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ORIGINAL ARTICLE
Year : 2019  |  Volume : 11  |  Issue : 1  |  Page : 19-24

Retinal nerve fiber layer and visual field changes in patients undergoing trabeculectomy at Sub-Himalayan Region


Department of Ophthalmology, Indira Gandhi Medical College, Shimla, Himachal Pradesh, India

Date of Submission07-Jun-2019
Date of Decision26-May-2019
Date of Acceptance27-May-2019
Date of Web Publication10-Oct-2019

Correspondence Address:
Dr. Kalpana Sharma
Civil Hospital Theog, Shimla, Himachal Pradesh
India
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DOI: 10.4103/sjopthal.sjopthal_5_19

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  Abstract 


Introduction: Glaucoma constitutes a group of multifactorial optic neuropathies with changes in intrapapillary and parapapillary regions of optic nerve head and retinal nerve fiber layer (RNFL). Optical coherence tomography (OCT) measurement of peripapillary RNFL thickness may be the best among the currently available digital imaging instruments for detecting and tracking optic nerve damage in glaucoma. Objective: Analyzing changes in RNFL and visual field (VF) before and after trabeculectomy. Materials and Methods: The RNFL measurement using Topcon 3D OCT and VF assessment with Octopus 900 perimeter of 27 patients undergoing trabeculectomy were done at 1 week preoperatively and 1 week, 1 month, and 3 months postoperatively. Results: All the four RNFL quadrants showed improvement in thickness which was either numerically or statistically significant. In the VF analysis, the mean sensitivity (MS) was 8.73 ± 4.5493 at 1 week preoperatively. The mean value for MS at 3rd month was 9.859 ± 5.5606 (P = 0.043). Statistically significant improvement was observed at 3rd month postoperatively. The mean deviation observed within 1 week preoperative period was 19.044 ± 4.6111. The mean value was 18.26 ± 5.164 (P = 0.003) at 1 month. The mean value came equal to 17.926 ± 5.4928 (P = 0.012) at 3rd month. Statistically significant improvement was observed postoperative follow-up period. Conclusion: The vision in patients of primary open angle glaucoma can be restored through early detection of glaucoma by OCT and perimetry. As there is improvement in RNFL thickness and global indices of VF in patients undergoing trabeculectomy, further visual deterioration can be avoided.

Keywords: Optical coherence tomography, retinal nerve fiber layer, trabeculectomy


How to cite this article:
Sharma Y, Sharma V, Sharma K, Pandey M L. Retinal nerve fiber layer and visual field changes in patients undergoing trabeculectomy at Sub-Himalayan Region. Sudanese J Ophthalmol 2019;11:19-24

How to cite this URL:
Sharma Y, Sharma V, Sharma K, Pandey M L. Retinal nerve fiber layer and visual field changes in patients undergoing trabeculectomy at Sub-Himalayan Region. Sudanese J Ophthalmol [serial online] 2019 [cited 2019 Dec 15];11:19-24. Available from: http://www.sjopthal.net/text.asp?2019/11/1/19/268795




  Introduction Top


The retinal nerve fiber layer (RNFL) is formed by the expansion of the fibers of optic nerve; RNFL thickness is greatest at the inferior and superior poles of the optic disc and thinnest at the temporal and nasal disc margins.[1] This has correlation with the histology of the RNFL which is thicker in inferior and superior peripapillary areas than the temporal and nasal. Various studies demonstrate that optical coherence tomography (OCT) can measure peripapillary RNFL thickness. The RNFL defects could be localized or generalized depending on the stage of the disease and because localized defects are very rare in normal eyes, they are highly specific for optic nerve damage. The reduction in visual field (VF) and loss of vision in glaucoma associated with damage to the nerve fiber at the optic disc has been widely regarded as irreversible. Certainly loss of VFs is the most important indication for surgery in glaucoma, and this field loss can perhaps be best demonstrated by the use of automated perimetry. It is important to know whether glaucomatous field defect can be improved after trabeculectomy for open-angle glaucoma.[2] In the present study, automated perimetry has been used to evaluate these changes.

The present study was to prospectively analyze VF (using Perimetry Octopus 900) and RNFL changes (using Topcon 3D OCT-1Maestro) before and after Trabeculectomy in primary open-angle glaucoma (POAG), in patients attending Department of Ophthalmology, I. G. M. C Shimla.


