Dr. Shreya Thatte, T04915
INTRODUCTION:
Trabeculectomy is the most popular form of glaucoma filtration surgery and remains the “gold standard” for uncontrolled, primary glaucoma [1]. It has a success rate of 67%–94%[2].Long-term success depends on preoperative and intraoperative conditions, but also highly depends on the persistence of filtration efficiency at the bleb site. Therefore, postoperative observation and care of the developing filtering bleb in clinical practice is an important tool [1]to ensure success of the surgery .
Bleb function is believed to depend on the degree of bleb fibrosis and obstruction of intrascleral aqueous humor flow.[3] Bleb appearance has been assessed using slit-lamp biomicroscopy, gonioscopy, ultrasound biomicroscopy (UBM) and optical coherence tomography (OCT).
However, morphology of bleb on slit-lamp biomicroscopy does not illustrate a bleb’s internal structures. Gonioscopy helps in assessing the internal window and the peripheral iridectomy anatomical position and shape. Cross-sectional imaging modalities such as UBM and OCT can depict internal structures of blebs, and thus provide information complementary to that obtained by slit-lamp biomicroscopy and gonioscopy about the structure and possible functionality of filtering blebs [4]
Dr. Charles Pavlinand Prof. Stuart Foster [5-7] developed UBM in 1989.It is a high frequency (50MHz) ultrasound technology using water bath that permits non-invasive in vivo imaging of the structural details of the anterior ocular segment at near microscopic resolution.[8,9]
AIM :
Evaluation and assessment of trabeculectomy bleb function using ultrasound-bio-microscopy, and to find out etiology in case of failed bleb.
MATERIAL AND METHOD:
This was a cross sectional study of 50 eyes, which were more than 3 months follow up cases of primary fornix based trabeculectomy. Consent was obtained from ethical committee for instigation of the study.
Inclusion Criteria:
Patients reporting to OPD post 3 months of trabeculectomy operation.
Exclusion Criteria
- Bleb infection
- Post-operative case of trabeculectomy within 3 months after operation
- 3. Abnormal morphology of the anterior segment
- Any other associated ocular disease.
Patients with more than 3 months post trabeculectomy, were assessed after a signed informed consent from the patients for study related examination. They constituted of patients with:
- Primary open-angle glaucoma(POAG)
- Pseudo exfoliative glaucoma
- Primary angle-closure glaucoma(PACG)
- Neovascular glaucoma
- Angle recession glaucoma
In our study, we have used the classification (Table 1) given by Avitabile et al in 1998[10]
Table 1
| Type of bleb | Scleral reflectivity | Route under flap |
| Good | Low | Seen (present) |
| Poor | High | Not seen |
| Fair | Any of the bleb which don’t fall in any of the above category | |
OBSERVATION AND RESULTS:
Three groups (Table 2) were formed according to IOP
Table 2
| Group | 1 | 2 | 3 |
| IOP | < 8 mm of Hg | 8-18 mm of Hg | >18 mm of Hg |
Comparison of Type of Glaucoma to IOP Range:
Table 3
| Cross table | ||||||
| IOP range | Total | |||||
| 1 | 2 | 3 | ||||
| Type
Of
Glaucoma |
PACG | Count | 1 | 13 | 2 | 16 |
| % of Total | 2.0% | 26.0% | 4.0% | 32.0% | ||
| POAG | Count | 2 | 23 | 5 | 30 | |
| % of Total | 4.0% | 46.0% | 10.0% | 60.0% | ||
| Neovascular | Count | 0 | 2 | 0 | 2 | |
| % of Total | 0.0% | 4.0% | 0.0% | 4.0% | ||
| Exfoliative | Count | 0 | 1 | 0 | 1 | |
| % of Total | 0.0% | 2.0% | 0.0% | 2.0% | ||
| Angle recession | Count | 0 | 1 | 0 | 1 | |
| % of Total | 0.0% | 2.0% | 0.0% | 2.0% | ||
| Total | Count | 3 | 40 | 7 | 50 | |
| % of Total | 6.0% | 80.0% | 14.0% | 100% | ||
This concludes that type of glaucoma preoperatively does not determine the IOP post trabeculectomy. There is no significant relation with each other (Table 3 ) .
