Preliminary Tests

  • Pupils
    • Note physical aspects of pupils (also assess during ophthalm.), note response to stimulation
    • Physical aspects: shape – generally round & regular, size – assess to nearest mm using pupil gauge (some say to 0.5mm), anisocoria (intraocular size difference), position – normally central
    • Pupil reactions: tested with slit lamp usually at the beginning of the Hirschberg assessment routine. Should be observed for: direct & consensual (indirect) reactions to light, response to accommodation, relative afferent defects via ‘swinging flashlight’ test, physical aspects may also be noted
    • Apparatus & technique (physical) – pupil gauge (Keeler specialist), recording made to nearest 0.5mm, px looking in distance, lower room lights but have enough light to gauge pupil size & reactions. Record size by use of gauge & Burton lamp for dark irides (WD = 15-20cm) held by side of px’s face (temporal by ~5-10 cm’s. Note any anisocoria (difference ≥5mm) – not always pathological (20% of normals) & if asymmetry is noted recheck in bright conditions
    • Pupil diameter decreases with age
    • Grade pupil reactions in terms of speed of reaction e.g. 0 (absent) through the 3 (brisk) or: +1 – slow, barely perceptible response; +2 – slightly faster response with slightly larger amplitude; +3 moderate response with moderate amplitude; +4 – brisk, large response of young px
    • Repeat for consensual reaction other eye, record reaction
    • Check & grade near reflex to “JUMP-convergence” / NPC
      • use close target ~15cm from px (must not be a light stimulus), should be visible for uncorrected px (may have to use correction with high refractive error), can use px’s own thumb, observe re-dilation as distance fixation resumed, grade accordingly (this is usually slower than direct/consensual responses)
    • Swinging flashlight test – used to check for RAPD, compares responses of each eye to light, darkened room therefore need a low level of illumination by an ophthalmoscope to observe consensual reflex, allow pupils to dilate for 10 secs, bright (flashlight) = 2-4 secs on RE observe consensual in LE with ophthalmoscope, swing to px’s LE & hold 2-4 secs, if lesion in optic tract of LE pupil will DILATE = afferent papillary defect, repeat cyclr 3-5 times, possible to use neutral density (ND) filter to judge depth or severity of lesion. If normal (i.e. same response other eye) record as –ive or no RAPD
      • The abnormal consensual reaction in the left eye is perhaps due to an afferent defect (Marcus Gunn reaction)
    • External eye
      • Structures: lids, lashes, conjunctiva, sclera, cornea, anterior chamber, irides, pupil & lens
      • Inspection methods: these structures should first be inspected with the direct ophthalmoscope followed by the slit lamp (general 2D followed by particular 3D)
      • Hand Slit Lamp: to inspect the px’s RE, hold hand slit lamp with thumb & forefinger of right hand, steady the slit lamp with remaining fingers of right hand on px’s forehead, defocus slit lamp to give diffuse illumination, hold x10 loupe with left hand & bring your dominant eye as close as possible behind the loupe

Begin inspection of anterior segment of px’s RE starting with lids & lashes, follow through with inspection of: puncta, caruncle, conjunctiva, sclera, anterior chamber, iris etc. Use diffuse & then focal illumination – (direct & indirect), repeat for LE

  • Lids: general observations – colour (redness? drying?), grading, swellings, lumps & bumps, position – ectropian/entropian. Specific observation – condition of lid margins glands (meibomian), puncta open/closed, tear prism
  • Lashes: general observations – number & length. Specific observation – condition of lashes/glands (zeiss), backward pointing. Infection
  • Conjunctiva – divide into bulbar & palpebral (latter by lid eversion), colour (grade redness w/ Efron scale), lumps & bumps, pigmentation (pinguecula, pterygium)
  • Sclera – bluish colour in infants, white in adults, yellowish in old age (or jaundice), vessels (redness) – scleritis vs episcleritis
  • Cornea – should be clear & avascular, requires focal illumination direct & indirect, grade scars/abrasions (deep/superficial?), check with staining agents, note presence of arcus
  • AC – check depth, grade depth from back of cornea to front of lens, correlate with measurement of iridic angle Van Herrick, check for inflammatory cells & KP
  • Iris – record colour, position of freckles etc, check for presence of BV’s
  • Pupils & lens – note size & shape of pupils, anisocoria, reflexes, note presence of cataract – size, location, link with symptoms
  • Pupil/Iris abnormalities & defects
    • Iris defects: sphincter tear, iridodialysis, sector iridectomy (surgical), iridotomy (laser/surgical hole in iris – made to help fluid drain from back to front), iris prolapse (iris sucked through hole in cornea), posterior synechiae (iris-lens adhesions after inflammation or trauma – fix with cycloplegics/mydriatics), iris coloboma (congenital, usually inferior, looks like sector iridectomy), Corectopia (congenital displacement of pupil from central position)
    • Pupil light pathways: for constriction – parasympathetic autonomic nerves respond to light stimulus of retina, afferent fibres on optic nerve (CN II) decussate at chiasma (nasal ones cross over), efferent fibres in oculomotor nerve (CN III)