  Materials and Methods Top


The present study was conducted in the Department of Ophthalmology, Indira Gandhi Medical College, Shimla. Twenty-seven patients undergoing trabeculectomy and/or from June 2016 to May 2017 were taken into study. Data was collected from one eye only, if both eyes required surgery then the one with the greater intraocular pressure (IOP) and glaucoma progression was taken in study.

The criteria for inclusion were patients aged 40–80 years with diagnosis of POAG. The patients with previous glaucoma surgery, cataract surgery, retinal, or neurological disease affecting VF were excluded from the study. While the patient was under maximally tolerant medication, the indication for surgery was optic nerve head parameter and RNFL which was high risk of glaucomatous progression as well as worsening of the VF. After trabeculectomy, the OCT scans of the patients were repeated at 1-week, 1-month, and 3-month postoperatively.

Statistics

Data collected was managed on an excel spreadsheet. Categorical data were expressed in terms of measured values, rates, ratios, and percentages. Continuous variables were expressed as mean ± standard deviation (SD). Data collected during the study were tabulated and analyzed using repeated measure ANOVA with Bonferroni correction. P < 0.05 was implied to be statistically significant.


  Results Top


There were 27 patients who underwent trabeculectomy. Of the total 27 patients, 18 were male members (66.7%) and 9 (33.3%). The number of patients in age group 40–50 years was 7, 51–60 year age group had 9 patients, 61–70 year age group showed 9 patients whereas 71–80 age group had 2 patients. The mean age was found to be 57.9 years. The mean IOP in the preoperative period was found to be 26.93 ± 2.786. There was a decrease in the postoperative 1st week, and the mean was observed to be 9.07 ± 3.43 (P< 0.05). In the 1st month of postoperative period, the mean IOP was 11.41 ± 4.254 (P< 0.05). In the 3rd month of the observation period, the mean was observed 11.81 ± 3.552 (P< 0.05).

Peripapillary retinal nerve fiber layer thickness (μm)

[Table 1] represents inferior quadrant of RNFL. The readings were observed on an OCT machine; in this, the preoperative mean value came to be equal to 63.3 ± 8.978. The mean values of inferior quadrant observed at 1-week postoperatively came to be 69.48 ± 9.002 (P = 0.000). The consecutive period of observation was at 1 month in which the mean value of inferior quadrant came to be 68.93 ± 11.19 (P = 0.096). The final readings of the inferior quadrant were observed to be equal to 66.67 ± 9.919 (P = 0.144).
Table 1: Inferior quadrant thickness (μm)

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[Table 2] depicts mean values of superior quadrant. In the preoperative period, the mean value for study group came to be equal to 67.52 ± 12.801. The superior quadrant was then observed postoperatively at 1 week, and the mean values came to be 67.85 ± 13.640 (P = 1.000). At 1-month postoperatively, the mean value came to be 69.37 ± 12.122 (P = 0.880). At 3-month postoperatively, the mean value was observed to be 69.81 ± 13.270 (P = 1.000).
Table 2: Superior quadrant thickness (μm)

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[Table 3] shows the mean and SD of the nasal quadrant. The mean value at preoperative period was equal to 62.63 ± 8.317. 1-week postoperatively, the mean value was observed to be equal to 63.22 ± 9.112 (P = 1.000). At 1st-month postoperatively, the mean value of SD of nasal quadrant was 64.22 ± 9.316 (P = 1.000). The follow-up was then done at 3rd month; the mean values came to be equal to 65.33 ± 8.256 (P = 0.846).
Table 3: Nasal quadrant thickness (μm)

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[Table 4] shows the mean and SD of the temporal quadrant. The mean value at preoperative period was equal to 50.81 ± 9.915. 1-week postoperatively, the mean value was observed to be equal to 50.52 ± 9.345 (P = 1.000). The temporal quadrant then was observed at 1-month postoperatively; the mean values were 51.48 ± 9.267 (P = 1.000). The follow-up was then done at 3rd month; the mean values came to be equal to 51.85 ± 10.117 (P = 1.000).
Table 4: Temporal quadrant thickness (μm)

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Automated visual field analysis

Mean sensitivity

[Graph 1] depicts mean and SD of the mean sensitivity (MS). The preoperative values were taken, and the mean values were 8.73 ± 4.5493. The mean values for MS were then observed at 1 month, and the mean value was 9.267 ± 4.9947 (P = 0.097). The mean value for MS was then observed at 3rd month, and the values came to be equal to 9.859 ± 5.5606 (P = 0.043). The mean values were then depicted in the form of a graph for all observational period.