Comparison of Ultrasound-bio-microscopy (UBM) to IOP Range
Table4
| Cross-table | ||||||
| IOP range | Total | |||||
| 1 | 2 | 3 | ||||
| UBM | Fair | Count | 3 | 16 | 2 | 21 |
| % of Total | 6.0% | 32.0% | 4.0% | 42.0% | ||
| Good | Count | 0 | 24 | 0 | 24 | |
| % of Total | 0.0% | 48.0% | 0.0% | 48.0% | ||
| Poor | Count | 0 | 0 | 5 | 5 | |
| % of Total | 0.0% | 0.0% | 10.0% | 10.0% | ||
| Total | Count | 3 | 40 | 7 | 50 | |
| % of Total | 6.0% | 80.0% | 14.0% | 100% | ||
In the good blebs (48%) IOP was in normal range, while in the poor bleb (10%) IOP was more than 18 mm of Hg. The fair category (21%) had IOP in both the controlled and the uncontrolled level. This shows that the type of blebs are directly significant for the maintenance of normal IOP post trabeculectomy (Table 4 ) .
Comparison of Route under the Flap (UBM) to IOP Range: (Table 6 )
| Cross table | ||||||
| IOP RANGE | Total | |||||
| 1 | 2 | 3 | ||||
| Route Under The Flap | 0 | Count | 1 | 4 | 6 | 11 |
| % of Total | 2.0% | 8.0% | 12.0% | 22.0% | ||
| 1 | Count | 2 | 36 | 1 | 39 | |
| % of Total | 4.0% | 72.0% | 2.0% | 78.0% | ||
| TOTAL | Count | 3 | 40 | 7 | 50 | |
| % of Total | 6.0% | 80.0% | 14.0% | 100% | ||
The route under the flap was not visible in 11 (22%) of the patients. Out of these 11 patients 6 had IOP more than 18 mmHg. While in 39 (78%) of the patients the route was visible and only 1 patient had IOP more than 18 mmHg rest all patients had normal IOP .This one patient had an encapsulated bleb which was responsible for theincrease in IOP despite functioning inner ostium and the visibility of the route under the flap.( Table 6 )
Comparison of Scleral Reflectivity (UBM) to IOP Range:
Table 8
| Cross table | ||||||
| IOP range | Total | |||||
| 1 | 2 | 3 | ||||
| Scleral
Reflectivity |
0 | Count | 0 | 25 | 0 | 25 |
| % of Total | 0.0% | 50.0% | 0.0% | 50.0% | ||
| 1 | Count | 3 | 14 | 1 | 18 | |
| % of Total | 6.0% | 28.0% | 2.0% | 36.0% | ||
| 2 | Count | 0 | 1 | 6 | 7 | |
| % of Total | 0.0% | 2.0% | 12.0% | 14.0% | ||
| Total | Count | 3 | 40 | 7 | 50 | |
| % of Total | 6.0% | 80.0% | 14.0% | 100% | ||
There is high positive significant correlation of type of reflectivity of the scleral flap judged on UBM to the IOP. The more is the reflectivity, the higher range of the IOP levels are present (Table 7 , 8 ).
Comparison of Increased IOP with Slit Lamp Morphology, Duration of surgery and UBM Findings:
Table 9
| Serial no. | IOP | UBM | Duration of surgery | Cause of failure | Post failure surgical management |
| 1 | 23 | FAIR | 3 Months | Iris in window | Repositioning of iris |
| 2 | 40 | POOR | 12 Months | Membrane at window | Removal of membrane |
| 3 | 25 | POOR | 14 Months | Absent route | Revision of bleb |
| 4 | 27 | POOR
(Encysted) |
12 Months | Open window | Needling |
| 5 | 42 | POOR | 24 Months | Absent route Fibrosis | Re- trabeculectomy |
| 6 | 22 | FAIR | 8 Months | Vitreous tag in window | Cutting vitreous |
| 7 | 23 | POOR | 30 Months | Absent route Fibrosis | Re trabeculectomy |
This table (Table 9) clearly observed that morphologically poor bleb has a reason to fail to function and reasons were identified and managed. Encysted bleb was treated with needling to achieve functioning bleb (Figure 2). In bleb fibrosis route under the flap was absent for which re- trabeculectomy was performed ( Figure 3) .Iris was blocking inner window in one case, which was reposited back along with revision of iridectomy ( Figure 4 ). In one patient inner window was blocked by vitreous, which was released by vitrectomy and window was opened (Figure 5). Fibrous band closing window and covering iridectomy was seen in one patient, which was cut and inner window was reformed (Figure 6).
