Hyaluronidase and Retinal Function
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Abstract:
Using the incubated isolated rat retina, the effects of hyaluronidase on the electroretinogram (ERG) and metabolic activities were investigated. Initial experiments established the activity of hyaluronidase needed to liquefy, within 15 to 30 minutes, the vitreous of postmortem human eyes; this concentration was 1,000 units/mL. Rat retinas were superfused with a bicarbonate-buffered, oxygenated medium to which hyaluronidase was added in activities ranging from 100 to 5,000 units/mL. These concentrations of hyaluronidase did not significantly alter the amplitudes of the a waves and b waves of the ERG in comparison to their control amplitudes. Measurements were also made of lactic acid production, oxygen consumption, glutathione content, and adenosine triphosphatase activities in control and hyaluronidase-exposed retinas. In the presence of hyaluronidase, their respective values were similar to the controls for all biochemical factors studied. The present experiments demonstrate that addition of hyaluronidase to an "ocular irrigating" solution results in normal ERGs and normal retinal metabolic activity and suggests the possibility that hyaluronidase may be useful in enzyme-assisted vitrectomy.Keywords:
Hyaluronidase
Bicarbonate
To develop an improved surgical technique making full-thickness retinal transplant possible, thereby achieving a normal laminated transplant with minimal rosette formation.A total of 23 rabbits underwent vitrectomy, retinotomy, and subsequent subretinal transplant of a complete embryonic neuroretina using a specially crafted glass cannula. Of the 23 animals, 15 received a prenatal day 16 or 19 (E16 or E19) retina; the remaining eight received an E15 retina. The animals were followed from 10 to 35 days, and after this period, the transplants were sectioned and stained for light microscopy.In 11 of the 15 transplants with E16 or E19 donors, histology showed regions up to 1.8 mm of straight, correctly positioned transplants with layering corresponding to their age. The eight animals kept alive longest postoperatively, 31 or 35 days, all showed normal retinal layers, including photoreceptor outer segments appositioned against the host retinal pigment epithelium. Tissue from the youngest donors (E15) yielded less well-organized transplants, indicating a critical stage in retinal embryogenesis before which transplant in this respect is less favorable.Our procedure makes it possible to transplant embryonic retina to the appropriate position adjacent to the host retinal pigment epithelium, keeping the transplant architecture intact. The transplants show good layering and well-developed photoreceptors abutting the retinal pigment epithelium.
Histology
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In Brief Purpose: To study retinal function after vitrectomy. Methods: Core vitrectomy was performed in 12 rabbits under standardized conditions using a vitreous cutting rate of either 600 or 1200 cuts/min. Full-field electroretinography (ERG) and multifocal electroretinography (mfERG) were performed pre- and postoperatively. Morphologic change was monitored by immunohistochemistry directed against glial fibrillary acidic protein (GFAP). Results: Three days postoperatively, the b-wave amplitudes of all cone and rod responses of the ERG were significantly reduced in all vitrectomized eyes. At 28 days, the rod response was still reduced, but returned to normal by 58 days. No correlation was found between vitreous cutting speed and ERG findings. No reduction in the central cone function was detected in the mfERG. GFAP upregulation was found in the entire retina of vitrectomized eyes 3 days after surgery. GFAP expression was present after 28 and 58 days in eyes in which the vitreous cutting rate had been set to 600 cuts/min, but not in the 1200 cuts/min eyes. Conclusion: Pars plana vitrectomy transiently affects retinal function in rabbit eyes. Vitreous cutting speed is not related to the reduced function but appears inversely correlated to Müller cell activation, indicating that high-speed vitreous cutters are more lenient to the retina. Retinal function and morphology was studied in rabbit eyes after vitrectomy using high- and low- speed vitreous cutting. Reduced electroretinogram amplitudes and upregulation of glial fibrillary acidic protein (GFAP) were found in all eyes after 3 days. Retinal function was restituted after 58 days, but GFAP upregulation persisted in eyes where a low cutting rate was used.
