Intraocular infusate with hemocoagulase for the control of bleeding during vitreous surgery

The effects of hemocoagulase in injectable form (hemocoagulating enzymatic fraction of South American snake Bothrops jararaca venom provided by Ravizza) on the control of intraocular bleeding during vitreous surgery were evaluated in rabbit eyes. Intraocular infusion solution with hemocoagulase (1 NIH thrombin unit/100 ml of BSS plus) significantly reduced the bleeding time. Electroretinogram b-wave and electroretinogram c-wave showed no abnormality. Infusate with hemocoagulase (1 NIH thrombin unit/100 ml of BSS plus) is not toxic to retinal tissue and appeared to be a useful agent for the control of intraocular bleeding during vitreous surgery.     

Changes in vitreous amino acid concentrations in a rabbit model of cataract surgery

PURPOSE: We previously reported marked elevation of glutamate, gamma-aminobutyric acid (GABA) and alanine in the vitreous after combined cataract surgery and vitrectomy for macular disorder. Photo-stimulation by the operating microscope and increased intraocular pressure (IOP) are possible causes of postoperative increases in amino acids. An animal model was used to verify this hypothesis. METHODS: Forty-five coloured rabbits were studied; stress was applied to simulate cataract surgery. Simultaneous photic and pressure stress, photic stress alone, or pressure stress alone were exerted for 20 mins. The vitreous was extracted at the end of the stress period, or 10 mins or 30 mins later. Levels of six amino acids (asparate, glutamate, glycine, taurine, alanine and GABA) in the vitreous were analysed quantitatively. RESULTS: Significant increases in vitreous glutamate concentrations in treated eyes were observed following simultaneous photic and pressure stress, as well as after pressure stress alone, whereas no difference was found after photic stress alone. The mean glutamate concentrations in treated eyes and fellow eyes, respectively, were 5.59 +/- 2.03 microM and 4.36 +/- 2.09 microM (p < or = 0.05) 10 mins after simultaneous photic and pressure stress, and 4.32 +/- 0.97 microM and 2.29 +/- 0.51 microM (p < 0.05) 10 mins after pressure stress alone. Taurine concentration was elevated by pressure stress alone at 0 min and at 10 mins post-stress. Alanine concentration was reduced by photic stress alone at 10 mins post-stress. In all protocols, no significant differences between treated and fellow eyes were observed at 30 mins after stress. Time-dependent changes were observed not only in the treated eyes, but also in untreated fellow eyes. CONCLUSIONS: Elevations of vitreous glutamate in cataract surgery may be caused by pressure stress due to irrigation. Photic stress caused by the operating microscope has little influence. Sympathetic response may be involved in amino acid changes due to stress in cataract surgery.     

Physiology of vitreous surgery

Vitreous surgery has various physiological and clinical consequences, both beneficial and harmful. Vitrectomy reduces the risk of retinal neovascularization, while increasing the risk of iris neovascularization, reduces macular edema and stimulates cataract formation. These clinical consequences may be understood with the help of classical laws of physics and physiology. The laws of Fick, Stokes-Einstein and Hagen-Poiseuille state that molecular transport by diffusion or convection is inversely related to the viscosity of the medium. When the vitreous gel is replaced with less viscous saline, the transport of all molecules, including oxygen and cytokines, is facilitated. Oxygen transport to ischemic retinal areas is improved, as is clearance of VEGF and other cytokines from these areas, thus reducing edema and neovascularization. At the same time, oxygen is transported faster down a concentration gradient from the anterior to the posterior segment, while VEGF moves in the opposite direction, making the anterior segment less oxygenated and with more VEGF, stimulating iris neovascularization. Silicone oil is the exception that proves the rule: it is more viscous than vitreous humour, re-establishes the transport barrier to oxygen and VEGF, and reduces the risk for iris neovascularization in the vitrectomized-lentectomized eye. Modern vitreous surgery involves a variety of treatment options in addition to vitrectomy itself, such as photocoagulation, anti-VEGF drugs, intravitreal steroids and release of vitreoretinal traction. A full understanding of these treatment modalities allows sensible combination of treatment options. Retinal photocoagulation has repeatedly been shown to improve retinal oxygenation, as does vitrectomy. Oxygen naturally reduces VEGF production and improves retinal hemodynamics. The VEGF-lowering effect of photocoagulation and vitrectomy can be augmented with anti-VEGF drugs and the permeability effect of VEGF reduced with corticosteroids. Starling’s law explains vasogenic edema, which is controlled by osmotic and hydrostatic gradients between vessel and tissue. It explains the effect of VEGF-induced vascular permeability changes on plasma protein leakage and the osmotic gradient between vessel and tissue. At the same time, it takes into account hemodynamic changes that affect the hydrostatic gradient. This includes the influence of arterial blood pressure, and the effect oxygen (laser treatment) has in constricting retinal arterioles, increasing their resistance, and thus reducing the hydrostatic pressure in the microcirculation. Reduced capillary hydrostatic pressure and increased osmotic gradient reduce water fluxes from vessel to tissue and reduce edema. Finally, Newton’s third law explains that vitreoretinal traction decreases hydrostatic tissue pressure in the retina, increases the pressure gradient between vessel and tissue, and stimulates water fluxes from vessel into tissue, leading to edema.     