For dilation – sympathetic autonomic nerves, affected by px level of arousal, when stimulated inhibit constriction pathway & excite pathway for dilation

  • Parasympathetic pupil pathways:
    • Afferent (in-flow or sensory): light stimulates retinal receptors à optic nerve (papillary fibres) à pretectal nucleus (synapse here in midbrain) à interconnections to ipsi & contralateral EWN
    • Efferent (out-flow or motor): EWN (midbrain) à ciliary ganglion (synapse) à short ciliary nerves à iris sphincter (synapse)
  • Sympathetic pupil pathways:
    • Pre-frontal cortex
    • Hypothalamus – response to arousal: inhibitory impulses decrease activity of parasympathetic pupil pathway in midbrain, sends excitatory impulses to ‘central neuron’ of sympathetic pupil pathway à cilio-spinal centre of Budge (pre-ganglionic neuron) à superior cervical ganglion (post-gang. neuron) à long ciliary nerves à iris dilator muscle (adrenergic transmitter)
  • Pupil NEAR pathway – shares much of parasympathetic pathway for light stimulation
    • Respond to visual stimulus on retina, afferent fibres in ON (CN II) decussate (chiasma) & then synapse in LGN, cortical areas A17, A18 stimulated, pathway via superior colliculus sends fibres to EWN, efferent fibres in oculomotor nerve (CN III) come back to eye.

(near response input to EWN more ventral than light response input)

  • Checking near response important if light response is abnormal – may have ‘light-near dissociation’, but not necessary if light response is entirely normal but still good to check
  • Essential anisocoria – physiological, 20% of population (≥4mm difference), may perhaps relate to differences in Rx, constant over illumination range
  • Pathological anisocoria – anisocoria varies according to light level, a dilated pupil (Adie’s pupil) may result from: paresis of iris sphincter (III nerve), irritation of dilator (uncommon). A constricted pupil (Horner’s syndrome) may result from: paresis of dilator (rare), irritation of sphincter (common)
  • Abnormal pupils
    • Amaurotic pupil = no direct/consensual response from stimulation of a blind eye, brisk direct & consensual response from good eye
    • Marcus Gunn = abnormal consensual reaction, detected by swinging flashlight test – v. useful in ON lesions & not at papillary innervation (efferent motor pathway) but at the patency of the afferent (ascending) pathway (looking at how good nerves are in pathway)
  • ‘Light-Near’ dissociation
    • Pupil pathway for light response is absent OR deficient
    • Pupil pathway for near is unaffected OR relatively normal
    • Specific conditions:
      • Argyll-Robertson pupil – small pupil, only responds to near. Miosis inhibiting fibres in mid-brain (Sylvian aqueduct) involved. Px may have small vessel disease (diabetes, arteriosclerosis) but traditional association was with untreated syphilis
      • Parinaud’s/dorsal midbrain syndrome – large pupil, only responds to near
      • Holmes-Adie syndrome/Adie’s tonic pupil – large pupil responding better to near than to light
    • Horner’s syndrome – paralysis of ocular sympathetic fibres. Signs – ptosis (sympathetic supply to Muller’s muscle), miosis (iris dilator affected), decreased facial sweating (if pre-ganglionic), apparent enophthalmos (palpebral aperture decreases), increased amplitudes (depth of focus increase), use flash photo in the dark = more dilated in the good (non-paretic) eye

4-10 % cocaine test to determine if Horner’s = poorer dilation of bad eye. Could also use 0.125% phenylephrine, bad eye dilates as extra sensitive (sympathetic denervation)

