Ophthalmic imaging in both the medical and veterinary fields is continuously evolving and advancing, and equine ophthalmology is no exception. However, due to the size of the equine globe and horses, in general, not all imaging modalities are available for this species. Digital external photography is widely available, but merely holding up a camera and snapping a picture does not routinely result in high-quality diagnostic images, and such images are crucial to furthering our understanding of equine ophthalmic diseases. Although specific photographic equipment is necessary to capture high-quality images, the observational skills of the clinician/ophthalmologist, their knowledge and experience in equine ophthalmology, and their knowledge and skills in photography are all essential in obtaining high-quality diagnostic images.1–4 This narrative review will cover advancements in equine ophthalmic imaging over the past 5 years. Magnification and image details are essential in improving our ability to recognize, describe, and advance our understanding of equine ophthalmic diseases. Using a combination of imaging modalities provides the clinician multiple and different views from the same ocular lesion or anatomical structure, allowing for more nuanced and in-depth interpretation.3,5–7 Many advanced imaging modalities capable of achieving high levels of image detail, such as spectral domain optical coherence tomography (SD-OCT)5,7–12 and confocal microscopy (CM),13–16 are only available at tertiary referral centers, such as academic institutions or referral ophthalmology practices. Their availability and use within the field of equine ophthalmology are even more limited. Nevertheless, the impact that these specialized diagnostic imaging modalities have made on our clinical understanding of equine ocular diseases, including immune-mediated keratitis (IMMK)9,13; corneal foreign bodies14; fungal keratitis15; Descemet membrane detachments, ruptures, and separations7; heterochromic iridocyclitis; and secondary keratitis,10 has been significant and will continue to help shape the future of advanced diagnostics in the years to come.
The importance of imaging lies not only in the ability to document specific clinical findings, but images can be used by clinicians to share information with colleagues or to request consultation with a specialist. Accurate and high-quality images (eg, the lesion of interest and surrounding structures are well-focused, and the image is properly illuminated with good contrast) allow for more accurate interpretation of the actual clinical situation that can often be achieved with a verbal description.
To further improve diagnostic accuracy, using a combination of multiple imaging modalities may provide more detailed and accurate visual representations of the clinical manifestations being evaluated.7,9,17–20 Most of the figures in this narrative review are composites created from 2 or more imaging modalities to highlight this advantage visually.
Ophthalmic Photography
Digital photography has become a mainstay of clinical ophthalmology and is extremely important to accurately document clinical signs of ocular and adnexal disease. Digital infrared photography, which involves replacement of the original camera sensor with 1 that is sensitive to either a specific infrared wavelength of light (eg, digital single-lens reflex camera) or that is sensitive to the entire spectrum of light (eg, full-spectrum camera sensor conversion, mirrorless camera) can provide additional insight into clinical diseases by allowing the clinician to recognize subtle changes that may otherwise go unnoticed, thereby improving their observational skills.21 A digital single-lens reflex camera that has been converted for infrared photography will no longer be able to capture color images and can only capture infrared images. Thus, a second, nonconverted camera is required for traditional color photography. In contrast, a mirrorless camera that is converted for full-spectrum photography can be used to photograph in color or any other specific wavelength of light, ranging from ultraviolet to infrared, by placing the appropriate and desired external filter on the front of the objective being used (www.lifepixel.com).
Despite the relatively ubiquitous nature of digital images available, obtaining high-quality (eg, the lesion of interest and surrounding structures are well focused, and the image is properly illuminated with good contrast) digital color, infrared, and fundus images requires a certain degree of knowledge of photography. Digital images, while frequently used for clinical case documentation, can also be used to enhance interpretation of the clinical signs being photographed. This is readily appreciated when dealing with fractious animals or nondomestic species. Often, in these cases, the digital images obtained provide the only means of prolonged observation, thus minimizing the amount of time necessary to perform an ophthalmic examination. Digital images also allow the clinician to revisit the examination and review the ocular signs repeatedly with additional magnification while viewing the images on a computer screen at a later time. However, obtaining high-quality clinical images is difficult and requires both sound knowledge and understanding of photography, and the clinician/photographer must possess keen clinical observational skills to accurately capture the intended lesions. The saying that a picture is worth a thousand words is hardly more fitting than in clinical ophthalmology (Figure 1). This is especially true when describing subtle clinical signs and documenting clinical manifestations of uncommon, new, or emerging ocular diseases.1–4,6,7,10
Digital color and infrared anterior segment imaging and spectral domain optical coherence tomography (SD-OCT) used to document chronic corneal stromal fibrosis and Descemet membrane (DM) and endothelial fibrosis in an adult Warmblood horse. A—Digital color anterior segment image. Note the subtle corneal haze in the ventrotemporal cornea. B—Digital infrared anterior segment image taken with an on-camera flash. Due to the longer wavelengths of light in the infrared spectrum, the targeted wavelengths can pass relatively freely through the (opaque) cornea, which results in these subtle opacities being relatively undetectable. C—Digital direct infrared retroillumination (830 nm light source) of the same eye as in (A) and (B). Note the short, dark linear and curvilinear opacities within the area of the pupil, especially in the ventrotemporal quadrant. These small opacities represent DM ruptures and/or tears. D—In this SD-OCT B-scan image, the area of diffuse ventrotemporal corneal haze appears as increased signal intensity throughout the visible corneal stroma, with the more anterior portion of the stroma being much brighter in intensity. Along the posterior aspect of the cornea there are 2 obvious bump-like areas of increased signal intensity within the posterior corneal stroma and DM. These areas of increased signal intensity represent areas of fibrosis within DM are the same lesions seen in (C).
