Evaluation of Capillary and Other Vessel Contribution to Macular Perfusion Density Measured with Optical Coherence Tomography Angiography

The protocol allows the identification of the proportion of an area with the circulation from dilated vessels. This dilation can be a response of clinical pathologic condition. This technique can indirectly outline vasodilation using an usual optical coherence tomography metrics to evaluate a group of patients.

Finding vasodilation could indirectly reveal low oxygenation in the stages of retinal vascular diseases before clinical signs appear. Demonstrating the procedure will be Jatziri Perez-Aragon a retinal surgeon from our lab. To begin, select the menu for retinal analysis in the OCTA device.

Select a three by three millimeter retinal map and select superficial if the OCTA device measures different capillary plexuses. Select vessel length density or its equivalent, like skeletonized vascular density. Measure vessel length density per millimeter in a three by three millimeter retinal map.

Return to the menu for retinal analysis. Select a three by three millimeter retinal map and select superficial if the OCTA device measures different capillary plexuses. Select perfusion density or its equivalent like vessel density.

Measure perfusion density in percent in a three by three millimeter retinal map. Verify that the density maps have a signal strength of more than seven, and then verify that the maps have no measurement errors resulting from artifacts or eye movements. Register the values of center vessel length density, center perfusion density, inner vessel length density, inner perfusion density, superior vessel length density, superior perfusion density, inferior vessel length density, inferior perfusion density temporal vessel length density, temporal perfusion density, nasal vessel length density and nasal perfusion density in the spreadsheet.

Select the variables to be evaluated. For example, center vessel length density and center perfusion density and select the values of both variables for a defined group. In the toolbar click on insert.

Click on the recommended charts button in the graph section and wait for a scatter chart to appear as a suggestion in a window. Click the okay button to accept the suggestion. Inspect the scatter chart of the data and right click on the series to display an options menu.

Select the Add Trendline option, and wait for a linear trend line to be added to the chart and for a menu on the right side of the screen. Displace the menu downwards to find the display R squared value on the chart option. Select this option to display the R squared value on the chart.

Select home on the toolbar, and then click on the copy button. Prepare a chart of coefficients of determination on a new page. Select a destination cell and click on the right mouse button.

Select paste with keeping source formatting. Prepare a new chart to show the percentage of perfusion density changes explained by changes in vessel density. Select the cell with the coefficient of determination in the previous chart.

Click on the right mouse button and select copy. Select a destination cell in the new chart. Click on the right mouse button and select paste.

Select the cell with the pasted value and then select a home in the toolbar, followed by a selection of percent style in the number menu. Select increased decimal in the number menu and click once. Prepare another table to show the percentage of perfusion density explained by the changes in vessels larger than capillaries.

Select a destination cell and subtract the last results from one. Select this cell and then select home in the toolbar. Select percent style in the number menu.

Click once on increased decimals in the number menu. Format the charts to display the contribution of capillaries and vessels larger than capillaries in the changes in perfusion density. Repeat the procedure to obtain the values of the inner vessel or perfusion densities and superior, inferior, temporal and nasal vessel or perfusion densities in group three.

Compare the coefficients of determination in three groups. One, healthy people, two, patients with arterial hypertension without hypertensive retinopathy, and three, patients with type two diabetes melitis without diabetic retinopathy. In group three, also compare the coefficients of determination between fields superior, inferior, temporal and nasal.

Compare the percentage differences in the contribution of capillaries and vessels larger than capillaries to perfusion density between groups and between fields in group three. The vessel and perfusion densities in group one were lower than in group two. The comparison between the coefficients of determination of center vessel and perfusion densities in the three groups showed that there was no significant difference between the groups.

The contribution of vessels larger than capillaries accounted for 18.2%in healthy subjects, 2.6%in patients with arterial hypertension and 16.4%in patients with diabetes. Although the inner region had a contribution of vessels larger than capillaries that accounted for 16.4%of perfusion density this contribution was 27.8%in the superior field, 20.7%in the inferior field, 33.4%in the temporal field and 13.8%in the nasal field. It's important to obtain the R square value as it is essential to calculate the percentage of perfusion density of dilated vessels.