Ophthalmology: Examination Techniques

Examination Techniques

• Patients with ophthalmic diseases require accurate vision measurement and eye examination by using specialized techniques
• Special investigations should supplement clinical examination findings
• Electrophysical tests, fluorescein angiography, and optical coherence tomography are discussed in later chapters

Psychophysical Tests

Visual Acuity

• Distance visual acuity (VA) is directly related to the minimum angle of separation
• The minimum angle of separation is the minimum angle of separation between two objects, allowing them to be perceived as distinct
• VA is commonly measured using a Snellen chart
• The Snellen chart utilizes black letters or symbols (optotypes) of varying sizes on a white background
• Distance VA is measured using refractive correction from glasses or contact lenses, Unaided acuity is recorded for completeness.
• The eye with worse vision should be tested first, and occlude the other eye
• Push the patient to read every optotype letter

Snellen Visual Acuity

• Normal monocular VA equals 6/6 (metric notation) or 20/20 (English notation) on Snellen testing; normal corrected VA in young adults is often superior to 6/6
• Best-corrected VA (BCVA) is the level achieved with optimal refractive correction

Pinhole VA

• Pinhole VA compensates for the effect of refractive error; it uses a pinhole aperture which consists of an opaque occluder with one or more holes approximately 1 mm in diameter
• Macular disease and posterior lens opacities may result in worse PH acuity than with spectacle correction
• Testing with a pinhole aperture is repeated if the VA is less than 6/6 Snellen equivalent

Binocular VA

• Binocular VA is usually better than the better monocular VA, specifically where both eyes have roughly equal vision

Very Poor Visual Acuity

• Counting (or counts) fingers (CF) indicated the patient can tell how many fingers the examiner is holding up at a specified distance and usually 1 metre
• Hand movements (HM) can distinguish whether the examiner's hand is moving when held in front of the patient
• Perception of light (PL) patients can discern light (e.g. pen torch,) but not shapes or movement and other eye must be carefully occluded

LogMAR Acuity

• LogMAR charts address deficiencies in the Snellen chart and are the standard VA measurement in research and clinical practice
• LogMAR provides the base-10 logarithm of the minimum angle of resolution (MAR) and refers to resolving optotype elements
• A letter on the 6/6 (20/20) equivalent line subtends 5' of arc, with each limb of the letter having an angular width of 1', and needing a MAR of 1' for resolution
• The 6/12 (20/40) line needs a MAR of 2', and the 6/60 (20/200) line needs a MAR of 10'

LogMAR Score

• The LogMAR score constitutes the base-10 log of the MAR where the log of the MAR 1' value is zero, so 6/6 is equivalent to logMAR 0.00.
• The 6/60 MAR log of 10' is 1, so 6/60 is equivalent to logMAR 1.00
• The 6/12 MAR log of 2' is 0.301, giving a logMAR score of 0.30, and scores better than 6/6 have a negative value
• Letter size changes can be categorized as 0.1 logMAR units per row and because there are five letters in each row each letter can be assigned a score of 0.02
• The final score can, therefore, take account of every correctly read letter, and the test should continue until half of the letters on a line are read incorrectly

LogMAR Charts

• The Bailey-Lovie chart are usually used on a 6 m testing distance
• Each line of the chart comprises five letters, with the spacing between each letter and each row related to the width and height of the letters
• The letter signs are rectangular (6/6 letter is 5' in height and 4' in width)
• The distance between two adjacent letters on the same row equals the width of a letter from the same row, and the distance between two adjacent rows is the same as the height of a letter from the lower of the two rows
• The Snellen VA values and logMAR VA are listed to the right and left of the rows respectively
• The ETDRS (Early Treatment Diabetic Retinopathy Study) chart is calibrated for 4 m; this chart utilizes balanced rows comprising Sloan optotypes, developed to confer equivalent legibility between individual letters and rows
• ETDRS letters are square, based on a 5 × 5 grid (i.e. 5' × 5' for the 6/6 equivalent letters at 6 m)
• Computer charts are available that present the various test chart forms on display screens
• Computer charts allow for other assessment means like contrast sensitivity

Near Visual Acuity

• Near vision testing can indicate macular disease
• A range of near vision charts (including logMAR and ETDRS versions) or a test-type book can be used
• Hold book at a comfortable reading distance, measure and note
• Patient wears any necessary distance correction together with a presbyopia correction if applicable (usually own reading spectacles)
• The smallest type legible is recorded for each eye individually and then using both eyes together