1% hydroxyamphetamine to localise – no dilation of bad eye = post-ganglionic

  • Dilated fixed pupil
    • Internal III nerve ophthalmoplegia – no accommodation, no near pupil reflex. (If complete paralysis have a fixed dilated pupil on affected side)
    • Adie’s tonic pupil – blockage of ciliary ganglion. (Defective pupil is larger & responds better to near than light)
  • Gross Fields
    • Peripheral arc test – recommended method for inclusion into normal optometric routine, targets presented along arc of constant radius from px’s corneal apex
    • Confrontation tests – less precise method, targets presented in plane equidistant from px & facing examiner
    • Target options for peripheral arc: black sphere in light background, white sphere in dark background, red sphere in any non-red background, small illuminated target (bulb) on dark wound – (can use these targets in confrontation methods too)
    • Recommended gross fields method: 5mm red spherical target on a rod, hand perimeter arc – best technique for gross peripheral field check, adequate illumination, correct target used, clear instructions to px (see BEAD not wand), examiner positioned correctly, px monocular, examiner binocular, move target correct speed from 8 points, 33cm arc – non-seeing to seeing then to fixation
    • Try to judge eccentricity to nearest 10°. Colour recognition field is much smaller
    • Facial features vary including nose & brows, eye prominence & separation, lid position
    • Confrontation tests – main method, examiner compares px’s field with own field (face each other). Examiner & px both monocular (cover opposite eyes), can test multiple meridians but difficult to test temporal limit
      • Face px, sit ~ 100/50 cm apart, px covers eye with occluder or frame rule, px asked to look directly at your LE with their RE, introduce target into one quadrant
    • Alternative methods – often a very gross target is used to test each of the four quadrants in turn, phenomenon of ‘extinction’ may be used to enhance sensitivity (e.g. if have a hemianopia when both half fields are stimulated together the normal one excludes the defected one so only see on normal fields side, but both fields appear normal when done separately)
    • Finger counting version – use 1/2/all fingers or clenched fist & ask how many fingers do you see? repeat for other 3 quadrants, switch occlusion etc & repeat for LE, no special equipment = advantage, okay for hemianopias/altitudinal defects
    • Simultaneous finger counting – use if finger-counting is normal: px must count number of fingers presented simultaneously in each half field, more sensitive technique owing to ‘extinction’ phenomenon (defective hemifield appears intact when tested alone but abnormal when both half fields stimulated together)
    • Colour comparison – could pick up early temporal field defects from chiasmal compression: present 2 fairly large red objects e.g. hat pins/bottle tops ~5cm either side of fixation. Ask ‘is there any difference in colour between the two objects? May appear redder in normal nasal field
      • Advantages of confrontation/peripheral arc tests: rapid, no expensive equipment, can be done almost anywhere, can test for extinction phenomenon
      • Disadvantages: sensitivity is not very high (though with a careful arc technique & ‘good’ observer can detect normal blindspot)
    • Testing ‘light projection’ sense – useful with very poor vision (perception of light) e.g. px with a total cataract, can’t see fundus – don’t know if functional, shine bright light e.g. anglepoise from eccentric position, check whether px can tell light direction i.e. if coming from up/down/right or left
    • Role of gross fields test: a ‘confrontation field’ = a ‘communication field’ – it explains to the px what a visual field is
    • All methods are limited in sensitivity in detecting subtle defects but best = examination of central 20° with a small red target
  • Cover Test
    • EsoT – affected eye is in, diplopic image falls in, px sees projected out (line on MR same side), use Base OUT to correct
    • ExoT – affected eye is out, diplopic image falls out, px sees projected in (line on MR opposite side), use Base IN to correct
    • 1cm ‘training’ grid viewed at 1m so each square = ~1∆
    • CT variations:
      • Subjective cover test: introduced in 1924 as ‘parallax test’, helpful to confirm small heterophorias (esp. <2∆), unreliable in heterotropias owing to sensory adaptations, px must be capable of giving a clear verbal response, alternating cover test is performed & px is asked to report whether target jumps in same direction as occluder (exo) or the opposite direction (exo), or moves down (hyperphoria) or moves up (hypophoria). Advisable to repeat to confirm
      • Prism cover test: (can only be done on non-strabismic px’s) objective method using a prism bar, done at D & N, enables more precise measurement of deviations, firstly a normal cover test routine is performed to determine direction & estimate size of any deviation. A prism of the estimated power is then selected & held in front of the deviating eye in a tropia or either eye in a phoria. The bar is positioned with this directly in front of the eye & its apex pointing in the direction of the tropia or phoria. The deviating eye is observed as the other eye is occluded. Prism power is adjusted until there is no movement of the eye behind the prism to take up fixation on alternate cover testing. The prism strength at this ‘null-point’ is recorded & represents the maximum angle of deviation
      • Head in non-upright positions: target (gaze) in primary positions, cover test firstly conducted with head in upright position, test repeated with the head turned or tilted/in px’s habitual non-upright position
      • Fixation target in peripheral positions – cover test firstly conducted with gaze in primary position, test repeated with the gaze in up to 8 peripheral positions
    • Purpose of procedures: to assess fixation & therefore estimate any ocular deviation from the position(s) of the corneal reflections when px fixates a penlight target presented in the primary position at near. Useful as a gross method, occasionally may be all that can be achieved with a wriggly toddler
    • Definition of angles: alpha – between visual axis & optic axis; gamma – between optic axis & fixation axis at centre of rotation of the eye; kappa – between visual axis & optic axis at nodal point of the eye; lambda – between visual axis & optic axis at centre of pupil
    • Kappa test (angle lambda) – allows objective estimate of monocular fixation, one of the px’s eyes is occluded, their open eye is directed to penlight held at 50cm in front of this eye, examiner sights monocularly over the light & notes relative position of catoptrics reflex vs pupil centre. Measurement is recorded in mm – a + sign means nasal displacement, a – sign means temporal displacement, angle is usually between 0 & 1.5mm & equal in each eye, a difference between the eyes suggests possibility of eccentric fixation
      • Another method = px looks at one end of a 15cm ruler held at 50cm, torch moved along ruler until its reflection is centred in pupil. Angle lambda (∆) = ~2 x distance along ruler in cm (requires reasonable cooperation)
    • Positive angle kappa can mimic EXO. Negative angle kappa can mimic ESO
    • Angle kappa at birth is on average twice adult magnitude (shorter eyeball)
    • Hirschberg technique – slows objective estimate of angle of strabismus under binocular conditions. Px fixates penlight at near (40-50cm), examiner sights monocularly over oenlight & records relative position of corneal reflexes in mm from centre of px’s apparent pupil. A difference of 1mm = 22∆ (usually symmetrical, slightly nasal as looking from near)
    • Nine diagnostic positions of gaze when testing EOMs
    • (px with LE restricted in abduction – LE palpebral aperture narrows in primary gaze & adduction + RE shows slight downshoot in R gaze) = Congenital Duane Retraction Syndrome
    • When considering how the eyes work together, a “version” or “conjugate” movement involves simultaneous movement of both eyes in a certain direction.  Agonist muscles in both eyes, which work together to move the eyes in the same direction, are said to be “yoked” together.  According to “Hering’s Law,” yoked muscles receive equal and simultaneous innervation. (e.g.’s of yoked muscles or synergistic muscle pairs: RSR & LIO, RIO & LSR, RMR & LLR, LMR & RLR, RIR & LSO, LIR & RSO)

