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ORIGINAL ARTICLE
Year : 2020  |  Volume : 12  |  Issue : 1  |  Page : 17-22

Prospective analysis of optic nerve head parameters before and after trabeculectomy at a tertiary institute of the Himalayan foothills (optical coherence tomography-based study)


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

Date of Submission26-May-2020
Date of Acceptance19-Jul-2020
Date of Web Publication27-Aug-2020

Correspondence Address:
Kalpana Sharma
Department of Ophthalmology, Indira Gandhi Medical College, Shimla, Himachal Pradesh
India
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DOI: 10.4103/sjopthal.sjopthal_11_20

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  Abstract 

Introduction: Glaucoma is a group of acute and chronic, progressive, multifactorial optic neuropathies in which intraocular pressure (IOP) and other contributing factors are responsible for a characteristic, acquired loss of retinal ganglion cell axons leading to atrophy of the optic nerve. Early detection of glaucoma through the use of optical coherence tomography (OCT) and perimetry and intervention through trabeculectomy in patients showing deterioration can avoid further damage to vision. Objective: The objective of the study was to analyze the optic nerve head (ONH) pParameters before and after trabeculectomy. Materials and Methods: This study was to prospectively study ONH before and after trabeculectomy using OCT in primary open-angle glaucoma in patients attending the Department of Ophthalmology, Indira Gandhi Medical College, Shimla. Results: The IOP decreased from 26.93 ± 2.786 mm to 11.81 ± 3.552mm Hg (P < 0.05) in the 3rd month. The rim area preoperatively was 0.5037 ± 0.27646 and at 3 months postoperatively was 0.6707 ± 0.29319 (P = 0.008), which was statistically significant. The mean value of rim volume preoperatively was 0.0463 ± 0.01904 and at 3 months was 0.0630 ± 0.0336 (P = 0.036), showing statistical significance. The preoperative cup area was 2.064 ± 0.5043, and at the 3rd month, it was 1.9393 ± 0.58619 (P = 0.027), showing statistical significance. The mean value of cup volume preoperatively was 0.6981 ± 0.33874 and at 3-month postoperative was 0.5933 ± 0.31274 (P = 0.000). Cup volume also showed a significant improvement postoperatively. Conclusion: ONH changes, being the physical manifestations of the IOP force distribution in the tissues, are essential to glaucoma pathophysiology. The early detection of glaucoma through the use of OCT and intervention through trabeculectomy in patients showing deterioration (progressive patients) can avoid further damage to the vision.

Keywords: Optic nerve head, optical coherence tomography, trabeculectomy


How to cite this article:
Sharma Y, Sharma V, Sharma RL, Pandey ML, Sharma K. Prospective analysis of optic nerve head parameters before and after trabeculectomy at a tertiary institute of the Himalayan foothills (optical coherence tomography-based study). Sudanese J Ophthalmol 2020;12:17-22

How to cite this URL:
Sharma Y, Sharma V, Sharma RL, Pandey ML, Sharma K. Prospective analysis of optic nerve head parameters before and after trabeculectomy at a tertiary institute of the Himalayan foothills (optical coherence tomography-based study). Sudanese J Ophthalmol [serial online] 2020 [cited 2020 Dec 4];12:17-22. Available from: https://www.sjopthal.net/text.asp?2020/12/1/17/293631


  Introduction Top


Glaucoma is characterized by progressive atrophy of the optic nerve head (ONH) secondary to the loss of optic nerve fiber.[1] It is characterized by the morphological changes in the intra-papillary and para-papillary regions of the ONH and the retinal nerve fiber layer.[2],[3] The optical coherence tomography (OCT) can measure optic disc topography. Trabeculectomy operation reduces the pressure on the optic nerve and prevents or slows further damage and further loss of vision in glaucoma. Control of the eye pressure with a trabeculectomy will not restore vision already lost from glaucoma.[4]

The rationale for the current study was to prospectively study ONH before and after trabeculectomy (using Topcon 3D OCT-1Maestro) in primary open-angle glaucoma (POAG) in patients attending Department of Ophthalmology, Indira Gandhi Medical College (I.G.M.C), Shimla.


  Materials and Methods Top


The present study was conducted in the Department of Ophthalmology, I.G.M.C, Shimla. Data of a minimum of 27 patients undergoing trabeculectomy and from June 2016 to May 2017 were taken for study. POAG diagnosed in the present study is based on a morphological change in the ONH, such as excavation of the cup and notching of the rim. It excluded the patients with advanced cases of glaucoma, secondary glaucoma, or non-glaucomatous cause of optic neuropathy. Patients with a history of ocular diseases such as diabetic retinopathy, uveitis, or cataract intraocular surgery were excluded from the study. Patients having an image quality of <30 in OCT were excluded from the present study.