Mean deviation

[Graph 2] shows the mean value for mean deviation (MD). The MD was observed at the preoperative period equal to 19.044 ± 4.6111. The mean value came to be equal to 18.26 ± 5.164 (P = 0.003) at 1-month period. The mean value came to be equal to 17.926 ± 5.4928 (P = 0.012) at 3rd month.



Square root loss of variance

[Graph 3] shows square root loss of variance (sLV). The preoperative value was observed, and the mean value was 7.822 ± 2.1344. The sLV at 1 month was 7.544 ± 2.1378 (P = 0.525). The last reading at 3rd month was observed to be 7.53 ± 2.138 (P = 0.851).




  Discussion Top


The prevalence of glaucoma is 2.65% in people above 40 years of age with primary open-angle glaucoma (POAG)being more prevalent than primary angle closure glaucoma (PACG).[3] POAG is generally bilateral, but not always symmetric disease characterized by adult onset, IOP >21 mm of Hg, an open angle of normal appearance, glaucomatous optic nerve head changes, and loss of VF. The most important risk factor for glaucoma is raised IOP. Glaucoma is an optic neuropathy characterized by loss of retinal ganglion cells and their axons. Loss of RNFL precedes measured optic nerve head changes, and VF damage was observed in 60% of eyes approximately 6 years before any detectable VF loss in glaucoma. Detection of optic nerve head and RNFL damage is, therefore, crucial for the early diagnosis and management of glaucoma.[4] Glaucomatous damage is compression of neurons by the distorted, posteriorly bowed lamina cribrosa, resulting in loss of nourishment to retinal ganglion cells. This distortion can be permanent in advanced glaucoma cases, many studies have given evidences that in less advanced disease, both the disc and VF can improve when the IOP is lowered after glaucoma filtration surgery. Similarly, increase in RNFL thickness postoperatively is the reversal or rebound of the physical compressive effect on the RNFL by the elevated preintervention IOP, leading to a recovery of normal shape and size by the retinal ganglion cell axons.[4],[5],[6],[7],[8],[9]

With the above background, this study was conducted to access changes in peripapillary RNFL thickness and VF after trabeculectomy. In the present study, 27 diagnosed POAG patients underwent trabeculectomy were studied. All patients fulfilling the inclusion criteria were included in the study. These patients were examined clinically for various signs of open angle glaucoma. Various tests were conducted primarily including OCT and perimetry. OCT was done within 1 week before trabeculectomy and 1-week, 1-month, and 3-month postoperatively. Perimetry was observed within 1-week preoperatively and at 1-month and 3rd-month postoperatively. The observations were then tabulated and statistically analyzed and compared with preoperative to postoperative results.

The patients included in the present study had age range older than 40 years and not more than 80 years. The mean age was found to be 57.9 years. In our study, 18 were male and 9 were female patients. The males comprised about 66.7% of the study group and females made up about 33.3% of the total study group.

Retinal nerve fiber layer

Glaucomatous optic neuropathy is characterized by optic disc cupping and progressive thinning of the RNFL. It is well known that patients with glaucoma could suffer approximately 40% loss of retinal ganglion cell axons before a VF defect is evident. Therefore, if one can elucidate early RNFL thinning, then glaucoma may be detected at a much earlier stage. The retinal nerve fiber analyzer or OCT is a computerized scanning device designed for the objective and quantitativein vivo relative measurement of RNFL thickness.[10] A possible explanation suggested for the immediate increase in RNFL thickness postoperatively is the reversal or rebound of the physical compressive effect on the RNFL by the elevated preintervention IOP, leading to a recovery of normal shape and size by the retinal ganglion cell axons. Another explanation that has been postulated may be retinal swelling from acute postoperative reduction in IOP.[5]

