests the development of PVD. Hyaluronidase cannot induce PVD in the rabbit over a 6-month period after vitreous injection.

A study of the ability of tissue plasminogen activator to diffuse into the subretinal space after intravitreal injection in rabbits

PURPOSE: Intravitreal injections of tissue plasminogen activator have been used to lyse fibrin from blood in the subretinal space, despite the lack of proof that tissue plasminogen activator can diffuse across the retina. We tested whether tissue plasminogen activator injected into the vitreous could penetrate the neural retina and enter the subretinal space. METHODS: We injected a mixture of 50 μg of tissue plasminogen activator (70 kD) labeled with fluorescein isothiocyanate and rhodamine B isothiocyanate–labeled dextran, which has a lower molecular weight (20 kD), into the midvitreous cavity of one eye in each of 18 rabbits. The eyes were enucleated after 3, 6, and 24 hours, and cryosections were examined with epifluorescent microscopy to determine the distribution of the labeled molecules. We also evaluated tissue plasminogen activator pharmacokinetics in one eye each of 18 rabbits in which a subretinal clot was induced by injecting autologous blood (50 μL) into the subretinal space through the sclera. Fluorescein isothiocyanate–labeled tissue plasminogen activator was injected into the vitreous 2 days after induction of the subretinal clot. RESULTS: Fluorescein isothiocyanate–labeled tissue plasminogen activator was present at the vitreal surface of the retina in a linear array in all 36 eyes studied, whereas the rhodamine B isothiocyanate–labeled dextran had diffused throughout the neural retina in the same sections. No fluorescein isothiocyanate signal was observed in the neural retina or in the subretinal clot. Vitreous hemorrhage caused by retinal perforation was observed in all eyes with intraretinal hemorrhage in which fluorescein isothiocyanate fluorescence was seen in the neural retina and inside the clot. CONCLUSION: Intravitreal tissue plasminogen activator did not diffuse through the intact neural retina to reach a subretinal clot. This study demonstrates no scientific rationale for the intravitreal tissue plasminogen activator treatment of submacular hemorrhage without vitreous hemorrhage presumably caused by an overlying retinal break.

Managing a dropped nucleus duringthe phacoemulsification learning curve

Three patients had a pars plana vitrectomy to remove retained nuclei within 72 hoursafter phacoemulsification performed by a surgeon making the transition from extracapsular cataract extraction to phacoemulsification. After vitrectomy, the nuclei were brought to the midvitreous cavity from the retinal surface with a posterior segment phacofragmenter, emulsified, and completely removed. Then, a posterior chamber intraocular lens was implanted in the sulcus through the previous cataract surgery incision and remained well centered postoperatively. Postoperative complications included cystoid macular edema in 1 patient and choroidal detachment in another. No other complications were detected. Final visual acuity ranged from 20/60 to 20/30.

Ofloxacin Levels after Intravitreal Injection

Purpose: This study was carried out to get an insight into the ofloxacin elimination after intravitreal injection in rabbits. We also studied the effects of trauma and inflammation on the vitreous ofloxacin levels after intravitreal injection of ofloxacin. Methods: A penetrating eye injury in the right eye was inflicted on 24 rabbits and another 12 animals were used as control. A standardized intraocular inflammation was induced by intravitreal injection of a suspension of Staphylococcus aureus in half of the traumatized eyes. Ofloxacin (200 µg/0.1 ml) was injected into the midvitreous cavity of both traumatized and control right eyes, and samples were obtained at 2, 8, 24 and 48 h after injection. Drug concentrations were measured using high-pressure liquid chromatography analysis. Results: Vitreous levels of ofloxacin were above the MIC₉₀ at 2 and 8 h in all groups for most of the common microorganisms causing endophthalmitis and also at 24 h in traumatized-infected eyes. At the second hour, the mean vitreous concentrations of ofloxacin both in traumatized and traumatized-infected eyes were lower than that in the control eyes (p < 0.05). At 8 h, the mean vitreous concentrations of ofloxacin in the traumatized and in the traumatized-infected eyes were higher than that in the control eyes (p < 0.05). At 24 h, the mean ofloxacin concentration was higher in the traumatized-infected eyes than that in control (p < 0.01) and traumatized eyes (p < 0.05), and also higher in the traumatized eyes than that in the control eyes (p < 0.05). The mean ofloxacin concentrations in the traumatized and traumatized-infected eyes were significantly higher (p < 0.01) than those in the controls at 48 h. The elimination half-life of ofloxacin in the control eyes was 5.65 h and trauma and inflammation prolonged the half-life to 9.47 and 9.72 h, respectively. Conclusion: Clearance of ofloxacin is fast and appears to be reduced by trauma and inflammation. Therapeutic drug levels in traumatized-infected eyes were maintained up to 24 h. This may be an important pharmacokinetic advantage in treating endophthalmitis unless the dose used has local toxicity and allows a longer dose interval when the dose is repeated.

Effect of inflammation on intraocular penetration of intravenous ofloxacin in albino rabbits.

