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392 Color Atlas of Ophthalm ology

Presentation

Th e con dit ion u su ally affect s th e younger age grou p . It is th ough t to be caused by irrit at ion of th e root of th e seven th cran ial n er ve by a com pressive lesion . MRI of th e cerebellopon t in e angle sh ould be obtain ed to rule ou t t u m or.

Differential Diagnosis

Bleph arospasm , facial m yokym ia, t rigem in al n euralgia, Parkin son disease, progressive supran uclear palsy, m u lt ip le sclerosis, st roke, Tou ret te syn drom e, an d tardive dyskin esia

Management

Man agem en t in clu des obser vat ion , bot ulin um toxin inject ion , or n eurosu rgical decom pression of th e seven th n er ve (Jan n et t a procedure).

Myasthenia Gravis

Myasth en ia result s from dysfun ct ion of th e n eu rom uscu lar jun ct ion caused by au - toim m un it y. It is a ch ron ic au toim m u n e disorder associated w ith a redu ced n u m - ber of acet ylch olin e receptors n eurom u scular jun ct ion s result ing in w eakn ess an d fat igabilit y of m uscle. Ocular m yasth en ia m ost com m on ly presen t s w ith diplopia, ptosis, or both , w h ich are variable an d ch aracterist ically w orse tow ard th e en d of th e day. Seru m an t ibodies to acet ylch olin e receptors are detected in 90% of th e pat ien ts w ith gen eralized m yasth en ia, but on ly 50%w ill be detected in ocu lar m y- asth en ia. Neon atal form s of m yasth en ia gravis occu r in 10 to 15%of ch ildren born to m oth ers w ith m yasth en ia gravis becau se of th e placen tal t ran sfer of an t ibodies to Ach (Acet ylch olin e) receptor.

The im pairm ent of the neurom uscular conduction causes weakness and fatigue of the skeletal m usculature but not of cardiac and involuntary m uscles. The disease affects fem ales tw ice as com m only as m ales and m ay be ocular, bulbar, or generalized.

Presentation

Myasth en ic sign s an d sym ptom s are variable an d ten d to w orsen w ith fat igue an d st ress.

Fat igabilit y: Du ring test ing for lid fat igue, th e pat ien t is asked to look up w ith ou t blin king at th e exam in er’s h an d for 1 to 2 m in utes. Lid fat igu e on prolonged upgaze is perh aps th e m ost frequen tly elicited sign (Fig. 13.15).

Peek sign: W h en th e pat ien t is asked to close th e lids gen tly, on e or both in ad - ver ten tly open sligh tly or p eek.

Absent Bell’s Phenom enon: Th ere can an absen ce of Bell ph en om en on .

Cogan lid t w itch: After prolonged dow ngaze refixat ion to th e p rim ar y posit ion result s in oversh oot ing of th e u pper lid .

Upper lid hop: Hop of th e upp er lid occu rs on looking to th e side.

Myasthenic ptosis: W hen unilateral is associated w ith contralateral lid retraction .

Oscillatory m ovem ent s: If on e eyelid is elevated m an u ally as th e pat ien t looks

up, th e fellow eyelid w ill sh ow fin e oscillator y m ovem en t s.

Ice pack test: Th e degree of ptosis im proves after th e ice pack is placed on th e eyelid for 2 m in u tes. Th e test is n egat ive in n on m yasth en ic ptosis.

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Fig. 13.15 Myasthenia gravis.

Diplopia: Th is is ver y frequ en tly ver t ical, alth ough any of th e m u scles can be involved . Th e pupil is n ot involved . A pseu doin tern u clear oph th alm oplegia can occur.

Saccadic abnorm alit ies: Abn orm alit ies su ch as hypom et ric large saccades, hyperm et ric sm all saccades, qu iver m ovem en t s, an d hyperfast saccades can occur.

