Fundus photography enables the detection and measurement of optic disk tilt and rotation. The tilted optic disk presents as vertically oval-shaped and is typically quantified using the ovality index (OI), calculated as the ratio between the longest and shortest diameters of the optic disk. According to the observation of Samarawickrama et al. (7), tilted optic disks have smaller disk diameters, cup diameters, and vertically and horizontally oriented cup-to-disk ratios (CDRs), which is consistent with Tong L’s finding using stereo fundus photographs (8). Rotation is measured between the long axis and the vertical meridian, identified as a vertical line 90°from the horizontal line connecting the fovea and the center of ONH. In non-glaucomatous eyes, superior rotation is more prevalent than inferior rotation, with the latter positively correlated with intraocular pressure (IOP), AL, and the area of the beta-zone peripapillary atrophy (PPA) (5). Based on deep learning, Cho et al. developed an automated system for detecting optic disk tilt, demonstrating outstanding agreement with established clinical criteria (9). Optic disk tilt or torsion results in a redistribution of retinal nerve fiber layer (RNFL) thickness, manifested as decreased RNFL visibility on red-free fundus photography (RFP) (10).

Both the OI and rotation angle, derived from flat projection measurements, are susceptible to observer eye position and thus subject to variability. Optical coherence tomography (OCT), an emerging technology for high-resolution cross-sectional imaging, offers more precise measurements by replacing the optic disk edge with BMO and facilitating quantification (Figure 1). Leung et al. utilized Cirrus SD-OCT to measure the angle between the superotemporal and inferotemporal RNFL bundles, noting a reduction in angle magnitude with increasing AL (11). Since the optic disk shape is determined by the configuration of the neural canal opening on OCT imaging, Jonas interpreted the oblique orientation of the ONH and the oval shape of the optic disk as outcomes of BMO shifting, suggesting a correlation between disk tilt and other morphological alterations (12).

PPA represents one of the earliest clinically observed fundus signs in progressive myopia, exhibiting varying colors due to structural misalignment of the disk margin and variations in pigmentation. The outer boundary of PPA was delineated as the visible scleral edge in color photographs, aligning with the termination of the hyperreflective region in infrared (IR) images. Based on size and morphological features, a succinct classification scheme, including temporal PPA (confined to the temporal aspect of the optic disk), advanced PPA (extending to both superior and inferior aspects of the optic disk), and annular PPA (encompassing the entire peripapillary region), is introduced to intuitively indicate the severity of myopia (15). Lu et al. developed a computer-aided measuring tool, enabling the quantification of PPA size on two-dimensional fundus images, marking the first instance of such quantification (16). Sharma et al. proposed a unified model combining deep neural networks and statistical techniques, which demonstrated excellent accuracy and specificity for automated PPA detection in retinal images (17).

Delimiting the borders of PPA on fundus images can pose challenges, particularly in eyes with optic disk distortion. Using en face images generated from SS-OCT three-dimensional data, Atsuya Miki succeeded in effectively identifying PPA zones, even in the presence of distorted disk margins (18) (Figure 2). Their investigation revealed an association between the beta zone and glaucoma, as well as age, whereas the gamma zone exhibited a correlation with myopia but not with glaucoma. Despite the typical association between PPA area size and AL, studies by Chen et al. and Hu et al. using SS-OCT images indicated a weak correlation between PPA area size and RNFL thickness (19, 20).

The introduction of OCT has provided fresh insights into PPA. According to Saito, the beta zone corresponds to canal retinal pigment epithelium (RPE) atrophy, while the gamma zone is characterized by an externally oblique configuration of the choroidal border tissue (21). In SS-OCT images, the gamma zone serves as an indicator of the extent of misalignment between the BMO and the anterior scleral canal opening (ASCO), showing a stronger correlation with AL compared to other deep ONH parameters.

OCTA enables the exploration of choroidal microcirculation features within PPA. Tang et al. observed a reduction in peripapillary vessel density (PVD) in patients’ eyes, notably in the superior nasal (SN), nasal superior (NS), nasal inferior (NI), inferior temporal (IT), temporal inferior (TI), and superior temporal (ST) directions, accompanied by a significant expansion of PPA area (15). The OCTA choroid map delineated a localized microvasculature dropout (MvD) within the beta zone-PPA region, consistent with hypofluorescence observed in indocyanine green angiography (ICGA) (22). Hu et al. identified topographic disparities in radial peripapillary capillaries (RPCs) and choroidal microvasculature across PPA subzones. Both gamma and beta zones exhibited notable reductions in choriocapillaris density compared to the alpha zone, with widths showing negative correlations (23). Additionally, this altered perfusion status coincided with central scotoma, suggesting potential vascular involvement in the progression of visual field (VF) loss and implicating vascular aspects in glaucomatous damage.

