|Year : 1981 | Volume
| Issue : 3 | Page : 173-176
An investigation of the mechanism of function of trabeculectomy (operation)
JD Batra, B Patnaik, G Singh, R Kalsi, BS Jain, DP Agarwal
Guru Nanak Eye Centre, Maulana Azad Medical College, New Delhi, India
J D Batra
Guru Nanak Eye Centre Maulana Azad Medical College New Delhi
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Batra J D, Patnaik B, Singh G, Kalsi R, Jain B S, Agarwal D P. An investigation of the mechanism of function of trabeculectomy (operation). Indian J Ophthalmol 1981;29:173-6
Since the introduction of Trabeculectomy a number of mechanisms of its function have been claimed to be operative by different authors e.g., (i) a simple fistulising operation, (ii) to provide a direct communication between the anterior chamber and Schlemm's canal by passing the diseased trabecular meshwork, (iii) by directly draining into the collector channels and aqueous veins by passing even the Schlemm's canal, (iv) acts by a localized cyclodialysis, (v) phenomenon of hyposecretion, (vi) the drainage is believed to be taking place through newly developed aqueous veins, flowing out through lymphatic channels and lastly drainage is said to be occuring through normal aqueous veins.
Therefore in this paper it is proposed to present some hard evidence on the mechanism of action of this operation.
| Material and methods|| |
Total of 64 glaucomatous eyes of 54 patients operated and followed up at this Centre is the subject material for this study.
These were placed in 2 groups
I. Group : (Cases operated for trabeculectomy)
This group was divided into two subgroups
(A) Eyes operated during the period of study
Twenty six eyes with difierent types of glaucoma (chronic simple glaucoma : 13 eyes; acute congestive glaucoma : 9 eyes; absolute glaucoma : 4 eyes) requiring glaucoma surgery were investigated preoperatively. Trabeculectomy was performed in all types of glaucoma by modified Watson technique, after controlling the tension.
(B) Eyes operated before the period of this study
This group comprised of 34 eyes with different types of glaucoma (chronic simple glaucoma : 26 eyes; acute congestive glaucoma : 6 eyes; secondary glaucoma : 2 eyes) which underwent trabeculectomy (by modified Watson technique) during the period of last 2 years.
II. Group (Eyes operated for glaucoma by other techniques)
Four eyes, out of which two had undergone iridencleisis and rest punch sclerectomy were also included in the present study.
Preoperatively in all the patients a brief history and visual acuity was recorded. Examination of anterior and posterior segments, intraocular tension by Applanation and Schiotz tonometer, tonography with a Mueller electronic tonometer, gonioscopy with Goldmann's single mirror contact lens were performed. Efforts were made to procure the retrospective detailed data of group II
Postoperatively in all the patients of Groups I & II, visual acuity, examination of anterior segment (especially the site of operation), ophtbalmoscopy, intraocular tension by Applanation and Schiotz tonometer, tonography were performed.
The site of operation was studied meticulously on the slit lamp. A note was made of the following points
- Whether obvious bleb was present or absent.
- If bleb was present, whether it was raised or flat.
- Whether bleb was localised or diffuse.
- Condition of the conjunctiva over the site of operation was noticed in terms of vascularity, avascularity and thinning (devitalisation). Fibrosis of the bleb or any fibrosis in the vicinity of bleb was noticed.
Insufficiently pressure regulated eyes were those where intraocular pressure was 21 mmHg or more.
An eye was said to be hypotonic when intraocular pressure was less than 6.5 mmHg. Out flow factlity was determined by conducting tonography using a Mullers electronic tonometer. C value was taken as normal when it was more than 0.17% suspicious when betwhen 0.13% to 0.17% pathological when less than 0.13 %.
Study of Aqueous Veins
Aqueous veins and drainage at the operation site were studied by the Fluorescein injection method.
