How to avoid problems when managing patients with sensory strabismus.

Transcription

1 How to avoid problems when managing patients with sensory strabismus. John J Sloper MA DPhil FRCS FRCOphth; Gillian G Adams FRCS(Ed) FRCOphth; Christine Timms DBO(T) Moorfields Eye Hospital, London Sensory strabismus is a common problem and occurs when impaired vision in one or both eyes causes a loss of binocular function. It is important to identify those patients where vision in an affected eye can be restored, but in particular to predict whether fusion can be restored, as recovery of vision without fusion can lead to intractable diplopia 1. Loss of fusion may be secondary to poor visual acuity or visual field in one or both eyes or may occur when there is incompatibility between the images from the two eyes. Children with sensory strabismus tend to converge whereas adults more commonly diverge 2 Loss of fusion may be caused by problems at any point along the visual pathways. Common causes of loss of fusion are: Keratoconus 3 Corneal opacity Dense unilateral cataract 4,5,6. Retinal displacement following retinal detachment repair Retinal dystrophies or disease Optic nerve anomalies or injury Loss of visual field from glaucoma or neurological disease Amblyopia Questions determining management strategy 1. Is there any prospect of restoring vision? 2. What is the prospect of restoring binocular function? 3. Is there a risk of double vision after surgery if there is no fusion? 1. Is there any prospect of restoring vision? History - Is the condition inherently reversible? - What is the risk of unseen posterior segment damage behind an opacity? Examination Investigations - Evidence of past trauma, cornea, sclera, pupil, lens, fundus, afferent defect - Accurate projection of light? - Associated motility problems - Ultrasound - Electrophysiology 1

2 2. Will the patient regain fusion if vision is restored? Immediate factors Is there visual incompatibility? - Asymmetric astigmatism - Anisekonia, commonly from anisometropia. - Emmetropia in a patient previously adapted to anisometropia - Distortion from a macular hole 7 or epiretinal membrane 8 Refractive adjustments to assist fusion - For asymmetric astigmatism omit cylindrical correction and use spherical equivalent in poorer eye to minimize differential image distortion. - For anisekonia use spectacle lens to correct image size difference and cancel refractive effect with a contact lens. Are there long-term changes in the central visual pathways leading to loss of fusion? Effects of visual deprivation in adults. Risk factors - Visual acuity - Duration of visual loss - Duration of divergence - Nature of visual loss - Age of patient Longstanding asymmetric keratoconus 3 20 patients with severe unilateral keratoconus corrected with a scleral contact lens With contact lens 14 phoric, 6 microexotropia Without contact lens 19 were exotropic with suppression and one had diplopia All except one had poor or absent stereopsis Longstanding dense unilateral adult-onset cataract 6 Eleven patients with longstanding dense unilateral, adult onset cataract either present for at least a year or else divergent All 6/9 or better on day 1 after cataract surgery Nine fused, one had diplopia which recovered spontaneously and one remained divergent with diplopia Mean VEP delay from affected eye of 9.8 msec which resolved over about 3 months No delay for 8 control patients with early cataracts Two patients with diplopia had initial delays of 29 and 16 msec 2

3 3. If the patient is unable to fuse, will they suppress or ignore any second image? Post-op diplopia test If positive, temporary realignment with Botulinum toxin Prism wear Patients with divergence from poor vision from bilateral advanced retinal dystrophies appreciate squint surgery, even though they cannot themselves see their squint. However, even with very poor vision they can experience troublesome double vision and need to be fully assessed before surgery, preferable by being temporarily aligned using Botulinum toxin 9. Intractable Diplopia Assessment Loss of fusion due to changes in central visual pathways 4,5,6 Nine patients following removal of a longstanding unilateral cataract or prolonged aphakia 10,11. At least 6/9 each eye Reduced contrast sensitivity in affected eye Delayed and reduced pattern reversal VEPs Reduced binocular beat VEPs Orthoptic examination, especially synoptophore if vision allows Postoperative diplopia testing with prisms Heimann-Bielschowsky phenomenon predicts lack of fusion potential and so risk of intractable diplopia 12,13. Refractive correction and realignment with Botulinum toxin patients with secondary exotropia Trauma 36% Congenital anomalies Refractive error Retinal detachment Senile cataract Cornea Glaucoma 43% proceeded to surgery 8% required no further treatment Management options for patients with intractable diplopia Occlusion e.g. Bangatter foil or occlusive contact lens Occlusive intraocular lens 15,16. The fundus can now be monitored through an opaque lens with ultrasound or SLO/OCT 17. 3