A PHOMS presents as an elevated and blurred disk margin in fundus photography, while its exact boundary appears as a hyporeflective ring nasal to the disk margin on IR or near-infrared reflectance (NIR) (28). However, other causes of disk swelling, such as papilledema, may also exhibit similar features, leading to clinical misdiagnoses (29).

Differential diagnosis can be facilitated through fundus autofluorescence (FAF), where PHOMS typically show no autofluorescence except for occasional small hyperautofluorescent spots, distinguishing them from ODDs (28, 30).

As suggested by their name, typical PHOMS present ovoid atop BM with a diffusely hyperreflective signal on OCT, resembling the reflectivity of the RNFL, and lacking complex geometric shapes or signs of intruding surrounding tissues (31). EDI-OCT, which plays a central role in diagnosis, reveals a distinctive feature wherein hyporeflective borders surround hyperreflective structures (30).

In ultrasonography, Mezad et al. identified a novel feature of PHOMS as small hyperechoic structures without posterior shadowing. Furthermore, ultrasound aids in distinguishing the coexistence of PHOMS with optic nerve head drusen (ONHD), indicated by significant posterior shadowing, or with suspicious papilledema, indicated by excessive optic nerve sheath fluid (28).

Fluorescein angiography (FA) may not be an optimal method for identifying PHOMS, as it merely reveals a hyperreflective optic disk with an indistinct boundary (30).

OCTA demonstrates a flow signal within the hyperreflective lesion, suggesting an intrinsic vascular supply (Figure 3) (32). This hypothesis was subsequently supported in an OCTA-based observation, wherein the presence of a vascular complex within the hyperreflective structure was detected. Additionally, OCTA facilitated the identification of the potential progression of PHOMS into choroidal neovascularization (32). Meanwhile, as reported by Ahn et al., papillary and peripapillary vessel densities decreased significantly in eyes harboring large PHOMS (height ≥ 500 μm) compared to controls (33). Further studies on quantification and determining the permeability of vascular structures in and around PHOMS are warranted.

Color fundus photography (CFP) may not consistently reveal an obvious LCD; however, occasionally, a dark yellowish-orange lesion can be discerned in the area of the myopic disk. Utilizing fundus stereophotographs, Tatham et al. confirmed the correlation between LCDs and localized RNFL defects in glaucomatous eyes (34).

Recent advancements in OCT imaging modalities have facilitated in vivo imaging of the LC. En face volume images offer improved visualization of LC defects, identified as hyporeflective spots amidst the highly reflective LC (35). In SS-OCT images, a focal LC defect is characterized as a loss of high reflectivity from the anterior–posterior border of the full-thickness LC in the vertical, horizontal, and axial serial B-scan images. Originally, Kiumehr et al. delineated five categories of LCDs based on their shape: smooth indentation, moth-eaten appearance defect, step-like depression, hole-like defect, and altered laminar insertion (35). Similarly, after comparing 3D SS-OCT images with en face images, Takayama et al. classified LC defects into lamina cavity and lamina disinsertion, both exhibiting irregular and full-thickness loss of lamina reflectivity, distinguishable from artifacts attributed to vascular shadowing (36). EDI-OCT further improved the visualization of the whole structure, particularly beneath the neuroretinal rim. Based on EDI-OCT, Han et al. proposed another classification, distinguishing between lamina holes, indicating localized discontinuities, and LC disinsertion type, denoting the detachment of the peripheral LC and a downward slope toward the neural canal wall. They additionally noted that the latter were predominantly situated in the gamma zone and displayed a stronger correlation with glaucoma and parameters associated with myopia (37).

The entire shape of LC defects was still hindered by optic disk tilts and rotations in highly myopic eyes until recently. Ota-Itadani et al. developed a deep convolutional neural network (DCNN) trained on manually labeled cross-sectional OCT data extracted from 256, 222 3D OCT images to automatically segment LC defects and generate three-dimensional images. Through this method, they initially identified common locations of LC defects in stereo space (38). The application of such novel methodologies may also aid in identifying regions of structural weakness that may predispose individuals to diseases.

In glaucomatous eyes, histological and OCTA-based studies have unveiled a strong topographic correlation between focal LC defects and dropout of parapapillary capillaries (39–41). Lee et al. further confirmed that glaucomatous LC defects were more likely to originate from circulation loss than mechanical strain (42). However, this conclusion might not be applicable to highly myopic eyes, as researchers excluded eyes with myopic tilted disks and gamma zones. Choe et al. initially demonstrated a significant reduction in PVD or perfusion density (PD) using OCTA with the development of focal LC defects in young myopic patients, suggesting an increasing risk of glaucoma in the future (43).