Contrast Sensitivity

• Contrast sensitivity is a measure of visually distinguishing an object against its background
• Target must be large enough to be seen with enough contrast with its background or it will be difficult to see, with light grey being less well seen than black on a white background
• Contrast sensitivity is a different aspect of visual function to the above spatial resolution tests, all using high-contrast optotypes
• Most conditions reduce contrast sensitivity and VA, but some (e.g. amblyopia, optic neuropathy) are normal -If patients with good VA complain of visual symptoms in low illumination, contrast sensitivity testing can reveal functional deficits and advantage despite uncommon clinical practice.
• The Pelli-Robson contrast sensitivity letter chart is viewed at 1 metre and has rows of letters of equal size but decreasing contrast of 0.15 log units for groups of three letters
• Patient reads down rows of letters until the lowest-resolvable group of three
• Sinusoidal (sine wave) gratings require the subject to view a sequence of increasingly lower contrast gratings
• The Spaeth Richman contrast sensitivity test (SPARCS) is performed on computer, can be accessed online, ,measures central and peripheral contrast sensitivity
  • Each patient is supplied with an identification number and instructions
• Test takes 5-10 minutes per eye
• Test involves gratings and can be used on illiterate patients

Amsler Grid

• Evaluates the 20° of the visual field centred on fixation
• It is principally useful in screening for and monitoring macular disease, but will also demonstrate central visual field defects originating elsewhere
• Patients with a substantial CNV (choroidal neovascularization) risk should regularly use an Amsler grid at home.
• An Amsler grid is a monitoring method for central visual field, and usually abnormal in patients with muscular disease

Charts

• The charts have seven forms, each consisting of a 10-cm outer square
• Chart 1 features white grid on a black background, has 400 smaller 5-mm squares where each small square visually subtends an angle of 1°
• Chart 2 is similar to chart 1 but has diagonal lines that aid fixation for patients with a central scotoma
• Chart 3 is identical to chart 1 but has red squares to stimulate foveal cones that detects subtle desaturation in maculopathy, optic neuropathy
• Chart 4 features dots to distinguish scotomas from metamorphopsia, as there is no form to be distorted
• Chart 5 features horizontal lines designed to detect metamorphopsia along meridians and is mainly used in evaluating reading issues.
• Chart 6 is similar to chart 5 but has a white background, and the central lines are more closer together enabling more details
• Chart 7 involves a fine central grid, with each square subtending an angle of a half degree and beingmore sensitive

Technique

• The pupils should not be dilated to avoid the photostress effect, and the eyes should not yet have been examined on the slit lamp
• A presbyopic refractive correction should be worn if appropriate
• The chart should be in a well illuminated environment and be held at a reading distance which translates approximately to 33 cm
• The uncovered eye needs to fixate directly at the central dot with the uncovered eye, to keep looking at this
• Report any distortion or waviness of the lines on the grid
• Reminding the patient to maintain fixation on the central dot
• The patient must report if there are blurred areas or blank spots on the grid due to patients with macular disease -Macular disease patients report lines are wavy -Optic neuropathy reports lines are missing or fainting -Missing borders raise the the possibility of causes other than macular disease and glaucomatous field defects/retinitis pigmentosa
• Patients are then asked to record anomalies with a recording sheet and pen

Light Brightness Comparison Test

• Test of optic nerve function which is normal in early and moderate retinal disease and is performed as follows Test procedure: -The light from an indirect ophthalmoscope first shone in normal eye, then eye with suspected disease -The patient is asked whether the light is symmetrically bright in both eyes -If optic neuropathy is present, patient reports that the light is less bright in the affected eye -Asked to assign a relevant value from 1-5 to the brightness of the light in the diseased eye, vs the normal eye.

Photostress Test

• Gross test of dark adaptation in which visual pigments are bleached by light which results in temporary retinal insensitivity perceived as a scotoma Recovery depends on the photoreceptors to resynthesize visual pigment -To detect maculopathy when ophthalmoscopy equivocal, e.g mild cystoid macular oedema or CSR(central serous retinopathy). -Can differentiate visual loss due to macular disease from optic nerve lesion

Technique

-Determine the best-corrected distance VA -The patient fixates on pen torch light (or IO) held 3 m away for 10 sec -PSRT(photostress recovery time) taken to read test acuity letters, normally 15-30 sec, and should be recorded

Colour Vision Testing

• Assessing colour vision is useful in evaluating optic nerve and determining if there is a congenitally anomalous defect
• Dyschromatopsia may develop in retinal dystrophies before other visual parameters impair patients
• Colour vision depends on three populations of retinal cones with blue peaking at 414-424 nm, green peaking at 522-539 nm and red peaking at 549-570 nm
• Normal colour perception requires all these primary colours to match everything within the spectrum

Cone Types

• A given cone pigment may be deficient, or be entirely absent
• Trichromatic possess all three types of cones (but don’t necessarily functioning perfectly) -Absence of 1 or 2 types of cones renders the individuals a dichromat or monochromat, respectively. -Most colour defect patients are anomalous trichromats use abnormal proportions of the three primary colours to match those in the light spectrum.

