Retinal Morphological Characterization of Collared Scops Owl ( Otus lettia ) Using Optical Coherence Tomography and Histological Techniques

ABSTRACT

Objective

To establish normative retinal imaging and measurement data for the Collared Scops Owl ( Otus lettia ), a nocturnal raptor clinically free of systemic and ophthalmological disorders, using optical coherence tomography and histopathology.

Animal Studied

Ten eyes from 6 Collared Scops Owls ( Otus lettia ) were included in the study.

Procedures

As part of the standard pre‐release assessment, ocular reflex tests and basic ophthalmic examinations were performed prior to anesthesia induction. Routine X‐ray and blood work were then conducted under general anesthesia, followed by OCT imaging for high‐resolution retinal analysis. Parameters assessed included the pecten‐foveal distance, foveal width, foveal depth, total retinal thickness (TR), neurosensory retinal thickness (NS), and ganglion cell complex thickness (GCC). Retinal images acquired through OCT were compared with corresponding histological sections to validate the findings and evaluate structural correlations.

Results

A single fovea was identified on the superior and temporal side of the pecten. The measured pecten‐foveal distance was 5959.7 ± 147.45 μm (mean ± SD), while the foveal width and depth were 656 ± 41.81 μm and 65.3 ± 6.34 μm, respectively. The TR was 299.8 ± 23.08 μm, and the NS averaged 272.9 ± 21.94 μm; the GCC was 87.9 ± 6.24 μm. Histology revealed all retinal layers distinctly, which were well cross‐referenced and correlated with OCT images.

Conclusions

The morphology and measurement values of the retina in Collared Scops Owls were first established using OCT and histological analysis. These findings, which are fundamental to raptor ophthalmology, offer valuable support for medical care efforts and conservation.

1. Introduction

Vision is essential for avian survival in natural habitats, as it facilitates interspecies interactions and acquisition of critical environmental information, including foraging and avoiding danger [1, 2]. Raptors possess a relatively large eye globe size in proportion to their body, a distinctive anatomical adaptation that enhances their visual sensitivity and acuity, which is beneficial for thriving in the wild [3]. However, this adaptation also increases their vulnerability to ocular trauma [4, 5, 6]. Impairment of vision can significantly affect the feasibility of their release back into their natural habitat [7]. Therefore, assessing the retinal structure in live raptorial birds is essential for evaluating visual function [8].

The Collared Scops Owl ( Otus lettia ) is a small nocturnal raptor, commonly found in human‐populated areas and listed as a protected species. It is the most frequently rescued owl species in our country [9].

The retinal structure demonstrates significant interspecies variation among raptor species [8]. As avian species possess an avascular retina, nutrients and oxygen are supplied to the retinal tissue via the lamina choriocapillaris and the pecten. The pecten is a pleated, pigmented, and highly vascularized structure that extends into the vitreous from beneath the optic nerve head in the ventro‐temporal region of the fundus [10]. The functional photoreceptor cells in the retina of raptors are significantly more numerous compared to humans, contributing to their excellent vision. In diurnal raptors, cone cells predominate over rod cells, reflecting enhanced visual acuity, whereas in nocturnal raptors, rod cells are more abundant than cone cells, indicating heightened visual sensitivity under low‐light conditions [11]. Another notable adaptation that further enhances visual acuity is the presence of a fovea [12]. The number, morphology, and position of the fovea on the retina vary among different raptor species [11, 13]. Retinal diseases associated with trauma are commonly observed in raptor species [14, 15].

Optical Coherence Tomography (OCT) is a non‐invasive imaging technique based on the principles of low‐coherence interferometry, capable of generating high‐resolution images of both the anterior and posterior segments of the eye. OCT is a powerful diagnostic tool for retinal and optic nerve diseases, such as glaucoma and retinal detachment [16, 17]. In avian species, OCT enables the detailed examination of the complete retinal morphology, including the layered structure, fovea location and depth, and the shape and region of the pecten [2, 18]. Another approach for examining normal and pathological retinal tissue is histopathology. Previous studies have demonstrated that the retinal layer structure observed in OCT imaging shows good correspondence with histological findings [8].

This study aims to employ OCT to evaluate the retinal structure of Collared Scops Owls and to compare the OCT images with histological examinations and fundus photographs obtained via direct ophthalmoscopy, in order to gain a better understanding of retinal structure in raptors. This research represents the first OCT‐based retinal study and the first retinal histological examination of the Collared Scops Owl. In addition to describing retinal morphology, we incorporated quantitative measurements of the fovea and individual retinal layers, thereby providing more detailed morphometric data than previous reports. Furthermore, we compared OCT findings with corresponding histological sections, enabling cross‐validation of retinal structures observed in vivo.