In the present study, all the four quadrants were analyzed; differences between normal and glaucomatous eye has been well documented. The changes in four quadrants: inferior, superior, nasal, and temporal were analyzed. Inferior quadrant of RNFL preoperative mean value was 63.3 ± 8.978, 1-week postoperatively was 69.48 ± 9.002 (P = 0.000), 1 month – the mean value of inferior quadrant was 68.93 ± 11.19 (P = 0.096), and at 3rd month, reading of inferior quadrant was 66.67 ± 9.919 (P = 0.144). Hence, inferior quadrant thickness showed significant improvement in the 1st week postoperatively but were tending to preoperative values in the 1 month and 3rd month of follow-up [Table 1]. Similar results were observed by Raghuet al. (2012) in their study; the RNFL parameters, average of inferior and temporal quadrant RNFL thickness increased significantly at 1 week after surgery, but reverted to baseline levels at the subsequent follow-up visits. Aydin et al. (2003) in his study found a significant increase in the peripapillary nerve fiber layer (NFL) thickness, as determined by OCT, after glaucoma filtration surgery.

In present study, the mean value of superior quadrant preoperatively was 67.52 ± 12.801; postoperatively at 1 week, the mean values was 67.85 ± 13.640 (P = 1.000); at 1 month, the mean value was 69.37 ± 12.122(P = 0.880); and at 3rd month, the mean value was 69.81 ± 13.270 (P = 1.000). There was only numerical improvement in RNFL superior quadrant thickness but the thickness was not statistically significant [Table 2].

In present study, the thickness of nasal quadrant, mean value at preoperative period was equal to 62.63 ± 8.317, and postoperatively at 1 week, the mean value was 63.22 ± 9.112 (P = 1.000), at 1 month, the mean values was 64.22 ± 9.316 (P = 1.000), and at 3rd month, the mean values was 65.33 ± 8.256 (P = 0.846). The results showed improvement of (RNFL) nasal quadrant thickness at 3rd month as compared to preoperative value [Table 3]. Similar study done by Sarkar et al. (2014) shows that the RNFL thickness changes among the patients of preoperative and postoperative glaucoma (52.56 ± 17.40 and 58.48 ± 20.20, respectively); cases were statistically significant. There was an increased RNFL thickness (superior quadrant: 4.45 ± 7.61 μm, nasal quadrant: 6.57 ± 11.19 μm, inferior quadrant: 7.57 ± 12.16 μm, and temporal quadrant: 3.27 ± 12.32 μm) in all quadrants, but more changes were found in nasal quadrant. The improvement was confined to the nasal quadrant and the adjacent RNFL thickness because this area might be least affected by the disease.[4]

Temporal quadrant thickness of the present study shows the mean value at preoperative period as 50.81 ± 9.915, and postoperatively at 1 week, the mean value was 50.52 ± 9.345 (P = 1.000), at 1-month postoperatively, the mean values was 51.48 ± 9.267 (P = 1.000). The 3rd-month mean values came to be equal to 51.85 ± 10.117 (P = 1.000). Although no statistical significance was shown, yet numerical improvement in thickness was observed [Table 4]. Aydin et al. (2003) studied that NFL thickening was significant for the overall measurement and in all quadrants except the inferior quadrant. Segmental analysis should be performed cautiously because the reproducibility decreased for quadrant measurements in glaucoma individuals, especially in the temporal and nasal quadrants. He found significant increase in the NFL thickness for the overall measurements in all quadrants except inferior quadrant.[7] Figus et al. (2011) in their study observe that the mean RNFL thickness showed statistically significant changes and the thickness increased by 0.05 mm of the baseline at 3 months (P < 0.05), and 0.03 mm at 6 months (P < 0.05). The mean value of RNFL in normal elderly patients is 0.23 ± 0.07 mm; on the basis of their results, they raised the hypothesis that the increase of RNFL thickness may reflect the recovery of the compressed RNFL, which would regain its original shape, thanks to IOP reduction. As compression on the axons is relieved by IOP reduction, the axons may recover their normal shape and size, with resultant increase in RNFL thickness as claimed by previous studies.[9],[10],[11]