Citation: Journal of the American Veterinary Medical Association 262, S2; 10.2460/javma.24.06.0376
Ocular and Orbital Ultrasonography
Ocular and orbital ultrasonography (US) provide additional views and perspectives of the globe and orbit that are not otherwise readily available due to opacifications of, or within, various ocular structures (eg, cornea, anterior chamber, lens, vitreous). Modern US machines capable of producing high-quality diagnostic images are readily available in most equine practices. Familiarity with the equipment and the relatively flat learning curve when evaluating the eye, and to a lesser extent the orbit (Figures 2 and 3), makes US one of the most widely used diagnostic imaging modality in equine ophthalmology. High-quality US images (eg, good image contrast and clear anatomical details) can be routinely obtained (and interpreted) regardless of the clinical setting. Generally, ocular and orbital US can be performed using a 7.5- to 12-MHz linear probe using a transpalbebral or transcorneal approach. Despite the lack of microscopic details provided by more specific ocular imaging modalities (eg, CM, SD-OCT), US allows for good visualization of ocular and orbital structures that are otherwise hidden from view or challenging to visualize during a routine ophthalmic examination and are demonstrated in these 2 studies20,22 evaluating Descemet membrane detachments. The specific advantage of US to identify specific intraocular or orbital lesions that cannot be directly visualized during routine ophthalmic examination is further highlighted in studies23,24 evaluating specific ocular or periocular lesions using multiple imaging modalities.
Fundus, ocular ultrasonography (US), and SD-OCT images of an adult Warmblood horse with chronic equine recurrent uveitis. A—Fundus image depicting peripapillary traction-band retinal detachments. These lesions can be readily identified as radiating lines extending from around the periphery of the optic disc. The optic nerve head is slightly hyperemic, and the retinal vasculature cannot be readily identified; however, the entire fundic image is out of focus, largely due to the aqueous flare and diffuse immature cataract that were also present. B—Ocular ultrasonography reveals a diffusely hyperechoic lens capsule, anterior and posterior cortical hyperechogenicity, and an undulating linear hyperechoic opacification along the posterior wall of the globe (linear peripapillary retinal detachments seen in [A]). C—B-scan SD-OCT image of multiple linear peripapillary retinal detachments along the ventral border of the optic disc. D—This volume intensity projection represents the area being scanned, and the green horizontal line identifies the position of the B-scan frame in (C).
Citation: Journal of the American Veterinary Medical Association 262, S2; 10.2460/javma.24.06.0376
Digital color and infrared anterior segment imaging, US, and SD-OCT of an adult miniature horse with a corneal perforation and iris prolapse. A—Digital color image of a paraxial corneal perforation. Note that hyphema (blood in the anterior chamber) occupies the inferior third of the anterior chamber. The superior aspects of the superior granula iridica are visible, but the pupil cannot be visualized. B—Digital infrared image of the same eye as in (A). The hyphema takes on a pale hue and the temporal portion of the pupil is now visible. A portion of the granula iridica can be seen being pulled into the corneal perforation, which prevents further leakage of aqueous humor through the perforated cornea. C—Transpalpebral US of the globe using a distilled water-filled examination glove finger as a standoff. This allows uniform contact between the small linear transducer and the curved surface of the eyelids/globe. Note the triangular-shaped iris extending toward and attaching to the apex of the cornea. The juvenile and adult lens nuclei are hyperechoic while the fetal lens nucleus remains transparent. D–F—Serial SD-OCT B-scans from the corneal perforation. D—Inferior peripheral aspect of the perforation. Note the slightly thickened corneal epithelium superficial to a stromal depression. Posterior to this there is a triangular-shaped protrusion invading the posterior stroma. The periphery of the triangle has a hyperintense appearance, and the center of the triangle appears black (no signal intensity). This is a result of iris tissue (granula iridica) being incarcerated in the corneal perforation. As infrared light does not pass through pigmented iridal tissue, the signal is completely absorbed by the iris, leaving only the most anterior surface visible. E—Direct visualization of the corneal perforation using SD-OCT. Note that corneal epithelium has already began to migrate posteriorly toward the anterior chamber along the edges of the stroma lining the corneal perforation. F—Superior peripheral B-scan of the corneal perforation with iris tissue (granula iridica) lining the edge of the perforation as well as the neighboring corneal endothelium/DM complex. This is visible as an area of increased signal intensity to the right of the perforation.