This test was done in all the 64 eyes of Groups I & 11. In this test a drop of sterile fluorescein dye (2%) was instilled over the area of operation and slight pressure was applied on the globe, whereupon the flow of coloured fluid could be seen on slit lamp examination under Cobalt blue filter.
| Observations|| |
The facility of outflow in all the 51 pressure regulated eyes was normal (C> 0.18). The majority (43=84.31%) of the these eyes were showing a well formed bleb. The remaining 8 eyes had either flat or no bleb.
In the 20 eyes having well vascularised conjunctiva over the area of operation (bleb area) the average I.O.P. was 13.1 mmHg and C value 0.28.
The 31 eyes with areas of avascularity over the area of operation (bleb area) were having an average I.O.P. of 11.3 mmHg and C value 0.29
In the 37 eyes where there was no transconjunctival seepage of aqueous the average I.O.P. was 12.4 mm Hg. and C value 0.29. On the other hand the average I.O.P. was 10.9 mmHg. or C value 0.30 in 14 eyes where there was transconjunctival seepage.
The 4 eyes with hypotony the bleb had avascularity and thinning.
Most (8 out of 9) of the eyes with insufficiently regulated I.O.P. there was either flat or no bleb. There was only one eye in this group with a seemingly well formed bleb. However, the C value was low (C=0.09).
Out of the 60 eyes, well formed blebs were seen in 44 eyes (73.33%). Of these all but one were pressure regulated.
The remaining 16 eyes eyes where there was either flat or no bleb-50% (8 eyes) were pressure regulated and other 50% were not.
C Value : 32 eyes were tested for C-value pre-and post-operatively. Of these the average C-value of 27 pressure regulated eyes preand post-operatively were 0.06 and 0.28 respectively. The remaining 5 cases which were insufficiently pressure regulated the average pre-and post-operative C-values were 0.07 and 0.11 respectively.
Aqueous Veins (26 eyes) : Twenty six eyes were studied for aqueous veins both pre-and postoperatively. The number of aqueous veins in 22 pressure regulated eyes preoperatively was 28. Postoperatively they were reduced to 12. Aqueous channels carry aqueous more often in eyes with flat (4 out of 6; 66.5%) or no bleb (2 out of 2; 100%) than with well formed bleb (15 out of 43; 35%). On the other hand there were 11 aqueous veins seen preoperatively in 4 eyes which were insufficiently pressure regulated. The number did not change postoperatively. Study by Fluorescein Injection (Pre-and postoperative group)
Thirteen eyes with trabeculectomy were studied by intravenous fluorescein injection technique both pre and post operatively. Out of these 9 were pressure regulated (R.P.) and 4 were not (I.P.R.).
The number of channels draining aqueous before operation in 9 pressure regulated eyes were 23. After the operation these were reduced to 7. In remaining 4 eyes which were insufficiently pressure regulated the number of aqueous veins both pre and postoperatively remained at 11.
In one eye of P.R. group there was a relatively flat bleb draining aqueous well which had developed a new aqueous draining channel.
All these eyes were also studied by intracameral injection technique. Precisely the same was the observation. There after the eyes were studied by either technique.
(a) Pressure regulated 51 eyes (chronic simple glaucoma : 34, Absolute glaucoma : 4, acute congestive glaucoma : 13).
In 30 out of 51 eyes no aqueous veins could be demonstrated. However in all the 54 eyes with controlled pressure the dye was demonstrated in the subconjunctival tissue in the area of operation (bleb area). The value varied between 0.18 to 0.54.
Fourteen of these eyes also showed transconjunctival seepage of the dye as demonstrated by Seidel test.
In 2 eyes of this group the bleb was apparently flat (considered to have had no bleb). Both of them showed normal aqueous channels. But there were new aqueous channels draining aqueous from from the bleb area was seen one in each eye. The C-value in them was 0.20 and 0.27 respectively.