The surgical method of trabeculectomy involved the following steps:

  1. No pupillary dilatation and a bridle suture/corneal traction suture was inserted (commonly superior cornea). The site of trabeculectomy was superonasal or superotemporal
  2. A fornix-based flap of conjunctiva and Tenon capsule was fashioned superiorly. Epi-scleral tissue was cleared, and major vessels cauterized
  3. An incision was made through about 50% of sclera thickness to create a trap-door lamellar sclera flap. This flap was triangular according to preference
  4. The superficial triangular flap was dissected forward until the clear cornea was reached
  5. A paracentesis was made in temporal peripheral clear cornea and air was injected. The anterior chamber was entered along most of the width of the trap-door base
  6. After the initial linear incision into anterior chamber, sclerotomy is fashioned with sclera punch. A fistula 0.5 mm to 1 mm in height and 1.5–2 mm in width was created.
  7. Peripheral iridectomy was created. Superficial scleral flap was sutured to its underlying bed tightly with apex sutures, using nylon 10-0 suture
  8. The patency of the fistula was checked using a balanced salt solution. Conjunctiva/Tenon capsule flap was sutured. Irrigation through the paracentesis was repeated to produce a bleb
  9. Steroid and antibiotics were injected under the inferior conjunctiva


Postoperatively, steroid and antibiotic drops were used four times daily for 2 weeks and then changed to steroids alone for a further 812 weeks.

After trabeculectomy, the patients' OCT scans and disc photography were repeated at 1 week, 1 month, and 3 months postoperatively.

Statistics

Data collected were 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. The probability value (“P”-value) was calculated and a value of <0.05 was implied to be statistically significant.


  Results Top


The age and gender distribution of the patients is shown in [Table 1] and [Table 2]. The number of patients in the age group 40–50 years was 7, 51–60 year age group had nine patients, 61–70 year age group showed nine patients, whereas 71–80 age group had two patients. The mean age was found to be 57.9 years. Twenty-seven individuals underwent trabeculectomy. Out of the total study group, 18 were male members who contributed to 66.7% of the total study group. Of 27 individuals, 9 were females who composed about 33.3% of the total study group.
Table 1: Age distribution

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Table 2: Gender distribution

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The mean intraocular pressure (IOP) and SD in the age group of 40–80 years (n = 27). The mean 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 the postoperative period, it was observed to be 11.41 ± 4.254 (P < 0.05). In the third month of the observation period, the mean was observed 11.81 ± 3.552 (P < 0.05), depicted in the form of [Graph 1].



  • ONH Parameters
  • Disc area
  • Rim area
  • Rim volume
  • Cup area
  • Cup volume
  • (Optic Cup Disc Ratio) OCDR.


Disc area

Disc area [Table 3] was analyzed preoperatively and the mean was observed to be equal to 2.5493 ± 0.34513. The disc area postoperatively at 1 week was found 2.6181 ± 0.39821 (P = 1.000). At 1 month, the mean disc area was found to be 2.7281 ± 0.45585 (P = 0.259). The mean disc area at the 3rd month postoperatively was 2.6307 ± 0.60255.
Table 3: Disc area (mm2)

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Rim area

Rim Area (mm2) – rim area found preoperatively to be 0.5037 ± 0.27646. The mean value of rim area 1 week postoperatively was 0.587 ± 0.26172 (P = 0.124). The rim area was then observed in the follow-up period of 1 month postoperatively; in this period; it was seen that the mean value is 0.6452 ± 0.25913 (P = 0.044). The mean rim area in the 3-month postoperatively of follow-up period was observed to be 0.6707 ± 0.29319 (P = 0.008). The mean values were compared and are depicted in [Graph 2].



Rim volume

The mean value of rim volume preoperatively was found to be 0.0463 ± 0.01904. The mean rim volume postoperatively at 1 week was 0.0541 ± 0.02438 (P = 0.039). The mean value of the rim volume postoperatively at 1 month was at 0.0630 ± 0.02383 (P = 0.000). The mean value of the rim volume at 3 months came to be 0.0630 ± 0.03361 (P = 0.036). The rim Volume for the study was then depicted in the form of [Graph 3].



Cup area

The preoperative cup area was observed to be 2.064 ± 0.5043. The mean cup area during the 1st week of postoperative period came to be 1.996 ± 0.5082 (P = 0.951). The cup area observed during the 1st month of the follow-up was 2.029 ± 0.5336 (P = 1.000). During the 3rd month of the follow-up, the mean cup area was observed to be 1.9393 ± 0.58619 (P = 0.027). The cup area is depicted in the form of [Graph 4].



Cup volume

The mean cup volume preoperative was observed to be 0.6981 ± 0.33874. The mean cup volume 1 week postoperative was found to be 0.6515 ± 0.32375 (P = 0.003). The mean of cup volume at 1 month was found to be 0.617 ± 0.31518 (P = 0.001). The mean cup volume at 3 months postoperative was observed to be 0.5933 ± 0.31274 (P = 0.000). The values are depicted in the form of [Graph 5].