Electroretinography
Erg
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Epiretinal Membrane
Retinal Tear
Proliferative Vitreoretinopathy
Vitreous membrane
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Objective To evaluate the therapeutic effect of vitrectomy on bullous retinal detachment. Methods The clinical data of 7 patients (9 eyes) with bullous retinal detachment who had undergone vitrectomy due to useless photocoagulation were retrospectively analyzed. Bullous retinal detachment of the patients had been diagnosed by examination of slit-lamp microscope, three-mirror gonioscope, indirect ophthalmoscope, B-mode ultrasound, and fundus fluorescein angiography. All of the affected eyes underwent vitrectomy with closed triple incisions through the pars plana after release of subretinal liquid under the local anaesthesia. The cortex of vitreous body was taken out, and exsuction of subretinal liquid was carried out via retinal incision. Photocoagulation closed the incision and the effusion area of the retina, and intraocular filling matter was injected after exchange of air and liquid. The follow-up period lasted 3 months to 8 years with the average period of 47 months. Results Reattached retina was found in all of the affected eyes during the follow-up period. One eye underwent a second vitrectomy due to local retinal redetachment caused by a new retinal hole formed by the pull of pre-retinal proliferative membrane and a silicon vesicle entered the subretinal space, but the retina reattached after 1-year follow-up examination. The visual acuity improved in different degree after the operation in 8 eyes, but remained unchanged in 1 eye. Conclusion Vitrectomy for terminal bullous retinal detachment may promote the reattachment of retina safely and effectively, and save partial visual acuity of the affected eyes.
Fundus (uterus)
Retinal Tear
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Abstract Clinical studies have established that retinal laser photocoagulation on one hand and vitrectomy on the other have a positive clinical effect on the development of diabetic retinopathy and other ischemic retinopathies. Both reduce retinal neovascularization and macular edema. The clinical effect of laser and vitrectomy is related to the physiological effect of these treatment modalities. Both improve retinal oxygenation, but through different mechanisms. Laser treatment destroys some of the photoreceptors, reduces the oxygen consumption of the outer retina and allows oxygen to diffuse from the choroid to the inner retina. In vitreous surgery the viscous vitreous gel is replaced by low viscosity water. According to the Stokes‐Einstein equation viscosity is inversely related to the diffusion coefficient. Diffusion (and convection) of any substance is many times higher in water than vitreous gel, and this includes oxygen, growth factors and drugs. In the vitrectomized eye, oxygen diffuses more easily from well perfused to hypoxic areas of the retina. At the same time growth factors are cleared from the retina more rapidly than before and may indeed be transported to the anterior segment and produce iris neovascularization. Laser and vitrectomy reduce retinal hypoxia and thereby reduce the production of hypoxia induced growth factors such as VEGF. Vitrectomy also clears VEGF away from the retina at a more rapid rate than when the vitreous gel is in place. VEGF and other growth factors influence both neovascularization and capillary permeability, and the latter influences the osmotic balance between blood and tissue and the osmotic arm of Starling´s law. In addition, improved oxygenation reduces the hypoxia‐induced vasodilatation and this decreases capillary blood pressure and reduces edema formation according to the hydrostatic arm of Starling´s law. By understanding the physiological effects of laser and vitrectomy, we can understand the mechanism of the clinical effect. Classical laws of physiology and physics help complete the picture and give us an understanding of the nature of these treatment modalities and how they may be combined with other agents. For details and references please see Stefánsson E: Survey of Ophthalmology 2006.
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• The role of the cortical vitreous in persistence of experimental retinal detachments was evaluated in cynomolgus monkeys. Detachments were created by subretinal injection of 20% autologous serum in Ringer's solution. A pars plana vitrectomy was performed on selected eyes with a Douvas vitrectomy instrument before creation of the detachment. Retinal holes were created from the subretinal side with a hooked needle or from the vitreal side with the vitrectomy instrument. The rate of reattachment of the retina was rapid and independent of retinal hole size if cortical vitreous covered the retinal hole. If no cortical vitreous covered the retinal hole, the retina remained detached indefinitely (longer than three months). A spontaneous reduction in the size of the retinal hole occurred in many eyes in association with star-fold formation. It is concluded that cortical vitreous is capable of obstructing fluid movement through the retinal hole.
