gonioscopy: gonioscopic lenses, principle and clinical aspects

GONIOSCOPY

- Dr samarth mishra

Term gonioscopy: trantas (1907) Susequently,goldmann introduced the gonioprism & barkan

mastered the art of gonioscopy.

It is not possible to visualize the angle of anterior chamber directly.

This is because of lack of transparency of corneo-scleral junction & total internal reflection of light ( emitted from the angle structures) at anterior surface of cornea.

The total internal reflection at the cornea occurs because the angle of incidence of the rays from the anterior chamber angle structures >critical angle of the cornea-air interface( ~46 degrees)

Gonioscopic contact lenses where refractive index is similar to that of cornea eliminate the optical effect of the front corneal surface.

Therefore, light rays from the anterior chamber angle

enter the contact lens and are made to pass through the new contact lens-air interface by one of the following two basic designs: Direct & Indirect gonioscopes

Type of goniolens:

A) Indirect goniolens: provides the mirror image of opposite angle.The light rays are reflected by the mirror in the goniolens and leave the lens nearly at right angle to the contact lens-air interface.

e.g-goldmann & zeiss goniolens

B) Direct goniolens: provide direct view of angle.The curve of contact lens is such that the light rays are refracted at the contact lens-air interface

e.g- koeppe goniolens.

General Procedure:

-pt is seated upright on a slit lamp.

-cornea anaesthetized with 0.5 % proparacaine or 4% lignocaine.

-1 drop of methylcellulose is placed on the concavity of goniolens.

-with pt looking up, one edge of of lens is positioned in the lower fornix.

-the upper lid is elevated & the pt is instructed to look straight.

-lens is rotated into position against the eye.

-lenses are sterilized with 2% glutaraldehyde, 1:10 sodium hypochlorite or can be rinsed with soap/water & allowed to dry.

when checking the lateral and medial angles,the slit beam should be horizontal and for superior & inferior angles,slit beam should be vertical.

Angle structures seen from behind forwards:

-root of iris-anteromedial surface of ciliary body/ciliary band-scleral spur-trabecular meshwork and schlemm’s canal-schwalbe’s line.

DIRECT GONIOSCOPY:

-performed with a steep convex lens.

-this permits the light from the angle to exit the eye closer to the perpendicular at the lens-air interface.

-these lenses are used with a portable slit lamp or an operating microscope.

-direct gonioscopy is useful but impractical for routine use.

types of direct goniolenses:

-koeppe goniolens: most commonly used for diagnostic direct

gonioscopy. Can be practiced in both outpatient as well as

OT available in two sizes: 16mm( infants) &

18mm(adults).

-huskin’s barkan’s lens: prototype surgical goniolens used for goniotomy.

(surgical lenses)

-swan jacob’s lens: also used for surgical purpose.

-richardson-shaffer’s goniolens: basically a small koeppe lens used in infants.

-worth goniolens: anchors to cornea by partial vacuum.

-sieback goniolens: it is a tiny goniolens which floats on the cornea.

-layden goniolens: for evaluating neonatal angle.

Advantages:

Greater flexibility because position of observer can be changed.

Panoramic view is obtained.so one part of angle could be compared with the other.

Angle becomes deep in supine position.so it is easy to see the angle.

Detailed examination of minor structures is possible.

Causes lesser distortion of anterior chamber.

Can be used in sedated/anaesthetized patients as in infants.

Provides a straight view rather than an inverted view.

Using two lens,both eyes can be examined simultaneously.

Can be used for surgical procedures like goniotomy.

Disadvantages:

Inconvenient

Annoying light relexes from cornea.

Time-consuming.

Benefits of slit-lamp (like variable light & better clarity) are not available.

Indirect gonioscopy:

Uses mirror/prisms to overcome the problem of total internal reflection.

Have an angled mirror through which the light rays from anterior chamber are reflected so that they emerge perpendicular to the lens-air interface.

Is uses the slit lamp’s illumination & magnification system to its advantage.