Visual field: Global indices

Glaucomatous optic neuropathy causes progressive death of retinal ganglion cells and their axons. These structural changes precede VF defects as measured by standard automated perimetry.[12] VF assessment is an important clinical tool in the assessment of patients with acute and chronic ocular diseases. For these several tasks, there may be different strategies. With automated perimeters, users may select the appropriate stimulus duration and interval according to what seems best in the patients.[13] The MD on octopus perimetry is recorded as a positive value. Values for global indices (MD, pattern SD [PSD]/loss variance [sLV]) was taken for direct comparison as was value of MS. MS was automatically calculated on octopus results.[14] Figus et al. (2011) found a small change in MD after surgical IOP reduction. Dienget al. (2009) observed that among the factors studied, only age and graded follow-up time from surgery, had statistical significant influence on VF after trabeculectomy, the results (59% improvement or stability), in spite of the small sample size, argue in favor of this surgical treatment for some patients with POAG.[15]

In the present study, the MS preoperative value was 8.73 ± 4.5493; at 1 month, the mean was found to be 9.267 ± 4.9947 (P = 0.097). The mean value for MS at 3rd month was 9.859 ± 5.5606 (P = 0.043). The MS values showed significant increase at 3rd month [Graph 1]. Similarly, mean value of MD observed at preoperative period was 19.044 ± 4.6111 and the mean value of MD at 1 month was 18.26 ± 5.164 (P = 0.003). The mean value at 3rd month was found to be 17.926 ± 5.4928 (P = 0.012). The results showed a significant improvement in the follow-up period [Graph 2]. Bertrand et al. (2014) in their study evaluated the rates of MD loss before and after trabeculectomy and showed that there was a considerable reduction in the rate of MD loss after surgery. The average difference between the rates of MD loss before and after surgery was 0.20 dB/year (P = 0.15), a reduction of 56% on average. Although this difference was not statistically significant, an overall reduction of 56% of MD loss after surgery can be considered clinically significant.[16]

In the present study, the preoperative value of sLV was observed, and the mean value was 7.822 ± 2.1344. The sLV at 1 month was 7.544 ± 2.1378 (P = 0.525). The last reading at 3rd month was observed to be 7.53 ± 2.138 (P = 0.851). All values showed numerical improvement but none were statistically significant [Graph 3]. Similar studies done by various authors showed changes in the VF global indices; Figus et al. (2011) found the average preoperative MD and PSD were −14.05 ± 3.37 and 8.58 ± 1.79 dB, respectively. At 3 and 6 months, respectively, MD decreased to − 13.35 ± 3.26 and − 13.58 ± 3.54 dB (p¼0.06 and P¼0.06) and PSD increased to 9.20 ± 1.86 and 8.97 ± 1.52 dB (P¼0.08 and P¼0.06). He further adds that changes in functional parameters did not show statistical significant correlation.[11] Kotecha et al. (2001) in their study observed approximately one-third of eyes continued to display glaucomatous progression after trabeculectomy and that progression was detected predominantly by changes in VF sensitivity. Changes in VF sensitivity are present in only a small proportion of eyes. Similar results were also observed by Dieng et al. (2009), Sahli et al. (2012), Yildrim et al. (1990), Lazaro et al. (2007), Kalpana et al. (2014), and Fiona et al. (2014).

Various studies have shown that after trabeculectomy, VF global indices progression either stabilize or improve slightly showing the benefits of lowering IOP in POAG. In the present study, the mean IOP at 3rd-month postoperatively was found to be 11.81 ± 3.552, which could be a possible reason for the stabilization or improvement in parameters taken in the study. Our findings corroborate other reports regarding the significance of a lower IOP during follow-up. One possible explanation for RNFL thicker measurement is the restoration of normal axoplasmic flow, after reduction in IOP. Studies have reported that axial length of globe changes after glaucoma surgery leading to thickening of retina. The changes in the diameter of the globe may explain increasing RNFL thickness after IOP reduction postoperatively.

The limitation of present study was small study group which restricted the statistical outcome. The short period of follow-up was a big constrain as well.


