The purpose of this study is to measure the prevalence and severity of cardiac autonomic neuropathy (CAN), diabetic autonomic neuropathy (DAN) which in non-diabetics is termed advanced nervous system (ANS) dysfunction, and autonomic dysfunction as well as the overall sympathovagal balance (SB) in the CEFH population of diabetic patients versus non-diabetic patients undergoing elective vitreoretinal surgery.

The purpose of this study is to measure the prevalence and severity of cardiac autonomic neuropathy (CAN), diabetic autonomic neuropathy (DAN) which in non-diabetics is termed advanced nervous system (ANS) dysfunction, and autonomic dysfunction as well as the overall sympathovagal balance (SB) in the CEFH population of diabetic patients versus non-diabetic patients undergoing elective vitreoretinal surgery.

Inclusion Criteria:

• Type I and Type II Diabetic patients 19 or older who are scheduled for elective surgery to improve vision impaired by diabetic retinopathy
• Patients scheduled during the same time period without diabetes for retinal surgery will serve as an age and gender matched reference group to undergo the non-invasive ANS testing on the day of surgery

Exclusion Criteria:

• Inability to stand will only do baseline, deep breathing and Valsalva portions (A-D) of the testing as described in section 8.1
• Patients with syncope on standing will only do portions A-D of the test
• Inability to cooperate with deep breathing and Valsalva
• Tracheoscopy or otherwise not able to perform a Valsalva
• Not desiring to participate after informed consent
• Known history of idiopathic dysautonomia
• Pulmonary difficulties associated with hyperventilation, including acute URI
• Pacemaker dependent
• Persistently high intraocular pressure despite treatment
• Atrial fibrillation
• Ventricular arrhythmias greater than 10 beats per minute
• Taking MAO inhibitors

The study population will consist of patiented from the Callahan Eye Foundation.