ABSTRACT
I. Introduction .................................................................................................................. 1020 II. Omega-3 Fatty Acids and Ocular Health ..................................................................... 1020 A. Dry Eye ................................................................................................................... 1020 B. Retinal Disease ....................................................................................................... 1020 C. Glaucoma ................................................................................................................ 1022 III. Omega-3 Fatty Acids in the Nervous System .............................................................. 1022 A. Preferential Accretion and Retention of Omega-3 Fatty Acids by the Retina ........ 1023 IV. Methods of Achieving Omega-3 De+ ciency ................................................................ 1024 V. Functional Assessment of Vision ................................................................................. 1025 VI. Retinal Structure ........................................................................................................... 1026 VII. Retinal Signal Processing ............................................................................................. 1028 A. The Dark Current .................................................................................................... 1028 B. Photon Absorption .................................................................................................. 1029 C. Phototransduction Cascade ..................................................................................... 1031 D. Rhodopsin Deactivation and Regeneration of the Dark Current ............................ 1032 E. Visual Pigment Regeneration ................................................................................. 1032 VIII. Assaying Retinal Biochemical Responses ................................................................... 1033 A. The a-Wave ............................................................................................................. 1034 B. The b-Wave ............................................................................................................. 1036 C. Oscillatory Potentials .............................................................................................. 1036 IX. Retinal Dysfunction in Omega-3 De+ ciency ................................................................. 1037 A. Rhodopsin Activation ............................................................................................. 1037 B. The Phototransduction Cascade ............................................................................. 1037 X. Omega-3 De+ ciency Reduces Bipolar Cell Activity .................................................... 1038 XI. Adaptation and Slowed Rod Recovery ........................................................................ 1039 XII. Proposed Mechanisms Underlying Functional Losses ................................................ 1039 A. Membrane Biophysical Properties Modulate Retinal Protein Function ................. 1040 B. Relating In Vitro Predictions to In Vivo Findings: Experimental Power ................. 1041 C. Does Omega-3 Modulate Retinal Protein Content? ............................................... 1042 D. Does Omega-3 Modulate Protein Expression? ....................................................... 1042 E. Does Omega-3 Modulate Ion Channel Proteins? ................................................... 1043 XIII. Summary ...................................................................................................................... 1043 Acknowledgments ..................................................................................................................... 1044 References ................................................................................................................................. 1044
The association between low omega-3 polyunsaturated fatty acid (PUFA) intake and visual dysfunction has been well documented (Vingrys et al., 2001; SanGiovanni and Chew, 2005; Singh, 2005). This chapter reviews recent research that provides insights into the mechanisms through which these essential fatty acids can act to modulate neural function. A brief overview of the importance of dietary omega-3 fatty acids in sustaining ocular health precedes a discussion of the functional contribution that omega-3 PUFA have as structural components of membranes. The specialized metabolism of these lipids by the retina as well as its accessibility by way of electroretinography render this tissue a useful model in which to consider the functional consequences of omega-3 de+ ciency. These functional losses are discussed with respect to the roles that omega-3 polyunsaturates are known to have in modulating membrane biophysical characteristics and membrane-bound protein function. Laboratory trials indicate that omega-3 metabolites should impact on membranebound protein activity in a predictable fashion, although in vivo animal or human studies fail to consistently demonstrate these effects. This review details possible explanations for the lack of concordance between the in vivo and in vitro outcomes.
