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The Role Of Trabeculectomy In The Treatment Of Glaucoma: Predicting the Need For Surgical Intervention


In the treatment of glaucoma, surgical intervention is considered as a last resort, which should be performed only after an unsuccessful medical treatment. This view is based on three main arguments:

  1. There is wide and expanding range of possibilities for medical treatment
  2. As opposed to other surgical interventions, anti-glaucoma operations are not followed by immediate and impressive change of the visual functions.
  3. By itself, the intraocular tension reduction reached by the operation will not always halt the progress of glaucoma.
Because of these, doctor and patient will initially reject surgical intervention. However, surgery will eventually be inevitable, and it will take place at the time when serious functional damage has already developed. This explains the reason why the recent years' literature contains so few references on trabeculectomy, that are useful for statistical purposes. A rare exception is Alemu's over 400 cases in Ethiopia.
At the Eye Department of Saint John Hospital, Budapest 169 trabeculectomy were performed during the last 4 years, and of these 142 patients were followed for at least one year. The patients were classified in three groups, based on the severity of visual field defect. The patients with none or minimal visual field defect are in group 1. Those with medium visual field defect are in group 2,  and group 3 contains the ones with severe visual field defect. (Table 1)
 
Group 1 Group 2 Group 3
Number of patients 24 46 72
Sex (male/female) 7/17 16/30 31/41
Average age 60.6 65.9 73.7
Age 52-68 46-79 32-87
Table 1.: The patient groups

All of the operations were performed by the same surgeon using the same method: limbus based conjunctival flap and wide basal iridectomy through the trabeculectomy.
Of the 142 patients, 16 had narrow angle glaucoma and 126 had open angle glaucoma (of these 12 cases with pseudoexfoliation) . With the exception of three, all patients were subject to earlier medical treatment for several week, months or even years. They all had incorrigibly high intraocular tension before the operation.
The surgical intervention was considered successful if the intraocular tension dropped below 20 mmHg.
Figures 1 and 2 show the intraocular tension 6 weeks and one year after the operation. While the patients in the first group had normal intraocular tension after one year, the patients in the third group had suffered a setback after the initial good results. Practically this meant that for these patients in was necessary to restart medical treatment.
 

Figure 1.: IOT 6 weeks after operation

 
Figure 2.: IOT one year after operation

The change in the visual acuity is similar: in group 1 the visual acuity improved in more cases than in which it decreased. however, in group 3 there were only few cases with improved visual acuity.  (Figure 3).
 

Figure 3.: Visual acuity one year after operation

The most promising results were achieved with the visual field. The number of patients with improved visual field is much higher than the number of cases with worse result. This is specially true for group 3.  (Figure 4).
 

Figure 4.: Visual Field 6 weeks after operation

For these patients the improvement in the visual field was not only measurable but visible for the patient also. See visual field charts.
Most of the early complications of the surgery were haemorrhage in the anterior chamber and iritis, while later cataract was common (Figures 5 and 6). While cataract may be of serious concern for the patient and the doctor, it can be surgically treated at a later time. After the successful lens implantation, patients have experienced large scale improvement, even in the case of group 3.
 

Figure 5.: Complications after 6 weeks

 
Figure 6.: Complication after 1 year

If the success of the surgery is defined as the reduction of intraocular tension, than surgical intervention performed on patient group 1 were in 100% successful. In group 2 the percentage of success is 82%, and in group 3 it is 73%.
Thus we can safely assume, that in certain cases the surgical treatment of glaucoma can be used as a first treatment.
If surgery is used at the time of large scale functional damage, after an unsuccessful medical treatment, then the results are not so good. This also means, that the sooner the decision is made for surgery, the better the results will be.
During a retrospective analysis of our surgical cases, we were collecting those symptoms, that indicate the necessity of a surgical intervention. Based on the results obtained, a scoring table were developed to predict the need for surgery after glaucoma attack (Table 2) and primary glaucoma (Table 3)..
 

Symptoms Score
Pupil remains dilated 1
Pupil irregular 1
IOT over 24 mmHg 2
IOT borderline 1
Chamber angle mainly closed 1
Surgery if total score is at least  2
Table 2.: Predicting the need for surgery after glaucoma attack

 
Symptoms Score
Initial IOT > 30 mmHg 1
IOT often over 24 mmHg during medical treatment 1
Pathological chamber angle 1
Visual field defect 2
Optic nerve head excavation 1
Maximal medical treatment 2
Age below 50 1
Low blood pressure 2
Myopia 1
Surgery if total score is at least  4
Table 3.: Predicting the need for surgery for open angle glaucoma

Assessing a glaucoma case by this scoring system at the time of first diagnosis or at any later time, decision can be made to continue medical treatment and risk further deterioration or perform - a possibly inevitable - surgery as soon as possible.
To summarize:

Finally, the problems associated with the surgical treatment of glaucoma are well illustrated by the following:
One of our patient (with very high initial IOT) said when he lost his vision due to cataract developed after a trabeculectomy: "Doctor, you only needed 20 minutes to do what nature would need months for". He immediately changed this opinion, with great joy, after a successful lens implantation later.
This means that all complications of a glaucoma surgery can be remedied after the intraocular tension is normalized, but no functional damage developed during an insufficient medical treatment be redone.
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