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Abstract:Objective
To describe and to establish normative data for the feline optic nerve and peripapillary retina using SD‐OCT (Spectralis® HRA+OCT2).
Methods
Slit‐lamp biomicroscopy and rebound tonometry were performed in seven male‐intact (0.65 ± 0.02 years;4.34 ± 0.33 kg) and seven female‐spayed (0.74 ± 0.03 years; 3.13 ± 0.28 kg) cats. All eyes were pharmacologically dilated with 1% tropicamide prior to indirect ophthalmoscopy examination. Animals were then placed under general anesthesia. Optic nerve and peripapi… Show more
“…Diffusion weighted imaging provides an alternative approach to early evaluation of glaucoma, a group of diseases characterized by the loss of RGCs and their axons. The technique we describe does overcome a major limitation associated with OCT, which is increasingly reported in the veterinary literature for assessment of the retina and ONH 46‐63 . Canine glaucoma is commonly associated with corneal opacities and drug‐induced miosis which both preclude reliable OCT assessment, but do not affect measurements of the white matter tracts using DTI.…”
Objective
To describe measurements of in vivo structures of the visual pathway beyond the retina and optic nerve head associated with canine primary angle‐closure glaucoma (PACG).
Methods
A prospective pilot study was conducted using magnetic resonance diffusion tensor imaging (DTI) to obtain quantitative measures of the optic nerve, chiasm, tract, and lateral geniculate nucleus (LGN) in dogs with and without PACG. 3‐Tesla DTI was performed on six affected dogs and five breed, age‐ and sex‐matched controls. DTI indices of the optic nerve, optic chiasm, optic tracts, and LGN were compared between normal, unilateral PACG, and bilateral PACG groups. Intra‐class correlation coefficient (ICC) was calculated to assess intra‐observer reliability.
Results
Quantitative measurements of the optic nerve, optic tract, optic chiasm, and LGN were obtained in all dogs. There was a trend for reduced fractional anisotropy (FA) associated with disease for all structures assessed. Compared to the same structure in normal dogs, FA, and radial diffusivity (RD) of the optic nerve was consistently higher in the unaffected eye in dogs with unilateral PACG. Intra‐observer reliability was excellent for measurements of the optic nerve (ICC: 0.92), good for measurements of the optic tract (ICC: 0.89) and acceptable for measures of the optic chiasm (ICC: 0.71) and lateral geniculate nuclei (ICC: 0.76).
Conclusion
Diffusivity and anisotropy measures provide a quantifiable means to evaluate the visual pathway in dogs. DTI has potential to provide in vivo measures of axonal and myelin injury and transsynaptic degeneration in canine PACG.
“…Diffusion weighted imaging provides an alternative approach to early evaluation of glaucoma, a group of diseases characterized by the loss of RGCs and their axons. The technique we describe does overcome a major limitation associated with OCT, which is increasingly reported in the veterinary literature for assessment of the retina and ONH 46‐63 . Canine glaucoma is commonly associated with corneal opacities and drug‐induced miosis which both preclude reliable OCT assessment, but do not affect measurements of the white matter tracts using DTI.…”
Objective
To describe measurements of in vivo structures of the visual pathway beyond the retina and optic nerve head associated with canine primary angle‐closure glaucoma (PACG).
Methods
A prospective pilot study was conducted using magnetic resonance diffusion tensor imaging (DTI) to obtain quantitative measures of the optic nerve, chiasm, tract, and lateral geniculate nucleus (LGN) in dogs with and without PACG. 3‐Tesla DTI was performed on six affected dogs and five breed, age‐ and sex‐matched controls. DTI indices of the optic nerve, optic chiasm, optic tracts, and LGN were compared between normal, unilateral PACG, and bilateral PACG groups. Intra‐class correlation coefficient (ICC) was calculated to assess intra‐observer reliability.
Results
Quantitative measurements of the optic nerve, optic tract, optic chiasm, and LGN were obtained in all dogs. There was a trend for reduced fractional anisotropy (FA) associated with disease for all structures assessed. Compared to the same structure in normal dogs, FA, and radial diffusivity (RD) of the optic nerve was consistently higher in the unaffected eye in dogs with unilateral PACG. Intra‐observer reliability was excellent for measurements of the optic nerve (ICC: 0.92), good for measurements of the optic tract (ICC: 0.89) and acceptable for measures of the optic chiasm (ICC: 0.71) and lateral geniculate nuclei (ICC: 0.76).