2. Materials and Methods

This research was conducted in compliance with the Guidelines for Ethical Research in Veterinary Ophthalmology (GERVO). Ethical approval was obtained from the Institutional Animal Care and Use Committee of the National Taiwan University, approval number: NTU‐113‐EL‐00044. Animals were not captured, restrained, sedated, or anesthetized solely for the purposes of this study.

Free‐living Collared Scops Owls ( Otus lettia ) admitted to a certified Wildlife Rescue Center in Taiwan between May 2024 and December 2024 were eligible for enrollment in this study. All owls were rescued due to various traumatic injuries, including head trauma, falling out of the nest in juvenile birds, and limb fractures, and were undergoing rehabilitation. The average time between trauma and the start of rehabilitation prior to release was approximately 1.5–2 months. Ophthalmic examinations were first performed upon admission to the rescue center and were repeated prior to rehabilitation. As part of the standard pre‐release protocol, ocular reflex tests and basic ophthalmic examinations were performed prior to anesthesia induction. Routine X‐ray and blood work were then conducted under general anesthesia, followed by OCT imaging. The age and sex of the owls were unknown. Body weight was measured prior to rehydration and anesthesia.

Ten eyes from six owls that exhibited no abnormalities on these examinations were selected for inclusion in the study. Ophthalmic evaluations included assessments of the menace response, palpebral reflex, dazzle reflex, direct pupillary light reflexes, fluorescein staining (Omni Fluro, Omni Lens Pvt. Ltd., Gujarat, India), slit‐lamp biomicroscopy (SL‐17, Kowa, Nagoya, Japan), rebound tonometry (Tonovet, Icare, Vantaa, Finland), and indirect ophthalmoscopy with a 40‐diopter condensing lens (Volks Optical Inc. OH, USA). The fundus photographs were obtained using a portable ophthalmoscope imaging system (oDocs nun, oDocs Eye Care, Otago, NZ).

OCT was performed under general anesthesia. Prior to induction, the owls were placed in an oxygen chamber for 10 min to minimize stress. Anesthesia was induced with 5% isoflurane (Attane, Piramal Critical Care) via chamber induction, followed by tracheal intubation, and maintained at 1.5%–2% isoflurane. Vital parameters, including heart rate, respiratory rate, and body temperature, along with anesthesia depth, were closely monitored throughout the procedure by an exotic animal anesthetist. Upon completion of the OCT and other examinations, gas anesthesia was discontinued and extubation was performed. The owls were then transferred to an oxygen chamber until full recovery of consciousness. All individuals were returned to their original enclosures on the same day, and subsequently prepared for release into the wild. The entire process, from anesthesia induction to complete recovery, was completed within 1 h.

Without the use of mydriatics, pupil size remained adequate for scanning under general anesthesia, allowing for a clear retinal image. A wire eyelid speculum (F1‐101 Speculum, Ultra‐Vision Vet. Co., Taipei, Taiwan) was applied to keep the eyes open (Figure 1), and the cornea was kept moist throughout the procedure with artificial tears Blink (AMO, MA, USA).

FIGURE 1.

Image showing an anesthetized owl under isoflurane anesthesia via tracheal intubation, with an eye speculum used to keep the eyelids open.

The spectral domain OCT machine used was the OCT SPECTRALIS (Heidelberg Engineering, MA, USA), running Heidelberg Eye Explorer version 1.10.4.0. We measured the pecten‐foveal distance, foveal width, foveal depth, total retinal thickness (TR), neurosensory retina thickness (NS), and ganglion cell complex thickness (GCC).

The distance between the pecten and the fovea was measured on infrared images, from the base of the pecten to the center of the fovea (Figure 2). The measurement methods were as follows: first, we identified the deepest point of the fovea in the image and drew a horizontal line connecting the inner retinal areas on both sides of the fovea, representing the fovea width. Then, we drew a line perpendicular to the first line from the deepest point of the fovea, representing the fovea depth (Figure 3). The perifoveal area was defined by drawing a horizontal line from the deepest point of the fovea and identifying the location 1000 μm away, where retinal thickness was measured (Figure 4). Retinal thickness was also assessed along a perpendicular line: total retinal thickness (TR) was measured from the innermost retinal surface adjacent to the vitreous to the outer boundary of the retinal pigment epithelium (RPE) (Figure 5); the neurosensory retina (NS) was measured from the nerve fiber layer (NFL) to the outer segments of the photoreceptor cells (Figure 6); and the ganglion cell complex (GCC) was measured from the NFL to the inner plexiform layer (Figure 7).

