Ординатура / Офтальмология / Английские материалы / Moorfields Manual of Ophthalmology_Jackson_2007

Anatomy and physiology

Table 13.1: The actions of the extraocular muscles

Table 13.2: The actions of the extraocular muscles examined in

the nine cardinal positions of gaze

RSR,RIO

LSR,LIO

History and Examination

Background Eyes that are correctly aligned are described as orthophoric or ‘straight’. A manifest deviation or heterotropia is when one or other visual axis is not directed towards the fixation point – esotropia if convergent, exotropia if divergent, hypertropia if up, and hypotropia if down. In heterophoria (latent deviation) both eyes are directed towards the fixation point but deviate on dissociation – esophoria (latent convegence), exophoria (latent divergence) or hyperphoria/hypophoria (latent vertical deviations). A constant deviation typically refers to a deviation that is present for near and distance, whereas an intermittent deviation is only present at one distance, e.g. near fixation, or certain conditions, e.g. without spectacles. A concomitant deviation occurs when the angle of deviation is the same in all directions of gaze, whichever eye is fixing, unlike an incomitant deviation where the angle between the two eyes is different in different gaze positions, or with asymmetrical accommodative effort.

History Ask about the presenting complaint and its duration. If diplopia (double vision) is a symptom, ask whether it is monocular or binocular, constant or intermittent, the position of gaze in which it occurs, or whether it produces vertical, horizontal or tilted images. Does it stop the patient from doing anything? Is the deviation socially embarrassing? Check medications and allergies. In children, take a birth history, ask about any family history of amblyopia, strabismus, or refractive error, and make brief developmental assessment if appropriate. Inquire about any previous ophthalmic treatment including spectacles, prisms, occlusion therapy, and surgery. Ask adults about their occupation and if they drive. If in doubt about a prior eye position or abnormal head posture, ask to see old photographs.

General examination and cover testing

■Measure VA and record refraction.

■Observe any abnormal head posture (AHP). The AHP may include head tilt, face turn, or chin elevation or depression. Deafness, torticollis, and cervical spine abnormalities may also cause an AHP.

Observe ocular posture including an obvious manifest squint, wide epicanthic folds (pseudosquint), spectacles, and any spectacle prisms (‘stick-on’ Fresnel or incorporated prisms).

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History and examination

or slightly nasal in most people. Not all abnormal-appearing CRs are due to strabismus, e.g. high refractive errors can produce a pseudosquint – a pseudoesotropia in high myopia.

■Perform cover test (CT) at near (33 cm) to a light and then accommodative target (e.g. reduced Snellen letter at VA of worst eye, or pictures/toys for children). CT involves two manoeuvres.

1.Cover-uncover test : to detect manifest strabismus. Cover one eye and look at the noncovered eye. Movement inward to take up fixation indicates an exotropia. Movement outward indicates an esotropia. If the eye is slow to fix the target, this may indicate poor VA or amblyopia. Note any manifest or manifest latent nystagmus (MLN) – horizontal jerky, often very fine nystagmus with fast phase towards the uncovered eye. Note any movement of the covered eye, particularly dissociated vertical deviation (DVD) associated with infantile esotropia.

2.Alternating cover test : to detect latent strabismus. Alternately occlude left and right eye for 1–2 seconds each. Do not allow both eyes to view in between covering as fusion may then take place. A latent deviation sometimes becomes temporarily manifest after fusion is disrupted by testing. Note how fast the eyes resume binocular single vision (BSV) once testing is complete (rapid or slow recovery) indicating how well the deviation is compensated.

■Move the target occasionally to check fixation.

■Perform CT at distance to a suitably sized chart letter or picture/toy.

■Repeat CT with/without glasses, and then with/without AHP.

Eye movements (cranial nerves III, IV, VI)

■If suggested by the history, check for monocular diplopia by occluding each eye seperately. Note VA. If not already known, clarify if diplopia is horizontal, vertical, or tilted.

■Observe any head tilt, proptosis, ptosis, or lid retraction.

■Ask the patient to follow a light held at 50 cm and report if they see diplopia. Go from primary position and back again in the other 8 cardinal positions of gaze (p. 583). Ensure the CRs are always visible; the patient or examiner may need to lift the lids, particularly in downgaze. Check for lid-lag on

Brown’s syndrome) of the palpebral aperture on adduction; observe any pupillary changes, e.g. constriction of the pupil in adduction or other gaze position may occur with aberrant 3rd nerve regeneration.

■If diplopia occurs in any position, check which image disappears when an eye is covered; the more peripheral image comes from the eye with the paretic muscle(s).