A PICC can manifest as a well-circumscribed, yellow-orange lesion along the border of the optic disk on fundus photography or as a peripapillary dark reflective region on IR reflectance. It is noteworthy that while most lesions are positioned adjacent to the inferior edge of the optic disk, other sections and even the entire peripapillary circular region may be affected. However, such appearances are evident in only 46.7–53% of PICCs detected via OCT.

Multi-color images (MCIs) of PICC illustrate a well-circumscribed, caesious lesion contiguous with the ONH. Despite their advantages over fundus color photographs in detecting “pits” in retinal layers, MCIs might struggle to identify PICCs due to their greater depth and the absence of melanin within the choroidal cavitation (47, 48).

Based on OCT manifestations, PICC is characterized as a hyporeflective triangular thickening of the choroid with the base at the optic disk border in horizontal or vertical sections, occasionally displaying discontinuity of the normal overlying RPE (49, 50) (Figure 4).

Similar OCT-morphologic changes have been observed at the border of colobomas, which was considered a different stage of the same disorder as PICC (51). The utilization of SS-OCT provides more detailed imaging that may elucidate the correlation between PICC and other complications as well as visual function. Ehongo et al. described a shared anteroposterior alignment among expanded subarachnoid space (SAS), exclusive staphyloma-related choroidal excavation (SCD), and the wedge configuration of the posterior choroidal wall, along with the discontinuity of the embedded ONH border tissue and additional choroidal thickness coinciding with dural traction. They hypothesized that PICC is actually a type of suprachoroidal detachment, following the collapse of the scleral flange caused by the tensile forces of the optic nerve sheaths during adduction (52). Based on SS-OCT, Xie et al. assessed the correspondence between structural characteristics and VF defects, highlighting that instead of the presence of PICC itself, herniation and eventual loss of local retinal tissue may be the true reason behind VF defects (30).

Efforts have also been made to obtain the three-dimensional or volume parameters of PICC. Rohan et al. achieved a side profile view of PICC through three-dimensional disk cube reconstruction imaging. Additionally, Fujimoto et al. successfully implemented a deep learning-based denoising, delineation, and 3D rendering system to establish PICC volume as a new three-dimensional parameter (53, 54). They subsequently demonstrated its ability to reflect the correlation between PICC volume and VF sensitivity.

The vascular characteristics of PICC are accessible through multimodal angiography.

FA reveals early hypofluorescence of the lesion followed by progressive staining without any dye pooling, which can be attributed to the disorganization of choroidal architecture and subsequent scleral impregnation. This helps differentiate PlCC from pigment epithelial detachment, peripapillary choroidal neovascularization, and other potentially confounding entities. Meanwhile, ICGA demonstrates absent choroidal flow, resulting in hypofluorescence throughout the sequence (55).

In highly myopic eyes with PICC, OCTA has revealed a significant reduction in vessel density not only at the choroidal level but also at the level of the RPC. Based on B-scans of OCTA, Kim et al. observed a preserved choriocapillary signal against Bruch’s membrane, which completely vanished within the hyperreflective cavity (56). Another notable vascular abnormality involves the TI vein, which has been described in several cases as either submerging into the intrachoroidal cavitation (ICC) or covering the sinkhole of the PICC (48, 57). The advancement of OCTA technology allows for the early recognition of subtle losses in the microcirculatory network in PICC, facilitating a detailed exploration of its pathophysiological mechanisms.

The presence of a myopic APON is scarcely discernible with CFP. A review of medical records from 198 myopia patients revealed that only 2 out of 32 cases of peripapillary pits were successfully observed as yellowish-gray to dark circular spots, with color variation depending on the quantity and distribution of glial tissue within the pit (58).

En face views of the optic disk area presented the triangular hyporeflective opening of most pits, with the base at the outer edge of the optic disk and the apex heading into the center of the disk. Utilizing en face images from vertical and horizontal SS-OCT scans, Ohno-Matsui et al. identified pits in 16.2% of highly myopic eyes (mean AXL: 30 ± 2 mm), categorizing them into optic disk pits (located in the optic disk area) and conus pits (located in the myopic conus outside the optic disk) (58).

A definitive diagnosis of myopic APON requires OCT imaging, which reveals a deep excavation localized in the superior/inferior border of the optic disk (optic disk pits) or the nasal/temporal side of the scleral ridge (conus pits). This excavation is accompanied by discontinuous laminar architecture and overlying nerve fiber tissues. Moreover, there is little or no rim tissue remaining adjacent to the pit, which manifests as a hyporeflective gap at the junction of the LC and the peripapillary sclera (58). The accompanying structural characteristics of the pits vary, ranging from the dehiscence of the sclera to an attached ICC (59).