4 Practical aspects of surgery Non-fusing eyes tend to rediverged following surgery. 85% straight after 5 years 18 75% straight after 10 years So in a young patient plan for the long term and anticipate the need for further surgery for redivergence. A generous medial rectus resection and lateral rectus recession using adjustable sutures allows later surgery to fellow eye for redivergence. If there is a history or evidence of previous trauma, dissect gently without pressure on the sclera. If the lateral rectus of the affected eye has already been recessed or previous trauma is a major concern, then surgery to the fixing eye may be the best option if it is acceptable to the patient. Long-term management with repeated Botulinum toxin may be the best option if further surgery is unacceptable to the patient, if there is a risk of phthysis or if the patient is infirm. Surgery with adjustable sutures Binocular patient - adjust to fuse comfortably. Non-binocular patient - Leave as far esotropic as the patient (and family) will accept Adjustable sutures allow adjustment for Accuracy of alignment for fusion, especially if fusion is weak More generous correction for non-binocular patients as any overcorrection can be adjusted back Minimise diplopia risk - may allow a suppression scotoma to be found. Illustrative case histories will be discussed with audience participation. Summary: The selection of patients for surgery to restore vision and/or ocular alignment will be presented. The causes and underlying mechanisms of the development of sensory strabismus in children and adults will be described. The clinical and orthoptic assessment of such patients will be discussed, together with the use of Botulinum toxin for both assessment and treatment. 4

5 References:. 1. Sloper J. Visual deprivation in adults. Strabismus. 2008; 16: Havertape SA, Cruz OA, Chu FC. Sensory strabismus--eso or exo? J Pediatr Ophthalmol Strabismus. 2001; 38: Sherafat H, White J, Pullum K, Adams G, Sloper J. Anomalies of binocular function in patients with longstanding asymmetric keratoconus. Br J Ophthalmol 2001; 85: Pratt-Johnson JA, Tillson G. Intractable diplopia after vision restoration in unilateral cataract. AmJ Ophthalmol. 1989; 107: Sharkey J, Sellar PW. Acquired central fusion disruption following cataract extraction. J Pediatr Ophthalmol Strabismus. 1994; 31: Sloper J, Collins A. Delayed visual evoked potentials in adults after monocular visual deprivation by a dense cataract. Invest Ophthalmol Vis Sci. 1995; 36: Mireskandari K, Garnham L, Sheard R, Ezra E, Gregor ZJ, Sloper JJ. A prospective study of the effect of a unilateral macular hole on sensory and motor binocular function and recovery following successful surgery. Br J Ophthalmol 2004; 88: Asaria R, Garnham L, Gregor Z, Sloper J. A prospective study of binocular visual function before and after successful surgery to remove a unilateral epiretinal membrane. Ophthalmology. 2008; 115: Dawson E, Leung H, Webster AR, Lee JP. I can't see my squint... but I know it's there! J AAPOS 2010, 14; e Sloper JJ, L.Kousoulides I, Garnham C. Delayed visual evoked potentials in patients with intractable diplopia following removal of a longstanding cataract or with prolonged uncorrected aphakia. Invest Ophth Vis Sci, 1996, 37: S Hollick EJ, Mason AJS, Sloper JJ, Morgan MJ. Contrast sensitivity abnormalities in patients with intractable diplopia following surgery for a unilateral cataract. Invest Ophth Vis Sci, 1996, 37: S Lawton-Smith, Flynn JT, Spiro, HJ. Monocular vertical oscillations of amblyopia. The Heimann-Bielschowsky Phenomenon. J Clin Neuro-ophthalmol 19892; 2: Davey K, Kowla L, Frilling, R, Georgievski, Sandbach J. The Heimann-Bielscholwsky phenomenon: Dissociated vertical nystagmus. Aus NZ J Ophthalmol : Dawson E, Sainani A, Lee J. Does Botulinum toxin have a role in the treatment of secondary strabismus. Strabismus. 2005; 13: Sandy CJ, Wilson S, Page A B. Frazer DG, McGinnity FG, Lee JP. Phacoemulsification and opaque intraocular lens implantation for the treatment of intractable diplopia. Ophthalmic Surgery & Lasers. 2000, 31: Hadid OH, Wride NK, Griffiths PG, Strong NP, Clarke MP. Opaque intraocular lens for intractable diplopia: experience and patients' expectations and satisfaction. Br J Ophthalmol. 2008, 92: Yusuf IH, Peirson SN, Patel CK, Occlusive IOLs for intractable diplopia demonstrate a novel near-infrared window of transmission for SLO/OCT imaging and clinical assessment. Invest Ophthalmol Vis Sci. 2011, 52: Moorfields audit data. 5