  Conclusion Top


OCT measurement of peripapillary RNFL thickness may be the best among the currently available digital imaging instruments for detecting optic nerve damage in glaucoma. While IOP is a major risk factor for glaucoma and IOP, lowering is the only proven treatment for the disease. Trabeculectomy lowers IOP by reversing the physical compressive effect on the RNFL by the elevated pre-interventional IOP thereby leading to a recovery of normal shape and size by the retinal ganglion cell axons and preventing the long-term progression of VF defects.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Dichtl A, Jonas JB, Naumann GO. Retinal nerve fiber layer thickness in human eyes. Graefes Arch Clin Exp Ophthalmol 1999;237:474-9.  Back to cited text no. 1
    
2.
Yildirim E, Bilge AH, Ilker S. Improvement of visual field following trabeculectomy for open angle glaucoma. Eye (Lond) 1990;4 (Pt 1):103-6.  Back to cited text no. 2
    
3.
Pascolini D, Mariotti SP. Global estimates of visual impairment 2010. Br J Ophthalmol 2012;96:614-8.  Back to cited text no. 3
    
4.
Sarkar KC, Das P, Pal R, Shaw C. Optical coherence tomographic assessment of retinal nerve fiber layer thickness changes before and after glaucoma filtration surgery. Oman J Ophthalmol 2014;7:3-8.  Back to cited text no. 4
[PUBMED]  [Full text]  
5.
Raghu N, Pandav SS, Kaushik S, Ichhpujani P, Gupta A. Effect of trabeculectomy on RNFL thickness and optic disc parameters using optical coherence tomography. Eye (Lond) 2012;26:1131-7.  Back to cited text no. 5
    
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Fujishiro T, Mayama C, Aihara M, Tomidokoro A, Araie M. Central 10-degree visual field change following trabeculectomy in advanced open-angle glaucoma. Eye (Lond) 2011;25:866-71.  Back to cited text no. 6
    
7.
Aydin A, Wollstein G, Price LL, Fujimoto JG, Schuman JS. Optical coherence tomography assessment of retinal nerve fiber layer thickness changes after glaucoma surgery. Ophthalmology 2003;110:1506-11.  Back to cited text no. 7
    
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Kotecha A, Spratt A, Bunce C, Garway-Heath DF, Khaw PT, Viswanathan A. Optic disc and visual field changes after trabeculectomy. Invest Ophthalmol Vis Sci 2009;50:4693-9.  Back to cited text no. 8
    
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Chang PT, Sekhon N, Budenz DL, Feuer WJ, Park PW, Anderson DR. Effect of lowering intraocular pressure on optical coherence tomography measurement of peripapillary retinal nerve fiber layer thickness. Ophthalmology 2007;114:2252-8.  Back to cited text no. 9
    
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Lee VW, Mok KH. Retinal nerve fiber layer measurement by nerve fiber analyzer in normal subjects and patients with glaucoma. Ophthalmology 1999;106:1006-8.  Back to cited text no. 10
    
11.
Figus M, Lazzeri S, Nardi M, Bartolomei MP, Ferreras A, Fogagnolo P. Short-term changes in the optic nerve head and visual field after trabeculectomy. Eye (Lond) 2011;25:1057-63.  Back to cited text no. 11
    
12.
Sahli E, Tekeli O. Evaluation of retinal nerve fiber layer thickness with spectral domain Oct in primary open angle glaucoma and ocular hypertension. J Clin Exp Ophthalmol2012;3:247.  Back to cited text no. 12
    
13.
Sharma K, Chaudhary KP, Gupta RK, Sharma RL. Diseases causing visual field defects at Shimla Hills. Delhi J Ophthalmol 2014;25:95-8.  Back to cited text no. 13
    
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Rowe RJ, Wishart M, Spencer S. Perimetry comparisons for octopus G top and dynamic programmes versus Humphrey 24-2 SITA fast and SITA standard programmes. Ophthalmol Res 2014;2:24-42.  Back to cited text no. 14
    
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Dieng M, Wane A, Ba E, Roth PN, Demeideros M, Ndiaye M, et al. Visual field progression after trabeculectomy in primary open-angle glaucoma: Preliminary results. J Fr Ophtalmol 2009;32:474-80.  Back to cited text no. 15
    
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Bertrand V, Fieuws S, Stalmans I, Zeyen T. Rates of visual field loss before and after trabeculectomy. Acta Ophthalmol 2014;92:116-20.  Back to cited text no. 16
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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