FIGURE 2.

The infrared image displays the black, pleated pecten on the left and a small, sharply defined, dark circular shape representing the fovea on the right. The distance from the base of the pecten to the center of the fovea is measured as the pecten‐foveal distance. A scale bar shown at the bottom of the image.

FIGURE 3.

The centrally located fovea appears as a shallow, saucer‐shaped depression in the optical coherence tomography (OCT) image. Foveal width and depth were measured from the deepest point; the yellow line represents the foveal width, and the red line represents the foveal depth.

FIGURE 4.

Retinal thickness measurement in the perifoveal area. The perifoveal area was defined as 1000 μm from the fovea. The asterisk indicates the deepest point of the fovea, and the yellow line illustrates the 1000 μm distance to the measurement site.

FIGURE 5.

Total retinal thickness (TR) measured in the perifoveal area, extending from the innermost retinal layer adjacent to the vitreous to the outer boundary of the retinal pigment epithelium (RPE). The yellow line indicates the location 1000 μm from the fovea, and the pink line represents the TR measurement.

FIGURE 6.

Neurosensory retinal thickness (NS) measured in the perifoveal area, extending from the nerve fiber layer (NFL) to the outer segments of the photoreceptor cells. The yellow line indicates the location 1000 μm from the fovea, and the blue line represents the NS measurement.

FIGURE 7.

Ganglion cell complex (GCC) thickness measured in the perifoveal area, extending from the nerve fiber layer (NFL) to the inner plexiform layer (IPL). The yellow line indicates the location 1000 μm from the fovea, and the green line represents GCC measurement.

One globe was obtained postmortem from an owl that had been euthanized due to non‐ophthalmic traumatic injuries. Although the initial ophthalmic examination revealed no significant abnormalities, the owl's physical trauma had severely impaired its flight and hunting abilities. Following a comprehensive release evaluation, it was determined that the owl was unsuitable for reintroduction into the wild, and humane euthanasia was performed. The globe was collected after euthanasia for histological structure analysis and comparison with OCT imaging findings.

To preserve the eye for further analysis, 10% neutral phosphate‐buffered formalin was injected into the anterior and posterior chambers, and the entire eyeball was subsequently fixed in the same solution and stained with hematoxylin and eosin (H&E) stain.

All data analyses were conducted using IBM SPSS Statistics, version 25.0 (IBM Corp. USA). Retinal measurements including pecten‐foveal distance, foveal width, foveal depth, total retina thickness (TR), neurosensory retinal thickness (NS), ganglion cell complex (GCC) were analyzed as mean, standard deviation (SD), minimum, maximum and 95% confidence interval. A Kolmogorov–Smirnov test (p < 0.05) was employed to determine whether the data followed a Gaussian distribution, and all the data were confirmed to be normally distributed. Reference intervals were defined using the central 95% percentiles (mean ± SD).

3. Results

Owls' body weight ranged from 150 to 180 g. The fundus photograph of the Collared Scops Owl is shown in Figure 8, in which the black, pleated pecten and the choroidal blood vessels are distinctly observable.

FIGURE 8.

Fundus photograph of the owl showing the black, pleated pecten and prominent choroidal blood vessels.

The pecten and retinal layers are visualized with high resolution and are clearly distinguishable in infrared and OCT images (Figure 9). Using the pecten as an anatomical landmark within the avascular retina, a single fovea was identified on the superior and temporal side of the pecten, consistent with anatomical descriptions reported in other nocturnal owl species. In the infrared image, the fovea appears as a small, sharply defined, dark circular shape (Figure 2). In OCT layered imaging, the fovea presents as a saucer‐shaped, shallow depression, which can be classified as the concaviclivate type (Figure 3).

FIGURE 9.

The image on the left presents an infrared view of the owl's retina, highlighting the pecten structure. The image on the right displays a cross‐sectional optical coherence tomography (OCT) image with clearly distinguishable retinal layers.