DISSCUSION:
We had 50 patients out of which 29 were females and 21 were males. The mean age of presentation was 62.16 years. There were more number of females (n= 29, 58%) as compared to the males (n=21, 42%) in our study. We divide the patients into 3 groups with IOP > 18 mmHg. 10 to 18 mmHg and equal to or less than 10mmHg.The group with IOP more than 18 mmHg was considered failure while rest were considered successful [10].
On statistical analysis, the correlation of IOP to the type of glaucoma was not significant. These findings are consistent with findings of Sihota et al [11] where they studied long-term follow up of the 64 patients after trabeculectomy in both POAG and PACG and concluded that trabeculectomy is equally effective in both for controlling the IOP.
In the examination of the UBM grading, all the patients with good blebs (48%) (Figure 1) had IOP in normal range, while all patients with poor bleb (10%) had IOP more than 18 mmHg. The fair category (21%) had IOP in both the controlled and the uncontrolled level. This signifies that the low reflectivity and the presence of the route under the flap are significant for the maintenance of normal IOP post trabeculectomy. The correlation of UBM grading with IOP levels was found to be highly significant (p < 0.01). Similar findings were seen by Avitabile et al[10] who also did same kind of study graded the bleb into good, fair, poor on the basis of type scleral reflectivity and the visibility of route under the flap and concluded that the UBM grade function of the bleb was significantly associated with IOP control (p < 0.01). Similarly, Yamamoto et al [12] considered these two criteria important for the prediction of the functioning bleb.
Considering the individual findings on UBM, the route under the flap was not visible in 11(22%) of the patients. Out of these 11 patients, 6 had IOP more than 18 mmHg. While in 39 (78%) of the patients the route was visible and only 1 patient had IOP more than 18 mmHg rest all patients had IOP less than 18. The visualization of the route under the flap in the post trabeculectomy patients on UBM is significantly correlated [p < 0.01] to the IOP. These findings are consistent with the findings of Yamamoto et al [12] and Avitabile et al [10] who quoted that presence of route under flap is correlated with the IOP of glaucomatous eyes that underwent trabeculectomy in their study.
The high scleral reflectivity was present in 7 patients, out of these 6 patients had IOP more than 18mmHg signifying that high scleral reflectivity point to impending failure. All the patients with low reflectivity had patients with IOP less than 18 mmHg. Hence, the low reflectivity foretells the good prognosis of the bleb. These findings were also highly significant (p < 0.01) showing that the scleral reflectivity is correlated to the IOP. Our findings are consistent with the findings of Yamamoto et al [12] and Avitabile et al [10] who also concluded the high correlation of scleral reflectivity to IOP. They also found that the failing or failed bleb do show high reflectivity on UBM.
In Our series, cause for bleb failure could be identified and they were managed accordingly to achieve goal of functioning bleb and maintaining IOP.
CONCLUSION:
UBM can be used for the prediction of the anatomical results post trabeculectomy. On UBM, both the scleral reflectivity and the route under the flap are significant in predicting the outcome of the bleb. UBM allowed us to appreciate the aqueous humour drainage mechanisms in the living eye. In patients where the gonioscopy and slit lamp is not conclusive for the cause of failure and assessment, UBM is helpful for the assessment of trabeculectomy.
References:
1.Furrer et al.: Evaluation of filtering blebs using the ‘Wuerzburg bleb classification score’ compared to clinical findings. BMC Ophthalmology 2012; 12:24
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