The effect of inflammation on the intraocular penetration of ofloxacin was studied in 20 albino rabbits (New Zealand White). Inflammation was induced in the left eye by inoculation of a suspension of 10(9) CFU of heat-killed Staphyloccus epidermidis per 0.1 ml of saline solution (0.9%) in the midvitreous cavity. The other eye was kept as a control. Twenty-four hours following inoculation, ofloxacin was administered in the marginal ear vein at a dose of 15 mg/kg over 20 min with an infusion pump. Animals were sacrificed at different times up to 24 h following drug administration. Ofloxacin levels were determined in aqueous humor, vitreous humor, and serum by a bioassay. Inflammation was scored on the basis of perilimbal and corneal reactions and vitreoretinal statuses. Inflammation had a relevant effect on intraocular penetration of ofloxacin, with levels in the ocular fluids of the inflamed eye markedly exceeding the ones of the control eye. In the uninflamed eye, the levels were rapidly decaying below assay sensitivity and were no longer detectable at approximately 5 h following drug administration while they were still detectable in both ocular fluids of the inflamed eye at 24 h. Ofloxacin levels in the ocular fluids of the inflamed eye were superior to the MIC for several of the bacteria which commonly cause endophthalmitis, including Staphylococcus epidermidis, Staphylococcus aureus, most members of the family Enterobacteriaceae, Haemophilus influenzae, and strains of Pseudomonas aeruginosa.

VANCOMYCIN LEVELS AFTER INTRAVITREAL INJECTION

Vancomycin hydrochloride for intraocular injection is the drug of choice for the treatment of suspected gram-positive endophthalmitis. To study its intraocular pharmacokinetics, we injected vancomycin into the vitreous cavity of phakic, aphakic, and aphakic-vitrectomized rabbit eyes and determined its rate of clearance. Inflamed eyes were compared to control eyes in each group. Three groups of eyes were prepared. The eyes in Group 1 were phakic, the eyes in Group 2 had the lens removed, and the eyes in Group 3 had both the lens and central vitreous removed. Each group was subdivided into a control group and a group made inflamed by injection of heat-killed Staphylococcus epidermidis. Vancomycin hydrochloride 1 mg in 0.1 cc of diluent was injected into the midvitreous cavity and samples obtained at 2 or 3, 8, 24, and 48 hours after injection. Vancomycin concentrations were measured and clearance rates were calculated for each of the groups. Vancomycin was cleared substantially faster from aphakic-vitrectomized eyes (half-life 9.0 hours) and aphakic eyes (half-life 8.9 hours) than phakic eyes (half-life 25.1 hours). Inflammation increased the rate of elimination of vancomycin only in the aphakic group. Clearance of vancomycin from the phakic eye is prolonged compared to that of beta-lactam antibiotics, an important pharmacokinetic advantage in treating endophthalmitis. Its clearance from aphakic-vitrectomized eyes is dramatically faster than from phakic eyes and is similar to that of other antimicrobial agents.

Use of Perfluoroperhydrophenanthrene in the Management of Posteriorly Dislocated Crystalline and Intraocular Lenses

We describe a series of 28 patients in whom a posteriorly dislocated crystalline or intraocular lens was successfully removed with the intraoperative use of perfluoroperhydrophenanthrene (Vitreon), a heavy liquid perfluorocarbon. The Vitreon was used to float the lens into the midvitreous cavity, thereby avoiding hazardous micromanipulation with intraocular instruments in the macular area. In addition, the Vitreon served to protect the posterior retina by keeping the posteriorly dislocated lens fragments from falling backward onto the posterior pole as the lens was being removed from the eye. Postoperative visual acuity improved in 73% of the patients, remained the same in 15%, and worsened in 12%.

Toxicity and Pharmacokinetics of Ciprofloxacin

Ciprofloxacin is a fluorinated quinolone antibiotic with a broad spectrum of activity against both gram positive and gram negative organisms. Previous studies have indicated that oral or parenteral preparations of ciprofloxacin resulted in therapeutic concentrations in the aqueous humor but intravitreal levels were found to be only marginally higher than the MIC90 for gram positive cocci. Toxicity was evaluated following intravitreal doses of ciprofloxacin injected into the mid-vitreous cavity of one eye of pigmented rabbits. As a control, an identical volume of normal saline was injected into the fellow eye. Four doses of ciprofloxacin were studied, 100 micrograms, 250 micrograms, 500 micrograms and 1000 micrograms. Electroretinograms (ERGs) were recorded prior to injection and 1, 7 and 14 days after injection. These were analyzed as b-wave amplitude ratios between treated and untreated eyes. On ophthalmoscopic examination focal areas of retinitis were observed following injection of both 500 micrograms and 1000 micrograms of ciprofloxacin but not at 250 micrograms. Additionally, ERG amplitude ratios were significantly reduced following the 1000 micrograms dose. At the 100 or 250 micrograms ciprofloxacin dose histological sections are comparable with control eyes and appear normal; ERG ratios were unchanged from the baseline level and careful indirect ophthalmoscopic examination revealed no alterations. Pharmacokinetic analysis after single intravitreal injection of 250 micrograms of ciprofloxacin (N = 3 rabbits/dose) disclosed vitreous fluid levels (microgram/ml) of 146 at 0 hr, 77 at 4 hr, 32 at 8 hr, 0.49 at 24 hr and 0.24 at 48 hr.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative Treatment of Experimental Staphylococcus epidermidis Endophthalmitis