(b) Insufficiently Pressure Regulated : 9 eyes (chronic simple glaucoma : 5, Acute congestive glaucoma : 2, Secondary glaucoma : 2).
In all the 9 eyes aqueous veins were demonstrable. Though the bleb area showed fluorescence it was of very small quantity.
(c) Control group of conventional surgery for chronic simple glaucoma : 4 eyes (Iridencleisis : 2 eyes, Punch sclerectomy : 2 eyes.)
The pressure was regulated in all these eyes. There were no demonstrable aqueous veins. No no new channels either were visible. The C value varied between 0.30 to 0.37.
The blebs were localised, markedly thinned out and avascular and showed transconjunctival dye seepage
| Discussion|| |
After a study of the blebs in pressure regulated and insufficiently pressure regulated eyes, it is seen that by and large a well formed bleb means good drainage and introcular pressure control. However, no bleb or a flat bleb need not mean poor drainage or bad control. 50% of such eyes in this series, infact were well controlled. However, fluorescein study did show a good subconjunctival aqueous drainage in the pressure regulated eyes and a poor drainage in those where intraocular pressure was not well controlled.
What was even more interesting is that in one eye with apparantly well formed bleb but with insufficiently controlled intraocular tension and poor C value showed a deficient drainage of aqueous, studied by fluorescein injection technique.
Many authors in literature support the view of subconjunctival route of drainage of aqueous though their methods of study have been different. Only Benedikt has conducted the study in the manner in which the present study has been conducted i.e., colour marking of the aqueous with sodium fluorescein dye. In Benedikt's as well as in the present study, the subconjunctival route of drainage of aqueous was present in all the pressure regulated eyes.
Aqueous veins were also taking part in drainaging the aqueous after trabeculectomy in both the studies.
Benedikt has detected lymphatic vessels in his cases in the area of bleb. No such vessels has been found in the present study.
He has reported the presence of new channels in the area of apparent bleb in few eyes whereas no such channels were found in the present study.
The number of demonstrable aqueous veins either decrease or disappear after trabeculectomy in pressure regulated eyes. On the other hand in insufficiently pressure regulated eyes the number of aqueous veins do not decrease after operation. This is conformity with observation of Benedikt.
| Summary and conclusion|| |
It was noticed that a well formed bleb means goon drainage of aqueous and well controlled intraocular tension. However, no bleb or a flat bleb need not mean poor drainage of aqueous or bad control of intraocular tension. What was even more interesting was that the eye with apparently well formed bleb but with insufficiently controlled intraocular tension and poor C-value showed a deficient drainage of aqueous studied by fluorescein injection technique. Hence, the look of the bleb can not be the sole basis of assessment of the functioning quality of trabeculectomy. The fluorescein method of examination does provide direct and satisfactory evidence on the state of drainage of aqueous through the trabeculectomy wound.
The avascular spots on the conjunctiva over the operated area (bleb) seems to be due to localised stripping of the tenon's capsule from the conjunctival flap during operation has little to do with nature (degree) of drainage of aqueous.
The transconjunctival seepage of aqueous through the avascular areas seem to depend on the size of these areas and degree of devitalisation rather than nature of aqueous drainage.
Since controlled intraocular pressure (pressure regulated eyes) was associated with:
(a) Copious subconjunctival drainage of aqueous through the operated area (as demonstrated by fluorescein studies).
(b) A normal C-value.
(c) Decrease or disappearance of aqueous carrying channels (aqueous veins).
(d) Convincing evidence to prove that the cut ends of the Schlemm's canal at the edge of the operated area were obliterated. The mechanism of functioning of the trabeculectomy operation seems to be simple filtration through the operated area (points (a) and (b) ) and not a direct flow of aqueous through the cut ends of the Schlemm's canal and then the aqueous veins (points (c) and (d) ).
| References|| |
Benedikt, 1975, Zur wirkungsweise den Trabekulektomine Min. Mbl. Augen Heilk. 167: 679.