intra-operative gonioscopy: a key to successful angle...
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Intra-operative gonioscopy:a key to successful anglesurgeryExpert Rev. Ophthalmol. Early online, 1–13 (2014)
Shakeel Shareef*1,Wallace Alward2,Alan Crandall3,Steven Vold4 andIke Ahmed5
1Flaum Eye Institute, University of
Rochester School of Medicine and
Dentistry, 601 Elmwood Avenue,
Box 659, Rochester, NY 14642, USA2Department of Ophthalmology and
Visual Sciences, University of Iowa
Carver College of Medicine, 11190C
PFP, Iowa City, IA 52242, USA3John A. Moran Eye Center, University
of Utah School of Medicine, 65 Mario
Capecchi Drive, Salt Lake City, UT
84132, USA4Vold Vision, 2783 N Shiloh Dr,
Fayetteville, AR 72704, USA5Credit Valley Eye Care, 3200 Erin Mills
Parkway, Unit 1, Mississauga, Ontario
L5L 1W8, Canada
*Author for correspondence:
Tel.: +1 585 276 6104
Fax: +1 585 276 0292
Since its inception, gonioscopy has been primarily utilized for angle assessment, lasertrabeculoplasty and surgery limited to the pediatric age group. Three-fourths of a century wouldpass since Barkan’s description of goniotomy before intra-operative gonioscopy would come intovogue with the advent of micro-invasive glaucoma surgery. Over the last decade, several clinicaltrials have been conducted or are currently underway in evaluating devices and instrumentstargeting different surgical spaces within the angle. However, a rate-limiting step of successfulangle surgery requires good gonioscopy and has led to a renewed interest amongophthalmologists to master this skill. During this same time period, several goniosurgical lensprototypes have been introduced in the market with the goal of optimizing angle viewing includingclarity, globe stability, accessibility and simultaneous surgical manipulation of angle structures.Several non-gonioscopic methods have also been recently introduced to facilitate angle surgery.
KEYWORDS: angle surgery • anterior chamber angle • goniolens • gonioscopy • micro-invasive glaucoma surgery
Historical background‘Gonioscopy’ is a term coined by Trantas [1]
to describe a technique to visualize the irido-corneal angle structures [2]. Salzmann was thefirst to utilize a lens to directly view theangle [3]. Koeppe and Goldmann introduceddirect and indirect goniolenses in 1919 and1938, respectively [4]. With the introduction ofthe modern Zeiss slit lamp microscope in1920, significant advances in gonioscopy tookplace including angle evaluation in an uprightposition, accurate assessment of angle clo-sure [5], indentation gonioscopy to differentiateappositional angle closure versus peripheralanterior synechiae (PAS) by Forbes [6] andangle grading [7–9] including extent of trabecu-lar meshwork (TM) pigmentation [7]. Buildingon Tornquist’s [10] clinical description of pla-teau iris, Ritch [11] showed anterior chamber(AC) deepening confined to the central iriswith indentation versus peripherally as seen inrelative pupillary block. This was confirmedwith imaging [12] showing anteriorly displacedciliary processes at the iris root as the etiology.These discoveries spanning a century (FIGURE 1)
have laid the foundation for our currentunderstanding and approach to angle surgery.
In 1936, Barkan [13] first described goniot-omy using a special contact lens to directly visu-alize the angle. However, gonioscopic anglesurgery was limited primarily to congenitalglaucoma [14] until the US FDA approved theTrabectome (Neomedix) 70 years later in2006 [15] with a resultant expansion of anglesurgery beyond the pediatric age group.Although the ‘gold standard’ trabeculectomyhas shown successful long-term intraocular pres-sure (IOP) lowering [16], among Medicare bene-ficiaries from 1995 to 2004, Ramulu et al. [17]
showed a decline in filtration surgery in eyeswithout prior surgery by >50% from 1995 to2001. From 2001 to 2004, laser trabeculoplastyincreased by the same magnitude with a paralleltrend noted globally [18]. This increased utiliza-tion may reflect the trend to intervene earlier inglaucoma and avoid potential short- and long-term complications related to filtration andaqueous shunt surgery [19].
Micro-invasive glaucoma surgeryIndeed, with the introduction of micro-invasive glaucoma surgery (MIGS) [20–24] inthe last decade, there has been a major shift inthinking from an ab externo surgical approachto an ab interno one focusing on the natural
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drainage system instead of abandoning it and creating a newconduit with filtration or tube shunt surgery [25]. The defi-nition of MIGS [22] includes an ab interno microincision,minimal trauma, efficacy, high safety profile and rapidrecovery. Since FDA approval of the iStent (Glaukos) inJune 2012 [26], over 20,000 trabecular micro-bypass stentshave been sold for implantation [27] with 4000 devices usedin over 30 studies spanning 10 years [28]. Additionally, withthe prospect of taking anti-glaucoma medications indefi-nitely, a recent Canadian study suggests that there may be along-term cost savings to undergo angle surgery versus med-ications reflecting a trend toward earlier surgical interven-tion and less dependence on medications for thosediagnosed with early to moderate glaucoma [29].