■If CT shows a hypertropia/hyperphoria in the primary position (step 1) then do a CT in right and left gaze to see where the height is greatest (step 2). If greater in right gaze then repeat the CT up and down to the right. If the deviation is greater down to the right, a left 4th nerve palsy is suspected. Finally, compare CT (eyes in primary position, fixing at 3 metres) with the head tilted right and left, to see if the height differs (step 3). If the deviation is greater on head tilt left, a left 4th nerve palsy is likely. However, the head tilt test is not always reliable and other causes of hypertropia should not be ignored, e.g. thyroid eye disease. Park’s three-step test refers to steps 1, 2, and 3 combined. Step 3 is also called the Bielschowsky headtilt test. However, the diagnostic importance of testing in all 9 positions cannot be overemphasised. Vertical deviations can be associated with bilateral (often asymmetrical) muscle underor overactions.

■Examine saccades in suspected supranuclear lesions to help differentiate newly acquired palsies from mechanical strabismus (normal in the latter). Position a target to the right and left of the patient’s eyes, within the visual field; instruct the patient to look from one target to the other as quickly as possible, without moving the head. Repeat the test in the vertical plane. Compare the vertical and horizontal velocity of the excursion, as well as the velocity in each eye; e.g. a reduced excursion of the adducting eye on horizontal saccades may indicate an internuclear ophthalmoplegia (same side). Cerebellar disease and MS may produce hypermetric saccades (eyes overshoot the target). Myasthenia gravis and Parkinson’s disease may produce hypometric saccades (eyes undershoot the target).

■Test convergence to a detailed target, and observe normal pupillary constriction.

■If required perform Doll’s head manoeuvre to differentiate

supranuclear from nonsupranuclear lesions (e.g. Steele Richardson Olszewski Syndrome). Ask the patient to fixate a target in the distance. Inform the patient that you are going to gently move the head right, left, up and down. Observe the

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History and examination

extent of ocular rotations. Doll’s head movements may be absent in supranuclear lesions.

■Test optokinetic nystagmus with an OKN drum rotated slowly in front of the patient, both horizontally and vertically, and in both directions. Horizontal asymmetry may indicate a parietal lesion. Convergence retraction nystagmus with a downward moving drum (producing upward re-fixation saccades) suggests Parinaud’s syndrome.

Amblyopia

Background Amblyopia is a condition of reduced visual function, in one or both eyes, which is not improved by the correction of any refractive error, or by removal of a pathological obstacle to vision.

Causes are form deprivation and abnormal binocular interaction producing degraded retinal images in the sensitive or critical period of visual system development, particularly in the first 2–3 years of life, decreasing with age, up to 7 years of age. During this sensitive period, amblyopia can develop as well as respond to treatment.

Classification

■Strabismic amblyopia : from a constant, unilateral, manifest strabismus.

■Anisometropic amblyopia : >1 dioptre interocular difference.

■Ametropic amblyopia : bilateral moderate to high refractive errors.

■Meridional amblyopia : astigmatism >1.5 dioptres.

■Stimulus deprivation amblyopia : lack of adequate visual stimulus in early life, e.g. cataract; ptosis.

History Take a full ophthalmic history noting any previous eye surgery, squint, refractive error, and relevant birth history such as premature delivery. Review previous VA data if available and note poor compliance with glasses or occlusion.

Examination Crowded or logMAR-based VA tests increase the sensitivity to detect amblyopia. If vision testing is unreliable or unachievable, compare fix and follow responses. Suspect amblyopia with constant unilateral strabismus; suspect equal vision (good or bad) with alternating strabismus. Refract and undertake a media and fundus examination. Assess eccentric fixation, which can occur in strabismic amblyopes – under monocular conditions the amblyopic eye does not fixate centrally, but instead with a nonfoveolar area of the retina. Classify as macular, paramacular, peripheral, steady, or unsteady.

In children >6 years old, the presence of motor fusion affects whether to treat or continue to treat, and the risk of causing potentially troublesome diplopia. If good motor fusion is present, certain cases can be occluded after the usual 7–8 year cut-off. If motor fusion is poor or absent, warn parents to stop occlusion if diplopia occurs. Also assess with the Sbisa bar. Place the Sbisa bar over the better eye and record the filter at which diplopia is

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Amblyopia

appreciated. Readily appreciated diplopia indicates weak fusion or less dense suppression and occlusion should be avoided to reduce the risk of subsequent diplopia.

Treatment Prescribe the full spectacle correction to be worn full-time. If vision is 6/24 (0.7 logMAR) or worse, commence treatment (usually occlusion) at the same time; otherwise, reassess VA in spectacles at 6–8 weeks (some practitioners recommend waiting up to 12 weeks). Then commence therapy if:

■VA is stable at worse than 6/9.5 (0.2 logMAR).