We created experimental Staphylococcus epidermidis endophthalmitis of moderate severity in the aphakic rabbit eye by injecting 100,000 organisms of a standardized laboratory strain (ATCC 155) into the mid-vitreous cavity. This model of endophthalmitis self-sterilizes in about 4 days, but inflammatory signs continue to increase 5 to 7 days after the initial bacterial inoculum. Control eyes were compared with eyes treated with five different strategies 24 hours after bacterial inoculation: intravitreal cefazolin sodium, intravitreal cefazolin plus intramuscular corticosteroid, vitrectomy plus intravitreal antibiotics, vitrectomy plus intravitreal antibiotics and intramuscular corticosteroids, and vitrectomy plus intravitreal antibiotics and corticosteroids. Quantitative grading of inflammation and media clarity were compared at the end of weeks 1, 2, and 3 after treatment. At week 1, eyes treated with vitrectomy had significantly lower inflammatory scores; those treated with corticosteroids had significantly lower scores than those without. The two effects were independent. The best results were observed with treatment consisting of vitrectomy, intraocular antibiotics, and corticosteroids. This strategy also produced significantly more eyes with clear media at the end of week 3 than treatment with intravitreal antibiotics alone.

Retinal Toxicity of Recombinant Tissue Plasminogen Activator in the Rabbit

We studied the dose-dependent retinal toxicity of the available commercial preparation of human recombinant tissue plasminogen activator in the normal rabbit eye. Tissue plasminogen activator was injected into the midvitreous cavity of albino rabbits in doses (per 100 microL) of 25, 50, 75, and 100 micrograms. Control eyes received 100 microL of balanced salt solution or tissue plasminogen activator vehicle. No evidence of a retinal toxic reaction was seen in eyes receiving 25 micrograms of tissue plasminogen activator. One of four eyes injected with 50 micrograms showed loss of photoreceptor cells by light microscopy. Severe retinal damage was seen by ophthalmoscopy, electroretinography, and light microscopy in three of four eyes receiving 75 micrograms of tissue plasminogen activator and in all eyes treated with 100 micrograms of tissue plasminogen activator or equivalent vehicle. These results suggest that the commercial recombinant tissue plasminogen activator formulation has a narrow margin of safety in nonvitrectomized eyes and that a component of the vehicle is the toxic factor.

Intravitreal clearance of tissue plasminogen activator in the rabbit.

The clearance of tissue plasminogen activator (t-PA) injected into the midvitreous cavity was studied in the phakic, vitrectomized rabbit eye with and without intravitreal fibrin clots. The quantity and activity of t-PA in the vitreous, serum, and aqueous were determined at ten minutes and at 3, 6, 15, 24, and 48 hours after initial injection by an enzyme-linked immunosorbent assay (ELISA) and a spectrophotometric solid-phase fibrin assay (SOFIA). In eyes without an intravitreal fibrin clot, the estimated half-life for t-PA was 4.3 hours by SOFIA and 5.8 hours by ELISA. In eyes containing a vitreal fibrin clot, the half-life increased to 9.8 hours by SOFIA and 11.9 hours by ELISA. Both of these half-lives were significantly greater than the half-life for eyes without fibrin. Regardless of the presence of fibrin, intravitreal t-PA activity was significantly less than t-PA quantity, suggesting the presence of a t-PA inhibitor. A peak in aqueous t-PA occurred before six hours, indicating that t-PA was cleared in part through the anterior chamber. There was no measurable serum t-PA at any of the sampling times.

Hypotony and Choroidal Detachment as Late Complications of Trabeculectomy

Seven eyes of six patients with glaucoma developed a flat anterior chamber, hypotony, and choroidal detachment two to 26 months after technically uncomplicated trabeculectomy. No signs warranting immediate surgical intervention, such as wound or bleb leakage, contact between cornea and lens, or massive choroidal detachments touching in the midvitreous cavity were found on initial examination. After treatment with topical corticosteroids and cycloplegic eyedrops, five of seven eyes showed marked clinical improvement within one month. The two remaining eyes eventually returned to normal anterior chamber depth, but required repeat filtration surgery for intraocular pressure control.

Retinal Neovascularization After Intravitreal Fibroblast Injection

We have developed a new model of retinal neovascularization in the rabbit. After intravitreal autotransplantation of 250,000 tissue-cultured skin fibroblasts, we observed strand formation in the midvitreous cavity. These strands grew toward the vascularized part of the retina and attached to it. Once the attachment was established, retinal neovascularization began with growth of vessels along the fibrous strand. After three months, this retinal neovascularization regressed. The presence of immature capillaries was confirmed by electron microscopic examination. Of 43 eyes, 31 (72%) developed neovascularization.