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Y. Chang, C. Chou, P. Lin, C. Tsai; The ERG Electrical Pathway . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2251.
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ERG electrical pathway has long been studied but with controversy. Many reports indicate that vitreous and extraocular tissues are the ERG pathway. But some show that the replacement of vitreous by silicon oil does not alter the ERG at all. To verify the actual ERG pathway, we re–examine this old issue.
Four non–pigmented and three pigmented rabbits were used in this study. ERGs and VEPs were measured before and after the following treatments: Firstly, cryotherapy was performed on the sclera for about 30 sec in the 4 non–pigmented rabbits that formed a 3–mm width of full, 3/4, 1/2, and 1/4 circular band respectively that ensured the retina, choroid and sclera were damaged in the band. This band was about 4–5 mm in distance from the corneal edge to block the possible conducting route of ERG. Secondly, laser therapy with wavelength of 532 nm and 810 nm that formed a circular ring with radius about 39 degrees in two of the pigmented rabbits respectively. The delivered powers were 130 mW/0.2 sec for 532 nm and 125 mW/0.2 sec for 810 nm respectively. Medical treatments to prevent infection were carried out right after surgery. ERG and VEP were measured in the post 3rd and following days. For the pigmented rabbits, the light stimulation was confined within the retinal area where was enclosed by laser treatments.
Table shown below reveals the ERG a– and b–wave recorded before and after surgery. The unit of the amplitude is in uV. It indicates that both a– and b–wave are significantly decreased right after surgery but slowly recovered. It seems that the ERG pathway nearly complete blocked by full anf 3/4 circular cryo–therapy. However, laser–therapy doesn’t seem to have similar results. This implies that the retina and choroid may play important roles as an electrical return loop in the ERG pathway.
This study provides additional information of the ERG conductive pathway to the known vitreous and extraocular tissues. It shows that retina and choroid are possibly involved in the return loop of the ERG electrical pathway.
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