The pecten‐foveal distance had a mean ± SD of 5959.7 ± 147.45 μm (95% CI: 5854.22–6065.18 μm), with a minimum of 5800 μm and a maximum of 6192 μm. The mean ± SD foveal width was 656 ± 41.81 μm (95% CI: 626.09–685.91 μm), with a minimum of 602 μm and a maximum of 751 μm, and the foveal depth was 65.3 ± 6.34 μm (95% CI: 60.72–69.83 μm), with a minimum of 55 μm and a maximum of 74 μm. The total retinal thickness (TR) measured 299.8 ± 23.08 μm (95% CI: 283.29–316.31 μm), with a minimum of 275 μm and a maximum of 337 μm. Neurosensory retinal thickness (SR) averaged 272.9 ± 21.94 μm (95% CI: 257.21–288.59 μm), with a minimum of 247 μm and a maximum of 308 μm, while the ganglion cell complex thickness (GCC) was 87.9 ± 6.24 μm (95% CI: 83.43–92.37 μm), with a minimum of 79 μm and a maximum of 97 μm (Table 1).

TABLE 1.

Mean ± SD, minimum, maximum and 95% confidence interval values (all in μm) of pecten‐foveal distance, foveal width, foveal depth, total retinal thickness (TR), neurosensory thickness (NS), and ganglion cell complex (GCC) obtained by optical coherence tomography (OCT) in 10 eyes of Collared Scops Owls ( Otus lettia ).

Parameter	Mean ± SD	Min	Max	95% CI
Pecten‐foveal distance	5959.7 ± 147.45	5800	6192	5854.22–6065.18
Foveal width	656 ± 41.81	602	751	626.09–685.91
Foveal depth	65.3 ± 6.34	55	74	60.72–69.83
Total retinal thickness (TR)	299.8 ± 23.08	275	337	283.29–316.31
Neurosensory retinal thickness (NS)	272.9 ± 21.94	247	308	257.21–288.59
Ganglion cell complex (GCC)	87.9 ± 6.24	79	97	83.43–92.37

The histological segmentation of the Collared Scops Owl retina is shown in Figure 10, with all retinal layers distinctly visible and cross‐referenced with OCT images. The OCT scans displayed distinct grayscale contrasts among retinal layers, which could be consistently matched with their histological counterparts, demonstrating good overall correlation, while histology provided clearer delineation of layer boundaries.

FIGURE 10.

Histologic section of the owl retina (left) and a corresponding optical coherence (OCT) image (Right) demonstrating layer‐by‐layer correlation. ELM, external limiting membrane; GCL, ganglion cell layer; INL, inner nuclear layer; IPL, inner plexiform layer; NFL, nerve fiber layer; ONL, outer nuclear layer; OPL, outer plexiform layer; PRL, photoreceptor layer; RPE, retinal pigmented epithelium.

The density of the nerve fiber layer varies in different regions with consistent thickness. A large majority of one nuclear layer composes the ganglion cell layer. In addition, the inner nuclear layer consists of 4–8 nuclear layers. The outer nuclear layer, closely connected to the thin external limiting membrane, comprises predominantly cell bodies of rods with a few cones. Cells of the retinal pigment epithelium of the retina are flat and contain a few dome‐shaped pigment granules. Between the retina and the sclera lies the choroid, which is highly vascularized and composed of variably sized capillaries interspersed with abundant pigmented cells (Figure 11) The sclera is primarily made up of dense collagen fibers arranged in layers, forming a thicker region around the optic nerve. Within the sclera, hyaline cartilage extends from both sides of the optic nerve posteriorly to the anterior region, where it contacts the ciliary body. The optic nerve, consisting of numerous nerve fiber bundles, passes through the optic disc into the posterior region of the eyeball. Located in the ventral part of the optic disc is a partial pecten with abundant pigmented cells (Figure 12).

FIGURE 11.

Histologic section of the owl eye showing a highly vascularized choroid interspersed with abundant pigmented cells. C, choroid; Ca, hyaline cartilage; R, retina; S, sclera.

FIGURE 12.

Histologic section of the owl eye showing the optic nerve, consisting of numerous nerve fiber bundles and part of the pecten. *, pecten; Ca, hyaline cartilage; ON, optic nerve; S, sclera.

4. Discussion

The Collared Scops Owl ( Otus lettia ) is one of the most frequently encountered nocturnal raptors in Taiwan and is classified as a protected species. However, habitat destruction and vehicle collisions have led to a significant number of injured individuals requiring rescue and rehabilitation. In recent years, heightened conservation awareness has resulted in the establishment of more organizations dedicated to rescuing, rehabilitating, and conserving injured raptors, leading to a substantial increase in medical demands. This growing need has also underscored the scarcity of fundamental medical information regarding local raptors, including limited ophthalmological knowledge. A thorough understanding of the anatomical and physiological features of the raptor visual system is essential for accurate ophthalmic diagnosis, monitoring, and treatment [19].