Cone Deficiencies

• With abnormality of red sensitive cones (red-green deficiency), the protanomalous exist
• With abnormality of green sensitive cones (green-green deficiency), the deuteranomalous is applicable
• Tritanomalous are attributed to those with blue-green deficiency caused by the abnormality of blue cones
• Macular disease produce blue-yellow defects and optic nerve lesions red-green defects

Ishihara Test

• Designed to screen for congenital protan and deuteran defects
• The test is simple, widely available widely screened of a red-green colour vision deficit to help in the optic nerve funtion
• Consist of test plate then 16 plates of dots arranged to show the central shape number where the subject is asked to identify, if it is identified(Fig. 1.12A, and is performed with VA that is sufficient
• Colour-deficient person = only identifies some figures
• Inability to identify the test plate indicates non-organic visual loss The university consist of 10 plates each of central and 4(Peripheral-coloured), in figure 1.13B, is asked to choose close match.

Farnsworth-Munsell 100-Hue test

• Sensitive and longer test for congenital + acquired colour defects
• 85 caps of different hues + 4 racks where randomized caps need to rearranged in order to properly progress colour
• Recordings are placed on a cirucular chart, where forms of dichromatism by characterised failures specific to the meridian of the chart are used

Plus Lens Test

• A temporary hypermetropic shift may occur d/t an elevation of the sensory retina - the CSR(Classic Example = central serous chorioretinopathy), + +1.00 D lens will demonstrate the phenomena.
• If there is an elevation of sensory shift, with that shift the CSR(central serous chorioretinopathy occurs)

Perimetry

• The visual field can be represented as a 3 dimensional(Hill of vision) structure that increases to its relative sensivity
• The outer extent to, respectively superior 50, nasal 60, inferior 70 and temporal =90 degrees
• Sharpest VA at top of hill, and degrades in a progress toward the periphery,
• Slopes on nasal, are steeper the temporal parts where, in what? Blind-spot -’bottomless pit where, temporally 10, below horizontal 20 degrees

Visual Representation

• An isopter is a line connecting points of the same sensitivity, and on a two-dimensional isopter plot encloses a visible area, where a stimulus on a strength Given
• If a field is represented as a hill, then isopters resembles the counter lines of map view.
• Scotoma = Vision loss surrounding "seeing" area/ reduced or total
• Luminance=Brightness + light measured in asb, higher the stimulus in intensity and with value

Measurements for Sensivity

• A lumincear rather linear scale is assessed for Sensivity where changes in factor X10 occur, what to test and what to do with scale?
• dB = 1log unit simple + log unit is non clinically used in perimetry but rather "decibels" - varying between visual field machines
• Therefore, dB readout increases as retinal sensitivity increases -dB is used 1 for increase -Sensitivity of of an test location=20 dB (2log units), point + sensivity 30 -The blind dB spot =0 d B -Seeing a stimulus of gives a value of is asb for

Differentiation of the Sensivity

• Differencial sensitivity: required luminance , how? What do before?

Static and Kinetic Perimetry

• Static Perimetry -Usually automated=Fixed stimulus remains/Intensity increased =threshold reached

• Kinetic(Dynamic Perimetry) Stimus of contant intensity is moved from the non seeing area. - standardized speed + intensity in standardized/chart at point of recognition.

• Manual goldamann or automated

Reliability of Tests and Factors That Affect Performance

• Inexperienced or poorly skilled technicians during setup- explanation-
• Patient Details - enter the correct DOB
• Correct any refractive errors
• Miosis, pupil dialtions with 3mm require dilation, must be consitent in test
• Media Opacities such Cataract
• Indentation, Ptosis.

Techniques in Automated Perimetry

• Computer based.
• Automated for test
• Head mounted BIO
• Manual Perimetry involves presentation and recording for those cannot interact in testing

Terminology and Definitions

• Perimetry is used to assess visual field and record its defects/impairments.
• Isopter is used to describe visual function of fixed strength
• Scotoma refers to non areas that are non seen within the seeing areas
• Static- Automated = location intensity

Frequency Doubling

• In Frequency Doubling test (FDT) Axon =Magnocellular = preferentially lost @
• The frequncey is produced with a low spatial at frequency counter which exceeds 15 hz