Ординатура / Офтальмология / Английские материалы / Textbook of Visual Science and Clinical Optometry_Bhattacharya_2009

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Trabecular Meshwork (TM)

•It has a soft velvety appearance which contributes to it’s identification even in the absence of pigmentation.

•It is most easily identified at 12’o clock position since the typical pigmentation (Sampaoelesi’s line) which collects at the Schwalbe’s line inferiorly does not create any confusion.

•Anterior 1/3rd of the TM is nonfiltering and is usually devoid of visible pigmentation.

•Usually Schlemm’s canal is not visible during gonioscopy. Schlemm’s canal will be visible only when it is filled up with blood. Then it becomes visible behind the anterior nonpigmented 1/3rd of the TM.

Scleral Spur (SS)

•It is a narrow, solid, translucent and whitish band.

•Width of this band is ½ of the TM.

•It is most easily identifiable at 12’o clock position where it is least likely to be covered with pigments.

Iris Processes

•These are prominent in young people and decrease with advancing age.

•They should be differentiated from peripheral anterior synechias (PAS) when present. PAS simulates tiny volcanoes, some with the apices missing and others with the apices in place. PAS of inflammatory origin are prominent inferiorly whereas PAS developed from angle closure glaucoma are prominent at superior angles.

Ciliary Body (CB)

•Width of the ciliary body is same as the width of the trabecular meshwork (TM).

•If the width of the ciliary body band is wider than the TM band, then a suspicion of angle recession should be considered.

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•Instill one drop of topical anaesthetic (proparacaine HCl 0.5% or lignocaine HCl 4%) into the lower fornix of both eyes.

•Ask him to keep his eyes open. Place his chin and forehead firmly against respective rests.

•Fill half of the cup of the lens with coupling liquid (K-Y jelly, methylcellulose 2% or carboxymethyl cellulose 10%). Hold the lens in your dominant hand and ask the patient to look up. However, some newer 3-Mirror models are designed which require only normal tearfilm as the fluid interface.

•Retract upper lid of the patient firmly against the superior orbital rim with the other hand. Use ring finger of the dominant hand to retract the lower lid. Place the lower rim of the lens into the lower fornix and then position the lens quickly and gently against the cornea to avoid spilling of the coupling fluid. Ask the patient to look straight.

•During observation of the angle structures of the right eye, hold the lens in your left hand and vice versa. It is convenient to use an elbow rest on the slit-lamp table. Index finger of the hand holding the lens may be used to support on the patient’s upper eyelid.

•The incident light beam should be perpendicular to the mirror.

•After completion of gonioscopy the suction seal is broken by applying gentle pressure under the lower lid.

Standard Technique of Visualisation of Angle Structures

•While using the Goldmann 3-Mirror, use the dome-shaped mirror to view angle structures.

•Start with the mirror at 12’o clock position to visualise the 6’o clock, i.e. inferior angle. Sweep your gaze up from the pupillary margin to the angle recess and try to identify the angle structures particularly the velvety and pigmented trabecular meshwork. Then, set your gaze on the Schwalbe’s line. Note whether Sampaoelesi’s line is present or not.

•Now with your eyes focussed on the Schwalbe’s line, the gonioscopy lens is rotated clockwise so that your view moves from 6’o clock to 12’o clock through 9’o clock, never loosing sight of the Schwalbe’s line. As the mirror is rotated, the

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Technique of Zeiss 4-Mirror Gonioscopy

•The technique is quite similar with few exceptions.

•Coupling fluid is not required and the lens is simply touches the cornea after topical application of anaesthetic.

•The patient is asked to look straight at the fixation light.

•Achieve additional support by resting the hand holding the handle of the gonioscopy lens against patient’s check.

•Indentation gonioscopy is not possible with the Goldmann 3- Mirror gonioscopy lens. In this technique, Zeiss gonioscopy lens is gently pressed against the cornea. This is performed to distinguish angle closure between appositional and synechial. This manoeuvre will force aqueous humour into the periphery of anterior chamber. The interpretation is based on the following findings:

i.Synechial angle closure–It will remain closed even on indentation.

ii.Appositional angle closure–Previously hidden angle structure, e.g. trabecular meshwork will become visible on indentation.

•Zeiss lens has 4 identical mirrors. So, 4 quadrants are examined without rotation of the lens. The little areas in between the mirrors can be visualised by turning through the lens only few degrees (approx. 8°–12°).

DIFFERENT WAYS OF GRADING OF ANTERIOR CHAMBER DEPTH AND ANGLE OF THE ANTERIOR CHAMBER

Van Herick-Shaffer Technique

It is used for estimation of depth of the angle. The patient is seated in a slit-lamp. The thinnest slit beam is used to illuminate cornea perpendicularly near temporal limbus. The optical section thus created is viewed at 60° from the light source. Ratio between AC depth (cornea-iris distance visible as dark shadow) and corneal thickness (width of the optical section of cornea) is noted (Fig. 16-19).

•Grade 0 (closed): There is no black shadow, i.e. iris is in contact with the corneal endothelium.

•Grade I: AC depth is less than 25% of corneal thickness.

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image is erect, virtual, binocular and stereoscopic, i.e. 3-dimensional (Fig. 16-21). It is located 18 mm in front of the retina, if the Hruby lens is positioned 10–12 mm in front of the cornea (Table 16-3 and Fig. 16.21). The concave surface of the lens should face the cornea.

GOLDMANN 3-MIRROR LENS

Fig. 16-22: Goldmann 3-Mirror Lens with functions of different mirrors

Mirror A (59°) dome-shaped = Gonioscopy, to view pars plana and extreme retinal periphery

Mirror B (67°) square-shaped = To view retina from equator to periphery, i.e. ora serrata

Mirror C (73°) largeand oblong-shaped = To view retina from equator to outer periphery of 30° of posterior pole of retina Mirror D (- 64.00D) central = To view central 30° of the posterior pole of retina.

Technique

•Pupil should be maximally dilated with instillation of tropicamide 1% and phenylephrine HCl 5%.

•Insertion technique is discussed in details in Goldmann 3- Mirror gonioscopy.

•However, the use of the 2-Mirrors angled at 67° and 73° (Fig. 16-22) for peripheral retinal examination needs elaborate discussion. The image is simply inverted but lateral orientation is not reversed. The retinal area facing the mirror is viewed.