The ocular examination

image of The ocular examination
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The ocular examination is an extremely rewarding procedure for the examiner because the eye lends itself to visual inspection like no other organ and often allows an instant clinical diagnosis to be made at the time of consultation. This chapter looks at technique; equipment, examination with ambient illumination and without instruments; Schirmer tear test; sample collection; vision testing and neuro-ophthalmic reflexes; ophthalmoscopy; slit lamp examination; external staining techniques; fluorescein angiography; tonometry; gonioscopy; retinoscopy; electroretinography; ocular centesis.

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1.1 The patient is seated on a height-adjustable examination table and gently supported by an assistant. Note how the muzzle is elevated and supported by the assistant’s palm.
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1.2 Finoff transilluminator for mounting on an ophthalmoscope handle.
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1.3 Hand-held battery-operated direct ophthalmoscope.
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1.4 Condensing lenses for ocular examination: (L–R) Pan-retinal 2.2, 20 D and 30 D.
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1.5 To assess for possible retrobulbar space-occupying lesions, both globes are gently retropulsed with pressure applied to the closed upper eyelids.
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1.6 When examining patients with facial droop or excess facial skin, care must be taken to assess the eyelid conformation not only when the head is elevated but also during a time of low head posture because trichiasis associated with facial droop will otherwise not be diagnosed.
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1.7 For improved visualization, the third eyelid can be protruded temporarily by applying pressure on the globe through the upper lid whilst the lower lid is pulled down.
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1.8 Correct position of the Schirmer tear test strip.
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1.9 Kimura spatula, cytobrush and scalpel blade which can be used for collecting cytological samples.
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1.10 Visual tracking.
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1.11 The Purkinje image can provide important information about the health of the ocular surface. In the healthy eye, the image is sharp and bright. In mild cases of KCS, only subtle changes to the edges of the image may be seen. In eyes with severe KCS and corneal ulceration, the image is broken up and less bright.
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1.12 The phenomenon of parallax can be recreated with three milk bottles placed on a table in front of the examiner, representing the three Purkinje images on the cornea and the anterior and posterior lens capsules. When the examiner stands directly in front of the bottles they obscure each other and it is not possible to distinguish them. If the examiner moves to the right, the first and second bottles appear to move away from the examiner, whilst the third bottle moves with the examiner. When moving in the opposite direction, the same phenomenon occurs. This demonstrates that opacities of the cornea and anterior lens capsule appear to move away from the examiner, whilst those on the posterior lens capsule move with the examiner.
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1.14 Direct ophthalmoscope headpiece. Viewer’s side. Patient’s side with viewing aperture and reflecting mirror, as well as a filter and switches to change the light beam size and shape.
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1.15 The dioptric strengths required to allow examination of the structures in front of the retina with direct ophthalmoscopy. In a patient with optic neuritis, the swollen optic nerve head is blurred and the retina is in focus on a setting of 0 D. To focus on the swollen optic nerve head, the examiner must insert positive (black) lenses to move the focus within the eye forward. In this patient, the optic nerve head was in focus at +6 D, which translates into swelling of the optic nerve head of 1.5 mm. (a, Courtesy of J Mould; b–c)
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1.16 Distant direct ophthalmoscopy. The examiner picks up the fundic reflex at arm’s length.
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1.17 Nuclear sclerosis has minimal impact on the visibility of the fundic reflex using distant direct ophthalmoscopy and only subtle concentric rings are visible. A cataract stands out as a dark opacity against the fundic reflex.
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1.18 Close direct ophthalmoscopy. The examiner’s eye is as close as possible to the patient’s eye.
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1.19 Example of an ocular examination chart.
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1.20 Head-mounted indirect ophthalmoscope with integrated battery.
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1.21 Binocular indirect ophthalmoscopy.
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1.22 Monocular indirect ophthalmoscopy.
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1.23 Hand-held slit-lamps are extremely versatile for the examination of veterinary patients.
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1.24 Slit image deflected towards the examiner in the case of an iris melanoma. (Courtesy of the Animal Health Trust)
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1.25 Slit image deflected away from the examiner in a patient with a stromal corneal ulcer. The degree of slit deflection allows accurate assessment of corneal ulcer depth. (Courtesy of N Wallin Hakansson)
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1.26 Protein within the anterior chamber is highlighted by the slit beam of light, showing the Tyndall effect. (Courtesy of the Animal Health Trust)
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1.27 Subtle corneal lesions are best highlighted with indirect illumination. Note how the corneal ghost vessels are visible in the area adjacent to the directly illuminated cornea. (Courtesy of the Animal Health Trust)
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1.28 Slit-lamp examination demonstrating transillumination of iris cysts. (Courtesy of the Animal Health Trust)
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1.29 Fluorescein is available as an impregnated paper strip (top and middle) or as a ready-made solution in a single-use vial (bottom). Note that the paper strip has been wetted with saline and is ready to use.
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1.30 Fluorescein is applied to the conjunctiva overlying the dorsal sclera. Contact between the strip and cornea should be avoided because this may result in false-positive stain uptake.
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1.31 Exposed corneal stroma taking up the fluorescein stain in a case of superficial ulceration. Note the loose epithelial edges, which indicate the presence of a spontaneous chronic corneal epithelial defect.
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1.32 With this stromal ulcer, fluorescein stain is seen diffusing from the exposed stroma into areas of the cornea which have not yet lost their epithelium.
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1.33 With melting ulcers, large amounts of fluorescein are retained by the degenerate stromal tissue and the ulcer stains strongly.
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1.34 For assessment of corneal ulceration, particularly deep ulcers where stain might pool and be interpreted as positive stain uptake at the bottom of the ulcer, the stain is flushed out with saline solution.
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1.35 Descemet’s membrane does not retain fluorescein stain, which identifies the deep part of this ulcer as a descemetocele.
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1.36 Fluorescein on the ocular surface is diluted (seen as a dark rivulet) by the aqueous humour escaping from the full-thickness focal corneal perforation in this patient.
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1.37 A negative Jones test result is the failure of fluorescein to appear at the nostril on the ipsilateral side of a nasolacrimal duct blockage, which may indicate lacrimal drainage obstruction.
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1.38 Schiøtz tonometry. Note how the head of the patient is held by the assistant to maintain the cornea in a horizontal plane without excessive pressure on the neck.
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1.39 Incorrect placement of the rubber tip cover on the Tono-pen can make it difficult to obtain reproducible measurements. The cover should be a snug fit (top left) but not be too loose (top right) or too tight (bottom left).
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1.40 To obtain IOP measurements, the Tono-pen is gently touched in small and rapid movements on the surface of the cornea, following the application of local anaesthetic. Care must be taken not to apply pressure to the globe when keeping the eyelids open as this could result in falsely elevated IOP readings.
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1.41 The TonoVet confers the lowest risk of corneal damage, which may be of importance in brachycephalic patients and those with corneal disease. As with the Tono-pen, care must be taken not to apply pressure to the globe when opening the eyelids.
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1.42 Retinoscopy being performed on a canine patient.
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1.43 Correct placement of the needle for aqueocentesis.
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