Citation: Journal of the American Veterinary Medical Association 262, S2; 10.2460/javma.24.06.0376
While ocular US remains a widely utilized imaging modality, orbital US is often supplanted by other diagnostic imaging modalities such as CT or MRI due to their increased availability and better anatomical overview.
In addition to ocular US allowing visualization of intraocular structures through a variety of dense corneal (eg, edema or fibrosis), lenticular (eg, cataracts) or vitreal opacifications (eg, vitreal membranes), it can also be used to obtain accurate globe measurements (ocular biometry), which can be used to calculate intraocular lens power25 or provide comparative interocular biometry data (eg, anterior chamber depth, crystalline lens thickness, vitreal chamber depth) and overall globe size (axial globe length) for comparison between eyes.19
Ultrasound Biomicroscopy
A recent study17 evaluated the use of a 70-MHz linear transducer and described imaging parameters associated with equine infectious ulcerative keratitis and corneal stromal abscess treatment outcomes. However, the 35-MHz and 50-MHz transducers, fitted with a water reservoir tip that serves as a direct-contact corneal standoff, remain the most used ultrasound biomicroscopy (UBM) probes in veterinary ophthalmology. Thus, it is important to perform local eyelid blocks and apply a topical corneal anesthetic to the surface of the eye to facilitate the examination on horses under sedation. Most recently, UBM has been used to evaluate a variety of corneal diseases17,26; to obtain measurements of the corneal thickness and anterior chamber depth27; to describe findings associated with Descemet membrane detachments, ruptures, and separations in a group of adult horses7; and to evaluate the iridocorneal angle (ICA).28 The availability of UBM is generally limited to referral ophthalmology practices or academic institutions due to the imaging modalities’ narrow spectrum of use.
Collins et al17 were able to determine that horses with deep corneal lesions as well as those with Descemet membrane detachments during UBM examination were more likely to result in the eye requiring removal (enucleation). They also determined that neither the lesion diameter (estimated during ophthalmic examination) nor corneal thickness measured by UBM were associated with the outcome.17 The authors further concluded that eyes with corneal lesions at greater than 50% corneal depth, those with Descemet membrane detachments, and those with increased aqueous humor cell counts had a poorer prognosis.17 They also provided evidence suggesting that UBM is superior to slit lamp and SD-OCT assessment of deep stromal abscesses as the central part of such lesions cannot be reliably visualized using either of these methods.17
Two recent studies27,28 have evaluated the equine anterior segment anatomy in a group of research horses using UBM. Corneal thickness was compared between transcorneal UBM using a 50-MHz probe and ultrasonic pachymetry (eg, direct contact method of corneal thickness measurement), and the anterior chamber depth was measured.27 Consistent with the findings from SD-OCT studies11,12,27 evaluating corneal thickness, the central cornea was the thinnest location, followed by the nasal and temporal peripheral corneal locations, with the superior and inferior peripheral corneal locations being the thickest as measured by both ultrasonic pachymetry and UBM. The values obtained using UBM were consistently thicker than with pachymetry, and the authors concluded that ultrasonic pachymetry provided more consistently accurate measurements of the corneal thickness as the corneal probe could be more easily misaligned during the examination when performing UBM.27 The increased corneal thickness values obtained with UBM were consistently thicker across all corneal measurement locations than those obtained with ultrasonic pachymetry and SD-OCT.11,12,27
A recent study28 evaluating the use of UBM to image the ICA in a group of horses free from signs of ocular disease described the normal anatomy and determined that high-resolution images could be readily obtained from the superior, temporal, inferior, and nasal ICA. The authors established that there were morphologic similarities between the nasal and temporal ICA, which differed slightly in appearance from the superior and inferior ICA.28 The corneoscleral junction (ie, limbus) in the superior and inferior regions has a less acute angle, with the sclera extending further axially than in the nasal and temporal ICA regions.28 As UBM evaluation of the equine ICA can be performed on standing horses under sedation, there is significant potential to improve our understanding of the impact of various equine ocular diseases on this anatomical region.17,27,28
Confocal Microscopy