At present, there are a number of publications and videos thatdescribe surgical techniques for a variety of MIGS proceduresincluding optimal hand positioning, instrument handling and inci-sion or device insertion in the angle [28,30–40]. This anatomicallyconfined space houses the semi-transparent TMmeasuring approxi-mately 700 microns [41] and provides access to three surgical targetdrainage routes within the angle (FIGURE 2): Schlemm’s canal (SC) viaTM, uveoscleral and sub-conjunctival space. There has been con-siderable investment in these surgical spaces to develop new MIGSdevices (TABLE 1). However, the rate-limiting step in achieving suc-cessful surgical outcomes requires good intra-operative gonio-scopy [42], the only means of viewing the proximal anatomy of theconventional outflow system and the uveoscleral pathway.A technology assessment report by the American Academy of Oph-thalmology noted that although anterior segment imaging can pro-vide quantitative measurements of the AC angle, it is not asubstitute for gonioscopy [43] not only in assessing angle structures,including degree of pigmentation, presence of blood or PAS, butalso its 3D relationship with the cornea and iris plane. Despite rec-ommendations by the American Academy of Ophthalmology Pre-ferred Practice Patterns in performing gonioscopy [44], only 49% ofMedicare beneficiaries underwent this procedure 5 years prior to
glaucoma surgery in 1999. Resources to train physicians in gonio-scopy through videography [45] and online teaching modules toobtain certification for surgical implantation have become available.Glaukos Corp. recently reported 572 physicians as being ‘fullytrained’ to implant their device [46].
Over the last decade, there has been an exponential growthin several different MIGS devices and procedures that havebeen FDA approved or authorized to conduct clinical trials.Such a growth demands good visualization in a surgically con-fined space for introducing surgical instruments to preciselymanipulate the delicate angle structures in order to optimizeoutcomes. During this same time period, a number of surgicalgoniolenses with varying properties have become commerciallyavailable to meet surgeon preference (FIGURE 3).
Intra-operative gonioscopyPre-operative gonioscopy needs to be performed in the office toascertain adequate viewing of the anatomic target routes for plan-ning purposes. In the presence of extensive PAS, surgical manip-ulation may not be possible. With appositional closure, however,angle surgery may still be possible following cataract surgery.
For successful angle surgery, attention needs to be first directedtoward external factors, which include patient cooperation, headpositioning and rotation, surgical microscope adjustment andsurgeon hand positioning. If a patient is anxious or has involun-tary eye movements, tolerability of topical versus alternate routesof anesthesia need to be taken into consideration. From a tempo-ral approach, the head is rotated approximately 30–40 degreesaway and the microscope is tilted 30 degrees toward the surgeon.The goal is to find the right combination of head and microscopeadjustments to optimize direct viewing of the angle parallel tothe iris plane and facilitate proper entry of instruments for surgi-cal manipulation [28]. Use of a coaxial light source with eitherxenon or halogen, high magnification, increased light intensityand a smaller diameter of light to reduce reflections provides foradequate illumination of the angle.
Trantas –1st to studyangle in human withlimbal depression anddirect ophthalmoscope;coined ‘gonioscopy’
Salzmann –viewed angle withcontact lens;described blood inSC
Koeppe – introducesdirect goniolens
Zeiss – introducesmodern slit lamp;Curran – describes angle closure
Barkan –described‘goniotomy’under directvisualizationwith contact lens
Goldmann –introducedindirect goniolens
Gradle andSugar – firstto grade theangle
Scheie –introducedpost-TMgrading scale
Shaffer –gradedanglewidth indegrees
Forbes –introducesindentationgonioscopy
Spaeth –graded irisinsertion, angleof irisapproach andconfiguration
1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 1970
Figure 1. Historical milestones in gonioscopy.SC: Schlemm’s canal.Adapted from Alward’s ‘A History of Gonioscopy’ [2].
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The surgical goniolens is held in the non-dominant handresting either on the forehead or cheek depending upon theeye being operated on. The lens is coupled to the corneal sur-face with a viscoelastic agent to eliminate any air bubbles. Thisallows the dominant hand to have access to the temporal inci-sion 180 degrees away from the nasal angle structures (FIGURE 4).
