Purpose In cases with multiple retinal breaks and in combination with vitrectomy in eyes with Proliferative vitreoretinopathy (PVR) for retinal detachment surgery often an encircling band is used. Usually the encircling band is fixed with non absorbable sutures. Methods A fixation method for an encircling band in retinal detachment surgery with one scleral tunnel in every of the 4 quadrants is reported. We describe our experience and biomechanical calculations of this fixation technique. Results In comparison to conventional fixation technique we found the following advantages: No suture is necessary, this means no additional foreign body can produce irritations. The scleral tunnel is safe and the preparation under the microscope can be performed fast and well controlled. Sclera tunnel fixation is very comfortable in combination with a vitrectomy. Conclusion With a short learning curve the operating time is as short as with conventional suture fixation of the encircling band. There is less perforating risc, less irritation and less patient discomfort postoperatively. A sutureless encircling band with sclera tunnel fixation is a very usefull operation technique in clinical routine.
Purpose: Impaired vascular regulation might contribute to glaucomatous damage. Whether retinal branch arteries and veins of healthy persons and primary open angle glaucoma (POAG) patients show different reactions in response to flickering light stimulation (FLS) is investigated. Methods: Retinal vessel reactions to FLS were examined in 28 POAG patients (stage I, 54,3±9,9 years old) after 4 week wash‐out of eye drops and in 28 age and gender matched medically healthy volunteers. Vessel diameters of retinal vessel segments were assessed by Dynamic Vessel Analyzer (DVA). After baseline measurement (50 s) monochromatic rectangular FLS (530‐600 nm, 12,5 Hz, 20 s) was applied. Results: In most subjects fast vessel dilation compared to baseline and an ensuing reactive arterial constriction were observed. In detail we found: ...........................................................................POAG.......control mean arterial dilation at the end of FLS, %...........3,3±2,7......3,4±2,7 time of max arterial constriction following FLS,s....49,9±26,7*.25,5±18,1 mean venous dilation at the end of FLS,%........... 2,9±1,9......3,8±2,2 area under the venous curve following FLS,s*%..‐1,1±16,9*...27,9±34,3 We found statistically significant differences between the two examined groups as marked with *(p<0,01) (U‐test). Conclusions: Functional retinal arterial and venous dilation in response to FLS does not differ between POAG patients and healthy subjects. Reactive arterial constriction following the FLS appeared later and venous restoration occurred faster in POAG. These findings might be an indication for alterations in the vascular endothelium and vessel wall rigidity in POAG, leading to impaired regulation following metabolic demand.
The term ocular rigidity is widely used in ophthalmology. Generally it is assumed as a measurable physical parameter related to biomechanical properties of the whole eye globe. Formulas for clinical tonometry and tonography methods include the concept of ocular rigidity. Unfortunately ocular rigidity represents an elusive concept that means many things to many people. First of all, there is no consensual view on ocular rigidity in ophthalmology. The most of the formulas for ocular rigidity are based on discrete or continuous tonometric measurements in living or enucleated human eyes. Surprisingly ocular rigidity is measured in different units and has a different meaning by different authors. Finally, there is no clear consent between biomechanical engineers and ophthalmologists on the concept of ocular rigidity. In biomechanics parameters for the elasticity and viscoelasticity are accepted, which represent mechanical properties of a tissue an can consider its morphology. These are for example: Young’s moduli of the sclera, Poisson’s ratios of the cornea etc. Ophthalmological concepts on ocular rigidity are based on the consideration, that biomechanical properties of the corneoscleral shell are involved in the pressure‐volume relationship of the eye globe. Ocular rigidity defined in such a way climes to describe the total response of the eye without detailed considerations on its morphologic and material properties. In the proposed review several formulations of ocular rigidity are analysed and classified. It is attempted to link these conceptions with each other.
Ocular rigidity in ophthalmology is generally assumed to be a measurable surrogate parameter related to the biomechanical properties of the whole globe. Clinical tonometry and tonography, as well as recently developed methods to assess the ocular pulse amplitude and pulsatile ocular blood flow and measurements with the ocular response analyzer are based on the concept of ocular rigidity. Clinical concepts of ocular rigidity describe a resulting effect without considerations of possible diverse morphology and material properties of the different ocular tissues. It is commonly accepted that ocular rigidity is related to the elasticity of the sclera. Many formulations are however dependent on the internal volume of the globe, intraocular pressure, corneal biomechanics and thickness of the corneoscleral shell. Sometimes this is extended to biomechanical properties of the ocular vasculature and perfusion pressure. Therefore ocular rigidity is expressed in various units and has different physical meanings but the same name is used which is confusing. Ocular biomechanics introduces parameters of elasticity and viscoelasticity of the sclera, cornea and other tissues which consider the morphology of the different tissues describing their mechanical properties such as: Young’s modules of the sclera and Poisson’s ratios of the cornea. When applying these rigorous statements and methods of biomechanical modeling a unified concept for ocular rigidity can be developed in order to link the limited clinical concepts, to improve them and to better understand the results of clinical measurements.
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