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Ophthalmology Review

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Ophthalmology short review for USMLE
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  Case 29 FLAT ANTERIORCHAMBER Martha Motuz Leen,M.D.HISTORY  A 53-year-old woman with a history of bilateralchronic angle-closure glaucoma presented witha shallow anterior chamber in the right eye 1 day after a mitomycin trabeculectomy.Examination revealed a visual acuity of 20/400 in the right eye and 20/40 in the left eye.In-traocular pressures (IOPs) were 24 mm Hg in theright eye and 12 mm Hg in the left eye.Slit-lampexamination of the right eye showed a moderately elevated filtration bleb that was negative for Seideltesting.The anterior chamber was shallow withiridocorneal contact extending from the periphery to within 1 mm of the pupillary margin.Centralshallowing was also present with a posteriorchamber intraocular lens located 0.5 mm posteriorto the corneal endothelium.Anterior chambercells were graded 3  .A surgical iridectomy wasconfirmed to be patent since ciliary processes wereeasily visible.Slit-lamp examination of the left eyeshowed a filtration bleb,deep anterior chamber,patent surgical iridectomy,and pseudophakia.Fundus examination demonstrated a poor view with an excellent red reflex in the right eyeand moderate glaucomatous cupping with anotherwise unremarkable retina in the left eye.B-scan ultrasonography of the right eye revealeda flat retina and absence of choroidal effusions. DIFFERENTIAL DIAGNOSIS— KEY POINTS 1. Shallowing or flattening of the anterior chamber  after filtration surgery is common,especially in the early postoperative setting.It is usefulto identify those clinical features that are typ-ical of each of the potential causes of shal-lowing (Table 29–1).For instance,if the IOPis low,overfiltration or choroidal effusionsare suspected.If the IOP is normal or high,pupillary block,choroidal hemorrhage,andaqueous misdirection are considerations.It isalso useful to classify whether shallowing of the anterior chamber involves the periphery only or both central and peripheral areas(Figs.29–1A  and B).Using bleb height as a criterion for differentiating diagnoses is notas helpful,since the bleb may be either highor low with each of these entities.In additionto these features,the response to a surgicalconfirmatory intervention,an iridectomy,canpoint to the correct diagnosis. 2. Overfiltration is the most common cause of shallow anterior chamber after filtration sur-gery.In the early postoperative period,over-filtration may occur through a large bleb orloose scleral flap with little resistance to out-flow,a conjunctival buttonhole,a conjuncti- val wound leak,or a cyclodialysis cleft.In thelater postoperative period,overfiltration may occur by transudation or leak from a blebthat is avascular and very thin,especially if antimetabolites were used.Chronic overfil-tration itself without hypotony is not ex-pected to shallow the anterior chamber asthe hydrostatic pressure in the anteriorchamber and vitreous cavity equalize.How-ever,when overfiltration is associated with alow IOP,the ciliary body and choroid tend tobecome diffusely edematous.This results inan anterior rotation of the ciliary body,lead-ing to shallowing of the anterior chambercentrally and peripherally in phakic andpseudophakic eyes.A patent iridectomy isidentified.Choroidal effusions are not pres-ent on fundus examination,but overfiltrationis often a precursor for their development. 3.  A choroidal effusion is an accumulation of serous fluid in the suprachoroidal space,most commonly in eyes that are severely   hypotonous in the early postoperative pe-riod.Although the suprachoroidal spacemay be considered one continous area,firmconnections of the choroid to the sclera at the vortex veins and optic nerve head lead to a lob-ulated appearance of choroidal effusions.Thisresults in an anterior rotation of the ciliary body with shallowing of the anterior cham-ber both centrally and peripherally in phakicand pseudophakic eyes.The presence of thisfluid contributes to a vicious cycle of reducedaqueous production and possibly enhanced 114 S ECTION IIIG LAUCOMA  ã TABLE 29–1 Causes of Shallow Anterior Chamber  Anterior Chamber Relief with Common Diagnosis Shallowing IOP Iridectomy Features Overfiltrationcentral and peripherallownobleb leak often