Cup/disc ratio

The cup area and disc area were analyzed to find the ratio between both. It was observed that the cup-to-disc (C/D) ratio in patients during the preoperative period came out to be 0.7896 ± 0.7004. In the 1st week postoperatively it was observed that the C/D ratio came to be equal to 0.7563 ± 0.13342 (P = 0.021). During the 1st month observational period, it came equal to 0.73 ± 0.1321 (P = 0.020). In 3rd month, the C/D Ratio came to be 0.7004 ± 0.18039 (P = 0.000). The mean cup/disc ratio is depicted [Graph 6].




  Discussion Top


Glaucoma is an optic neuropathy characterized by loss of retinal ganglion cells and their axons. Detection of ONH damage is, therefore, crucial for the early diagnosis and management of glaucoma[5] Glaucomatous damage is compression of neurons by the distorted, posteriorly bowed lamina cribrosa (LC), 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 visual field can improve when the IOP is lowered after Glaucoma filtration surgery. Hence, one of the main reasons for an perceptible improvement in optic nerve appearance with IOP reduction is a reduction in the posterior bowing of the LC, giving relief to the compressed nerve fiber bundles.[5],[6],[7],[8],[9]

The patients included in our study had age range older than 40 years and not more than 80 years [Table 1]. 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.

In our study, IOP decreased from 26.93 ± 2.786 mmHg preoperatively to 9.07 ± 3.43 mmHg (P < 0.05) at 1 week postoperatively. IOP then reduced to 11.41 ± 4.254 mm Hg (P < 0.05) at 1 month to 11.81 ± 3.552 mm Hg (P < 0.05) at 3rd month respectively after trabeculectomy. This corresponds to reduction of IOP to about 33.7% at 1 week and 42.3% and 43.8% at 1 month and 3rd month respectively as compared to preoperative IOP. The reduction in IOP was statistically significant in all postoperative follow-up period [Graph 1].

Similar results were also observed by Figus et al. they studied that IOP decreased from 24.4 ± 5.0 mmHg preoperatively to 12.1 ± 3.1 mmHg (P < 0.001) and 10.6 ± 2.8 mmHg (P < 0.001), respectively, at 3 and 6 months after trabeculectomy; this corresponded to a reduction of 48 ± 18% at 3 months and of 54 ± 20% at 6 months.[10] Bertrand et al. observed in their study that trabeculectomy resulting in at least 36% reduction in IOP and was effective in considerably reducing the rates of change in the visual field in his study population.[11]

Optic nerve head parameters

Reversal of optic disc cupping following IOP reduction is a well-known phenomenon in congenital and juvenile glaucoma. Although it has been reported in adult patients also, the results of these studies seem conflicting. The clinical relevance of “reversal” has not been established with certainty, although reports have suggested that there may be an associated improvement of visual function that corresponds to this increase in disc appearance.[6]

Although obstruction to axoplasmic flow may be involved in glaucoma pathophysiology, it is still unclear how mechanical, vascular, and cellular mechanisms would participate in this process. The mechanical theory of damage postulates that elevated IOP causes LC distortion, resulting in the damage of retinal ganglion cell axons at the ONH. The reduction in IOP was associated with an increase in the neural rim area and a decrease in the cup size, probably due to anterior shifting of the LC. The inverse mechanism was observed after IOP elevation.

The various ONH parameters observed in our study were disc area, rim area, rim volume, cup area, cup volume, and OCDR. The Disc Area analyzed preoperatively and postoperatively at 1 week, 1 month, and 3rd month. There was a numerical improvement in the disc area throughout the postoperative follow-up period, though that was not statistically significant [Table 3]. The mean rim area within 1 week preoperatively was 0.5037 ± 0.27646 and at 1-week postoperatively, the mean was 0.587 ± 0.26172 (P = 0.124). The mean value at 1 month was 0.6452 ± 0.25913 (P = 0.044). The mean rim area at 3rd month postoperatively of was 0.6707 ± 0.29319 (P = 0.008). The rim area showed statistically significant improvement at 1st month and 3rd month postoperatively. The rim area showed improvement in the follow-up period though the significant improvement was observed at 1 month and 3rd month postoperatively. [Graph 2]. Similarly, rim volume was analyzed and showed significant improvement during the follow-up period after trabeculectomy [Graph 3]. Similar results were observed by Figus et al., who observed that borderline ONH changes and negligible functional changes. The lack of an absolute structure–function correlation may be due to the different levels of measurement noise displayed by the devices used to detect the change, and it has been suggested that structural and functional methods can be considered as independent indicators of glaucoma damage. Irak et al. observed that mean rim area and rim volume increased significantly after trabeculectomy.[12]

In our study, cup area preoperative value within 1 week was 2.064 ± 0.5043. The mean at 1st week postoperative period was 1.996 ± 0.5082 (P = 0.951). The mean value at 1st month was 2.029 ± 0.5336 (P = 1.000). At 3rd month, the mean cup area was observed to be 1.9393 ± 0.58619 (P = 0.027). Cup area showed a significant improvement at 3rd month postoperatively. Cup area decreased during the postoperative follow-up period, but statistical significance was observed at 3rd month [Graph 4], whereas cup volume decreased consistently in postoperative period, showing statistical significance throughout the follow-up [Graph 5].