Commercially available gonioprisms:

Gonioprisms requiring coupling agents:

a) Goldmann three mirror gonioprismb) Goldmann two mirror gonioprismc) Goldmann single mirror gonioprsm.

A) GOLDMANN THREE MIRROR GONIOPRISM:

-mirror having inclination of 59 degrees & domed border is used for viewing the angle structures.

-goldmann goniomirror has broad area of contact(~12 mm) with cornea.

-so, under pressure it may artificially close the angle.

-the mirror inclined at 67 degree is used to examine pars plana area of ciliary body .

-the mirror having inclination of 73 degrees is used to examine ora serrara area of the peripheral fundus.

B)GOLDMANN TWO MIRROR GONIOPRISM:

-both mirrors are inclined at an angle of 62 degrees.-it needs to be rotated once to examine the whole angle.

C)GOLDMANN SINGLE MIRROR GONIOPRISM:

-mirror is inclined at an angle of 62 degrees.-It is a prototype diagnostic gonioprism.-it is rotated three times to examine the whole angle.

Advantages:-easy to use.

-excellent view.

-stabilizes the globe( can be used in laser trabeculoplasty)

-peripheral retina can be seen.

-goldmann two mirror gives best in situ view of angle.

Disadvantages:

-curvature of lens is more than that of cornea.so a coupling material is required.

-it blurs vision & fundus. So, field charting,direct & indirect ophthalmoscopy cannot be done immediately after its use.

-only one mirror is there for gonioscopy.so, it needs to be rotated 360 degrees.

-it cannot be used for indentation gonioscopy.

-broad area of contact with the cornea is there in case of goldmann three mirror & so can lead to artefactual closure of angle under pressure.

D) ALLEN THORPE GONIOLENS:

-it has got four prisms instead of mirrors.

-allows examination of the whole angle without rotating the prisms.

GONIOPRISMS NOT REQUIRING COUPLING AGENTS:

A) Zeiss four mirror gonioprism:

-it has four identical mirrors at 64 degrees.

-allows four quadrant examination without rotation of lens.

-by turning 11 degrees the smaller areas inbetween the mirrors can be visualised.

- Has a small area of contact with the cornea(~9mm).

Advantage of zeiss four mirror goniolens:-

coupling material not required.-easy to perform.-all 4 quadrants visible at same time.-indentation gonioscopy can be performed.-as coupling agent is not required,visualisation of

fundus is possible.

Disadvantage of zeiss four mirror goniolens:-difficult to master.-doesn’t stabilize the globe.-may open the angle artifactually.

B)POSNER GONIOPRISM:-same as zeiss gonioprism but is made of plastic rather

than glass.-has fixed rather than a detachable handle.

C)SUSSMAN LENS:-it has no handle.

D)TOKEL GONIOPRISM:-single mirror gonioprism.-has wider field of view.

ADVANTAGE OF INDIRECT GONIOSCOPY:

-easier-faster.-less instrumentation

-slit lamp provides better optics and lighting.

-corneal wedge can be used to localize angle structure.

-indentation gonioscopy can be done.

-magnified stereoscopic view of optic disc can be obtained.

DISADVANTAGE:

-comparison is not possible.

-limited positioning of light rays.

-difficult to perform in horizontal meridian.

-mirror image is seen, so confusing.

-excessive pressure may open or close the angle artefactually.

-exaggerates the degree of angle closure.

MANIPULATIVE GONIOSCOPY:

-The angle structures cannot be identified in eyes with a steep iris configuration & a narrow angle.

-this technique of manipulating the lens to visualize over a steep iris is known as dynamic/ manipulative gonioscopy.

-goldmann lens are used.

Patient is asked to look at the direction of mirror or the mirror is moved towards the angle being viewed.

-this allows us to look for peripheral anterior synechiae.

INDENTATION GONIOSCOPY/COMPRESSION GONIOSCOPY:

-if manipulation does not reveal the angle,it can be achieved by indentation.