Second, for intra-operative gonioscopy, a number of factorsare desirable in a surgical goniolens [42] (FIGURE 5). These includeclarity in viewing the angle structures; absence of Descemet’sfolds; globe stability, particularly when using topical anesthesia;accessibility of instruments via the peripheral cornea; simulta-neous viewing and surgical manipulation of the angle structuresand fine tuning and positioning of the eye to optimize angle visu-alization. TABLE 2 outlines the physical properties of commerciallyavailable surgical lenses for intra-operative gonioscopy [47,48]
including corneal contact, static field of view (FOV), magnifica-tion, handle length and notable pros and cons for each lens. Alllenses can be steam sterilized. With exception of the Ahmed andOsher lens, all are direct gonio lenses. The variability in handlelength (72–88.5 mm) takes into consideration the engineering ofeach goniolens prototype encompassing optical performance,functionality and ergonomics including surgeon hand size, com-fort and fatigue [RAYMOND GRAHAM, PERS. COMM.].
The preferred ophthalmic viscosurgical devices (OVD) forangle surgery are the viscocohesive OVD as they are best forcreating and maintaining space, visualization and adequateaccess of instruments. During TM surgery where blood reflexcan occur upon entering SC, unlike a viscodispersive agentwhere heme can admix within the OVD, a cohesive forms abarrier and can serve to push aside the heme with additionalOVD injection.
In phakic eyes undergoing angle surgery, unlike SC micro-stents, the use of agents to induce pupillary constriction isimportant when implanting suprachoroidal micro-stents toplace tension and draw the iris away from the iris root facilitat-ing access to the target surgical site. In combined procedureswith SC implantation, some advocate angle surgery prior tophacoemulsification as there may be an alteration in transpar-ency of the cornea not only around the temporal keratomeincision, but also a generalized haze or edema due to endothe-lial compromise obscuring the angle view particularly in casesinvolving dense cataracts. Additionally, loss of globe rigidityfollowing cataract surgery can decrease visibility during surgicalmanipulation of the angle [28,49]. However, for suprachoroidaland sub-conjunctival devices, we prefer to implant them afterlens implantation in order to prevent irrigating into thesespaces during phacoemulsification.
Intra-operative gonioscopy can be used for both therapeuticand diagnostic purposes. In patients undergoing lensectomy forangle closure glaucoma, one can assess the angle before andafter lens removal to ascertain angle opening, identify presenceof PAS and consider performing goniosynechialysis. Duringtrabecular bypass surgery, gentle depression of the cornealwound with subsequent lowering of the IOP will result inblood refluxing into SC. This will allow for easy identification
of collector channels and targeted SC stenting during gonio-scopy. This can also be achieved with diagnostic provocativegonioscopy by increasing the episcleral venous pressure exter-nally with the goniolens resulting in focal reflex of blood intoSC facilitating stenting (FIGURE 5).
Barkan, the prototypical surgical goniolens [2,42], is a modifi-cation of the Koeppe lens, the latter primarily used for diagnos-tic purposes in children. The angle is viewed as an uprightimage in the absence of a mirror with no distortion [4]. TheSwan-Jacob (SJ) goniolens is a further modification with a han-dle enabling lens manipulation during angle surgery.A 9.5 mm contact, 90 degree FOV with a 1.2� image magni-fication enables adequate visualization to perform goniotomyand MIGS surgery. A variant of the SJ has a relieved anteriorwith an 8.0 mm contact increasing access to clear cornea forintroducing surgical instruments. It should be noted that over
1. Conventional outflow via trabecular meshwork (brown)
2. Uveoscleral outflow
3. Scleral/subconjunctival space
Schlemm’s canalwith collector channel draining to episcleral vessel externally
PotentialSuprachoroidal space between ciliary bodyand the sclera
Ciliary bodywith longitudinalmuscle fibers (red)inserting into thescleral spur(green)
Figure 2. Target angle surgical spaces.
Table 1. Surgical procedures/devices categorized byanatomic surgical space in the angle.
Micro-invasive glaucoma surgery
Targeted angle
surgical space
Trabecular
meshwork
Hydrus
iStent/iStent Inject
Trabectome
Excimer laser trabeculostomy
Gonioscopy-assisted
transluminal trabeculotomy
Suprachoroid CyPass
iStent supra
Sub-conjunctiva Xen
Future micro-invasive
glaucoma surgery in clinical
trials or yet to be
conceptualized
Intra-operative gonioscopy Review
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half a century earlier, Barkan modified the Koeppe lens for thesame purpose by flattening one side to allow passage of a knifefrom a temporal corneal approach [2]. With topical anesthesia,these lenses pose a potential risk for sudden involuntary ocularexcursions during surgical manipulation placing the patient atincreased risk for intra-operative complications including irido-dialysis or bleeding. Furthermore, excessive indentation during
angle surgery can lead to Descemet’s folds compromising angleclarity. Using the tip of a surgical glove to create a skirt aroundthe SJ lens, Nakasato-Sonn et al. [50] have used this design toelevate the lens 1–2 mm without touching the cornea and per-fused saline into this space via a 20-gauge cannula mounted tothe handle, eliminating air space, need for viscoelastic,Descemet’s folds and rinsing away any blood, thereby achievinga clear view in all cases when performing iridocorneal anglesurgery.