Retinal Tear
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Proliferative Vitreoretinopathy
Laser coagulation
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PURPOSE. Long-term results, more than 10 years after successful retinal detachment surgery, have shown gradually decreasing visual acuity in some cases. It is unclear if reduced functional recovery postoperatively is caused by anatomic changes or biochemical disorders. To determine the etiology of the reduced visual acuity, we cytochemically examined the changes in the cellular responses of the edges of retinal detachments. METHODS. We histochemically studied the glucose-6-phosphatase (G6P) and 5'-nucleotidase (5'-Nase) activity in the rabbit retina. Experimental rhegmatogenous retinal detachment was produced in a rabbit model after partial vitrectomy, followed by retinal tear formation. RESULTS. Although 5'-Nase activity gradually decreased during the period of detachment, activity was still detectable after 24 weeks. G6P activity increased in the region of the detached neural retina. Around the border of the detached retina, the decrease in 5'-Nase activity extended approximately 140 micrometers into the adjacent attached retina at 2 weeks after detachment and 270 micrometers at 24 weeks. CONCLUSIONS. These observations suggest that some anatomical and biochemical damages may occur in the retina adjacent to bullous retinal detachment and may explain the reduction in postoperative vision in some clinical cases.
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Objective To evaluate the surgical efficacy of vitreorectomy combined with silicon oil tamponade and retinal photocoagulation for retinal detachment secondary to acute retinal necrosis syndrome. Methods 10 cases(10 eyes) which suffered acute retinal necrosis syndrome,developed to retinal detachment were underwent vitrectomy,membrane peeling,photocoagulation and silicon oil tamponading.3 eyes were underwent lensectomy because of the blerry lens.Equatorial retina was photocoagulated with argon laser at the third week before silicon oil was taken out. Results all retinal reattachment wereachieved in all eyes in the short time(less1 month),they were followed-up by 14-26months,8 eyes'retina reattached well,the rate was80%(8/10),2 eyes retina redetached because ofproliferated membrane on retinal surface.Post-operation vision acuity:light perception 2eyes,hand motion 1 eye,CF/20cm-CF/50cm 3eyes,0.05-0.1 3 eyes,0.12 2 eys. Conclusions The management of vitrectomy,silicon oil tamponade combined with retinal photocoagulation improved the retinal reattachment rate for retinal detachment secondary to ARNS,but post-operation vision acuity was low because of the retinal destruction of the disease.
Retinal Tear
Acute retinal necrosis
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To examine retinal changes after vitrectomy with internal limiting membrane (ILM) peeling, we used a cynomolgus monkey model and focused on surgical damages of ILM peeling for long observational period of 3 years.Vitrectomy was performed followed by ILM peeling similar to clinical settings in humans. Ultrastructural changes of the retina were investigated by light, transmission, and scanning electron microscopy at 3 months and 3 years after ILM peeling.Ultrastructural study showed that the ILM peeled area was still clearly recognized after 3 years. The Müller cell processes covered most of the retina; however, the nerve fiber layer was partly uncovered and exposed to the vitreous space. The arcuate linear nerve fiber bundles were observed as comparable with dissociated optic nerve fiber layer appearance. Small round retinal surface defects were also observed around macula, resembling the dimple sign. Forceps-related retinal thinning was also found on the edge of ILM peeling, where we started peeling with fine forceps.The ultrastructural studies showed that most of ILM peeling area was covered with glial cells during wound healing processes. Retinal changes were found comparable with dissociated optic nerve fiber layer appearance or dimple sign, which were clinically observed with optical coherence tomography.
Inner limiting membrane
Internal limiting membrane
Optic disc
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