presentChoroidal effusioncentral and peripherallownolight-brown choroidalsPupillary blockperipheral onlynormal or highyesiris bombéChoroidal hemorrhagecentral and peripheralnormal or highnodark-brown choroidals;acute pain Aqueous misdirectioncentral and peripheralnormal or highnohistory of chronic angleclosure glaucoma FIGURES 29–1 Differentiation of (A) peripheral shallowing from (B) peripheral withcentral shallowing.In (A),the anterior chamber is more shallow peripherally than cen-trally due to iris bombé,as seen with pupillary block.In (B),the anterior chamber is moreuniformly shallow despite a patent iridectomy due to anterior rotation of the ciliary body,as seen with overfiltration,choroidal effusion,choroidal hemorrhage,and aqueous mis-direction.(Reprinted with permission from Skuta GL.The angle closure glaucomas.In:Kaufman PL,Mittag TW,assoc eds. Glaucoma.  Vol.7.In: Podos SM,Yanoff M,eds. Textbook of Ophthalmology. Philadelphia,PA: Mosby-Year Book; 1994:8,23.)  uveoscleral outflow,in turn aggravating hy-potony and the tendency for more choroidaleffusion.Overfiltration is often identified asthe initial cause of hypotony.A patent iridec-tomy is present.Smooth light-brown or tanchoroidal elevations are seen on funduscopy.In some cases,choroidal effusions are very low and can’t easily be discerned without ul-trasonography.In severe cases,surgicaldrainage of straw-coloredsuprachoroidalfluid reverses the cycle. 4.  Pupillary block occurs when there is appositionof the iris to the lens in phakic or pseudopha-kic eyes,or to the anterior vitreous face inaphakic eyes.The aqueous is unable to flow anteriorly and accumulates just beneath theiris causing a convex bowing of the iris (irisbombé).Peripheral anterior chamber shallow-ing results in appositional closure of the angle.It is important to recognize that the centralchamber tends not to be as shallow.The IOPmay be normal initially and then progressively elevated.A patent iridectomy is not present. Although creation of an iridectomy is a routinepart of most glaucoma filtration surgery,acomplete opening may not always be present, with underlying iris pigment epithelium stillintact or iris incarceration into the sclerotomy.The iridectomy may also become obstructed with ciliary processes,blood,or vitreous,orbecome bound down by synechiae in an in-flamed eye.If the surgical wound was dis-sected too posteriorly,ciliary body tissue ratherthan iris may have been excised.The anteriorchamber will readily deepen after an iridotomy is created.If there is any doubt about its pa-tency,another iris opening should be created. 5.  A choroidal hemorrhage is an accumulationofblood that occurs in the suprachoroidalspace in either the early or the late postoper-ative period,usually acutely and in associa-tion with severe pain.The ciliary body rotatesanteriorly,shallowing the anterior chamberperipherally and centrally in phakic andpseudophakic eyes.Since the choroidal cir-culation is not subject to autoregulation,hy-pertensive patients with fragile vessels may be unable to accommodate the increasedchoroidal blood flow when the IOP islowered,increasing the risk of choroidalhemorrhage.Aphakic eyes may also be athigher risk.Unlike choroidal effusions,theIOP tends to be normal or high.A patent iri-dectomy is present.Smooth dark-brown orred choroidal elevations are seen on fundus-copy,sometimes requiring ultrasonography for confirmation when small in size.In se- vere cases,surgical drainage of red or dark-brown suprachoroidal fluid is required. 6.  Aqueous misdirection occurs when aqueousisunable to flow anteriorly past a relativeblock at the junction of the ciliary processes,lens equator (when present),and anterior vitreous face.Subsequently,aqueous is di- verted posteriorly within or adjacent to the vitreous body (Fig.29–2). As the aqueous ac-cumulates the vitreous is displaced forward,causing anterior ciliary body rotation andC  ASE 29F LAT  A  NTERIOR  C HAMBER   115 ã FIGURE 29–2  Aqueous misdirection in a phakiceye.Apposition of anteriorly rotated ciliary processes,lens,and anterior hyaloid (arrows) predisposes to pos-terior misdirection of aqueous (A) into the vitreous cav-ity.The lens and iris become progressively displacedanteriorly,closing the angle,and increasing the IOP.(Reprinted with permission from Skuta GL.The angleclosure glaucomas.In: Kaufman PL,Mittag TW,assoceds. Glaucoma.  