Differential Diagnosis

Isolated or com bin ed palsies of th e th ird, four th , sixth , or seven th cran ial n er ves; decom pen sated st rabism u s; thyroid disease; Eaton -Lam ber t m yasth en ic syn - drom e; bot u lism ; ch ron ic progressive oph th alm oplegia; m yoton ic dyst rophy

Management

Tensilon test

In t raven ous inject ion of edroph on iu m is th e gold st an dard for th e diagn osis of ocular m yasth en ia. Edroph on iu m is a sh or t-act ing an t ich olin esterase th at in creases th e am ou n t of acet ylch olin e available at th e n eurom u scular ju n ct ion . In m yasth e- n ia th is resu lts in t ran sien t im provem en t of sym ptom s an d sign s such as w eak- n ess, ptosis, an d diplopia. Un com m on com plicat ion s in clude bradycardia, loss of con sciousn ess, an d even death . Lacrim at ion , salivat ion , an d abdom in al cram ps are m en t ion ed as com m on m in or side effects. Th e test sh ould be don e w ith a resu scitat ion t rolley in h an d in case of sudden cardiorespirator y arrest .

Object ive baselin e m easu rem en t of ptosis or dip lopia w ith a Hess ch ar t sh ould be t aken .

In t raven ous inject ion of at ropin e 0.3 m g is given to m in im ize m u scarin ic side effect s.

In t raven ous dose of 0.2 m L con tain ing 2 m g of edroph on ium hydroch loride is

given . If defin it ive im provem en t is n oted th e test can be term in ated .

If n o respon se th en th e rem ain ing 0.8 m L of 8 m g is injected after 60 secon ds if th ere is n o adverse react ion . Th e respon se lasts on ly for 5 m in utes.

Per verse react ion such as w orsen ing of th e st rabism u s or a paradoxical respon se su ch as righ t hypert ropia becom ing a left hyper t ropia after th e inject ion is con sidered posit ive by som e.

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Neostigmine Test

In t ram u scu lar inject ion of n eost igm in e is u seful in ch ildren . Th e effect last s for 15 m in utes to p eak an d last s for on ly 30 m in utes.

Presen ce of acet ylch olin e receptor an t ibodies is vir t ually diagn ost ic of m yasth e- n ia gravis.

On elect rom yography, repet it ive st im ulat ion of a single m u scle fiber w ill sh ow a decrem en tal respon se.

Sleep Test

Usefu l in n eon ates an d in fan t s. Th ere w ill be im provem en t after sleep .

Im aging th e ch est w ith CT or MRI for th e p resen ce of thym om a

Optica l Treatment

Becau se of th e variabilit y of sign s an d sym ptom s, it is difficu lt to t reat . For bin - ocu lar diplopia occlusion of on e eye can h elp, but it forces th e pat ien t to view m on ocularly.

Fresn el prism can be t ried if th e ocular deviat ion is stable for w eeks.Cru tch glasses are h elpful in th e case of ptosis.

Medica l Trea tment

An t ich olin ergic drugs such as pyridost igm in e (60 m g) th ree t im es a day. On e m u st be aw are of ch olin ergic crisis if too m u ch of pyridost igm in e is given . Th e pat ien t sh ou ld be told to stop if bu lbar sym ptom s or gen eralized w eakn ess occu rs.

Cor t icosteroids are used along w ith pyridost igm in e. Th e pat ien t sh ou ld be m ain tain ed on steroids for m on th s before t apering slow ly t apering. W h en th e pat ien t is m ain t ain ed on a low dose of steroids, th ere can be a relapse or un - m asking of gen eralized m yasth en ia.

Im m un osupp ressan t azath iop rin e is effect ive again st m yasth en ia at a dose of 2 to 3 m g/kg/day.

Cyclosporin e A, plasm aph eresis, m ycoph en olate, an d in t raven ous gam m a globulin can also be u sed in gen eralized m yasth en ia.

Surgica l Trea tment

Thym ectom y is ver y effect ive for ocu lar m yasth en ia. Th e resu lts of thym ectom y for gen eralized m yasth en ia are ver y favorable, w ith ~35%en tering com plete re- m ission an d 50%im proving.

Eyelid surger y or ptosis an d eye m u scle surger y for diplopia are con sidered on ly if it is st able for a few m on th s an d as a last resor t .

An t ibodies to acet ylch olin e receptors are th e et iology beh in d th e disorder.