The debut of the Hill, Khaw and Ritch surgical goniolenses(FIGURE 3) represent additional alterations of the SJ lens [42]. TheHill Gonioprism has unique features that include a left andright hand version with the handle held in the non-dominanthand and an extended peripheral flange to help stabilize theglobe providing some back resistance to the eye tissue beingpushed away from the surgeon during surgical manipula-tion [28,47]. Ridges on the metal surface holding the optics pro-vide further eye stabilization. These specifications enable thesurgeon to optimally view the filtering angle parallel to the irisplane and not the peripheral corneal plane.
Unlike the SJ and Hill lens with a 90 degree FOV, both theKhaw and Ritch goniolens provide 120 and 160 degree pan-oramic FOV, respectively suitable for performing goniosyne-chialysis from one sitting position. The Khaw lens has aposteriorly attached fixation ring providing globe stabilizationwhereas with the Ritch, half the cornea closest to the surgeonis uncovered enhancing access to corneal incisions with instru-ments and permits placement of corneal sutures [47]. The Khaw
Hill –peripheralflange fixates globeKhaw –fixation ringstabilizes globe Ritch –
panoramiclens
Mori – 2 mirror designredirects gonio imageto coaxial position
Double Mirror –holding ring forambidextroushand control
Ahmed – 1.5x; ideal forgoniosynechiolysis; noneed to change sittingposition
iStent –FDA approvedJun’ 12 + CE
Marketed goniolenses
MIGS FDA approved devicesand select clinical trials
with start dates
Hydrus –(Phase 3) + CE(Jan’ 12)
XEN 45 Implant: (Phase 3) for ‘refractoryglaucoma’ (Jan’ 13)
iStent inject:(Phase 4)randomization to 2 stents or a prostaglandin(Sep’ 11)
Transcend vold goniolens – cleat ring fixation,control and rotation ofglobe; free floating lens
CyPass: : COMPASS study –Implant + CE in OAG (Sep’ 09)
iStent supra: (Phase 3) Implant + CE inOAG (Oct’ 11)
Trabectome:FDA approved2006
2004 2006 2008 2010 2012 2014
Figure 3. Timeline overlap of marketed surgical goniolenses with the US FDA-approved MIGS devices or ongoing clinical tri-als. With exception of Transcend goniolens (Transcend Medical Inc.), Ocular Instruments, Inc., provided launch year for each lensindicated. Select clinical trials with start dates accessed from [76]. Trabectome (NeoMedix Inc.); CyPass (Transcend Medical Inc.);iStent Supra, iStent inject and iStent (Glaukos Corp.); Hydrus (Ivantis Inc.); Xen implant (AqueSys). Note: Swan Jacob lens debuted priorto ’76; Osher lens debut ’96; Timeline not inclusive of all MIGS clinical trials.CE: Cataract extraction; OAG: Open angle glaucoma; COMPASS trial [77].
Figure 4. The non-dominant hand holding the goniolensenabling the surgical hand to enter temporally withinstrumentation. Inset: a combination of head and microscopetilt optimizes entry and surgical manipulation of angle structuresalong the iris plane.
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lens provides a 1.4� image magnification making it more suit-able for MIGS versus Ritch with a 0.73� magnification.
Ocular surgery is performed using coaxial illumination froman operating microscope. However, the SJ-style gonioscopiclenses require head and microscope repositioning resulting in acoaxial view from an oblique angle in addition to an increasedworking distance during angle surgery. Based upon principlesof the double mirror peripheral vitrectomy lens [51], a prototypedouble mirror gonioscopic lens was designed with two internalmirrors to allow coaxial illumination with upright image view-ing of angle structures [52] eliminating the need for head tilt ormicroscope adjustment. With a desire to monitor the 3D loca-tion of surgical instruments in the AC during surgery,Mori et al. [53] combined the two internal mirrors with a cen-tral direct path creating a ‘dual viewing system’ during gonio-surgery [54] (FIGURE 6). This provides not only clear visualizationof the angle with a wider 110 degrees FOV, but also the ACvia the central view. They randomized 20 patients undergoingangle surgery to either the modified lens or the SJ noting nocomplication in either group. However, the former eliminatedthe need to tilt either the microscope or the head >30 degreesduring surgical manipulation of the angle. They proposed useof their lens for all types of angle surgery including placementof trabecular micro-bypass stents.
