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The fundus

image of The fundus
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Abstract

The term 'fundus' describes the part of the posterior segment of the eye that is viewed with an ophthalmoscope. The chapter covers embryology, anatomy and physiology; investigation of disease; the retina and choroid; the optic nerve and optic nerve head.

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Figures

Image of 18.1
18.1 Gross photograph of the posterior part of the eye and accompanying illustration demonstrating the anatomical structures that contribute to the ophthalmoscopic appearance of the typical canine and feline fundus. These structures include the optic nerve head (ONH) and the neurosensory retina, within which lie the retinal blood vessels (BV). The retinal pigment epithelium (RPE), choroid and sclera (S) may also contribute to the fundic appearance, depending on their degree of pigmentation and the presence or absence of a tapetum (T) within the inner choroid. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
Image of 18.2
18.2 Photomicrograph demonstrating both the inner (neurosensory) layer (*) and the outer, retinal pigment epithelial layer (RPE) of the optic cup (OC) as the eye forms from an outpouching of the forebrain in a canine embryo. The developing lens (L) is also shown.
Image of 18.3
18.3 Histological detail of the retina and choroid in a normal dog showing the tapetum and choriocapillaris within the choroid, the retinal pigment epithelium (RPE) and the cells of the neurosensory retina. The neurosensory retina consists of the photoreceptor layer, the outer nuclear layer (ONL), the outer plexiform layer (OPL), the inner nuclear layer (INL), the inner plexiform layer (IPL), the ganglion cell layer (GCL), the nerve fibre layer (NFL) and the inner limiting membrane (ILM). The structures that are considered to represent the outer retina lie closer to the RPE and those of the inner retina lie closer to the vitreous. (Original photomicrograph courtesy of W Beltran)
Image of 18.5
18.5 Illustration relating the appearance of the ocular fundus to the underlying histological features. In this case, the neurosensory retina with retinal blood vessels has been removed from the image. The tapetum is a bright, shiny sweep of colour in the superior fundus and, on histological section, the retinal pigment epithelium (RPE) is non-pigmented where the tapetum (T) has developed within the inner choroid. The arrowheads indicate the relative locations of the vitreous and the outermost sclera. ONH = optic nerve head. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
Image of 18.6
18.6 Image of the fundus in a normal adult cat taken using special filters during fluorescein angiography. The arterial vasculature is highlighted by the injection of fluorescein. When viewed ‘end-on’ in cross-section, the small connecting vessels that traverse the tapetum appear as small, dark dots on ophthalmoscopy and are visible throughout the tapetal fundus. In this case they appear as white dots owing to the fluorescent dye.
Image of 18.7
18.7 Illustration of the anatomical relationship between the tapetal tissue (T; comprising cells in an orderly alignment) and the small connecting blood vessels (BV) that traverse it. These connecting blood vessels from the vascular choroidal stroma supply the choriocapillaris (*), which nourishes the outer retina (RPE and photoreceptors). (Courtesy of J Mould)
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18.8 Normal adult canine fundus in a Chihuahua showing the limited tapetal development that is commonly encountered in toy breeds.
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18.9 Normal adult canine fundus in an Old English Sheepdog (right eye with blue iris). The tapetum is absent, which is a common feature in subalbinotic eyes, and choroidal pigment is sparse.
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18.10 Normal immature canine fundus in a 7-week-old puppy. The tapetum has not yet fully developed within the superior part of the fundus.
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18.11 Normal adult canine fundus. The inferior, non-tapetal fundus is generally darkly pigmented.
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18.12 Normal fundus of an adult dog with a light brown iris. Dilution of pigment in the RPE and choroid lend a red–brown appearance to the non-tapetal fundus. (Courtesy of S Crispin)
Image of 18.13
18.13 Extreme pigment dilution. The lack of choroidal and RPE pigment exposes choroidal vasculature against a background of sclera. ONH = optic nerve head; RPE = retinal pigment epithelium; S = sclera. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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18.14 Image illustrating the effects of extreme pigment dilution on the appearance of the fundus in the blue eye of a normal merle Shetland Sheepdog.
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18.15 Normal subalbinotic fundus in a Siamese cat. The lack of pigment in the RPE and choroid lend a characteristic striped or ‘tigroid’ appearance to the non-tapetal fundus, as the choroidal vessels are seen against a background of white scleral tissue.
Image of 18.16
18.16 Normal adult canine fundus in a Cocker Spaniel. The ONH appears pale pink/almost white as a result of myelination of the nerve fibres as they converge before exiting the globe. Major retinal blood vessels form an almost complete circle on the surface of the ONH in dogs.
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18.17 Fundus of a normal adult Domestic Shorthaired cat showing the typical appearance of the unmyelinated feline ONH. There is no anastomosis of blood vessels on the surface of the ONH.
