Immunoelectrophoretic analysis of subretinal fluid and its diagnostic significance.
(1) Immunochemical examination shows that subretinal fluid can be divided into two major categories. A 'barrier pattern' is found in the presence of an effective blood-retinal barrier, whereas a 'barrier-damage pattern' emerges when there is a progressive increase in the permeability of the choriocapillarispigment epithelium complex. (2) The immunoelectrophoretic appearance of the subretinal fluid from a recent simple detachment shows a 'barrier pattern' and consists of only low molecular-size plasma proteins, since the choriocapillaris-pigment epithelium complex allows the smaller proteins to escape into the subretinal space more readily than the larger. There is, therefore, a general relationship between the clearance of any plasma protein in the subretinal space and its molecular size.(3) It is only in long-standing detachment that the permeability of the blood-retinal barrier is sufficiently altered to allow the passage of higher-molecular-weight proteins such as IgG and IgA. Increase in permeability of the choriocapillaris-pigment epithelium complex, due possibly to structural modifications, is responsible for the 'barrier-damage' pattern of the subretinal fluid. (4) There may be variations in the degree of barrier breakdown. In those retaining a highly selective barrier, little or no high-molecular-weight proteins escape in the subretinal fluid even in cases of long-standing detachment, whereas, in those with low selectivity, the leakage of high-molecular-weight proteins parallels that of the smaller proteins. (5) The apperance of very large molecules in the subretinal fluid indicates a preceding choroidal inflammation or neoplastic invasion; and the detection of IgM is, therefore, of value in the differential diagnosis of retinal detachment.