Confocal microscopy allows the user to obtain in vivo magnification like that obtained using histology. With some modifications, the necessary equipment can be altered to allow for examination and image capturing in horses under standing sedation.16 While there is a steep learning curve and the equipment availability is severely limited, the corneal tissue details that can be obtained are unlike any other imaging modality that is currently available. Most of the early work, conducted at Cornell University, falls outside of the time frame for this narrative review and will not be discussed in detail.13–16 However, a recent study13 from that group describes the CM characterization of equine IMMK. In that study,13 the authors were able to identify a specific combination of findings associated with endothelial IMMK, which included corneal stromal edema, endothelial leukocytes, endothelium disorganization, focal discontinuity of the endothelium, and multifocal accumulations of highly reflective material within the endothelium of the clinically affected region of the cornea. Additionally, each of the other forms of IMMK (epithelial, superficial stromal, and midstromal types) were characterized by a dense network of dendritic cells within the epithelial basement membrane and immediate subepithelial stroma.13 This proved to be the most distinguishing feature of these IMMK conditions and had not been previously recognized by the authors in any other types of corneal disease that they had evaluated in any of their previous CM studies.14–16 Despite CM having very limited availability, mainly due its cost and the necessary equipment modifications required before it can be used in standing horses under sedation, the data obtained with this imaging modality has helped to improve the current understanding of what changes are occurring within specific corneal cell layers in a variety of equine corneal disease presentations.13–16
Spectral Domain Optical Coherence Tomography
Over the past decade, the use of SD-OCT has helped to improve our understanding of equine corneal disease (Figure 3). One advantage of SD-OCT is that it can be used to obtain diagnostic images from the cornea, the retina, and even the lens in horses under standing sedation (Figure 2). Two early studies11,12 described the normal corneal and retina/optic nerve head anatomy in the horse and have provided the foundation for the use of SD-OCT in a clinical setting (Figure 4).3,7,9,10 The presence of corneal edema and cataracts severely limits or prevents imaging of the entire cornea and the retina, respectively. Despite these limitations, it is generally possible to obtain good-quality diagnostic SD-OCT imaging scans with the horse standing under sedation and local eyelid blocks, and image quality improves further following a retrobulbar block.8 In this study by Hefner et al,8 the SD-OCT image quality was compared between 3 groups of horses: (1) horses under sedation and with local eyelid blocks; (2) horses under sedation, eyelid blocks, and a retrobulbar block; and (3) SD-OCT imaging in horses under general anesthesia. The acquisition time parameters and the duration that the scan remained in the focus window during the examination were best for horses under general anesthesia, followed by horses under sedation with a retrobulbar block, followed by horses under sedation without a retrobulbar block.8 The authors concluded that good-quality images could be obtained from horses under sedation, and further increases in image quality were achieved following a retrobulbar block in those same horses.8 They further concluded that despite the increase in image quality in the group of horses examined under general anesthesia, the inherent risks associated with recovery from general anesthesia in horses does not warrant putting horses under general anesthesia for the purpose of performing SD-OCT.8
Fundus and SD-OCT images of an adult Quarter Horse with chronic optic neuritis in both eyes (oculus uterque). A–C—Right eye. A—Fundus image revealing a slightly abnormal optic disk shape and proliferative opacifications extending vitread from the 3 to 5 o’clock and 7 o’clock positions along the inferior border of the optic disc. B and C—Horizontal B-scan SD-OCT image through the center of the optic disc. C—Volume intensity projection of the optic disc. The lamina cribrosa is thick, and its reticulated pattern is readily visible. Note the poorly defined area adjacent to the optic disk (occupying an area between 3:30 and 5:30 o’clock). This area is not captured in the B-scan but represents the proliferative lesions described in A. D–F—Left eye from the same horse. The lesions described in these 3 images are like those described in (A–C). However, note the difference in appearance of the optic disk in (B) and (E) despite the clinical appearances in the fundus images ([A] and [D]) being relatively similar. The optic disk is more swollen/edematous in (E) than in (B), and there is a large vascular channel visible in the temporal edge of the optic disk visible in (B).