In this study, we present the first OCT‐based retinal study and the first retinal histological examination of the Collared Scops Owl ( Otus lettia ). Fundus photography was initially performed to obtain preliminary images of the fundus morphology. Subsequently, OCT was utilized to evaluate retinal layering, obtain quantitative measurements of the fovea and individual retinal layers, and determine the position and morphology of the fovea. These observations were further corroborated through comparative analysis with histological sections, ensuring the accuracy and reliability of the findings.

Histopathological examination remains an essential tool for confirming retinal pathology. It provides two‐dimensional images that are dependent on section orientation but offer cellular‐level resolution, enabling detailed evaluation of degenerative changes, inflammatory responses, and the entire globe, including anterior segment structures such as the cornea, ciliary body, and lens. Structures such as the pecten and fovea often require meticulous sectioning to achieve complete visualization [20]. However, this method carries notable clinical limitations, as it requires enucleation surgery or post‐mortem examination to obtain ocular tissue for diagnosis. In avian species, the presence of scleral ossicles surrounding the eyeball [21] may introduce artifacts during tissue fixation and trimming, potentially causing disruption of retinal layering or artificial retinal detachment [18].

In contrast, OCT provides a minimally invasive, real‐time, high‐resolution cross‐sectional imaging modality that allows in vivo visualization of retinal microstructure. Each retinal layer can be clearly identified, which is why OCT is often described as an “in vivo optical biopsy”. OCT enables both qualitative analyses, such as morphological assessment and reflectivity evaluation, and quantitative measurements, including mapping, thickness, and volume analysis [16, 22], thereby expanding the possibilities for ophthalmic diagnosis and enabling more accurate prognosis assessment [8].

OCT images are presented in varying degrees of grayscale, reflecting the optical backscattering properties of different cellular structures within the retina, which manifest as difference in grayscale intensity and facilitate layer segmentation [23]. In our analysis, the nerve fiber layer and plexiform layers displayed higher brightness due to their strong optical backscattering properties, while the nuclear layers, characterized by weaker backscattering, appeared relatively darker. These findings are consistent with observations reported in the previous studies in other avian species, such as parrots and raptors, as well as in mammals including dogs and rodents [11]. This characteristic of distinct grayscale patterns among different retinal cell layers also provided an important basis for correlating OCT with histology. In this study, OCT images could be matched with histological sections across all nine retinal layers, with comparable thickness, demonstrating good correlation between the two modalities.

At the same time, certain discrepancies were observed in this study. While OCT enables three‐dimensional visualization, it is limited to localized regions and is susceptible to signal attenuation [16]. Histology, although inherently two‐dimensional and dependent on section orientation, provides cellular‐level resolution; consequently, the boundaries of retinal layers, particularly the ganglion cell layer, appeared clearer in histology than in OCT. Importantly, histological examination confirmed all major features observed in OCT, reinforcing the reliability of OCT as a noninvasive tool for detailed retinal assessment in raptors.

The thickness of retinal layers varies across different regions of the retina [24]. In the present study, OCT revealed greater total retinal thickness in the central/perifoveal region compared with more peripheral areas. This finding is consistent with previous reports in other avian species—such as pigeons and raptors—where high‐acuity foveal regions exhibit increased densities of photoreceptors and ganglion cells [25, 26], resulting in greater thickness. Similar central–peripheral thickness patterns have also been reported in mammals, such as dogs [27]. Moreover, factors such as age and ocular diseases have been shown to influence retinal thickness in both nocturnal owls and dogs [28, 29].

In studies of mammalian species, the optic disc and retinal blood vessels are commonly utilized as anatomical landmarks and boundaries for retinal measurements [27, 30, 31]. However, in avian species, such as the Collared Scopes Owl, the optic nerve is obscured by the pecten and lacks retinal blood vessels [10, 32], necessitating the adoption of alternative measurement criteria [2, 18, 33]. In this study, a location 1000 μm from the fovea was designated as the perifoveal area, and retinal thickness was measured at this point. This method was applied because the fovea is a distinctive structure within the owl's retina, representing an area of enhanced visual acuity and serving as a key reference point for regional analysis.

