This longitudinal interventional case series will utilize the patients at the University of Michigan W.K. Kellogg Eye Center scheduled to begin treatment for diabetic macular edema. Baseline measures will be taken which include structural assessments such as circulatory capacity utilizing fluorescein angiography, in addition to retinal layer integrity and thickness using high resolution optical coherence tomography. Also, functional assessments such as visual acuity, contrast sensitivity, photostress recovery, dark adaptation, perimetry, and cellular fluorescence will be tested. Adverse events will be recorded and compared with historical controls to ensure that currently accepted interventions are safe. Finally, potential confounding variables for DME including those related to the eye, systemic factors, and patient demographics will be recorded to assess the influence of these variables on treatment response.

The primary objective is to develop hypotheses that might better explain the retinal structural (anatomical) and/or functional (physiological) mechanisms of visual impairment in eyes receiving treatment for diabetic macular edema (DME).

Inclusion Criteria:

• Males and females age ≥ 18 years
• DME involving the central fovea (≥325 micrometers central subfield thickness on Spectralis SD-OCT)
• Scheduled to undergo treatment of DME with intravitreal bevacizumab or ranibizumab
• Willing to sign informed consent, comply with study protocol requirements, and undergo at least 2.5 hours of testing per visit;

Exclusion Criteria:

• Lens opacity ≥ grade 3 ARLNS on standard photographs
• Incisional ophthalmic surgery of any kind within 4 months of study enrollment
• Treatment for DME within the past 4 months
• Active proliferative diabetic retinopathy
• History of vitrectomy
• Glaucoma
• Uncontrolled hypertension (≥ 180 systolic or ≥ 110 diastolic on two successive measures)
• Females of childbearing potential who are unwilling or unable to use an acceptable method of contraception throughout the study
• Females who are pregnant, lactating or breastfeeding at time of enrollment
• Subjects with a history of a serious hypersensitivity reaction to treatment or components of the study assessment
• History of any radiation in or around the eyes
• History of visually significant non-diabetic retinopathy or choroidopathy (e.g. age-related macular degeneration, polypoidal choroidal vasculopathy, central serous retinopathy, retinal vein occlusion, sickle cell retinopathy)
• History of optic neuropathy
• Neurological conditions that can impair vision (e.g. Parkinson's disease, multiple sclerosis, Alzheimer's disease)
• Liver disease (e.g. cirrhosis, hepatitis)
• History of small bowel surgery
• Anticipated need for intravitreal triamcinolone injections
• Dilated pupil diameter less than 6 millimeters
• High myopia (refractive error spherical equivalent ≥ -6 diopters)
• Currently being treated for cancer or any disease likely to adversely affect participation in a 2 year trial
• Participation in any interventional clinical study requiring IRB approval within 3 months of enrollment
• Any findings deemed unacceptable by the Principal Investigator

Individuals undergoing treatment for diabetic macular edema at the University of Michigan W.K. Kellogg Eye Center.