Citation: Journal of the American Veterinary Medical Association 262, S2; 10.2460/javma.24.06.0376
Skull Radiographs
Skull radiographs are less commonly used in equine ophthalmology, mainly due to the availability of ocular ultrasound to equine practitioners and CT and MRI in equine referral centers. Skull radiographs can still be useful, especially in cases of suspected head trauma or orbital neoplasia, where other imaging modalities, such as CT or MRI, are not available.29,30 Dacryocystography (DCG), or the fluoroscopic contrast examination of the nasolacrimal system, has been previously described and is a useful procedure to determine the precise location of a nasolacrimal duct obstruction or distal punctal atresia. However, CT-based DCG is the preferred diagnostic modality of choice due to the ability of the clinician to view the nasolacrimal system in multiple cross-sections and even as a virtual 3-D reconstruction.31,32 This imaging modality may not always be available, or it may not be desired based on financial constraints of the owner.
Magnetic Resonance Imaging
Despite the distinct image quality advantages associated with MRI compared with CT, especially for soft-tissue evaluation, this advanced imaging modality is used less frequently than CT in equine ophthalmology. Even in cases requiring additional advanced diagnostic imaging, CT is often preferred due to its more widespread availability and ability to be performed under sedation.
A recent case report describing retinal detachment secondary to vitreoretinopathy in 2 closely related Warmbloods presented postmortem MRI images of the affected globes.23 The retinal detachment was visible in both the T2-weighted (T2W) and fluid-attenuated inversion recovery (FLAIR) Scans but did not provide much additional information than the in vivo–obtained ocular US images.23
Evaluation of MRI DCG in the horse was recently evaluated.31 Cross-sectional imaging, such as in MRI and CT, avoid superimposition of surrounding structures. Image evaluation is thus superior to conventional radiography. Comparison between DCG using CT and MRI revealed no differences in humans, and the indications for both imaging modalities are not sharply delineated.31
Although the study was carried out in dogs, a recent study33 evaluating 3 Tesla high-resolution MRI (3T-HR-MRI) results compared with conventional US and UBM highlighted the advantages of 3T-HR-MRI over both of these modalities. The authors concluded that all structures seen in conventional US and UBM could be visualized in much greater detail in the 3T-HR-MRI images.33 Additionally, Tenon capsule and sub-Tenon space, structures not routinely visible using conventional US or UBM, were readily visible in 3T-HR-MRI.33 The results from this study demonstrate the potential of HR-MRI as an advanced diagnostic imaging modality in equine ophthalmic research (Figure 5).
7 Tesla high-resolution MRI of an enucleated adult equine globe fixated in clear gelatin. A—Transverse high-resolution MRI image from the level of the corona ciliaris. B—Sagittal horizontal view of the globe through the level of the superior granula iridica. Note the hyperreflective horizontal band extending across the posterior aspect of the anterior chamber. This tissue layer represents the posterior pigmented epithelium of the iris and can be clearly identified as a separate layer to the superficial iris. C—Frontal section through the anterior chamber. The 2 hyperintense structures represent the anterior portions of the superior granula iridica. D—Sagittal vertical view of the globe through the center of the superior granula iridica.
Citation: Journal of the American Veterinary Medical Association 262, S2; 10.2460/javma.24.06.0376
Computed Tomography
A previous study evaluating CT and MRI anatomy of the normal equine orbit and eye concluded that CT is a more useful imaging modality for evaluating the orbit, with MRI being far superior at evaluating the globe and identifying soft-tissue structures in the orbit, such as the optic nerve (Figure 6).34 A recent retrospective anatomical study by Yoo et al35 compared multiple ocular and orbital CT dimensions and HU values of the lens and vitreous body of Jeju and Thoroughbred horses. In this study,35 the authors found significant differences across a wide range of ocular measurements (eg, anterior-posterior and latero-medial diameters of the globe, anterior chamber, posterior segment, lens, and orbital fossa) and HU of the vitreous body between Jeju and Thoroughbred horses.35 There was a difference in mean body weight between the lighter Jeju and heavier Thoroughbred horses of 197.2 kg.35 The authors concluded that the differences in ocular measurements between the Jeju and Thoroughbred horses may be attributed to the variation in body weight between the 2 breeds or that they may be attributed to the Jeju breed.35 An earlier study by Hollis et al36 measured the same ocular and orbital distances in 90 horses (59 geldings and 31 mares) of variable ages (range, 2 to 32 years), body weights (range, 180 to 797 kg), and breeds (26 different). All of the measurements except for the lens size and anterior-posterior distance of the anterior chamber correlated significantly with bodyweight.36 The authors suggest, based on the correlation between their study results and ocular biometry studies conducted using US,37,38 that CT may be a valuable tool for assessing variations in globe sizes and interpreting images acquired during routine CT scans.36
Computed tomography images from a 10-year-old Warmblood mare with a suspected nasal tumor extending through the cribriform plate, cranium, and right orbital septum. The tumor extended into the right orbit, resulting in moderate globe protrusion (exophthalmos) and complete blindness, and into the brain. Inset: mare undergoing CT imaging under sedation with foal at foot.