The Ocular Ahmed Surgical Goniolens (FIGURE 7) is unique inthat it is an indirect surgical goniolens that can be rotated on ahandle enabling full view with a 1.5� magnification of theangle [42]. It is ideal for conducting goniosynechialysis fromone sitting position. However, the inverted image requires sur-gical dexterity in introducing and manipulating instruments inthe angle 180 degrees away from the viewing mirror [55].
The Transcend Vold Gonio Lens (TVG) [48,56], distributedby Volk Optical Inc. (TABLE 2), has a unique ergonomic designfeaturing several characteristics desirable in a lens during anglesurgery [57]. Unlike other goniolenses that form a continuumwith the handle, a free-floating lens is suspended from a hingeon the main handle offering multiple pivot points. This mini-mizes pressure on the cornea eliminating Descemet’s folds,thereby providing an unimpeded clear view of angle structureswithout AC distortion. Additionally, a 14 mm cleat ring at thebase of the handle enables globe stabilization and control coun-tering any involuntary ocular movements under topical anes-thesia during surgical manipulation reducing risk of intraocularinjury. It provides additional rotation in the axis of thepatient’s head turn to fine tune viewing of angle structuresreducing the amount of head tilt and microscope adjustments.Patient discomfort under topical anesthesia and sub-conjunctival heme from the cleat ring are potential adverseeffects.
Non-gonioscopic methodsA number of non-gonioscopic approaches to angle visualizationand surgery have been introduced. This may reflect alternativesfor novice surgeons or those not comfortable in performinggonioscopy. For those adept at performing gonioscopy, this
emerging technology may supplement their surgical skills inoptimizing patient outcomes post-operatively.
Several ophthalmic endoscope systems have been designedfor use in both anterior and posterior segment surgeries.Endooptiks, Inc. (Little Silver, NJ, USA) is FDA approved andwas introduced in 1991 [58]. The E2 endoscope model com-bines a light source, diode laser, aiming beam and a fiberopticvideo camera [59]. It has the advantage of eliminating head andmicroscope tilt, though it requires viewing on a monitor duringintra-operative surgery. Although frequently used for ab internocyclophotocoagulation to decrease aqueous production, theendoscope can be utilized in a variety of anterior segment intra-ocular procedures [60] including assessment of angle structuresin presence of opaque media or during goniosynechialysis [61].It has been used in identifying the exact extent and localizationof cyclodialysis clefts with subsequent lasering [62], endoscopi-cally guided goniotomy [63], excimer laser trabeculotomy [64]
Clarity
Absence ofdescemet’s folds
Globe stabilitySimultaneous viewing and surgicalmanipulation
Accessibility ofsurgical instrumentsin peripheral cornea
Figure 5. Desired characteristics in a surgical goniolens.
A B
Figure 6. Oblique angle vs. dual viewing system. (A) Obli-que co-axial illumination and angle viewing with Swan Jacobgoniolens requires head and microscope tilt. (B) Mori dual view-ing system with 2 internal mirrors allows co-axial angle viewingin primary phaco position eliminating need for tilt. Central viewallows 3D monitoring of surgical instruments in theanterior chamber.
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Table
2.Surgicalgoniolenses.
Lens
Image
Contact
(mm)
StaticFO
V(degrees)
Gonio
Magnification
Handle
length
(mm)
Pros
Cons
Hoskins-Barkan
9.0
–premature
infant
10.0
–infant
11.5
–adult
360
Pan
oramicview
ofentire
circumference
1.30�
None
Direct,uprightim
age;
nomirror;angle
viewed
innaturalstate;
no
distortion;examineeyes
simultan
eously[4]
Designed
fortransverse
goniotomysurgery
Needforexaminer
totilthead
or
scope;
difficultto
learn;less
magnificationvs
indirect
techniques
Ahmed
10.0
90
1.5�
72mm
(lens
withhan
dle
design)
Largemirrorprovides
magnifiedview
Elim
inatesneedfor
head/scopetilt
Opticaldesigncorrects
cornealastigmatism
Ample
access
tocornea
With360-degree
rotation,
goniosynechiolysiscan
beperform
edfrom
one
sittingposition
Invertedim
age
requires
surgical
dexterity
toview
andperform
angle
surgery
180degrees
away[55]
Mori
11.5
110
0.80�
21.6
(lens
height)
Properlyoriented
uprightim
ageofangle
Cen
tral
view
enables
viewingofinstruments
crossingacross
AC
2mirrordesignredirects
obliquegonio-imageto
coaxial‘cataract’surgical
position;allows
360-degreeviewing
Largelim
bal
aperture
givesaccess
tocornea
Elim
inateshead/scope
tilt
Minificationof
images;reduction
oflight
tran
smission;
rotationoflensmay
notbeergonomic;
absence
ofglobe
stab
ility
under
topicalanesthesia
Lensesarelistedherein
noparticularorder
withspecificationsobtained
from
OcularInstruments,Inc.