Conclusion
Diffusivity and anisotropy measures provide a quantifiable means to evaluate the visual pathway in dogs. DTI has potential to provide in vivo measures of axonal and myelin injury and transsynaptic degeneration in canine PACG.
“…De Ramus et al 30 presented a uniform standard for murine OCT layer nomenclature, in which they identified the choroid as an intensely hyperreflective band directly external to the RPE/BM. Detailed images of outer retinal layer anatomy visible on canine 1,10,17,21,31–34 and feline 16,35 SD‐OCT scans have been published. Unfortunately, a consensus nomenclature of the outer retinal bands distinguishable on SD‐OCT scans, similar to that in humans 29 and mice, 30 has not been established in other species.…”
To evaluate the outer retinal band thickness and choriocapillaris (CC) visibility in four distinct retinal regions in dogs and cats imaged with spectral domain optical coherence tomography (SD-OCT). To attempt delineation of a fovealike region in canine and feline SD-OCT scans, aided by the identification of outer retinal thickness differences between retinal regions.Methods: Spectralis® HRA + OCT SD-OCT scans from healthy, anesthetized dogs (n = 10) and cats (n = 12) were analyzed. Scanlines on which the CC was identifiable were counted and CC visibility was scored. Outer nuclear layer (ONL) thickness and the distances from external limiting membrane (ELM) to retinal pigment epithelium/Bruch's membrane complex (RPE/BM) and ELM to CC were measured in the area centralis (AC), a visually identified fovea-like region, and in regions superior and inferior to the optic nerve head (ONH). Measurements were analyzed using a multilevel regression.
Results:The CC was visible in over 90% of scanlines from dogs and cats. The ONL was consistently thinnest in the fovea-like region. The outer retina (ELM-RPE and ELM-CC) was thickest within the AC compared with superior and inferior to the ONH in dogs and cats (p < .001 for all comparisons).
Conclusions:The CC appears a valid, albeit less than ideal outer retinal boundary marker in tapetal species. The AC can be objectively differentiated from the surrounding retina on SD-OCT images of dogs and cats; a fovea-like region was identified in dogs and its presence was suggested in cats. These findings allow targeted imaging and image evaluation of these regions of retinal specialization.
“…Several studies have shown that spectral domain OCT (SD-OCT) is a reliable method to evaluate different retinal layers and optic nerve morphology in colobomas in dogs, 15 in healthy or glaucomatous cats. [16][17][18] Recently, it has been published that outer retinal band and choriocapillaris can be identified in healthy dogs and cats, 19 and different vascular layers of the retina and choroid are nicely evaluated by OCT-A in cats. 20 The present report describes the clinical case of bilateral corneal dermoids associated with bilateral choroidoscleral colobomas in a cat, its SD-OCT fundus evaluation, the surgical outcome and the follow-up of lesions up to 18 months.…”
Purpose
To report a case of feline bilateral corneal dermoids, associated with unilateral iris coloboma and bilateral choroido‐scleral colobomas in the same dorsolateral position, to describe retinographic and optical coherence tomography (OCT) characteristics, surgical outcome, and follow‐up.
Animal studied
A 9‐month‐old domestic shorthaired cat in which a full ophthalmoscopic examination was performed for evaluation of dermoids resulting in a diagnosis of associated iris coloboma in one eye and posterior colobomas in both eyes.
Procedures
Retinographies and OCT were performed under anesthesia to characterize the lesions of both fundi and allow surgical excision of the corneal dermoids.
Results
Ophthalmoscopy and retinographies revealed oval lesions in the dorsolateral fundi of both eyes. The lesions precisely mirrored their respective dermoids' (10‐11 h OD and 1‐2 h OS) clock positions, lacked a tapetum lucidum and choroidal vessels, and featured thin retinal vessels plunging to a posterior plane of the fundus. OCT crossline scans demonstrated preservation of retinal thickness and morphological layering in the fundic colobomas leading to the conclusion that the colobomas were purely choroido‐scleral. The outcome of the surgical excision of the dermoids was satisfactory without hair recurrence and with acceptable corneal clarity making it possible to visualize the unilateral associated iris coloboma. Follow‐ups did not reveal any fundic evolution nor retinal detachment.
Conclusions
Retinographies and OCT made possible the characterization of choroido‐scleral colobomas associated with corneal dermoids in this first reported case in a cat. We hypothesize that the recently described superior ocular sulcus might be the embryological link between these anomalies.
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