Citation: Journal of the American Veterinary Medical Association 262, S2; 10.2460/javma.24.06.0376
Stieger-Vanegas et al39 recently evaluated the role of CT in imaging non-neurologic disorders of the head in equine patients. In this study, and in another study by Perrier et al40 that evaluated the heads of horses with signs of headshaking, little attention is given to the eyes and orbits despite these structures being routinely imaged during the individual CT studies.39 This is an area of clinical research that would benefit greatly from collaborative efforts between traditional equine services (ie, internal medicine and surgery) and ophthalmology services, especially those with a large equine case load.
Cone-beam CT, which is used for image-guided spine and neurosurgery in humans, has recently been used to image the equine head in standing horses under sedation.41 Although the eye and orbit were not targeted regions of interest in this study,41 there are some advantages of this imaging modality that would be beneficial for horses undergoing standing orbital or periorbital surgery requiring imaging, such as rapid image acquisition, mobility of the gantry in all directions, and a completely mobile imaging unit. The disadvantages include increased motion artifact sensitivity, increased radiation scatter, low soft-tissue contrast, and limited field of view.41
It is important to consider that while most individual imaging modalities provide valuable information on their own, their true value is realized when combining the results of 2 or more diagnostic imaging modalities to provide multiple perspectives, which allows the clinician to evaluate more nuanced and detailed information, resulting in a more accurate diagnosis and allowing for implementation of a more targeted treatment approach. Using multiple diagnostic imaging modalities allows the clinician to evaluate and assess the most valuable findings from each modality, which ultimately leads to improved and enhanced observational skills.
Acknowledgments
The author would like to thank Ron Beyers, from the Auburn University MRI Research Center, for his assistance and expertise in obtaining the 7 Tesla MRI images of the equine globe seen in Figure 5.
Disclosures
The author has nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.
Funding
The author has nothing to disclose.
ORCID
R. J. McMullen https://orcid.org/0000-0002-0635-0883
References
- 1.↑
Winter JC, Thieme K, Eule JC, Saliu EM, Kershaw O, Gehlen H. Photodermatitis and ocular changes in nine horses after ingestion of wild parsnip (Pastinaca sativa). BMC Vet Res. 2022;18:80. doi:10.1186/s12917-022-03162-2
- 2.
Charnock LN, Keys DA, McMullen RJ Jr. Clinical findings associated with blunt ocular trauma in horses: a retrospective analysis. Vet Ophthalmol. 2022;25(1):52–61. doi:10.1111/vop.12915
- 3.↑
Casola C, Pot SA, Lavaud A, Voelter K. Corneal cross-linking as a treatment for corneal dystrophy with secondary bacterial infection in a Friesian horse. Clin Case Rep. 2020;8(4):709–715. doi:10.1002/ccr3.2725
- 4.↑
Knickelbein KE, Stock M, Carrasco SE, Reilley CM, Lassaline ME. Traumatic phacocele in an American Miniature Horse. Vet Ophthalmol. 2019;22(1):61–66. doi:10.1111/vop.12563
- 5.↑
Charnock LN, Boveland SD, Groover ES, Moore PA, McMullen RJ Jr. Effects of corneoconjunctival transposition, posterior lamellar keratoplasty and modified deep lamellar endothelial keratoplasty on streak retinoscopy in equine cadaver eyes. Vet Ophthalmol. 2022;25(6):483–492. doi:10.1111/vop.13025
- 6.↑
Herb VM, Zehetner V, Blohm KO. Multiple congenital ocular anomalies in a silver coat Missouri Fox Trotter stallion. Tierarztl Prax Ausg G Grosstiere Nutztiere. 2021;49(5):350–354. doi:10.1055/a-1581-4810
- 7.↑
Rodriguez Galarza RM, McMullen RJ Jr. Descemet’s membrane detachments, ruptures, and separations in ten adult horses: clinical signs, diagnostics, treatment options, and preliminary results. Vet Ophthalmol. 2020;23(4):611–623. doi:10.1111/vop.12793
- 8.↑
Hefner EM, Lin HC, Cole RC, Moore PA, McMullen RJ. Comparison of image quality of corneal and retinal optical coherence tomography using sedation and general anesthesia protocols with or without retrobulbar anesthesia in horses. Am J Vet Res. 2021;83(1):72–79. doi:10.2460/ajvr.21.02.0029
- 9.↑
Blanchard A, Barr EM, Gilger BC. Evaluation of equine corneal disease using spectral domain optical coherence tomography (SD-OCT). Vet Ophthalmol. 2019;22(6):791–798.