[47],excepttheTranscendVold
Gonio
Lensfrom
TranscendMed
ical,Inc.
[48].
AC:Anteriorcham
ber;FO
V:Field
ofview;MIGS:
Microinvasive
glaucomasurgery.
Photosusedwithpermissionfrom
OcularInstrumen
ts,Inc.
andTranscendMed
icalInc.
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Table
2.Surgicalgoniolenses(cont.).
Lens
Image
Contact
(mm)
StaticFO
V(degrees)
Gonio
Magnification
Handle
length
(mm)
Pros
Cons
Double
Mirror
9.0
90
1.20�
49.0
(lens
height)
SimilarfeaturesasMori
lenswithabsence
ofa
centralviewingsystem
.
Inaddition,
Largerim
age
mag
nification(1.20�)
Holding
ring–ergonomic
ambidextroushand
controlofgoniolens
duringsurgery
Red
uctionoflight
transm
ission;light
reflections;absence
ofglobestab
ility
under
topical
anesthesia
Ritch
10.8
160
0.73�
77.5
4.56(lens
height)
Halfofcornea
closest
to
surgeonisexposedfor
ease
ofaccessing
corneal
incisions,
introducinginstruments
andplacingcorneal
sutures.Providesdirect
panoramicview
for
160deg
rees;usefulfor
goniotomy
Minificationof
imag
es;needfor
headandscope
rotation;absence
of
globestability
under
topical
anesthesia
Hill-Rightand
Left
9.0
90
1.20�
77.5
Peripheral
flangehelps
stab
ilize
globeduring
surgicalmanipulation.
Right/lefthanded
(RLH
)
handlesfacilitate
lens
handling.Usefulfor
goniotomyandangle
surgeries
Needforheadand
scoperotation;RLH
han
dlesnotoptimal
for
goniosynechiolysis;
requiressurgeon
repositioning/
reseating
Lensesare
listedherein
noparticularorder
withspecificationsobtained
from
OcularInstruments,Inc.
[47],excepttheTranscen
dVold
Gonio
Lensfrom
Transcen
dMed
ical,Inc.
[48].
AC:Anteriorcham
ber;FO
V:Fieldofview;MIGS:Microinvasive
glaucomasurgery.
Photosusedwithpermissionfrom
OcularInstruments,Inc.
andTran
scendMed
icalInc.
Intra-operative gonioscopy Review
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Table
2.Surgicalgoniolenses(cont.).
Lens
Image
Contact
(mm)
StaticFO
V(degrees)
Gonio
Magnification
Handle
length
(mm)
Pros
Cons
Swan
Jacob
9.5
90
1.20�
88.17
Direct
view
goniolens;
designedforgoniotomy
Needforheadand
scoperotation;
potentialforglobe
movementunder
topicalanesthesia
duringsurgical
manipulation
8.0
90
1.50�
88.17
Direct
view
goniolens;
relievedanterior
increasesaccessibility
to
limbus/clearcorneafor
surgicalinstruments
Osher
Gonio
andPost
Pole
14.0
38
0.84�
72
Providesboth
angle
and
posteriorpole
view
Two60-degreegonio
mirrors
provide
(i)wide-view;
(ii)confirm
ationof
proper
hap
ticplacemen
t
ofAClens
Canrotate
lenswhile
holdinghandle
Minificationof
images;
narrow
FOV;
inverted
image
requiressurgical
dexterity
toview
andperform
angle
surgery
180degreesaway;
largecontact
diameterlim
its
access
toclear
cornea
with
instruments
Lensesare
listedherein
noparticularorderwithspecificationsobtained
from
OcularInstruments,Inc.
[47],excepttheTranscen
dVold
Gonio
Lensfrom
Transcen
dMed
ical,Inc.
[48].
AC:Anteriorcham
ber;FO
V:Field
ofview;MIGS:Microinvasive
glaucomasurgery.
Photosusedwithpermissionfrom
OcularInstruments,Inc.
andTranscendMed
icalInc.
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Table
2.Surgicalgoniolenses(cont.).