The fovea is a specialized, pitted region of the avian retina that plays a crucial role in vision by enhancing visual acuity. The thinner retinal tissue within the foveal area minimizes light scattering before it reaches the photoreceptor outer segments, where visual pigments absorb light, thereby improving visual ability [34]. This structure and characteristics of the fovea vary among avian species, reflecting adaptations to their environments, foraging strategies, and other ecological factors [35, 36].

The number of foveae in birds ranges from one to two, depending on the species. Nocturnal raptors, including owls, generally possess a single, shallow fovea located in the temporal retina. Consistent with this pattern, the Collared Scops Owl ( Otus lettia ) in the present study had a single temporal fovea. When compared with other members of the family Strigidae, its foveal morphology demonstrated both notable differences and resemblances. For example, the Great Horned Owl ( Bubo virginianus ), a comparatively larger owl species, has a markedly deeper (177 μm) and wider (949 μm) fovea than O. lettia [13], differences that may be associated with body size and ecological conditions. In contrast, the Eurasian Scops Owl ( Otus scops ), another member of the same genus, has a fovea of similar depth (42 μm) and width (739 μm) to O. lettia [37], suggesting that closely related species may share comparable adaptations for nocturnal vision. By contrast, many actively hunting diurnal raptors, as well as certain carrion‐eating and insectivorous birds, exhibit two foveae: a central deep fovea and a shallower temporal fovea. Carrion‐feeding birds of prey, such as vultures and condors, typically possess a single central fovea. The central deep fovea, characterized by a higher density of photoreceptors, is optimized for exceptional visual acuity, enabling precise tracking of fast‐moving targets. The temporal shallow fovea, while offering slightly lower visual acuity, supports broader‐angle vision, advantageous for environmental monitoring and perception [11].

During OCT retinal examinations, the use of sedation or general anesthesia may be necessary depending on the bird species and individual temperament [2, 8, 18, 38]. Some studies have shown that the procedure can be performed on awake birds under physical restraint [4, 11, 33, 39], although this approach may not be suitable for all cases. In our experiment, as the Collared Scops Owls were wild individuals, inhalation of isoflurane was used to minimize stress, ensure safe handling and avoid potential feather damage caused by physical restraint, which could compromise flight ability and delay the release back into the wild.

Under general anesthesia, pupil size in the owls was sufficient to allow clear OCT imaging without the use of pupil‐dilating agents. This approach avoids the challenges associated with traditional mydriatic agents used in mammalian species, which are ineffective in birds due to the striated muscle composition of their irides. In other studies, topical application of lower‐toxicity neuromuscular blockers such as rocuronium bromide, has been used as an alternative to achieve pupil dilation in avian species [2, 4, 18]; however, this drug may still cause side effects such as corneal erosion, lower eyelid paralysis, and blepharospasm [40].

The limitations of this study included a relatively small sample size and the lack of basic signalment information, such as age and sex of the owls. Some Collared Scops Owls admitted to wildlife rehabilitation centers for conservation purposes already exhibited other medical conditions, rendering them unsuitable for inclusion in the study. Age‐related changes, including a decline in choroidal blood flow and substantial photoreceptor loss, have been documented in pigeon species, contributing to retinal thinning [41]. In addition, sexual dimorphism has been observed in mice, with female mice exhibiting greater retinal thickness compared to males [42]. However, whether similar age‐related alterations or sexual dimorphism occur in wild raptors remains to be investigated.

In conclusion, OCT provides detailed morphological images of the retinal structures in Collared Scops Owls, identifying a single fovea located in the temporal region. Quantitative OCT measurements enabled precise assessment of retinal thickness, foveal width and depth, and the distance between the fovea and the pecten, with results from histological layer‐by‐layer comparisons. Moreover, histology remains indispensable for definitive, high‐resolution confirmation at cellular and tissue levels. Otus lettia warrants specific attention not only because it is one of the most frequently rescued owl species, but also because it serves as an excellent model for understanding retinal characteristics of nocturnal raptors. The findings from this study provide a valuable foundation for future vision research and the development of therapeutic strategies for retinal diseases, and may serve as a reference framework for application to other species of nocturnal raptors, and the methodology used in this study can also be applied to other avian species.

Disclosure

Artificial intelligence statement: The authors have not used AI to generate any part of the manuscript.

Ethics Statement

This research was conducted in compliance with the Guidelines for Ethical Research in Veterinary Ophthalmology (GERVO). Ethical approval was obtained from the Institutional Animal Care and Use Committee of the National Taiwan University, approval number: NTU‐113‐EL‐00044. Animals were not captured, restrained, sedated, or anesthetized solely for the purposes of this study.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.