In the present study, cup area and disc area were analyzed to find the ratio between them. The C/D ratio decreased significantly after surgery during the follow-up period [Graph 6]. Previous studies done showed similar results, Irak et al. define mean cup area, cup volume, and C/D area ratio decreased significantly after surgery.[12] In adult patients, reversal of glaucomatous optic disc cupping is not generally recognized in clinical practice. However, reports have noted evidence of optic disc cup reversibility after IOP reduction in some adult patients using a variety of diagnostic methods including qualitative evaluation of stereophotographs and quantitative assessment using photogrammetric or computer videographic imaging methods. Similar study was done by Raghu et al. In his study Among the ONH parameters he observed that the cup area decreased significantly at 1 week from 2.33 ± 0.5 mm2 preoperatively to 2.0 ± 0.61 mm2 at 1 week (P¼0.014), but reverted close to baseline values by 3 months the C/D area ratios decreased significantly from preoperative 0.87 ± 0.13 to 0.73 ± 0.19 at 1 week (P¼0.005), but the change was not significant at 1 month (0.79 ± 0.15; P¼0.246) and 3 months (0.81 ± 0.16; P¼0.309) follow-up.[6] Figus et al. studied borderline ONH changes. He also adds that, ONH changes are usually short-lived and one would not expect them to be present at 3 and 6 months.[10] Paranhos et al. studied ΔIOP and ΔIOP% had a statistically significant effect on Δ cup disk area, Δ cup volume, and Δ mean cup depth. Changes in cup shape size were influenced significantly only by ΔIOP. Some optic disc parameters measured by Heidelberg Retinal Tomography (HRT) presented a significant improvement after filtering surgery, depending on the amount of IOP reduction. Long-term studies are needed to determine the usefulness of these findings as outcome measures in the management of glaucoma.[13]


  Conclusion Top


Thus it is concluded that the trabeculectomy helps to reduce IOP postoperatively in POAG. While IOP is a significant risk factor for glaucoma and IOP-lowering is the only proven treatment for the disease. Visual acuity deterioration was withheld or slightly improved corroborating with ONH parameters in the present study. Hence, early detection of glaucoma through the use of OCT and intervention through trabeculectomy in patients showing deterioration (progressive patients) further damage to the vision can be avoided, though it is yet to be evaluated whether these changes have any clinical significance in long-term follow-up.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Rand Allingham R. Shields Textbook of Glaucoma. 6th edition;Lippincott Williams & Wilkins 2011. (530 Walnut Street, Philadelphia, PA 19106 USA LWW.com).  Back to cited text no. 1
    
2.
Gandhi M, Dubey S. Evaluation of the optic nerve head in glaucoma. J Curr Glaucoma Pract 2013;7:106-14.  Back to cited text no. 2
    
3.
Goel M, Picciani RG, Lee RK, Bhattacharya SK. Aqueous humor dynamics: A review. Open Ophthalmol J 2010;4:52-9.  Back to cited text no. 3
    
4.
NHMRC Guidelines for the Screening, Prognosis, Diagnosis, Management and Prevention of Glaucoma; 2010. p. 39-45, 65-88.  Back to cited text no. 4
    
5.
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. 5
[PUBMED]  [Full text]  
6.
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 2012;26:1131-7.  Back to cited text no. 6
    
7.
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. 7
    
8.
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. 8
    
9.
Kotecha A, Spratt A, Bunce C, Garway-Heath DF, Khaw PT, Viswanathan A; MoreFlow Study Group. Optic disc and visual field changes after trabeculectomy. Investig Ophthalmol Visual Sci 2009;50:4693-9.  Back to cited text no. 9
    
10.
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 2011;25:1057-63.  Back to cited text no. 10
    
11.
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. 11
    
12.
Irak I, Zangwill L, Garden V, Shakiba S, Weinreb RN. Change in optic disk topography after trabeculectomy. Am J Ophthalmol 1996;122:690-5.  Back to cited text no. 12
    
13.
Paranhos A Jr., Lima MC, Salim S, Caprioli J, Shields MB. Trabeculectomy and optic nerve head topography. Braz J Med Biol Res 2006;39:149-55.  Back to cited text no. 13
    



 
 
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