Lens
Image
Contact
(mm)
StaticFO
V(degrees)
Gonio
Magnification
Handle
length
(mm)
Pros
Cons
Khaw
11.5
120
1.40�
88.5
Posteriorlyattached
fixationringstab
ilizes
globeduringsurgical
procedures
Wide-field
view
lens
provides
clearAC
viewing
Usefulforgoniotomy;
highmagnificationmay
beidealforMIGS
procedures
Needforheadand
scoperotation;
potentialdiscomfort
from
ringunder
topical
anesthesia
Transcen
dVold
Gonio
Lens
9.0
90
1.20�
84mm
Cleat
ring
diameter:
14mm
Freefloatinglens–
suspendedfrom
ahinge
onmainhandle
elim
inatescornealfolds.
Multiple
pivotpoints
provides
undistorted
view
withnoAC
distortion
Cleatringprovides
globecontroland
fixation
Allowsfinepositioning
withrotation
Needforheadand
scoperotation;
potentialforsub-
conjunctivalhem
e
from
ringand
discomfortduring
globefixation/
rotationwithtopical
anesthesia
Lensesare
listedherein
noparticularorderwithspecificationsobtained
from
OcularInstruments,Inc.
[47],excepttheTranscen
dVold
Gonio
Lensfrom
Transcen
dMed
ical,Inc.
[48].
AC:Anteriorcham
ber;FO
V:Field
ofview;MIGS:Microinvasive
glaucomasurgery.
Photosusedwithpermissionfrom
OcularInstruments,Inc.
andTranscendMed
icalInc.
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and endocycloplasty to open the angle in plateau iris syndromeby lasering the ciliary body and its processes [65]. The expandeduse of endoscopy has also been demonstrated in iStent implan-tation (FIGURE 8; [66]).
In contrast to the endoscope, angle structure viewing canalso be achieved with the RetCam (Clarity Medical Systems,Inc., Pleasanton, CA, USA), an external fiber optic video cam-era system with a coupling gel placed on the cornea [42,67]. Sur-geons can document the angle with photography and video.Placement of an iStent is demonstrated using this technology(FIGURE 9).
Ianchulev [68–70] has demonstrated a gonio-free technique inimplanting the CyPass suprachoroidal micro-stent intra-opera-tively with ‘direct goniometry’. Via a <1.5 mm clear cornealincision, a tactile gonioprobe is introduced into the AC andadvanced until it comes into contact with the ciliary bodyinsertion 180 degrees away. The angle depth is then measuredto the limbus using a measurement scale built into the probe.Subsequently, during implantation, the CyPass micro-stent isintroduced via an inserter into the AC and advanced into thesuprachoroidal space. The stent is then disinserted from theinserter when the corresponding measurement scale on theinserter matches that of the probe. This ensures that the deviceis precisely advanced with the proximal collar remaining in theAC. However, currently this technique requires follow-upgonioscopic assessment to confirm proper collar placement(FIGURE 10).
An emerging technology is intra-operative optical coherencetomography for the anterior segment. The optical coherencetomography is integrated into the operating microscopeenabling scanning during live surgery. Non-contact, non-invasive cross-sectional imaging of the eye is obtained in ‘realtime’ before, during and after microsurgery [71,72]. It has thepotential to provide instant feedback enabling the surgeon toevaluate implantation of a device in relation to surrounding tis-sues and assess proper placement with the option to repositionor re-insert the device if necessary in order to optimizesurgical outcomes.
Expert commentaryA pre-requisite in caring for glaucoma patients is to becomeproficient in performing gonioscopy starting in the office set-ting. An excellent resource for learning angle anatomy andfamiliarity in both health and disease including videography isavailable [45]. Indirect goniolenses such as the four mirror arean ideal starting point due to their convenience and lack ofneed for viscous coupling agents [73]. Additionally, performingargon laser trabeculoplasty requires not only proper handlingof a goniolens in order to clearly view the iridocorneal angle,but also delivering laser burns at the junction of the pigmentedand non-pigmented TM [74], the same anatomic surgical sitefor introduction and implantation of the SC micro-stents. Per-forming direct gonioscopy prior to or following routine cata-ract surgery in the operating room suite or on volunteers inthe minor procedure room with the microscope are initial steps
Figure 7. Ahmed Goniolens 1.5� angle magnification.Note TM landmark in view.
Figure 8. Endoscopic placement of iStent.Note snorkel being tapped into SC with Inserter.
Figure 9. RetCam viewing of angle structures.Note the iStent implant to the left of the inserter.
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one can take in attaining proficiency in intra-operative gonio-scopy. Webinars, workshops and online training modules lead-ing to certification for implanting devices provide additionalresources in learning to perform gonioscopy prior to embarkingon angle surgery.
