Characterizing the Retinal Microvasculature in Patients with Fabry Disease: a Prospective Observational Study

Dynamic retinal vessel analysis (DVA) is an established, non-invasive technique for evaluating the responsiveness of retinal vessels to flickering light stimuli. This technique allows for the measurement of changes in retinal vessel diameter in response to changes in blood flow, providing insight into the microcirculatory function of the retina. In the case of DVA, patients will asked to focus on a needle, and one arteriole and venule diameter were automatically and continuously recorded. Arteriole and venule segments between 0.5 to 1 mm will be analyzed approximately 2-disc diameters away from the optic nerve in a lower-temporal direction. The baseline recording will be 50 seconds, followed by a flickering phase of 20 seconds and then a recovery period of 80 seconds. Three of these cycles were performed.

Based on this, we will calculate the percentage of maximum arteriolar (aFID) and venular dilation (vFID) to baseline.

Collection of blood samples from participants for the purpose of performing clinical chemistry analysis. Peripheral blood mononuclear cells (PBMCs) will be isolated from the collected blood samples using standard techniques, such as density gradient centrifugation, and will be analyzed using fluorescence-activated cell sorting (FACS)

This study involves a comprehensive evaluation of life quality, pain, and gastrointestinal (GI) symptoms using a set of established and validated questionnaires. The tools employed include the SF-36 (Short Form-36 Health Survey) to assess overall health-related quality of life across multiple domains, the COMPASS-31 (Composite Autonomic Symptom Score) to evaluate autonomic dysfunction symptoms, and the Brief Pain Inventory (BPI) to measure pain severity and its impact on daily activities. Additionally, the Gastrointestinal Symptom Rating Scale (GSRS) is used to quantify the severity and frequency of GI symptoms, covering dimensions such as reflux, abdominal pain, indigestion, diarrhea, and constipation. Together, these questionnaires provide a multidimensional assessment of the patient's physical, emotional, and symptomatic experiences, allowing for a robust understanding of their health status and quality of life.

Cardiovascular magnetic resonance imaging (CMR or cardio MRI) will be utilized in patients with Fabry disease. This imaging technique will enable detailed assessment and monitoring of key cardiac abnormalities, including thickening of the heart walls, left ventricular hypertrophy, and decreased blood flow in the coronary vessels. Additionally, T1 relaxation time measurement will be conducted, offering a non-invasive means to detect myocardial tissue abnormalities such as fibrosis and sphingolipid accumulation, which are hallmarks of Fabry disease. Together, these measures provide a comprehensive evaluation of cardiac structure, function, and tissue characteristics in affected patients.

Optical coherence tomography (OCT) is a non-invasive, high-resolution imaging technique that utilizes low-coherence light to capture cross-sectional images of the ocular fundus. Based on the principle of interferometry, OCT employs low-coherence light, which is scattered by the tissue, to produce detailed, high-resolution images of the retina and its layers. This technology enables precise visualization of the different retinal layers, including the nerve fiber layer, the ganglion cell layer, and the inner and outer plexiform layers. Additionally, OCT can be used to detect and monitor subtle structural changes in the retina, offering critical insights into retinal microarchitecture and potential manifestations of systemic diseases such as Fabry disease.

Detection of signs of left ventricular hypertrophy, diastolic dysfunction, and valvular disease, which are common cardiac complications associated with Fabry disease, will be a key focus of the assessment. These abnormalities are indicative of the progressive cardiac involvement characteristic of the disease. Left ventricular hypertrophy reflects the thickening of the heart muscle, often caused by sphingolipid accumulation, while diastolic dysfunction highlights impaired relaxation and filling of the left ventricle. Valvular disease, including regurgitation or stenosis, further contributes to the cardiac burden in Fabry disease. Identifying and monitoring these conditions are essential for timely intervention and effective management of cardiac manifestations in affected patients.

Pulse wave analysis (PWA) is a non-invasive method used to assess the cardiovascular system. It uses a sensor to measure the pressure waves generated by the heart's contraction and the subsequent blood flow through the peripheral vessels. By analyzing these pressure waves, PWA can provide information about the elasticity of the arterial walls, the blood flow in the peripheral vessels, the blood pressure, and the arterial stiffness.

Blood pressure measurement to asses cardiovascular risk.

One hour ECG to asses autonomic dysfunction in patients with Fabry disease.

Evaluation and monitoring of ocular manifestations of Fabry disease.

Comparable to DVA, SVA is a non-invasive and quick tool to examine the retinal microvasculature. SVA pictures will be analyzed using Vesselmap 2® (IMEDOS Systems GmbH, Jena, Germany). One eye will be examined, and three images will be taken with a focus on the optic disc at an angle of 50°. Roughly one disc diameter away from the optic disc, retinal veins and arterioles segments will be semi-automatically labeled. The Paar-Hubbard formula averages the central retinal arteriolar (CRAE) and central venular (CRVE) equivalents.

The arteriolar-venular ratio will be calculated as CRAE/CRVE.