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18.18 Normal adult canine fundus in a Golden Retriever. Note the extensive myelination of the ONH.
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18.19 Normal adult canine ONH. There is a narrow rim of hyper-reflectivity at its margins. This ‘conus’ is the only example of ‘normal’ hyper-reflectivity. (Courtesy of C Heinrich)
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18.20 Normal adult canine fundus demonstrating tortuous retinal vasculature and a small ONH (micropapilla).
Image of 18.22
18.22 The effects of lesions that increase or decrease retinal thickness on the amount of light reflected by the underlying tapetum (T) during ophthalmoscopy relative to normal. Lesions that increase the thickness or opacity of the neurosensory retina (NSR) (such as subretinal exudates, infiltrates or disorganization), reduce the amount of reflected light from the tapetum and will appear dull (hyporeflectivity). Lesions that lead to thinning of the neurosensory retina (such as retinal degeneration or retinal tears), increase the amount of reflected light (hyper-reflectivity). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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18.23 Characteristic ophthalmoscopic appearance and relative retinal depth of preretinal, nerve fibre layer, intraretinal and subretinal haemorrhages.
Image of 18.24
18.24 Typical waveform showing a scotopic mixed rod–cone response to a bright 1 Hz flash in a non-sedated dog that had been dark-adapted for 20 minutes (short protocol). The a wave and b wave, along with the locations at which to measure their respective implicit times/peak latencies (la and lb) and amplitudes (a and b), are indicated on the trace. Rod responses (dim flash presented in a dark-adapted animal) are characterized by a relatively large b wave with longer implicit time/latency and a minimal or absent a wave. Cone responses (light-adapted responses to a bright flash) are characterized by a relatively large a wave, shorter implicit time/latency and a prominent negative response after the b wave (photopic negative response), and cone flicker (shown here) at a frequency of 30 Hz that largely eliminates any rod contribution.
Image of 18.27
18.27 Choroidal hypoplasia in the right eye of a Rough Collie with CEA. Note the pale patch lateral to the ONH. (Courtesy of SR Hollingsworth)
Image of 18.28
18.28 Choroidal hypoplasia and ONH coloboma in the right eye of a Shetland Sheepdog. (Courtesy of PGC Bedford)
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18.29 Extremely large colobomatous defect involving the ONH in a Border Collie with CEA. (Courtesy of R Elks)
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18.30 Multiple retinal folds and rosettes within the tapetal fundus of an American Cocker Spaniel with multifocal retinal dysplasia. (Courtesy NC Buyukmihci)
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18.31 Multiple retinal folds within the non-tapetal fundus associated with multifocal retinal dysplasia in an English Cocker Spaniel.
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18.32 Area of geographical retinal dysplasia within the tapetal fundus of an adult English Springer Spaniel.
Image of 18.33
18.33 Total retinal dysplasia with congenital non-attachment of the retina in a Labrador puppy with oculoskeletal dysplasia. The neurosensory retina lies just posterior to the lens and is visible through the dilated pupil as grey folds. (Courtesy of NC Buyukmihci)
Image of 18.35
18.35 Advanced GPRA in a Miniature Poodle with pronounced attenuation of the retinal vasculature.
Image of 18.36
18.36 Mottled pigmentation within the non-tapetal fundus of a dog with advanced GPRA. (Courtesy of NC Buyukmihci)
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18.37 Fundus of a 6-month-old Abyssinian homozygous for the PRA mutation. Note that the fundus still has a normal appearance.
Image of 18.38
18.38 Fundus of a 2-year-old Abyssinian homozygous for the mutation. The disease is at a moderately advanced stage with generalized discoloration of the tapetal fundus and slight vascular attenuation. (Reproduced from (Supple.1) 30–36 with permission)
Image of 18.39
18.39 Fundus of a 6-year-old Abyssinian homozygous for the PRA mutation. The disease is at an advanced stage. Note the generalized hyper-reflectivity and discoloration of the tapetal fundus and the severe vascular attenuation.
Image of 18.40
18.40 Fundus of an 8-year-old Siamese homozygous for the PRA mutation. The disease is at an advanced stage. Note the generalized hyper-reflectivity and discoloration of the tapetal fundus and the severe vascular attenuation. (Reproduced from (5) 288–291 with permission)
Image of 18.41
18.41 Total retinal detachment with disinsertion from the ora ciliaris retinae in a 9-year-old Shih Tzu with vitreous degeneration. The detached neurosensory retina hangs inferiorly, draped over the ONH. Absence of neurosensory retina from the superior fundus results in pronounced tapetal hyper-reflectivity.
Image of 18.42
18.42 Focal area of exudative retinal detachment superior to the ONH in a dog.
Image of 18.43
18.43 Idiopathic extensive serous/exudative detachment involving most of the inferior retina, which remains attached at the ora ciliaris retinae and ONH, in a German Shepherd Dog. No underlying infectious cause was identified and the detachment resolved in response to immunosuppressive corticosteroids.
Image of 18.45
18.45 Peripheral cystoid retinal degeneration (arrowed) involving the ora ciliaris retinae (o) in an elderly dog. (Courtesy of RW Bellhorn)
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18.46 Traction retinal detachment associated with a migrating vitreoretinal foreign body (grass awn) in a Border Collie.