Intra-operatively, the use of any commercially available sur-gical goniolens in the setting of a peri- or retrobulbar block orgeneral anesthesia would suffice. However, under topical anes-thesia, We prefer a goniolens such as the Hill or TVG thatprovides added globe stability from involuntary eye movementsduring angle surgery, thereby reducing potential risk of intraoc-ular complications. Both lenses provide fine-tuning to bringthe angle into view by rotating the globe further in the sameaxis and direction as the patient’s head turn. Given that areasof greater TM pigmentation have been suggested to occur inclose proximity to collector channels [28,35], the TVG cleat ringenables globe rotation in the z axis 30 degrees in either a clock-wise or counter clockwise direction bringing such areas into thesurgeon’s view to precisely place a SC implant to achieve opti-mal IOP lowering.
In combined procedures with SC implantation, We prefer toperform angle surgery prior to phacoemulsification for a num-ber of reasons: the patient is maximally anesthetized at the startof the surgery both topically and with i.v. sedation to tolerateany discomfort that may arise from placement of the peripheralflange or cleat ring on the globe at the start of the surgery, thesurgeon has a ‘bird’s eye’ view of angle structures through apristine cornea and unaltered keratome incision prior to intro-duction of the phaco handpiece. This is especially importantwhen one is operating in a surgically confined space along theiris plane limited by the anterior chamber depth of 2–3 mm.Any alteration would compromise visibility and introduction ofinstrumentation to safely perform angle surgery. Contrast thiswith the ‘full’ view of the cornea in the supine position duringcataract surgery. We prefer a soft shell technique that allows tonot only coat and protect the corneal endothelium with a dis-persive OVD, but also to take advantage of the cohesive OVDproperties by injecting it to create space in the angle for reasonsalready mentioned to safely perform surgery in a controlledmanner.
The demand on ophthalmologists caring for adults withglaucoma to acquire this skill set is unprecedented, espe-cially in light of merger of angle surgery combined withsmall incision phacoemulsification using micro-instrumentation and topical anesthesia. Gonioscopy, atpresent, is here to stay. Gonioscopic-assisted angle surgerywill enable surgeons to intervene much earlier in the glau-coma disease spectrum, decreasing dependence upon medi-cations with associated non-compliance and adherenceissues [75]. Glaucoma is transitioning into becoming a sur-gically treatable disease improving a patient’s quality of lifeand potentially averting more invasive surgical procedures.
Five-year viewAs several goniosurgical lenses have become commerciallyavailable in the last decade, it is anticipated that this trendwill continue into the future with further modification ofexisting prototypes to meet the specific needs of novelMIGS procedures yet to be conceptualized as well as thosecurrently seeking FDA approval. Novel methods toanatomically delineate SC and the distal outflow pathwayeither via imaging or with a dye akin to fluorescein angiog-raphy (i.e., canalography) will enable precise gonioscopi-cally targeted angle surgery in areas with the largest cross-sectional area of collector channels, thereby customizingoptimal IOP lowering in a given patient. In addition, theintroduction of non-gonioscopic methods may reflect aparallel trend of growth that one may anticipate in thenext several years to meet the growing needs of surgeonsperforming angle surgery. Given the dynamic nature ofgonioscopy in providing 3D information, rather thanbeing replaced by technology, an integration of these twoapproaches may perhaps provide the ideal medium in pre-cisely performing angle surgery with the goal of optimizingoutcomes in helping glaucoma patients lead productivelives by preserving visual function.
Financial & competing interests disclosure
I Ahmed has been a consultant for Alcon, AMO, Aquesys, Glaukos, Ivan-
tis and Transcend. S Vold has been a consultant for and receives research
support from Transcend Medical. All royalties from the Transcend Vold
Gonio Lens are donated to the Glaucoma Research Foundation. The
authors have no other relevant affiliations or financial involvement with
any organization or entity with a financial interest in or financial conflict
with the subject matter or materials discussed in the manuscript apart
from those disclosed.
No writing assistance was utilized in the production of this
manuscript.
Figure 10. Collar of CyPass suprachoroidal shuntprotruding into the anterior chamber.Note presence of blood in Schlemm’s canal superior to the collar.
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Key issues
• Historically, gonioscopy has been utilized primarily for angle assessment, trabeculoplasty and goniotomy.
• With the advent of micro-invasive glaucoma surgery (MIGS), more than three-fourths of a century after Barkan’s description of
goniotomy, intra-operative gonioscopy has come into vogue expanding beyond the pediatric age group with a renewed interest among
ophthalmologists to master this technique.
• Several MIGS clinical trials have been introduced in the last decade focusing on different target surgical spaces within the angle.
• The key to successful MIGS surgery requires good gonioscopy. This has led to a parallel introduction and commercialization of several
surgical goniolenses to optimize angle visualization with a focus on clarity, globe stability, instrument accessibility and simultaneous sur-
gical manipulation of delicate angle structures.
• Non-gonioscopic methods have recently been introduced to facilitate angle surgery.
References
Papers of special note have been highlighted as:
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