Angiography plays a pivotal role in imaging pits. Using SS-OCT combined with fluorescein and ICGA, Ohno-Matsui et al. demonstrated that two conus pits took the form of an enlargement of the emissary canals for the short posterior ciliary arteries (SPCAs) (58). These findings align with the hypothesis that mechanical expansion of the papillary and peripapillary regions may be the primary cause of the pits in these highly myopic eyes. Kita et al. separately observed localized retinal nerve fiber bundle and perfusion damages based on circumpapillary retinal nerve fiber layer (cpRNFL) OCT and OCTA, respectively. These damages spatially corresponded to the pit area and, more importantly, to a progressing visual field defect (VFD) (paracentral scotoma) (60).

Generally, PVAs appear as spindle-shaped or caterpillar-shaped dark areas along the major retinal vessels, particularly the temporal vascular arcades, in fundus photographs (63). On red-free images, they manifest as retinal rarefaction, characterized by increased contrast (61).

Using OCT, three distinct features can be observed in the paravascular region of the retina: microfolds, cysts, and lamellar holes. Microfolds appear as projections from retinal vessels into the vitreous cavity, cysts appear as hyporeflective spaces surrounding the vessels, and lamellar holes appear as discontinuities extending from the inner limiting membrane to between one-half and two-thirds the thickness of the neural retina, all adjacent to retinal vessels (64, 65) (Figure 5). Since PVAs may constitute the anatomic basis of retinoschisis and even detachment, timely identification and treatment become crucial (66, 67).

SS-OCTA en face structural images identified dark, scalloped regions along major retinal veins that match in location with PVAs on B-scans (68). Since PVAs can extend beyond the macula and optic disk areas, using wide-field en face imaging simplifies capturing PVAs across a wider range in a single shot, thereby enhancing efficiency in the process (61).

Generally, PRRS is nearly invisible in color fundus photographs. Nevertheless, traction-related displacement of split tissues may create the appearance of retinal thickening, manifested by a slight elevation of the local retina. This corresponds to the pattern observed in retinal thickness maps, commonly seen as retinal edema extending toward the optic disk (71).

In the IR image, PPRS manifests as a distinct, dark area with a smooth margin, featuring a narrower base connected to the optic disk border and expanding along the path of nerve fiber bundles. Contrarily, the red-free fundus photograph reveals only a localized RNFL defect, whose opening appears like a clear, spindle-like dark area (72, 73) (Figure 6).

First observed by Sherman et al. in highly myopic eyes using SD-OCT, PRRS was documented as splitting situated variably along the disk margin, involving multiple layers, particularly the inner and outer plexiform layers (70). Using wide-field en face SS-OCT, He et al. mapped the distribution of extrafoveal retinoschisis and delineated them as extending hyporeflective areas along the RNFL with well-circumscribed upper and lower margins. Additionally, they identified a distinct dehiscence within the maculopapillary bundles, suggesting a potential non-glaucomatous neuropathy exclusive to high myopia (74).

It is widely acknowledged that two opposing forces provided by posterior staphyloma and anterior vitreous traction contribute to the formation of macular schisis (75). In addition, paravascular microfolds, cysts, and lamellar holes have been implicated in this mechanism (67). Optic disks are also susceptible to the aforementioned abnormalities during axial elongation, as subsequently confirmed by OCT-based detection of their coexistence with PPRS (69). Nonetheless, little is known about the correlation between paravascular lesions and PRRS yet, calling for more detailed studies.

SS-OCTA and en face SS-OCTA images reveal dark back shadowing in the superficial capillary plexus (SCP) or deep capillary plexus (DCP), depending on whether inner or outer retinal layers are involved, accompanied by a markedly increased reflectivity in the RNFL, where retinoschisis occurs (71). During the late phase of FA, no signs of leakage are observed in the peripapillary regions (76).

OCT images usually depict a meshwork-like splitting of the superficial prelaminar tissue in the optic disk, accompanied by a disruption of the prelaminar tissue and an anterior protrusion of retinal vessels (Figure 7). Based on the size and depth of the voids, Lowry et al. categorized the lesions into four levels. They revealed that the presence and severity of these lesions were associated with common OCT parameters such as larger ONH size, thinner neuroretinal rim width, and greater cup depth, indicating a higher risk of ongoing glaucomatous damage (78).

As suggested by the OCT images, two initial factors contributing to the development of prelaminar schisis were discussed. Over four-fifths of the lesions are attributed to the stretching and anterior hanging of the retinal vessels, while vitreous or epiretinal proliferation is also considered an underlying cause. Consistent with the first hypothesis, OCTA scanning clearly demonstrated major retinal vessel trunks contained within anteriorly separated tissues in some cases of prelaminar schisis (78). Longitudinal studies investigating structural and vascular changes over time may shed light on the etiology and clinical importance of this abnormality.