Q-Switched neodymium: YAG laser surgery of the vitreous

Fifty-nine eyes underwent vitreous surgery (vitreolysis) with the Q-switched Nd:YAG laser. This was used to cut vitreoretinal bands and membranes in 16 eyes and to clear persistent vitreous opacities in 25 eyes. The use of appropriate specialized contact lenses and modification of the standard slit-lamp delivery system were essential for vitreous YAG laser surgery. Successful results occurred in eyes where the target tissues were located at distances greater than 2 mm from the crystalline lens and the retina. Vision was improved in 18 eyes, unchanged in 40 eyes, and worse in 1. Complications included focal opacities of the crystalline lens in 5 eyes, retinal holes with detachment in 1 eye, and minor retinal hemorrhages in 4. Methods of preventing complications are discussed.Presented at the 1984 meeting of the Club Jules Gonin in Lausanne, Switzerland     

玻璃体腔充满气体的情况下人工晶状体植入术的体会

目的: 探讨在玻璃体切割术中玻璃体腔充满气体的情况下人工晶状体植入的临床意义和技巧。方法: 回顾性分析了在玻璃体切割术中玻璃体腔充满气体的情况下植入人工晶状体的36例36眼患者的临床资料;术后随访3～12(平均5.6)mo。结果: 所有患者术后视力与术前最佳矫正视力相比均提高2～6行。无严重并发症发生。结论: 在非接触全视野镜下玻璃体腔充满气体、无人工晶状体的情况下能较容易地看清周边视网膜并进行光凝治疗,在玻璃体腔充满气体的情况下人工晶状体植入术简捷、无不必要的重复操作、手术无太大难度、安全有效。     

Intraocular lysozyme in experimental uveitis in rabbits: aqueous and vitreous assay.

We determined normal aqueous and vitreous lysozyme levels in rabbit eyes and induced experimental uveitis to record the uppermost aqueous and vitreous lysozyme levels. The normal aqueous humor of the rabbit eye contained 1.05 mug per milliliter lysozyme and the normal vitreous humor contained 0.45 mug per milliliter. After the intravitreal administration of a foreign protein, the aqueous and vitreous lysozyme levels rose within one day, reaching maximum values of 38.4 mug per milliliter and 114 mug per milliliter, respectively, at 14 days, and subsequently declining to minimal values by 28 days after injection.     

重视眼内屈光手术的安全性

有晶状体眼人工晶状体植入矫正屈光不正已在国内广泛开展,获得了可喜的临床疗效,在预期性和稳定性方面也有较大优势,但临床上手术并发症仍时有发生.手术的安全性是技术健康发展的前提.笔者在复习文献的基础上,从有晶状体眼人工晶状体发展、手术方案的科学性和个性化以及并发症预防的基本原则提出观点,以供同道讨论交流,共同提高我国眼内屈光手术的水平.     

