PURPOSE: To compare sharpness and visible retina area (VRA) on images taken with two different UWF imaging devices.
METHODS: Twenty eyes of 10 healthy volunteers were evaluated with mean age 37.50±16.25 years (range 23-68), refractive error (spherical equivalent) -1.71±2.89 diopters (range -7.50 to +3.0) and axial length 24.09±1.24 mm (range 22.47-26.88). For each study eye, UWF imaging with the Optos California (which utilizes phase plate adjustment) and Optos 200Tx (which does not) were acquired using a standardized protocol at the same visit (Stereoscopic on-axis 200o and monoscopic nasal, temporal, superior and inferior steered 200o images). All images were stereographically projected and evaluated at a centralized reading center. For each eye, the visible retinal area (VRA) was manually outlined on each UWF image and quantitated using customized software (Optos, plc). Total VRA area was determined from combining the VRA of all images. The mean image sharpness (defined as mean absolute % change in brightness/pixel after low pass filtering) was evaluated using an automated method within the full VRA of each image and within the peripheral region of the VRA located anterior to a circle of 4.5 disc-diameter radius centered on the fovea.
RESULTS: There was little difference in VRA between devices regardless of gaze direction other than for superior steered images where California provided a larger VRA (Table 1). Compared to on-axis imaging alone, eye steering enabled visualization of additional retinal area for both California (37.8%) and 200Tx (33.0%). For both devices regardless of gaze direction, mean sharpness of the full VRA was greater than that of the peripheral area. Sharpness results for on-axis imaging are shown in Table 2. Sharpness of the full VRA was 19.5% higher for California than 200Tx. The reduction in sharpness between the peripheral area and the entire VRA was not statistically different for California (-7.0%, P=0.26) but was -31.2% (P<0.0001) for 200Tx. Sharpness of the peripheral image area was 61.5% higher in California than 200Tx.
CONCLUSIONS: The Optos 200Tx and California image similar areas of the retina. However, the loss of sharpness in the image periphery is 4.4-fold less with California. The degree to which better peripheral image sharpness allows identification of individual retinal lesions without the need for image steering remains to be determined.
