
Hydraulic Conductivity of Fixed Retinal Tissue After Sequential Excimer Laser Ablation
Barriers Limiting Fluid Distribution and Implications for Cystoid Macular Edema
Richard J. Antcliff, FRCOphth;
Ali A. Hussain, PhD;
John Marshall, PhD
Arch Ophthalmol. 2001;119:539-544.
Objectives To measure the hydraulic conductivity (HC) of human retina and to determine
the presence and location of high-resistance barriers to fluid movement through
the retina.
Methods Forty-one pairs of human eyes were investigated using an HC chamber.
Once baseline HC had been determined, the effect of ablating through varying
thickness of retina from the vitreous or photoreceptor surface using an excimer
laser (193 nm) was investigated. Tissue samples were then processed for histological
investigation.
Results The HC of fixed intact human retina was 2.54 x 10-10 m/s per pascal at 539 Pa (range, 0.6 x 10-10
to 3.3 x 10-10 m/s per pascal; SD, 0.6 x 10-10 m/s per pascal [1 mm Hg equals 133 Pa]). Ablation from either
surface resulted in little change in HC until a critical depth was reached,
at which point there was an order of magnitude increase. The critical depth
was approximately 170 µm from the inner limiting membrane when ablating
from the vitreous surface and 70 µm from the inner limiting membrane
when ablating from the photoreceptor surface. Histological specimens showed
that these barriers were the synaptic portion of the outer plexiform layer,
and the inner plexiform layer, respectively.
Conclusions The 2 high-resistance barriers to fluid flow through the retina are
the synaptic portion of the outer plexiform layer, and the inner plexiform
layer.
Clinical Relevance These observations help to explain the distribution of cystoid macular
edema seen in histological studies and with optical coherence tomography.
From the GKT Department of Ophthalmology, The Rayne Institute, Saint
Thomas' Hospital, London, England.
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