- 10.↑
Pinto NI, McMullen RJ Jr, Linder KE, Cullen JM, Gilger BC. Clinical, histopathological and immunohistochemical characterization of a novel equine ocular disorder: heterochromic iridocyclitis with secondary keratitis in adult horses. Vet Ophthalmol. 2015;18(6):443–456. doi:10.1111/vop.12234
- 11.↑
Pirie CG, Alario AF, Barysauskas CM, Gradil C, Uricchio CK. Manual corneal thickness measurements of healthy equine eyes using a portable spectral-domain optical coherence tomography device. Equine Vet J. 2014;46(5):631–634. doi:10.1111/evj.12198
- 12.↑
Pinto NI, Gilger BC. Spectral-domain optical coherence tomography evaluation of the cornea, retina, and optic nerve in normal horses. Vet Ophthalmol. 2014;17(suppl 1):140–148.
- 13.↑
Ledbetter EC, Irby NL. Laser scanning in vivo confocal microscopic characterization of equine immune-mediated keratitis. Vet Ophthalmol. 2020;23(1):4–15.
- 14.↑
Ledbetter EC, Irby NL, Schaefer DM. In vivo confocal microscopy of corneal microscopic foreign bodies in horses. Vet Ophthalmol. 2014;17(suppl 1):69–75.
- 15.↑
Ledbetter EC, Irby NL, Kim SG. In vivo confocal microscopy of equine fungal keratitis. Vet Ophthalmol. 2011;14(1):1–9.
- 16.↑
Ledbetter EC, Scarlett JM. In vivo confocal microscopy of the normal equine cornea and limbus. Vet Ophthalmol. 2009;12(suppl 1):57–64.
- 17.↑
Collins EN, Barr EM, Westermeyer H, Gilger BC, Oh A. Ultrasound biomicroscopic imaging parameters associated with outcome in equine infectious ulcerative keratitis and stromal abscesses. J Am Vet Med Assoc. 2024:1–8. doi:10.2460/javma.24.02.0097
- 18.
Wafy MN, Hassan EA, Ahmed KA, Aboelmaaty AM, Abu-Seida AM. Ultrasonographic and histopathologic features associated with common ocular diseases in donkeys (Equus asinus). Vet Res Commun. 2023;47(3):1479–1491. doi:10.1007/s11259-023-10102-4
- 19.↑
Wafy MN, Hassan EA, El-Maaty AMA, Abu-Seida AM. B-scan biometry and color doppler ultrasound imaging of the eye in clinically normal donkeys (Equus asinus): effect of laterality, maturity and gender. J Equine Vet Sci. 2021;101:103419. doi:10.1016/j.jevs.2021.103419
- 20.↑
Slenter IJM, Hermans H, Ensink JM, et al. Clinical, ultrasonographic, and histopathologic findings in seven horses with descemet’s membrane detachment: a case series. Vet Ophthalmol. 2020;23(1):181–189. doi:10.1111/vop.12710
- 21.↑
McMullen RJ Jr, Clode AB, Gilger BC. Infrared digital imaging of the equine anterior segment. Vet Ophthalmol. 2009;12(2):125–131. doi:10.1111/j.1463-5224.2008.00688.x
- 22.↑
Buckley CN, Tollefson C, Telle MR, Lee AM. Increased ocular opacity and swelling associated with the left eye of a mare. J Am Vet Med Assoc. 2024;262(1):136–138. doi:10.2460/javma.23.07.0414
- 23.↑
Vercruysse E, Naranjo C, Sauvage A, Vandersmissen M, Grauwels M, Monclin S. Retinal detachment secondary to vitreoretinopathy in two closely related Warmblood horses. Open Vet J. 2021;11(4):672–679. doi:10.5455/OVJ.2021.v11.i4.18
- 24.↑
Narinx F, Monclin S, Sauvage A, et al. Identification of an ectopic periorbital lymph node in two horses. Open Vet J. 2022;12(5):768–773. doi:10.5455/OVJ.2022.v12.i5.23
- 25.↑
Meister U, Gorig C, Murphy CJ, Haan H, Ohnesorge B, Boeve MH. Intraocular lens power calculation for the equine eye. BMC Vet Res. 2018;14(1):123. doi:10.1186/s12917-018-1448-6