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Eye Movement Disorders

Nystagmus

Nyst agm us is a rhyth m ic to-an d -fro oscillat ion of th e eyes. In nyst agm u s, gen erally th e m ovem en t in slow p h ase is in on e direct ion an d th e fast ph ase is in th e opposite direct ion . Th e fast ph ase of nystagm u s is m ediated by th e saccadic system u n - der all con dit ion s. On e or m ore of th e oth er system s w ill m ediate th e slow ph ase. It is im port an t to rem em ber th at nystagm us is given its direct ion based on the fast phase. Th is m ean s th at if w e say a nyst agm u s is to th e righ t , th e fast ph ase of th e nyst agm us is to th e righ t . Bu t act u ally, th e im por t an t poin t of nystagm u s is th e slow ph ase. So act u ally, nystagm us should be given its direct ion depending on the slow phase—but this is not done. An abn orm alit y in th e slow ph ase is m ore sign ifican t . But by conven t ion th e direct ion of nystagm u s is described by th e fast ph ase (Fig. 13.16A). Th e n ull zon e is th e field of gaze in w h ich th e in ten sit y of nystagm u s is m in im al, w h ereas in th e n eut ral zon e a reversal of direct ion of jerky nyst agm u s occu rs an d any of several bidirect ion al w aveform s, pen du lar nyst agm us, or n o nystagm us m ay be presen t .

Laten t nystagm u s is n ot n orm ally presen t w h en both eyes are open bu t is elicited on covering eith er eye. In th e classic case th e nystagm u s ap pears on closing on e eye. Bilateral jerky nystagm u s is seen w ith th e fast ph ase tow ard th e un covered eye. An oth er con dit ion , called m an ifest laten t nyst agm u s, occu rs in pat ien ts w ith am blyopia or st rabism u s w h o, alth ough view ing w ith both eyes open , are fixing m on ocu larly. Again th e fast ph ase is tow ard th e direct ion of th e in ten ded view ing eye. Th e ph en om en on of laten t nyst agm us is par t icu larly eviden t w h en th e visu al acuit ies of th e t w o eyes are un equal. Som et im es if on e eye h as ver y poor vision , on covering th e bet ter eye, in stead of nyst agm us a conjugate deviat ion of both eyes occu rs tow ard th e side of th e closed eye. Th is is called th e latent devia- t ion of Kestenbaum . Th e cause of laten t nyst agm us is u n kn ow n . It cou ld be due to lack of coordin at ion of th e supran uclear cen ters. It cou ld also be du e to th e fact th at th e nystagm u s w as laten t bu t kept in ch eck by convergen ce so th at abolit ion of th e im pu lse to bin ocu lar convergen ce allow ed it to becom e m an ifest .

Presentation

Types of Nystagmus

Pendular nystagm us: Th is con dit ion con sists of an u n dulator y m ovem en t of equ al speed an d am plit ude in both direct ion s.

Jerk y nystagm us: Jerky nystagm u s dem on st rates a biph asic rhyth m w h erein a slow m ovem en t in on e direct ion is follow ed by a rapid saccadic ret u rn to th e

origin al posit ion . Jerky nyst agm u s usually in creases in am p lit ude w ith gaze in th e direct ion of th e fast com pon en t . Th is is called Alexander’s law .

Micronystagm us: Micronyst agm us a nystagm u s th at is subclin ical; it is in capable of being detected w ith ordin ar y clin ical tests becau se of it s ext rem ely sm all

am plit ude. Th e diagn osis is apparen t by th e fixat ion pat tern , w h ich sh ow s a regu lar jerky t ype of nystagm u s w ith fast an d slow ph ases of ext rem ely sm all am plit ude w ith in th e p arafoveal areas so th at it m ay be revealed on ly by a careful exam in at ion w ith th e visu oscope or direct oph th alm oscope.

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Fig . 13.16 (A) Types of nystagmus. (B) Miner’s nystagm us.

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Fig . 13.16 (Continued) (C) Methods to treat nystagmus.

Gra des of Nystagmus

Nyst agm us is divided in to th ree grades:

Grade I: Jerky nyst agm us is eviden t on ly in th e direct ion of th e fast ph ase (i.e., on conjugate deviat ion to on e side).

Grade II: W h en in addit ion , it is eviden t in th e prim ar y posit ion .

Grade III: Eviden t in all p osit ion s of th e eyes.

Pathologica l Ocula r Nystagmus

Am aurot ic nystagm us: Nyst agm u s of p en dular or rarely jerky t ype m ay occur in th ose w h o h ave been blin d for a long t im e. Th e nyst agm us is som et im es con - stan t , an d at oth er t im es it appears on ly w h en at ten t ion is arou sed .