Vol.7.In: Podos SM,Yanoff M,eds. Text-book of Ophthalmology, Philadelphia,PA: Mosby-YearBook; 1994:8,21.)  shallowing of the anterior chamber periph-erally and centrally.This can lead to a viciouscycle as the aqueous volume continues to in-crease in the space behind the vitreous,thepermeability of the compressed vitreousbody decreases further,and the apposition of the anterior hyaloid face with the ciliary processes and lens equator worsens.The IOPmay be normal initially and become progres-sively elevated as the cycle continues.Thepresence of a patent iridectomy must be con-firmed,and choroidal elevations are gener-ally not present.Aqueous misdirection canoccur in the early postoperative period orlater when cycloplegics are discontinued.Itmost commonly occurs after surgery on pha-kic eyes with chronic angle-closure glau-coma.Terms that have been used synony-mously with aqueous misdirection include ciliary block and malignant glaucoma.  A wide spectrum of presentations is possi-ble with each of these diagnoses,and more thanone can occasionally occur as a sequence of events.For example,an eye with chronic angle-closure glaucoma may have developed a woundleak resulting in hypotony with initial choroidaledema,then progressing to a small anteriorchoroidal effusion.As the ciliary body rotatesforward and the anterior chamber shallows,greater apposition occurs between the anteriorhyaloid,ciliary processes,and lens equator.Thisleads to misdirection of aqueous posteriorly  with progressive shallowing of the anteriorchamber and elevation of the IOP.Therefore,presence of a choroidal effusion does notentirely eliminate the possibility of aqueousmisdirection.In this example,drainage of thechoroidal effusion alone might result in reversalof aqueous misdirection. TEST INTERPRETATION Slit-lamp examination of anterior chamber depthmay reveal shallowing in the periphery only withan iris bombé configuration,features that wouldbe suggestive of a pupillary block mechanism.If the anterior chamber is shallow both centrally and peripherally,choroidal thickening,choroidaleffusion,choroidal hemorrhage,or aqueous mis-direction would be more likely.The bleb is inspected and checked for pin-point leaks and for slow transudation,especially if the tissue is very thin.A Seidel test can be per-formed to identify an area of leakage or transuda-tion by painting a bleb or incision site with a fluo-rescein strip and viewing the area with a cobaltblue light.Although a pinpoint leak can usually beseen immediately,delineation of an area of blebtransudation may require several seconds of ob-servation.If present,overfiltration with choroidalthickening,or choroidal effusion,is suspected.Determinination should be made if aniridectomy exists and is patent.Even with a pre- viously patent iridectomy,it may become blocked with iris,vitreous,blood or become bound downto the underlying lens.If a patent iridectomy isconfirmed,pupillary block can be ruled out,butnot the other entities.If ciliary processes are seenthrough a patent iridectomy and appear to beanteriorly rotated,or in apposition against the vitreous,aqueous misdirection is suspected.If there is any question of the patency of the iridec-tomy,it should be opened or a new iridotomy created with laser.If shallowing readily reversesas a result,a diagnosis of pupillary block is made.If the iridectomy is patent,the pupil shouldbe dilated.When choroidals are larger,they areeasily identified on fundus examination,appear-ing smooth and dome-shaped and varying fromone to four in number.The convex choroidalsmay occasionally be extensive enough that they meet in the mid vitreous,often referred to as“kissing”choroidals.Choroidal effusions tend tohave a tan or light-brown appearance,whereaschoroidal hemorrhages tend to have a dark-brown or red appearance.If choroidals are notseen,careful evaluation of the vitreous may sug-gest optically empty pockets indicative of fluidaccumulation typical of aqueous misdirection. A small pupil may prohibit adequate visu-alization of the posterior pole.In such cases,conventional B-scan ultrasonography is useful toidentify choroidal elevation or choroidal thick-ening.Utrasound can also help differentiatebetween a choroidal effusion that is echolucent,or choroidal hemorrhage that is echogenic. 116 S ECTION IIIG LAUCOMA  ã

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Jul 23, 2017
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