- 26.↑
Keenan AV, Townsend WM. Evaluation of equine corneal disease using ultrasound biomicroscopy. Vet Ophthalmol. 2022;25(suppl 1):179–184. doi:10.1111/vop.12881
- 27.↑
Knickelbein KE, Lassaline ME, Kim S, Scharbrough MS, Thomasy SM. Corneal thickness and anterior chamber depth of the normal adult horse as measured by ultrasound biomicroscopy. Vet Ophthalmol. 2022;25(suppl 1):17–24. doi:10.1111/vop.12971
- 28.↑
Knickelbein KE, Lassaline ME, Kim S, Kim S, Thomasy SM. Ultrasound biomicroscopy of the equine iridocorneal angle. Equine Vet J. 2022;54(6):1153–1158. doi:10.1111/evj.13585
- 29.↑
Mathes RL, Paige Carmichael K, Peroni J, Moore PA. Primary lacrimal gland adenocarcinoma of the third eyelid in a horse. Vet Ophthalmol. 2011;14(1):48–54. doi:10.1111/j.1463-5224.2010.00840.x
- 30.↑
Miesner T, Wilkie D, Gemensky-Metzler A, Weisbrode S, Colitz C. Extra-adrenal paraganglioma of the equine orbit: six cases. Vet Ophthalmol. 2009;12(4):263–268. doi:10.1111/j.1463-5224.2009.00706.x
- 31.↑
Manso-Diaz G, Garcia-Lopez JM, Lopez-Sanroman J, Taeymans O. Magnetic resonance dacryocystography in the horse: a feasibility study. Vet Ophthalmol. 2020;23(1):129–134. doi:10.1111/vop.12697
- 32.↑
Berkowski W Jr, Plummer CE, Ramos R, Czerwinski S, Brooks D, Gallagher A. Fluoroscopically guided neocanalization for treatment of nasolacrimal atresia in two horses. Vet Ophthalmol. 2019;22(4):538–544. doi:10.1111/vop.12653
- 33.↑
Ivan D, Ohlerth S, Richter H, Verdino D, Rampazzo A, Pot S. 3T high-resolution magnetic resonance imaging, conventional ultrasonography and ultrasound biomicroscopy of the normal canine eye. BMC Vet Res. 2022;18(1):67. doi:10.1186/s12917-021-03108-0
- 34.↑
D’Aout C, Nisolle JF, Navez M, et al. Computed tomography and magnetic resonance anatomy of the normal orbit and eye of the horse. Anat Histol Embryol. 2015;44(5):370–377. doi:10.1111/ahe.12149
- 35.↑
Yoo H, Lee S, Shin KY, Seo JP. Computed tomographic dimensions and densities of the normal eye in Jeju horses. J Vet Med Sci. 2024;86(3):308–311. doi:10.1292/jvms.23-0382
- 36.↑
Hollis AR, Dixon JJ, Berlato D, Murray R, Weller R. Computed tomographic dimensions of the normal adult equine eye. Vet Ophthalmol. 2019;22(5):651–659. doi:10.1111/vop.12636
- 37.↑
Grinninger P, Skalicky M, Nell B. Evaluation of healthy equine eyes by use of retinoscopy, keratometry, and ultrasonographic biometry. Am J Vet Res. 2010;71(6):677–681. doi:10.2460/ajvr.71.6.677
- 38.↑
McMullen RJ Jr, Gilger BC. Keratometry, biometry and prediction of intraocular lens power in the equine eye. Vet Ophthalmol. 2006;9(5):357–360. doi:10.1111/j.1463-5224.2006.00493.x
- 39.↑
Stieger-Vanegas SM, Hanna AL. The role of computed tomography in imaging non-neurologic disorders of the head in equine patients. Front Vet Sci. 2022;9:798216. doi:10.3389/fvets.2022.798216
- 40.↑
Perrier M, Manso-Diaz G, Dunkel B. Computed tomography findings in horses presented with signs of head-shaking. Equine Vet J. 2023;55(4):649–655.
- 41.↑
Bregger MDK, Koch C, Zimmermann R, Sangiorgio D, Schweizer-Goras D. Cone-beam computed tomography of the head in standing equids. BMC Vet Res. 2019;15(1):289. doi:10.1186/s12917-019-2045-z
