Glutamate and γ-aminobutyric Acid Release into the Vitreous During Cataract Surgery

Abstract

In cataract surgery, transient retinal ischemia and photostimulation-induced retinal damage occurs, even though only for a short duration. We suspected the possibility of excessive release of glutamate under these conditions, and therefore analyzed the amino acid contents in the vitreous body. The vitreous bodies of 32 eyes with disease of the macular area necessitating retinovitreous surgery were used as samples for amino acid analysis. Ischemic diseases such as diabetic retinopathy, venous occlusion, and retinal detachment were excluded. The vitreous amino acid contents were compared between 18 eyes that underwent combined cataract and vitreous surgery and 14 eyes that had vitreous surgery alone. An approximately 3-fold increase of glutamate, 6-fold increase of gamma-aminobutylic acid (GABA), and 2-fold increase of alanine were observed in combined cataract and vitreous surgery compared to vitreous surgery alone. Even in human eyes, acute pressure overload or photostimulation for a short duration cause excessive release of glutamate. A simultaneous increase of GABA suggests the possibility that when glutamate is over-released, the retina physiologically reduced the concentration of glutamate via GABA, in an attempt to suppress the neurotoxin action.