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Evaluation of bleb parameters using ultrasound biomicroscopy and its correlation to intraocular pressure control following trabeculectomy with adjuvant mitomycin C in high-risk glaucoma patients Ahmed A. Abdel-Kader, Riham S.H.M. Allam Faculty of Medicine, Cairo University Kasr ElAiny Hospitals, Cairo, Egypt Correspondence to Ahmed A. Abdel-Kader, MD, 7B Shattr Eltany Zahraa Elmaadi, 11435, Cairo, Egypt Tel: +20 100 170 9778; e-mail:
[email protected] Received 15 March 2013 Accepted 15 June 2013 Journal of Egyptian Ophthalmological Society 2013, 106:159–162
Purpose The aim of this study was to study the relationship between bleb parameters (height and extent) evaluated using ultrasound biomicroscopy and intraocular pressure (IOP) after subscleral trabeculectomy with mitomycin C in high-risk glaucoma patients.
Design
This was a prospective interventional observational uncontrolled study.
Patients and methods
Forty eyes of 26 patients with chronic glaucoma with uncontrolled IOP undergoing subscleral trabeculectomy with intraoperative mitomycin C (0.4%) applied for 2 min were followed up for 3 months. An ultrasound biomicroscopy was performed at day 90 to measure the bleb height and extent and a correlation was found between the mean IOP, the percent reduction in IOP, and the bleb height and extent at the same interval.
Results
The mean bleb height was 1.065 ± 0.991 mm (range 0–3.6 mm) and the mean bleb horizontal extent was 3.214 ± 1.997 mm (range 0–7.9 mm). A moderate positive linear correlation was observed for bleb horizontal extent between 1.8 and 4.97 mm and percentage change in IOP [ΔIOP (%), r = 0.374], and the results were statistically significant (P = 0.054). In terms of bleb height, the correlations with IOP and ΔIOP were found to be weak and of were not statistically significant.
Conclusion
We concluded that bleb extent is more representative of bleb function than bleb height and it appears that the percent reduction in IOP is more influenced by the bleb dimensions than the mean IOP.
Keywords: bleb dimensions,glaucoma, intraocular pressure, trabeculectomy, ultrasound biomicroscopy J Egypt Ophthalmol Soc 106:159–162 © 2013 The Egyptian Ophthalmological Society 2090-0686
Introduction Trabeculectomy has been the standard surgical treatment for glaucoma since its introduction in the 1960s [1]. Studies on outcomes of glaucoma surgery have frequently reported intraocular pressure (IOP) control and complications, less frequently visual outcomes, and have rarely reported bleb morphology in detail [2]. The bleb is the functional part of trabeculectomy and the part that largely determines long-term success, failure, and complications [2]. The early bleb grading systems were proposed by Kronfeld [3], Grehn et al. [4], Vesti [5], and Lederer [6]. These have now been replaced by more representative bleb grading systems such as the Indiana Bleb Appearance Grading Scale (IBAGS) [7] and the Moorfields Bleb Grading System (MBGS) [2]. However, these systems rely on the clinical external appearance of the bleb to predict the bleb functional outcome and are also considered subjective methods; the bleb internal structure can be a more sensitive predictor to the outcome of filtering surgery. One of the aspects of 2090-0686 © 2013 The Egypt Ophthalmological Society
internal bleb structure is bleb dimensions. In this study, we measured the bleb dimensions (height and extent) using ultrasound biomicroscopy (UBM) to determine the correlation between bleb dimensions and IOP being a major risk factor for glaucoma and an important factor in evaluating the success rate of filtering surgery.