Image of 18.49
18.49 Active chorioretinitis in a dog with distemper. (Courtesy of NC Buyukmihci)
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18.50 Multifocal circular areas of active chorioretinitis in a cat with infection.
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18.51 Multifocal chorioretinal inflammatory lesions with subretinal effusion in a Domestic Shorthaired cat with toxoplasmosis. (Courtesy of S Crispin)
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18.52 Perivascular cuffing with inflammatory infiltrates in a 14-month-old cat with feline infectious peritonitis. (Courtesy of S Crispin)
Image of 18.53
18.53 Large white subretinal granuloma superior to the ONH in a dog with ocular and systemic blastomycosis. (Courtesy of NC Buyukmihci)
Image of 18.54
18.54 Post-inflammatory chorioretinopathy within the peripheral tapetal fundus of a Jack Russell Terrier. These well circumscribed hyper-reflective lesions surrounding foci of pigment migration were considered inactive and of unknown cause. These lesions were non-progressive but did have a modest effect on vision.
Image of 18.55
18.55 Extensive depigmentation of the RPE and choroid in a Jack Russell Terrier with chronic uveodermatological syndrome. This region had previously been densely pigmented but the choroidal vascular pattern is now visible. The tapetal reflection was also lost in this dog.
Image of 18.56
18.56 Small focal chorioretinal scars (cause unknown) were an incidental finding in this otherwise normal adult mixed-breed dog and had no demonstrable effect on vision. Note that the retinal blood vessels are not altered in their calibre or course over these lesions, which suggests that the inner retinal layers remain intact. (Courtesy of the University of California-Davis Ophthalmology Service)
Image of 18.57
18.57 Appearance of the fundus in three cats with hypertensive chorioretinopathy. Multiple grey lesions throughout the tapetal fundus represent areas of subretinal oedema and focal bullous retinal detachment. Note the pinpoint intraretinal haemorrhage and irregular calibre of the main retinal blood vessels. There is extensive bullous retinal detachment with haemorrhage and oedema of the neurosensory retina. A previously extensive retinal detachment has largely reattached but extensive subretinal haemorrhage remains, as well as intraretinal and preretinal haemorrhage.
Image of 18.58
18.58 Retinal haemorrhage, subretinal oedema and multifocal areas of retinal detachment and degeneration in a 9-year-old Labrador Retriever with systemic hypertension. (Courtesy of NC Buyukmihci)
Image of 18.59
18.59 Retinal vascular changes, haemorrhage and detachment related to hyperviscosity syndrome in a dog with multiple myeloma. Note the sacculated appearance of the superior retinal venules.
Image of 18.60
18.60 Intraretinal and preretinal haemorrhage associated with vascular disease and coagulopathy due to multiple myeloma in an adult dog.
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18.61 Lipaemia retinalis in a kitten with primary hyperchylomicronaemia.
Image of 18.62
18.62 Fluoroquinolone retinotoxicity. Image from a control cat with a normal fundus (day 1). Serial images of the fundus of a cat treated with enrofloxacin (days 3, 5 and 7). Note the progressive change in granularity and greying of the area centralis (AC) and visual streak (VS), respectively, observed from day 3, vascular attenuation (VA) observed from day 5, and marked tapetal hyper-reflectivity (TH) by day 7.
Image of 18.63
18.63 Taurine deficiency retinopathy in a 2-year-old cat. Note the greyish discoloration along the visual streak. Taurine deficiency retinopathy in a 3-year-old cat. Note that the area centralis region is hyper-reflective and bordered by greyish discoloration.
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18.64 Taurine deficiency retinopathy in a 5-year-old cat. A hyper-reflective/atrophic band is seen, spanning the area of the visual streak.
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18.65 End-stage retinal degeneration in a 10-year-old European Shorthaired cat.
Image of 18.66
18.66 RPED in an English Cocker Spaniel with hypovitaminosis E. Multiple foci of light brown pigment are visible throughout the tapetal fundus and are associated with retinal degeneration (signalled by attenuation of the retinal blood vessels and mottled tapetal hyper-reflectivity).
Image of 18.67
18.67 Multicentric lymphoma in a 7-year-old Domestic Shorthaired cat. There is presumed neoplastic infiltration in the ONH and peripapillary region with detachment of the surrounding retina. (Courtesy of S Crispin)
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18.68 Choroidal infarction due to metastasis of a pulmonary carcinoma has resulted in a wedge-shaped area of tapetal discoloration in a 13-year-old cat.
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18.69 An extensive choroidal melanoma in an adult dog. (Courtesy of N Wallin-Håkansson)
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18.70 Optic nerve hypoplasia in an adult crossbreed dog. (Courtesy of SR Hollingsworth)
Image of 18.72
18.72 Optic neuritis and chorioretinitis of undetermined cause in an adult dog. Note the radiating, flame-like haemorrhages within the nerve fibre layer of the retina.
Image of 18.73
18.73 Optic neuritis in a Cavalier King Charles Spaniel with granulomatous meningoencephalitis.
Image of 18.74
18.74 Appearance of the fundus in the same dog as in Figure 18.73 following immunosuppressive therapy with an oral corticosteroid.
Image of 18.75
18.75 Advanced optic atrophy and glial scarring in an adult dog following orbital penetrating trauma (a bite wound) sustained within the first few months of life.

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