In the present study, we determined which filter facilitated the easier detection of the PAR in UWF fundus imaging in children undergoing ROP. We performed wide-angle fundus imaging using the Optos device in patients with a history of ROP and investigated the detectability/ease of detection of these areas using different colored filters among specialists. Our study results showed that the use of green filter significantly improved the detection and ease of detection of PAR areas. To the best of our knowledge, this is the first study to evaluate PAR using UWF fundus imaging with different filters.
In the literature, there is a limited number of studies evaluating not only peripheral retinal diseases, but also other eye segments using imaging along with colored filters. In a study, Iqbal compared image recordings taken during gonioscopy with a smartphone under standard halogen light photos, warm filter, and green filter conditions [8]. The author concluded that the green filter provided enhanced tissue visualization for the trabecular meshwork and highlighted that the use of digital technologies and color filters enables clearer visibility of both contrast and anatomical structures. Sharma et al. compared the use of yellow and green light during indirect ophthalmoscopy, suggesting that green light not only enhanced patient comfort but also facilitated the visualization of retinal tears, nerve fibers, and atrophies [9]. Ahn et al. compared green and red filters in wide-angle imaging presentations of patients with chronic Vogt-Koyanagi-Harada disease [10]. Despite the expected depigmentation of the retinal pigmented epithelium (RPE) and choroid due to the chronic process, they reported that, contrary to expectations, the green filter was beneficial in determining activation. Inoue et al., on the other hand, compared the use of green and red filters in wide-angle imaging of eyes filled with intravitreal gas after rhegmatogenous retinal detachment surgeries [11]. Following evaluation of 20 eyes, they reported that the green filter was effective for visualizing superior retinal tears and retinal vasculature, whereas the red filter was effective for choroidal vasculature. Wai et al. applied a digital green filter to UWF fundus imaging of retinal tears in 10 eyes using Optos device, giving 17 ophthalmology residents a maximum of 20 sec for each image to determine which filter they could see and how quickly [12]. The study results showed that retinal tears were more easily and quickly detected with the green filter. Similarly, Moon et al. attempted to detect peripheral retinal tears in 10 patients by capturing UWF fundus images and evaluating which filters allowed for faster detection of retinal tears [13]. Their study, similar to ours, demonstrated that participants detected tears more easily and quickly in images using green filters. The authors concluded that such imaging could prevent retinal tears from being overlooked in telemedicine and artificial intelligence applications.
Retinal imaging is an examination method used in the diagnosis and monitoring of several diseases. Many years ago, retinal imaging started with 20 degrees (Carl Zeiss Company in 1926) and has recently been replaced by wide-angle confocal imaging methods that provide 200 degrees of retinal field of view (cSLO; Optos PLC, Dunfermline, Scotland) [14]. The Optos, which has been in use since 2000, is a device that uses ellipsoid mirrors to obtain a 200-degree image with a single capture, capable of displaying 82% of the retina [6]. Taking the images by directing the device to the four cardinal positions (up, down, right, left), retinal imaging can extend up to 220 degrees, covering up to 97% of the retina, although it cannot display the upper and lower retina as wide as the temporal retina [15, 16]. The wide-angle imaging of temporal and nasal retina has popularized the use of the Optos device in peripheral retina diseases. The Optos device utilizes blue (488 nm), green (532 nm), and red (635 nm) laser wavelengths, providing the capability of three-channel color imaging. With its wide imaging capability and the use of different colored filters, it has been widely used in the diagnosis and monitoring of vitreoretinal interface, retinal, and choroidal diseases. The device's software allows for filtering in different colors, enabling acquisition of single-color, two-color (green-red), and three-color (blue-green-red) filtered images after capture [7, 17]. Blue light, with its short wavelength, shows superficial penetration and is particularly effective in highlighting retinal nerve fiber defects and epiretinal membranes. Green light, on the other hand, is effective in visualizing superficial retinal layers, retinal blood vessels, and hemorrhages. Longer wavelengths such as red or near-infrared penetrate deeper, showing choroidal vascularity (Fig. 3). As wavelength increases, larger choroidal veins and multiple vortex ampullae become visible. Therefore, red light, with its longer wavelength, plays an effective role in imaging choroidal lesions such as nevi and tumors [18–20]. In the current study, we obtained UWF images using the Optos device and, then, we used green and red color filters to evaluate which filter allowed for easier and faster detection of PAR areas. In the composite filter, both retina and choroid were visible, whereas in the red filter, the choroid was more visible, and in the green filter, the retina and vessels are more distinct. Our findings support that PAR areas are more easily and quickly detected with the green filter, consistent with the literature.
Persistent avascular retina is defined as the cessation of vascularization in the peripheral retinal area, leading to the persistence of non-vascularized areas. The most common cause of avascular peripheral retina is ROP [4]. The third edition of the International Classification of Retinopathy of Prematurity (ICROP) highlights that PAR can occur spontaneously or after anti-VEGF therapy in ROP patients [21]. Multi-center studies have shown that late complications of ROP such as vitreous hemorrhage, retinal detachment, and retinal tears are associated with avascular retina [5, 22]. Many researchers consider PAR to be an atypical reactivation of ROP, associated with an increased incidence of early and late-stage retinal detachments [5, 23]. However, the majority of these patients are likely to remain asymptomatic, and the development of these complications is rare in a small number of cases. Currently, there is no consensus on the treatment approach for PAR [22]. The approach to detecting PAR and determining which patients require close monitoring, as well as deciding on laser photocoagulation for PAR areas, is further facilitated by wide-angle imaging modalities [24]. The PAR areas can be identified through wide-angle imaging or fundus fluorescein angiography by administering oral or intravenous fluorescein [25, 26]. In the present study, we showed that peripheral retina examination could be conducted without fluorescein and dilation, and PAR could be detected with the aid of filters. Additionally, it is known that the gold standard for peripheral retina examination in children requires sedation and indentation [27]. Our study has indicated that PAR can be detected without the need for sedation and indentation using UWF fundus imaging.
Nonetheless, there are some limitations to this study. First, the number of participants and patients included in the study is relatively small and future studies with larger sample sizes are needed to obtain more reliable conclusions on this subject. Second, our findings may be subject to chance, as participants' knowledge levels, interpretations of the images within the designated time, and immediate responses can vary individually. Third, there is a limited number of studies on the use of UWF fundus imaging with colored filters and, to the best of our knowledge, our study is the first to evaluate PAR using colored filters. Therefore, comparisons with previous results regarding PAR cannot be made. Further research is warranted to assess the effectiveness of colored filters and gain new insights into PAR.