A new technique for separation of posterior vitreous in vitreous surgery

To describe a new and effective technique, hydroseparation, for use in detaching the posterior cortical vitreous from the retina by the simple injection of fluid into the subhyaloid space. This technique was used in 7 eyes of 6 patients with diabetic retinopathy who had limited posterior vitreous detachment. Following core vitrectomy, a 32 gauge cannula was inserted into the subhyaloid space and a balanced salt solution (BSS) was injected. The injected fluid spread easily to the periphery, causing the vitreous cortex to be smoothly separated, except for areas with firm vitreoretinal adhesion. In those areas, we also used microscissors to separate the tissue. No iatrogenic retinal break occurred in any case. This simple technique, which exerts minimal traction force on the retina, was safe and useful for inducing posterior vitreous detachment in patients with diabetes.     

Intraocular lens damage from Nd:YAG laser pulses focused in the vitreous. Part II: Mode-locked lasers

Damage can be induced within the interior of a plastic intraocular lens (IOL) by a mode-locked Nd:YAG laser when the beam's focus lies well behind the IOL. This type of damage, which has not been reported, is the result of cumulative, multiple exposures. The damage differs from that created by optical breakdown (plasma formation) within the plastic, which occurs only when the beam is focused within or near the IOL surface. This type of damage can be avoided clinically by minimizing the number of pulsed exposures along the same beam path.     

Intraocular lens damage from Nd:YAG laser pulses focused in the vitreous. Part I: Q-switched lasers

The damage resulting from laser-induced optical breakdown and plasma formation on or near an intraocular lens (IOL) has been well described, but there is another form of damage, not associated with optical breakdown, that can harm an IOL. The parameters that lead to this damage were investigated. Polymethylmethacrylate IOLs were irradiated by a Q-switched Nd:YAG laser beam focused so that plasmas were formed well clear of the IOL. Damage was induced in the volume of plastic through which the laser beam passed and was cumulative, not being visible until several laser pulses had passed through the lens. The number of pulses required to produce damage varied inversely with the distance between the IOL and the site of plasma formation. This damage is most likely to occur clinically when vitreous structures are targeted in the pseudophakic eye.     

Intraocular concentrations of clindamycin obtained by sequential parabulbar injections

PURPOSE: To measure the intraocular concentration of Clindamycin that can be maintained by sequential injection through a retained parabulbar catheter. MATERIALS AND METHODS: The peak intraocular concentration and half-life of Clindamycin after parabulbar injection was determined in a rabbit model. In a second experiment a parabulbar catheter was inserted and the maximum concentration that could be maintained by sequential injection through the catheter at intervals of 6 hours was determined. In a third experiment both eyes of the rabbit were catheterized and one infused with Clindamycin. The eyes were enucleated and studied by light and electron microscopy for changes induced by Clindamycin and the catheter. RESULTS: The concentration of Clindamycin after a single parabulbar injection of 10 mg/kg peaked in the retina and choroid at 2 hours and was 336 micrograms/g. The serum level at 2 hours was 2.2 micrograms/ml. The half-life in choroid and retina was 1 hour. Sequential administration at 6 hour intervals maintained a minimum concentration of 87 micrograms/ml. The vitreous concentration was maintained at 2 micrograms/ml. CONCLUSION: The level of Clindamycin in the retina and choroid obtained by sequential injections of 10 mg/kg exceeds the minimum lethal dose for organisms susceptible to the drug. The low serum concentration suggests that sequential doses of Clindamycin by the parabulbar route might be an effective therapy for toxoplasmic retinochoroiditis and would diminish the risk of colitis or other deleterious systemic side effects.     

实验性眼外伤玻璃体中细胞外基质变化规律的探讨

目的 探讨细胞外基质中层粘连蛋白（ＬＮ）、Ⅱ型胶原（ⅢＣ）、Ⅳ型胶原（ⅣＣ）和透明质酸（ＨＡ）在实验性眼外伤中的变化规律。方法 用放射免疫法检测４只正常眼和２４只外伤眼不同时期玻璃体中ＬＮ,ⅢＣ,ⅣＣ,ＨＡ的含量。结果 外伤后２周以内玻璃体中ＬＮ,ⅢＣ,ⅣＣ浓度增高（Ｐ〈０．０５）,２周以后ＬＮ下降ⅢＣ和ⅣＣ浓度未下降,ＨＡ在不同时期变化不明显（Ｐ〉０．０５）。结论 在穿孔性眼外伤的早期,细胞外基