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Horopter

The HOROPTER is an imaginary. surface whose points are all at the. same distance as the fixation point. Points on the horopter project to. corresponding locations on the temporal and nasal retinas, respectively. These corresponding locations. exhibit zero retinal disparity. i.e., D = dtemporal – dnasal = 0.

A horopter is an imaginary plane made up from an infinite number of points in space projecting from corresponding retinal areas in the two eyes. An object placed on the horopter will stimulate exactly corresponding points on the two retinae

  • Vieth-Müller circle
  • The Vieth-Müller circle (theoretical horopter) is based on certain geometric assumptions about the eyes. These are:
    • Each retina may be represented by a perfect circle
    • Corresponding points are evenly spaced across the nasal & temporal retinas of each eye
    • Both retinas are the same size & corresponding points are perfectly matched for their locations in the two eyes
  • Empirical Horopter
  • The empirical Horopter is much flatter than the theoretical horopter that forms part of the Vieth-Müller circle
  • Nasal & Temporal corresponding points differ in their distance to the fixation point
  • Each individual has their own individual empirical horopter (cannot calculate this, have to measure it for each individual)
  • Objects located exactly on the horopter are seen as fused, but what happens if the object is very slightly off the horopter, either closer or farther away?
  • FUSION – align the eyes & facilitates binocular vision
  • (when the two images are just outside horopter, fusion tries to align two eyes together make a single image; give binocular vision)
  • Motor fusion: (eye actually changes position to correct double vision, brain is aligning the two eyes)
    • A “closed loop” response to small disparities
    • It changes the vergence & reduces the disparity
  • Sensory fusion: (doesn’t change position of eyes, brain just overlaps images)
    • An “open loop” response to small disparities
    • Does not change the vergence – disparity analysis within Panum’s Areas (constant – feedback reaction)
  • Panum’s area
    • Within a small distance, either side of the horopter, objects can still be fused & seen as single. Strictly speaking, they fall on non-corresponding retinal points & there will be a small disparity
    • The zone on either side of the horopter within which it is still possible to see objects singly is known as Panum’s area
    • At periphery, Panum’s area is large, at fovea it is small
  • Panum’s Fusional Space indicates that:
    • Retinal correspondence is not just between pairs of points but between retinal areas centred on corresponding points
  • Panum’s Areas:
    • The receptive fields of cortical binocular neurons
    • Objects far enough from the horopter to be outside Panum’s area produce very large retinal disparities, so cannot be fused
    • They are seen as double

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