The purposes of this study are to identify indicators of vision problems and ocular abnormalities in patients with a Fontan circulation through a standardized questionnaire and to correlate the intraocular pressure measured with the Icare tonometer with central venous pressure measured with the VENUS 2000 CVP non-invasive system to determine whether intraocular pressure can be used as a surrogate measure of increased central venous pressure in patients with a Fontan circulation.