Ophthalmic history
Before examining the eye, a thorough ophthalmic history should be taken. The history can be divided into the following basic categories of questioning:
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Main complaint: (a) rapidity of onset, (b) circumstances surrounding the onset, (c) severity, (d) duration of symptoms, (e) frequency of symptoms.
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Past ocular history: e.g. previous surgery, inflammation, trauma.
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Past medical history: e.g. diabetes and hypertension.
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Systemic medication: e.g. corticosteroids, tamsulosin.
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Allergies: e.g. antibiotics, topical glaucoma medications.
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Family history: e.g. glaucoma, macular degeneration, inherited retinal disease.
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Occupation and hobbies
Common ocular symptoms
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Abnormality in vision: (a) visual loss and blurring (central or peripheral), (b) change in colour vision, (c) visual aberration (scotoma, distortion, flashing lights, floaters), (d) diplopia (monocular, binocular, neurological symptoms).
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Pain and discomfort: (a) ocular, (b) periocular (lids, sinus, temporal artery), (c) retrobulbar (orbital inflammation), (d) nonspecific (eyestrain, dryness, scratching).
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Change in appearance: (a) redness, (b) swelling of the eyelids, (c) displacement of the eyeball, (d) changes to the lids and periocular tissues, (e) discharge and watering.
Visual acuity
Visual acuity is directly related to the minimum angle of separation between two objects that allows them to be seen distinctly. Visual acuity should always be determined first, regardless of whether the patient complains of visual disturbance or not. Each eye is tested separately, with and without spectacles. A pinhole disc is a simple method of focusing light and temporarily removes the effect of refractive error.
Snellen visual acuity
A Snellen chart is used, with the subject reading the chart from a standard distance ( Fig. 1.1A ). Normal visual acuity equates to 6/6 (20/20 in non-metric notation). If the patient is unable to see the chart using either spectacles or a pinhole disc the vision can be determined by counting fingers (CF), seeing hand movements (HM), or by assessing the ability to see light (PL).
LogMAR visual acuity
LogMAR is an acronym for the base-10 logarithm of the minimum angle of resolution. A Bailey–Lovie chart is used, which has an equal number of letters on each line and the lines are balanced for consistency of readability ( Fig. 1.1B ). LogMAR 0.00 is equivalent to 6/6 and logMAR 1.00 is equivalent to 6/60. Because logMAR acuity addresses many of the deficiencies of the Snellen chart it is commonly used when research is undertaken.
Contrast sensitivity
Contrast sensitivity is a measure of the ability of the visual system to distinguish an object against its background. The Pelli–Robson contrast sensitivity letter chart is viewed at 1 m and consists of rows of letters of equal size, but with decreasing contrast of 0.15 log units for groups of three letters ( Fig. 1.2A ).
Amsler grid
The Amsler grid evaluates the central 20° of the visual field centred on fixation ( Fig. 1.2B ). It is an easy method of monitoring central visual field and is commonly abnormal in patients with macular disease.
Colour vision
Ishihara
This test is simple to undertake, is widely available, and is frequently used to screen for red-green colour anomalies. Inherited colour vision deficiency affects 8% of men and 0.5% of women. The test can also be used to assess optic nerve disease ( Fig. 1.3A ).
Farnsworth–Munsell 100-hue test
This test is sensitive but takes longer than the Ishihara to perform. It is used for congenital and acquired colour defects ( Fig. 1.3B ).
Visual field
Visual field results should always be used in conjunction with the clinical findings. The test is particularly important in glaucoma and neurological disease.
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The visual field: can be represented as a three-dimensional structure akin to a hill of increasing sensitivity. The outer aspect extends approximately 50° superiorly, 60° nasally, 70° inferiorly and 90° temporally.
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Static perimetry: is a method of assessing fields in which the stimulus remains fixed, with intensity increasing until it is seen by the subject or decreasing until it is no longer detected. Standard automated perimetry (SAP) uses this method ( Fig. 1.4 ).
Fig. 1.4
Humphrey SITA-Fast printout (A–F; see text).
(From Salmon JF, Kanski’s Clinical Ophthalmology: A Systematic Approach , 9th edition. Oxford, UK: Elsevier; 2020.)
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Kinetic perimetry: is undertaken by moving a stimulus of constant intensity from a non-seeing area to a seeing area at a constant speed until it is perceived.
Analysis of visual fields
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Reliability indices ( Fig. 1.4A ): with SITA strategies false positive or false negative responses over 15% should be considered significant. If the test is found to be unreliable, further evaluation of the printout is pointless.
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A numerical display ( Fig. 1.4B ): gives the threshold in dB at each point tested in the field. A grey scale ( Fig. 1.4C ) represents the numerical display in graphical form; decreasing sensitivity is represented in darker tones.
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Total deviation ( Fig. 1.4D ): shows the difference between a test-derived threshold at a given point and the normal sensitivity at that point for the general population.
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Pattern deviation ( Fig. 1.4E ): is the total deviation adjusted for a generalized decrease in sensitivity in the whole field (for example, the presence of cataract).
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Summary values ( Fig. 1.4F ): represent distilled statistical information: (a) visual field index (VFI) is a measure of overall visual field function expressed as a percentage, (b) mean deviation (MD) provides an indication of the overall sensitivity of the field, (c) pattern standard deviation (PSD) is a measure of focal loss (an increased PSD is an indicator of glaucoma), (d) the glaucoma hemifield test (GHT) compares corresponding areas in the superior and inferior hemifields.
Microperimetry
Microperimetry is a subjective visual field test that measures retinal sensitivity and fixation behaviour in patients with macular disease and glaucoma involving the central 9° of visual field ( Fig. 1.5 ).