Am blyopic nystagm us: Th is is du e to a defect in cen t ral vision in both eyes, w h ich preclu des th e n orm al developm en t of th e fixat ion reflex.

Spasm us nutans: In th is th e nyst agm us occurs w ith h ead n odding. It is also called Dunkel syndrom e. It gen erally occu rs w ith in th e first year of life. Th e cause appears to be difficu lt y in m ain tain ing fixat ion , w h ich is frequ en tly associated w ith in adequate ligh t . Th ere is also in su fficien t con t rol due to in stabilit y of th e m otor cort ical cen ters in early life.

Miner’s nystagm us: Th is is an acquired occupat ion al disease of th e n er vous system w ith special m an ifest at ion s in th e ocu lar m otor app arat us, occurring in w orkers in coal m in es (Fig. 13.16B). Basically it is due to lack of illum in at ion . In th e early laten t stage th ere is a m ild nyst agm us. Th e acute stage is ch aracterized by t rem bling of th e h ead an d h an ds, w ith m arked nystagm u s, an d a path ogn om ic post ure of th e h ead being th row n back. Th e late psych opath ic st age is ch aracterized by cram ps, h eadach es, t rem ors, an d in som n ia. Th e nyst agm us

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is gen erally pen du lar in t yp e in th e prim ar y posit ion bu t frequen tly ch anges to th e jerky t ype on lateral gaze. Th e t reat m en t of th is con dit ion is to give th e pat ien t surface w ork an d im prove th e gen eral h ealth .

Vest ibular nystagm us: Th e sem icircu lar can als are th ree fin e t ubes arranged in th e ear. Th e lateral sem icircular can al is t ilted up 30 degrees. Norm ally th e eyes at rest are in th e prim ar y posit ion . Im pu lses go from each sem icircu lar can al to th e respect ive vest ibular n u clei. From h ere, th e im pu lse goes to th e opposite pon t in e gaze cen ter, w h ich in t urn con n ect s to th e sam e side sixth -n er ve n ucleus an d opposite side th ird -n er ve n u cleu s. Th e im pu lses th u s reach th e m e- dial an d lateral rect i an d th e eyes are balan ced an d in th e p rim ar y posit ion .

Cerebellar nystagm us: Th e exact m ech an ism of cerebellar nyst agm u s is n ot kn ow n . W h en nystagm u s occurs it is opposite th at foun d in a vest ibu lar lesion . In a righ t-sided vest ibular lesion , th e slow ph ase of th e nyst agm us is to th e righ t an d th e fast p h ase to th e left . Th is m ean s th e nystagm u s is to th e left , in oth er w ords opposite th e side of th e lesion . In cerebellar disease, th e fast ph ase of th e nyst agm us is on th e sam e side of th e lesion . So, if th ere is a righ t-sided cerebellar lesion , th e fast p h ase of th e nystagm u s is tow ard th e righ t side. Th is could be du e to th e floccu lo-oculom otor path w ay, w h ich w orks in th e reverse of th e vest ibular path w ay. Th e left vest ibu lar path w ay push es th e eyes to th e righ t , w h ereas th e left floccu lo-ocu lom otor p ath w ay from th e left cerebellu m push es th e eyes to th e left .

Cent ral nystagm us: In cen t ral nyst agm us, th e nyst agm u s is of th e jerky t ype. It is occasion ally presen t w h en th e eyes are at rest bu t u su ally develops on ly w h en th ey are deviated to on e or th e oth er direct ion . Th e nystagm u s is sym m et rical. Th is m ean s th at th e m ovem en t st art s at th e sam e angle of eccen t ricit y an d h as approxim ately th e sam e excursion w h eth er th e gaze is directed to on e or th e oth er side.

Differential Diagnosis

Volun t ar y eye m ovem en t s, dysm et ria, flut ter, opsoclon u s, m yoclon u s, spasm us n ut an s, opt ic n er ve gliom a, superior obliqu e m yokym ia, m yasth en ia gravis (qu iverlike m ovem en t s), ocular bobbing

