Effective field of view of widefield fundus photography at the Stanford University Network for the Diagnosis of Retinopathy of Prematurity (SUNDROP)

In the past two decades, fundus photography in the management of ROP has been increasingly adopted in routine clinical settings as well as for research purposes. Numerous studies have supported its validity and diagnostic accuracy in the context of telemedicine with a remote physician or even trained technicians reading the images.6,7,8,9,10,eleven.12. Documentation provided by fundus photos also allows for direct comparison between sessions, allowing for monitoring of disease progression.13 and response to treatment14.15.

Ells et al. presented the first standardized protocol for telemedicine-based ROP detection consisting of five images per eye, including posterior pole, temporal, nasal, superior and inferior retinasixteen. Since then, this protocol has been used worldwide in both clinical and research settings, allowing comparisons to be made within and between different studies.17,18. The fully developed adult retina covers 72% of the inner eyeball.19corresponding to approximately 180° visual field per eyetwenty. Although a complete image of the retinal periphery cannot be obtained with this protocol, real-world data from the SUNDROP initiative revealed that no cases of ROP (TW-ROP) were missed without justified treatment (sensitivity = 1.0) in more than 1,800 babies examined to date10. Our study showed that when using this standardized protocol, the effective FOV is on average 144.54°, only 14.54° (11%) more than the single posterior pole image with a 130° view. However, the FOV provided by this average effective FOV of 144.54° was sufficient to detect all clinically relevant findings. Together, our data suggest that a single photo centered on the optic nerve from a hypothetical 145° lens might be enough to rule out TW-ROP. In contrast, we hypothesize that a system with a narrower FOV taking multiple photos at different angles might be sensitive enough if the composition of the photos can achieve an effective FOV of 145° or more.

In this study we demonstrated that the FOV was not symmetrically distributed around the optic nerve, with the temporal FOV being the widest followed by the superior, inferior and nasal fields. The optic nerve head was used as a reference because it is easily detectable at the posterior pole. However, the optic nerve lies nasally compared to the intersection between the pupillary axis and the retinal plane. At the same time, ROP often presents with a vascular wedge in the temporal retina with the apex pointing toward the optic disc.twenty-one. As a consequence, the temporal view is both the widest and the best performing for detecting disease.

The average FOV between the two eyes was similar in this study. Although not a statistically significant difference, the upper quadrant of the right eye tended to have more limited average vision compared to the left eye. Considering that most people are right-handed, this small discrepancy could be explained by the different ergonomics of the probe in the two eyeballs. The mean effective FOV of infants with ROP was comparable to that of patients without ROP. This suggests that all infants were imaged equally with no performance bias towards sicker patients. Furthermore, no correlation was found between effective FOV and GA, BW, or PMA.

We found that effective FOV was wider in men compared to women in all quadrants except bottom view, despite comparable GA, BW, PMA, and ROP status. Previous studies have shown that males have longer eyes during the neonatal stage even after correcting for BW and GA.22.23. This greater axial length could correlate with a larger retina, as well as a larger pupillary aperture providing a broader view of the periphery of the fundus. In addition, there could be different efficacies for mydriatic drops between the two sex groups due to ethnic imbalances, as eyes with dark irises are less responsive to mydriatics.24.25.

To summarize, five multidirectional fundus photos acquired by a 130° camera in a real environment yielded an average effective FOV of 144.54°. This was less than the assumed FOV of 180°, but was sufficient to detect 100% TW-ROP in the SUNDROP cohort in more than 1,800 infants screened to date. This implies that an imaging FOV during ROP detection considerably less than the hypothetical ideal of 180 is sufficient for patient safety. Males were found to have a larger effective FOV compared to females. Additional studies are warranted to answer the questions raised by our study and to further validate the use of fundus photography in the management of ROP.

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