Clinical Investigation on the Blood Oxygenation at the Optic Nerve Head in Fabry Patients

Contrast sensitivity test is made with targets alternating black and white lines. The larger the lines are, easier it is to see them. Targets are distributed in 5 rows, each oriented at a different angle. Contrast sensitivity level is determined by the smallest target seen by the participant, line by line. This test is done under dim lightning with the habitual visual correction worn.

Slit lamp is used to assess the presence of significant lens opacities known as Fabry cataracts. In fact, these opacities can induced a bias on the contrast sensitivity measurement and can increase the symptoms felt by the patient. A grade 2 (CFDI grading chart) of lens opacities is considered clinically significant and this will become an exclusion criteria for the following of the study. Intra-ocular pressure will be measured with a non contact tonometer (air pulsed) (Ocular Response Analyser, Reichert Instrumentation.)

Visual field will be assessed with an automated perimeter (Humphrey, Texas) using a threshold strategy. This implies that the subject has to identify not only if he perceives the visual stimulus but the minimal level of this stimulus (in decibels), to be seen, is also recorded. Visual field will be tested up to 30 degrees from the central point of fixation. In order to measure immediate variability of the visual testing among Fabry subjects, this test will be done at the beginning of the testing session (in the morning) and another time 1h00 later.

Pupils will be dilated with 1 drop of 1% tropicamide. The procedure is similar to the one used for taking a photo of the retina. Each measurement session represents a continuous recording of 20 simultaneous functions of reflectometry from the optic nerve area during 10 seconds. During all recording sessions, the systemic arterial oxygen saturation will be also monitored at the right index finger using a pulse oximeter (Escort M10, Invivo, Orlando, USA). Arterial blood pressure will be also monitored before and after the testing using a manual sphygmomanometer.

Used to dilate patient's pupil during testing

The OSOME system is the only technology able to perform on line and real time capillaries blood oxygenation measurement in the eye. The system operates with 1200 discreet wavelengths between 400 nm to 700 nm with 500 millisecond integration times. It is not invasive, functioning just like a fundus camera.