■There is more than one logMAR (0.1) line interocular VA difference.

■VA cannot be reliably tested and there is fixation preference.

Occlusion normally starts with 2 hours per day part-time total (light and form deprivation) using an adhesive patch. Increase to 4 hours, and if necessary continue to double hours if VA fails to improve. If necessary, full-time total occlusion can be used for dense amblyopia, particularly if there is poor compliance with occlusion in the past, and/or a VA of 6/24 (0.7 logMAR) or worse.

Penalization is the optical reduction of form vision in the nonamblyopic eye, usually with G. atropine 1% once daily to the better eye. It compares well to occlusion, and is acceptable to carers, but there is a slower improvement.

In children <2.5 years use minimal occlusion because of the risk of occlusion amblyopia, e.g. 20–30 minutes/day, or fixing eye 3 days/nonfixing eye 1 day. If using optical penalization, reduce the frequency of installation of drops.

Stimulus deprivation amblyopia (e.g. cataract) requires a more intensive regimen.

The key to success is compliance. If this cannot be achieved, consider inpatient admission for treatment.

Follow–up Regular follow-up is required. Continue with the dose of occlusion that works for that patient, aiming to achieve 6/9.5 or better, or less than one line interocular difference. Once therapy has ceased, observe for visual regression until 8 years of age. If VA drops more than one line, re-commence occlusion.

Esotropia

Background Esotropia is a manifest convergent squint. The following relates to concomitant esotropia (angle of deviation the same in all positions of gaze and regardless of which eye is fixing). For incomitant strabismus see page 601.

Classification

■Primary esotropia :

1.Constant.

a.Constant esotropia with an accommodative element : esotropia at near and distance with hypermetropic correction. Increases without glasses. Formerly called partially accommodative esotropia.

b.Early-onset esotropia (infantile esotropia) : esotropia at near and distance caused by failure of cortical motor fusion. Onset before 6 months of age. Associated with manifest latent nystagmus (MLN) and dissociated vertical divergence (DVD) where on cover test either eye elevates and extorts under cover.

c.Late-onset esotropia : A sudden-onset esotropia for near and distance usually in a child >5 years, often with diplopia.

2.Intermittent.

a.Fully accommodative esotropia : binocular single vision (BSV) with hypermetropic correction for near and distance. Becomes esotropic for near and distance on accommodation without correction.

b.Convergence excess esotropia : BSV at distance and near when fixing a light; esotropia at near with an accommodative target. Usually associated with hypermetropia but patients can be emmetropic and rarely myopic. Associated with a high accommodative convergence/accommodation (AC/A) ratio.

c.Near esotropia : BSV at distance; esotropia at near with both a light and accommodative target. Normal AC/A ratio.

d.Distance esotropia : BSV at near; esotropia at distance. No limitation of abduction, unlike a lateral rectus palsy

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Esotropia

which can appear similar. Often associated with myopia; if not, consider neurological disease.

e.Cyclic esotropia : varies between straight and large-

angle esotropia in rhythmic cycles, usually every 48 hours. Onset usually <5 years of age. Assess patients on alternate days to confirm the diagnosis. Rarely may occur in adults with a secondary squint. Can become a constant esotropia over time.

■Consecutive esotropia : esotropia in a previously divergent eye. May be constant or intermittent. Usually follows surgical overcorrection.

■Secondary esotropia : constant deviation secondary to visual loss or impairment occurring usually before 2 years of age.

History Ask about the nature of any double vision (rare in children), family history of strabismus, febrile illness (may precede accommodative esotropia), developmental delay, previous history of occlusion, spectacles, strabismus surgery, and birth history.

Examination Check VA, cover test with light and accommodative targets (near and distance, with and without spectacles), alternate cover test, and eye movements. ‘V’ patterns are common (p. 603). Obtain refraction (with cycloplegia in children).

Investigations Stereopsis, fusion, prism cover test, AC/A ratio, synoptophore, and postoperative diplopia test, as required.

Treatment More than one treatment option often applies.

■Optical correction : fully correct any hypermetropia (minus working distance) and treat amblyopia if appropriate. If myopic, reducing the myopic correction may help maintain

BSV but the patient must retain good VA to prevent amblyopia. Only in children <3 years might a low myopic correction be postponed. Executive bifocals (+3 D add) can help convergence excess esotropia, and the patient can then be weaned off as the condition stabilizes, e.g. postoperatively.

■Amblyopia therapy : if <8 years (p. 589).

■Observe : consecutive esotropia following exotropia surgery usually settles in a few months; correcting previously uncorrected low hypermetropia or prisms may help. Consecutive estropia should not be allowed to persist for more than 6 weeks without intervention. Consider botulinum toxin or