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ABSTRACT.Purpose: To establish a method allowing multifocal electroretinography (mfERG) recording with simultaneous fundus monitoring on anaesthetized pigs. In addition we characterize the peaks of the porcine mfERG trace, and compare the visual streak area with the optic nerve head, a known nonresponse area. Finally we illustrate the feasibility of the method by performing mfERG after an induced laser burn in the visual streak. Methods: Fifteen pigs underwent mfERG recordings at baseline, and after 1 and 6 weeks of observation. One pig was evaluated before and after retinal diode laser treatment in the visual streak. Results: The porcine mfERG trace appears similar to the human mfERG trace, and can be described by three peaks named N1, P1 and N2. Significantly faster implicit time was found in the visual streak regarding N1 (P < 0.001) than in areas outside the visual streak. Amplitudes of all three peaks were increased in the visual streak (P < 0.005). The laser-treated area was characterized by a response similar to what is found at the location of the optic nerve head. Conclusion: Porcine mfERG is similar in appearance to the human response and can be described by the same three peaks. Significantly higher amplitudes of all three peaks are found in the visual streak when compared to the optic nerve head and inferior retina. We have detected the functional deficit caused by a laser burn at the size of 3 · 3 mm.

This is the first study to show that the histological regeneration of hypopigmented RPE correlates to a return of the retinal function, measured by mfERG.

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ABSTRACT.Purpose: This study aimed to investigate the spatial resolution of a porcine multifocal electroretinogram (mfERG) protocol by testing its ability to detect laser-induced retinal lesions. Furthermore, we wanted to describe time-dependent changes in implicit time and amplitude of the different mfERG peaks after laser-induced retinal damage. Methods: Three pigs underwent a three-port pars plana vitrectomy, followed by laser photocoagulation of different lesion sizes within the visual streak. In an additional six non-vitrectomized pigs, we studied changes in mfERG signals with time after a uniform laser photocoagulation within the visual streak. The animals were evaluated with mfERG 1 and 6 weeks after treatment. After the last mfERG examination, selected eyes were processed for histological examination. Results: The size of the smallest lesion detected was approximately 1 ⁄ 4 of the longest diameter of the optic disc (LDOD) measured in pixels. When analysing the uniform lesions we found that signals deriving from the centre of the laser lesions were characterized by a significant reduction in the amplitude of all three peaks after 1 week of observation. After 6 weeks, the amplitudes of P1 and N2 were still significantly reduced. The implicit times were unaffected by laser treatment in the acute phase. After 6 weeks only P1 was significantly delayed. Conclusion: We have determined the spatial resolution of the mfERG in the porcine retina to be smaller than or equal to the area of two adjacent hexagons, corresponding to a width of approximately 288 pixels or 1.2 mm. Laser lesions of uniform size resulted in a significant reduction of the amplitudes 1 and 6 weeks after treatment.

PURPOSE. The objective of the study was to investigate the effect of glial cell line-derived neurotrophic factor (GDNF) on the multifocal electroretinogram (mfERG) following an induced branch retinal vein occlusion (BRVO) in pigs.METHODS. Electrophysiological examination of the retina was performed in 20 pigs with standard and four-frame mfERG 4 weeks after induced BRVO and intravitreal injection of GDNF or vehicle. BRVO was induced by intraocular diathermia of the superior retinal vein. Inner retinal function was measured by analysis of the four-frame mfERG (iN1) and outer retinal function with standard mfERG (P1).RESULTS. In GDNF-treated BRVO eyes, P1 and iN1 amplitudes (P ¼ 0.51 and 0.78) or implicit times (P ¼ 0.08 and 0.99) did not differ from those in healthy fellow eyes. After vehicle injection, P1 and iN1 amplitudes of BRVO eyes were significantly lower than in the healthy fellow eye (P ¼ 0.022 and 0.013). The log ratios of mfERG amplitudes between experimental and healthy fellow eyes were calculated (BRVO/healthy). GDNF improved the ratios of the four-frame mfERG CONCLUSIONS. GDNF appears neuroprotective on retinal electrophysiological function after BRVO. The efficacy and safety of GDNF remain to be investigated in primate eyes. (Invest Ophthalmol Vis Sci. 2012;53:6207-6213)

ABSTRACT.Purpose: The aim of the study was to determine the type and magnitude of detectable changes in pig multifocal electroretinography (mfERG) induced by the vitreoretinal surgical procedures necessary to gain access to the subretinal space.Methods: Twenty pigs underwent posterior segment surgery. Six animals had a vitrectomy (V), six had in addition a retinal bleb detachment (V + B); five had in addition a retinal diathermia on the bleb (V + B + D) and three received a retinotomy in the diathermized retinal area (V + B + D + R). mfERG evaluation was performed at baseline and 1 and 6 weeks postoperatively. Selected eyes were enucleated for histological evaluation. Results:The retinal detachments blebs all reattached spontaneously. All four surgical sequences resulted in slight, non-significant changes in the mfERG peaks. A trend towards an amplitude reduction of the mfERG peaks N1, P1 and N2 were observed within the first postoperative week. After 6 weeks, all amplitudes had normalized. Of the implicit times only that of peak N1 (after retinal diathermia) was prolonged significantly at 1 week (P ¼ 0.037). However, it returned to the preoperative level after 6 weeks. Histologically, the retinal detachment bleb was characterized by transient double layering of the retinal pigment epithelium (RPE) and loss photoreceptor outer segments.Conclusion: Access to the subretinal space in pigs can be gained without permanent detectable changes in the mfERG. A short-term retinal detachment was found to cause only reversible electrophysiological and histological changes in the outer retina, which suggests that this procedure is tolerated well in the porcine retina. The size of the known destructive lesion (retinotomy) was too small to be detected, given the spatial resolution of the mfERG method applied. In the future, the presented protocol can be used to assess the functional outcome of surgery and transplantation in the subretinal space in pigs.

A systems analysis and design of information requirements for an experimental farm is presented. This study was carried out on the university farm (UF) at the University of Copenhagen in Denmark. The UF has several farm sites, many employees and clients, and collects data on the spatial variability of sites for site-specific management, and is responsible for running field trials. Soft and hard system analyses were performed to better understand the information needs and design an information system for the UF. Soft systems methodology was used to analyse the human activities and to identify user requirements, while a hard systems methodology was used to structure the data handling inside the farm office. The resulting information management system (IMS) includes modules for storage, processing and presentation of spatio-temporal data for research trials and site-specific management. A GIS-based farm IMS including the necessary interfaces was implemented and validated by the UF manager and staff. Limitations and constraints to the full implementation of the IMS in an experimental farm are also discussed.