Patients and methods Study participants
This is a prospective study of 40 eyes of 26 patients with chronic glaucoma with high-risk bleb failure criteria who underwent primary trabeculectomy with mitomycin C (MMC) or repeat trabeculectomy with MMC with or without concomitant cataract extraction. Indications for surgery were based on the following: (1) IOP values above the target IOP on the maximum tolerated medical therapy (IOP values that are associated with high probability of glaucoma DOI: 10.4103/2090-0686.127371
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progression or evidenced glaucomatous visual field loss or optic disc changes indicative of glaucomatous damage). (2) Noncompliance or intolerance of the patient to medical treatment. Informed surgical consent, including indication, risks, and complications of the surgical procedure, was provided by all patients. Surgical technique
All patients underwent subscleral trabeculectomy with adjuvant MMC 0.4% as follows: general or peribulbar anesthesia was administered. Sterilization was performed using betadine 10% for the eye lids and surgical field. Betadine 5% eye-drops were used. Application of sterile drapes was performed and corneal stay suture was performed by 8/0 vicryl suture at the upper cornea with exposure of the superior part of the bulbar conjunctiva. Fashioning of a fornix-based conjunctival flap was performed using a Westcott scissor (blunt type, Geuder®, Germany), and fashioning and dissection of a rectangular half-thickness scleral flap (5 × 4 mm) were performed using a number 15 blade and a crescent knife. MMC at a concentration of 0.4% was applied under the conjunctiva using a cellulose sponge for 2 min. This was followed by copious irrigation with a sterile saline solution. Paracentesis was performed using MVR 20 G, (20 gauge, Alcon Surgical®, USA) and punch trabeculectomy and peripheral iridectomy were performed using a vannas scissor. Suturing of the scleral flap was performed using two 10/0 nylon sutures. Assessment of filtration was carried out through the paracentesis and additional sutures were added, if needed, in cases with excess filtration. Suturing of the conjunctiva was performed with interrupted water tight 8/0 vicryl sutures. Suturing of the conjunctiva to the corneoscleral junction was performed with two 10/0 nylon sutures. An antibiotic eye ointment was placed in the fornix and then an eye patch was applied. In the early postoperative period, all patients were treated with topical antibiotics and corticosteroids (four times daily) for 2 weeks; corticosteroids were tapered off slowly over 6–8 weeks.
In cases scheduled for combined phacotrabeculectomy
Phacoemulsification and posterior chamber intraocular lens implantation were performed after MMC was copiously irrigated and before trabeculectomy was performed. Postoperative follow-up
All patients were followed up for a period of 3 months (90 days) for IOP control and an UBM was performed at day 90 to measure the bleb height and extent in millimeters (Fig. 1). Statistical analysis
Pearson’s moment correlation coefficient was used to assess the linear correlation between bleb height and extent on the one hand and the mean IOP, change in IOP from preoperative value (∆IOP), and the percent reduction in IOP [∆IOP (%)] on the other.
Results Our study was carried out on 40 eyes of 26 patients who underwent primary trabeculectomy with MMC or repeat trabeculectomy with MMC with or without concomitant cataract extraction between 1 April 2012 and 31 May 2012 at the Ophthalmology Department, Kasr Al-Aini School of Medicine. The preoperative data are summarized in Tables 1 and 2. Intraoperative complications
Surgery was performed in 40 eyes with no intraoperative complications. Table 1 Preoperative data of the study group Range 41–70 13 : 13 17–38
Age (years) Sex (M : F) Preoperative IOP (mmHg)
Mean ± SD 56.125 ± 7.875 24.57 ± 4.945
IOP, intraocular pressure.
Table 2 Type of glaucoma and surgical intervention performed for patients Type of glaucoma
Number of Number of eyes patients Primary open angle 13 7 Chronic angle closure 11 8 Pseudoexfoliation 3 2 Angle recession 2 2 Neovascular Pseudophakic Late-onset juvenile Total
1 7 3 40
1 4 2 26
Surgical intervention Trabeculectomy Phacotrabeculectomy 10 5 3 2
3 6 0 0
Previous trabeculectomy 2 1 None None
1 7 3 31
0 0 0 9
None 1 1 5
Previous conjunctival surgery None None None 2 cases of repaired scleral ruptures None 3 None 5
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Postoperative evaluation
All patients were followed up at day 1, 7, 14, 30, 60, and 90 for a total period of 3 months (90 days) for IOP control and an UBM was performed at day 90 to measure the bleb height and extent in millimeters.
IOP at day 90 and bleb extent r=-0.191469 IOP at day 90 and bleb height r = -0.02674
The intraocular pressure
The IOP at day 90 ranged between 8 and 16 mmHg, with a mean of 12.55 ± 2.516 mmHg, whereas the change in IOP from the preoperative value (∆IOP) at day 90 ranged between 3 and 36 mmHg, with a mean of 11.95 ± 2.475 mmHg, and the percent reduction in IOP [∆IOP (%)] at day 90 ranged between 47.07 and 68.42%, with a mean of 17.65% ± 0.1399 mmHg. The ultrasound biomicroscopy
An UBM was performed at day 90 to measure bleb height and extent as shown in Table 3. The height of the bleb was measured from the most elevated point of the bleb and a line was drawn perpendicular to the scleral surface as a normal. The length of this line in millimeters was used to represent the bleb height.
Change in IOP at day 90 (∆P) and bleb extent r = 0.108952 Change in IOP at day 90 (∆P) and bleb height r = -0.07619 Percent reduction in IOP [∆P (%)] at day 90 and bleb extent r = 0.172884 Percent reduction in IOP [∆P (%)] and bleb height r = -0.09416 Table 3 Mean values of bleb dimensions as measured by UBM at day 90 Range 0–3.6 0–7.9
Mean 1.065 ± 0.991 3.214 ± 1.997
The horizontal extent of the bleb was represented by a line parallel to the scleral surface at the widest area of the bleb.
