|Year : 1974 | Volume
| Issue : 3 | Page : 9-12
KR Mehta, SN Sathe, SD Karyekar
Municipal Eye Hospital, Grant Road, Bombay, India
K R Mehta
Municipal Eye Hospital, Grant Road, Bombay
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Mehta K R, Sathe S N, Karyekar S D. Trabeculectomy ab-externo. Indian J Ophthalmol 1974;22:9-12
Trabecular operations rank as one of the significant advances in the surgical treatment of glaucoma.
Trabeculectomy, a technique whereby localised excision of the trabecular meshwork is undertaken, has been designed to circumvent the trabecular obstructive site in glaucoma which is chiefly located in the region of the inner wall of Schlemm's canal.
Watson's modification of Cairn's operation of trabeculectomy ab-externo has proved to be an efficient antiglaucoma operation. This operation was performed in 135 cases. The merits and demerits of this operation are discussed.
| Observations|| |
135 eyes were subjected to trabeculectomy ab-externo with a resultant over all success rate of 77.8%. [Table - 1] gives the percentage of success in controlling the tension in different types of glaucoma.
The blebs were usually diffuse. [Table - 2] gives the ratio of blebs to quantum of lowered intraocular tension, the blebs were seen in 64.5% of cases, but if only the successful cases are considered, the percentage rises steeply to 80%, with diffuse blebs occuring three times more frequently than the larger focal blebs so typical of an iridencleisis operation.
A correlation between bleb formation, (focal and diffuse) and no bleb formation with tension control was evaluated utilising the outflow facility ('C' ratio). [Table - 3] shows the preoperative and post operative mean `C' values. The outflow is lower in the focal blebs but in the diffuse type it almost equates with no bleb. The corollary being that the outflow facility is helped but not hindered by the presence or absence of a bleb.
| Complications and failures|| |
[Table - 4] tabulates the tentative causes of failure. The immediate complications are linked to an inappropriate technique. Inaccurate positioning of the scleral flaps, inadequate removal of trabecular tissue and improper suturing of the flaps were only noted in the early cases and subsequently rarely occured. Hyphema was noted in seven cases. Flat anterior chamber was seen in two cases.
Trabeculectomy was repeated in another segment in 19 out of 30 cases where tension was not controlled after first operation. The tension was controlled in 47.3% of these cases [Table - 5].
| Follow up|| |
Though every attempt was made to maintain accurate follow up and regular attendance, we succeeded in only 96 of the successful cases. [Table - 6] briefly outlines the duration of follow up.
| Post operative visual acuity|| |
[Table - 7] displays the changes in the visual acuity following surgery. In 64.3% of the cases there had been no change, while in 19.80% there was a fall in one line and only in 16.1% of the cases the fall was over one line.
| Iridectomy in trabeculectomy|| |
In the first twenty cases iridectomy was done as a routine. Post operative gonioscopic examination revealed that in some cases the two limbs tended to adhere to the edges of trabecular excision with subsequent tension rise. Following this observation, iridectomy was done when (a) pre-operatively the chamber was shallow with marked goniosynechae (b) iris prolapse during trabecular excision (c) lenticular intumescence or a forward bowed iris.
| Discussion|| |
All surgical procedures for glaucoma aim at controlling the intra-ocular tension with minimum changes to the structural integrity of the eye. Trabeculectomy was conceived in an attempt to by-pass the juxta-canalicular trabecular block and permit aqueous to filter out via the cut ends of the Schlemm's canal, though there is controversy that in many cases filteration is playing important role to control introcular tension. Welsh  felt that blebs should be present for good control and created intentional fistula for bleb formation. Many workers do not agree with him. In our series 21 cases had a good control with no bleb [Table - 2].
The frequency of blebs as reported in the literature varies. Cairns  had five cases with blebs in his first series of seventeen and had blebs in 50% of his second group of 49 cases. Watson  reported that in 85% of his cases control was achieved but that the blebs were diffuse and barely visible.
The large focal blebs occured mainly in our earlier cases. With a better technique, and better apposition of the scleral flap the rate of bleb formation was reduced.
The answer to this vexing problem lies in a simple explanation that blebs are present and have to be looked for carefully as they may appear as a mere bogginess which diminishes as the time passes. Secondly, presence or absence of the bleb seem to be unrelated to outflow facility values and adequate tension control. There was a significant difference between preoperative and post operative outflow readings but there was no significant difference between diffuse blebs and the absence of blebs in the tension controlled series. This was also commented upon by Kessing  . It is understandable that an incorrectly done trabeculectomy with an incorrectly apposed scleral flap would drain fluid subconjunctivally, and on its sclerosis led to a tension rise but the reciprocal that bleb must be there for tension to control, is in our opinion, not true.
Gonioscopy confirms the correctness and precise placement of the trabeculectomy which shows a hiatus in the band of trabecular tissue corresponding in its rectangular shape to the shape of the excised portion in the early post-operative period. After sometime it shows much less obvious signs of surgical interference with blurring of incisional edges, and shows a shallow crater or pit in the trabecular band with loss of tissue at the apex. This blurring seems to proceed faster in eyes which get mild subacute iritis.
A recrudescence of tension rise is usually demonstratable in advance by gonioscopic evidence of internal scleral fibrosis.
The low result in absolute glaucoma may be attributted to an obliteration of the Schlemm's canal  .
The modern trabeculectomy operation has the undermentioned advantages:
- The integrity of the iris and depth of the anterior chamber are maintained. Shallow chamber is a rare.
- Incidence of hyphema is low.
- Surgical manouevers are performed under direct vision.
- There is low rate of infection as the thicker diffuse conjunctivotenon bleb is safe.
- Surgery in another quadrant can be repeated if the first operation fails.
| Conclusion|| |
Trabeculectomy was done in 135 eyes. Results in chronic simple and angle closure glaucoma are gratifying.
The post operative results are stable, (follow up 2-16 months). The technique is practicable and has low rate of complications.
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[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5], [Table - 6], [Table - 7]