intra-operative gonioscopy: a key to successful angle...

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

[email protected]

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

informahealthcare.com 10.1586/17469899.2014.973022 � 2014 Informa UK Ltd ISSN 1746-9899 1

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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].

Review Shareef, Alward, Crandall, Vold & Ahmed

doi: 10.1586/17469899.2014.973022 Expert Rev. Ophthalmol.

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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


[47],excepttheTranscen

dVold

Gonio

Lensfrom

Transcen

dMed

ical,Inc.

[48].

AC:Anteriorcham

ber;FO

V:Fieldofview;MIGS:Microinvasive

glaucomasurgery.



andTran

scendMed

icalInc.



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Table


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

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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

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www.youtube.com/watch?v=T9Ss3YTa_go

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www.youtube.com/watch?v=mZlvHZjQR6A

www.youtube.com/watch?v=mZlvHZjQR6A








www.gonioscopy.org

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www.youtube.com/watch?v=itZ4Y39Vj_4

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http://eyetube.net/video/endoscopic-istent-placement-with-ecp/

http://eyetube.net/video/endoscopic-istent-placement-with-ecp/

https://eyetube.net/video/cypass-microstent-implantation-technique-goniometric-implantation-without-use-of-gonioscopy–huled/




www.opmedt.com/index.php/en/intraoperative-oct-eng?id=50:oct-kamera-fuer-moeller-hi-r900a




www.clinicaltrials.gov

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www.compassclinicalstudy.com


http://informahealthcare.com/action/showLinks?system=10.3109%2F02713683.2012.700757

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