Bleb height (mm) Bleb extent (mm)
The correlation between IOP and bleb dimensions was assessed and Pearson’s moment correlation coefficient was determined as shown in Tables 4–6.
Table 4 Linear correlation between IOP, ∆IOP, and ∆IOP (%) together with bleb height (mm)
Figure 1
∆IOP
UBM, ultrasound biomicroscopy.
IOP at day 90 (mmHg) Mean IOP
∆IOP (%)
Correlation Type of coefficient correlation –0.0267 Negative linear –0.0762 Negative linear 0.1729 Positive linear
Strength of correlation None or very weak None or very weak Weak
P value 0.87 0.64 0.563
IOP, intraocular pressure. Table 5 Linear correlation between IOP, ∆IOP, and ∆IOP (%) together with bleb extent (mm) IOP at day 90 (mmHg) Mean IOP ∆IOP ∆IOP (%)
Correlation Type of coefficient correlation –0.1915 Negative linear 0.1089 Positive linear 0.1729 Positive linear
Strength of correlation Weak Weak Weak
P value 0.237 0.5 0.286
IOP, intraocular pressure.
a
b
c
Examples that show how measurements of bleb height and extent were taken by the ultrasound biomicroscopy. (a) Plain ultrasound biomicroscopy pictures; (b) the vertical blue dashed line represents bleb height and (c) the horizontal orange dotted line represents the bleb extent.
Table 6 Linear correlation between ∆IOP (%), with bleb extent ranging between 1.8 and 4.97 mm ∆IOP (%) at day Correlation Type of Strength of 90 (mmHg) coefficient correlation correlation ∆IOP (%) 0.374 Positive Moderate linear IOP, intraocular pressure.
P value 0.054
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Extent between 1.8 and 4.97 mm and percent reduction in IOP [∆P (%)]
Discussion Subscleral trabeculectomy is still the gold standard surgical treatment for various types of glaucoma. The clinical assessment of surgical success in the early postoperative period is clinically based on IOP control on the one hand and the development of a filtering bleb on the other. Currently available bleb grading systems are all based on the bleb morphologic features as a guide to subsequent bleb function. However, these systems are considered relatively subjective and are prone to interobserver variability. In our study, we attempted to determine the correlation between the bleb parameters represented by bleb height and extent as measured by UBM and the IOP at day 90 after filtering surgery. This might provide more objective data on subsequent bleb function. Unfortunately, the posterior extent of the bleb was not accessible in many cases, especially those located in the upper nasal quadrant; thus, the horizontal extent was considered in all cases to standardize measurements. In our study, we found that there was no or a very weak negative linear correlation between the mean IOP and the bleb height (r = –0.0267) that was not statistically significant (P = 0.87); the same was observed between the ∆IOP and bleb height (r = –0.0762), which was also not statistically significant (P = 0.64). However, a weak positive linear correlation was observed between the percent reduction in IOP [∆IOP (%)] and bleb height (r = 0.1729), which was also not statistically significant (P = 0.563).
a classification system for filtering blebs. Blebs were classified into four distinct groups: type L (lowreflective) blebs showed good IOP control, with moderate–high bleb height, and identifiable microcysts; type H (high-reflective), type F (flattened), and type E (encapsulated) were associated with poor IOP control, and both E and F types were generally discernible with slit-lamp biomicroscopy alone. However, the study did not provide numerical assessment of the bleb parameters, it only evaluated the bleb morphology. We concluded that the bleb extent is more representative of bleb function than bleb height and it appears that the percent reduction in IOP is more influential on the bleb dimensions than the mean IOP. Our study was limited by the short postoperative follow-up. Also, the inability to measure the posterior limit of the bleb in many cases by the UBM appears to be an obstacle to the proper assessment of the actual bleb extent. Further research is needed to clarify these points.
Conclusion We conclude from our study that the bleb extent is more representative of bleb function than bleb height and it appears that the percent reduction in IOP is more influential on the bleb dimensions than the mean IOP.
Acknowledgements Conflicts of interest
There are no conflicts of interest.
In terms of the bleb extent, our study showed a weak negative linear correlation with the mean IOP (r = –0.1915) that was not statistically significant (P = 0.237) and a weak positive linear correlation with both ∆IOP (r = 0.1089) and ∆IOP (%) (r = 0.1729), both of which were not statistically significant (P = 0.5 and 0.286, respectively).
References
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