-sussman four mirror lens is preferred,since it is held in hand while zeiss four mirror and posner lenses have to be held by handle.

-it requires more of patient’s cooperation.

-it helps us to differentiate between angle closure due to synechiae from appositional closure.

-indentation deepens appositionally closed angle because of aquaous being pushed in the angle.

Schematic drawing of gonioscopic findings:

Gonioscopy involves various systems of classifying the anterior chamber angle but they stop short of giving information about other pathologies seen.

Becker came out with a scheme of representing the gonioscopic findings which involves:-

-drawing a dark circle( depicting scleral spur)-drawing three lighter circles outside that for trabecular

meshwork.-drawing three circles inside it, depicting various levels of

insertion of the iris.-drawing the pupil at the centre.

A)NeovascularisationB)Peripheral anterior synechiaeC)Level of insertion of iris.D)peripheral iridectomy

Colour coding:

BIOMETRIC GONIOSCOPY:

New method for objective measurement of the anterior chamber angle.

Proposed by congdon et al.

performed with the help of a special reticule.

The anterior chamber angle is viewed under the following condition on a haag-streit 900 BM slit-lamp:ambient lighting from a small side lamp is used to provide only an indirect illumination with

a total magnification of 16x, power : 6W,middle filter setting slit lamp beam : 4mm length,1mm width.

The reticule is mounted on a slit lamp 10x ocular & ruled in 0.1mm units.

it is used to measure the distance between the insertion of iris & schwalbe’s line.

-if the angle is closed , a measurement of 0 is recorded.

-occludable angle is defined as one with an average measurement of 0.25 or less for four quadrants.

RP CENTRE GONIOSCOPIC GRADING:

Grade 0 – no dipping of beam

Grade 1 – dipping of beam

Grade 2 – SL &ant. 1/3rd of TM

Grade 3 – middle 1/3rd of TM

Grade 4 – post. 1/3rd of TM

Grade 5 – SS visualised

Grade 6 – CB visualised

Clinical uses of gonioscopy:

To differentiate b/w primary open angle glaucoma & primary angle closure glaucoma.

To diagnose Congenital glaucomas. Secondary glaucomas Angle recession glaucoma(ARG) Uveitic glaucoma Neovascularization ICE (Iridocorneal endothelial)

syndrome

Tumors of anterior segment Cyclodialysis Ciliary body cysts Intraocular foreign body Early detection of KF ring Unusual cases of glaucoma

e.g a haptic of posterior chamber lens protruding through the peripheral iridectomy.The resultant pseudophakic pigmentary glaucoma can only be diagnosed by gonioscopy.

To perform: - Argon laser trabeculoplasty -Laser iridoplasty -Laser cytophotocoagulation

Follow up of patient who had undergone -Peripheral iridotomy -Trabeculectomy

Indentation gonioscopy can be used to break an attack of acute angle closure glaucoma.

Some gonioscopy images…

SLIT LAMP PHOTOGRAPH.STROMAL EDEMA WITH DESCEMET’S FOLDINGS IS SHOWN IN THE INFERIOR CORNEA AFTER 20G PARS PLANA VITRECTOMY

THE PATIENT SHOWED THE TIP OF THE 20G VITRECTOR LODGED IN THE ANTERIOR CHAMBER

Sampaolesi line

Iris stromal cyst

View through Goldmann 3 mirror. The iris drapes over the ciliary body producing the characteristic "sine wave" or double-hump

This gonioscopy photo shows a haptic from a three-piece cataract lens that has poked through the iris and is sitting in the iris-cornea angle.

Axenfeld reiger syndrome: posterior embryotoxon & iris strands.

Angle recession

Limitation of gonioscopy:

Cannot be performed in painful inflamed eyes.

Difficult to perform in cases of acute glaucoma.

Contraindicated in abrasions, infection & corneal edema/opacity.

Mydriatics obscure angle by bunching up iris;therefore it is not possible to perform gonioscopy in such cases.

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