Management

Man agem en t can con sist of t reat ing th e cau se, u se of prism s, or su rger y in w h ich th e Faden operat ion is perform ed . Th e m eth ods to t reat nystagm u s are sh ow n in Figure 13.16C. Th e t reat m en t can be gen eral, w h ere th e cau se is t reated, or specific, w h ich can be m edical or surgical. In m edical t reat m en t on e can im prove th e visu al acu it y by using prism s, base ou t , to sim u late fusion al convergen ce. On e can use prism s to elim in ate an om alous h ead post ures also. For a h ead t urn to th e left , th e n eut ral zon e is in dext roversion an d a p rism base ou t before th e righ t eye an d base in before th e left eye w ill sh ift th e eyes conjugately along w ith th e n eut ral zon e tow ard th e prim ar y posit ion . On e can also u se occlusion , in w h ich par t ial occlusion of th e sou n d eye w ith a n eu t ral den sit y filter decreases visu al acuit y in

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th e fixat ing eye to a level below th at of th e am blyopic eye bu t n ot dark en ough to elicit th e nyst agm us. Su rgically on e can perform th e Faden operat ion , in w h ich th e requ ired m u scle creat ing th e nyst agm us is sut ured to th e sclera at th e equator.

Internuclear Ophthalmoplegia

Lesion s affect ing th e path w ays by w h ich th e variou s ocu lar n u clei are lin ked togeth er [i.e., lesion s of th e m edial longit udin al fascicu lus (MLF) or m edial longit udi- n al bu n dle] produ ces in tern uclear oph th alm oplegia. Th e MLF con n ects th e th ird - n er ve an d th e sixth -n er ve n uclei. If a lesion occu rs in th is th ere is preven t ion of th e h arm on iou s coordin at ion of th ese n u clei in p rodu cing conjugate m ovem en t s. So on e eye carries ou t a volu n t ar y m ovem en t of gaze, w h ereas th e oth er eye does n ot , th us leading to failure of th e conjugate m ovem en t (i.e., both eyes m oving in th e sam e direct ion ). Th is leads to a m isalign m en t of th e eyes an d th us to diplop ia. Th is feat ure differen t iates th e in tern uclear palsies from th e oth er supran uclear lesion s.

Depen ding on w h eth er th e lesion is un ilateral or bilateral, various cau ses of in - tern uclear oph th alm oplegia are p resen t . Th e com m on cau ses are vascu lar lesion s or m u lt iple sclerosis (Fig. 13.17A).

Presentation

In tern uclear op h th alm oplegia (INO) m ay presen t as th ree t yp es as en um erated below :

Type I: In th is t ype, th e lesion is n ear th e th ird cran ial n er ve n uclei, in clu ding th e convergen ce area (Fig. 13.17B). Essen t ially th ere is paralysis of both m edial rect i. Th e im pu lses com ing from th e pon t in e gaze cen ter go to th e sixth -n er ve an d th ird -n er ve n u clei. Becau se th e con n ect ion s to th e sixth -n er ve n u clei are n ot affected n o dist urban ce is presen t in lateral rect us m ovem en ts. Th e eyes are divergen t ow ing to bilateral involvem en t of th e m edial rect i an d th ere is loss of convergen ce. It occu rs in hyper ten sive brain stem lesion s an d m u lt iple sclerosis. Divergen ce m ay be com plicated by skew deviat ion of th e eyes in w h ich on e eye m ay be u p an d ou t an d th e oth er eye looks dow n an d ou t . Th ere m ay be a seesaw nystagm u s presen t in w h ich th e eyes jerk u p an d dow n altern ately.

Type II: In th is relat ively com m on variet y of INO, th e MLF is dam aged an d th e m edial rect i fail to m ove syn ch ron ou sly w ith th e lateral rect i (Fig. 13.17C) on at tem pted lateral gaze to eith er side. Yet w h en each eye is tested alon e, th e m e- dial rect i fu n ct ion is eviden t but in com plete. Test th is by covering th e abdu ct ing eye an d m aking th e adduct ing eye follow th e finger. In t ype II INO convergen ce is n orm al because th e convergen ce area is n ot affected . Th is occurs in m u lt iple sclerosis, pon t in e gliom a, or en ceph alit is

Type III: Th e th ird variet y of INO occu rs in m u lt iple sclerosis. In th is t ype of INO (Figs. 13.17D,E), n on e of th e eye abdu cts com p letely, w h ereas addu ct ion is com plete. Th e relay to th e sixth cran ial n er ve n uclei is affected on both sides. If you test th e eye in dividually by closing th e oth er eye, th e eye w ou ld abdu ct , differen t iat ing th is from an in fran u clear lesion (sixth -n er ve palsy).

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