Corneal topographic changes after trabeculectomy and deep sclerectomy in patients with primary open angle glaucoma.

Document Type : Original Article

Authors

Ophthalmology department, Faculty of Medicine, Al-Azhar University,Cairo,Egypt

Abstract

ABSTRACT
Background: The refractive outcome of glaucoma operations principally their influence on astigmatism, aren’t completely explained.
Objective: to evaluate corneal topographic changes following sub-scleral trabeculectomy (SST) versus non penetrating deep sclerectomy (NPDS) in cases with primary open-angle glaucoma (POAG).
Patients and Methods: 30 eyes of 30 cases were allocated into 2 similar groups: (Group A) comprised cases who had SST with adjuvant intra-operative usage of 0.2 mg/ml Mito-mycin C (MMC) for 2-min, and (Group B) comprised cases who had NPDS with adjuvant intra-operative usage of 0.2 mg/ml MMC for 2 mins. Complete ophthalmic examination and computerized topography were performed preoperatively, then 3-mths post-operatively .The pre-operative and post-operative data were subtracted and statistically analyzed. Data included K1, K2, average keratometry (avgK), corneal astigmatism (value & axis) and apical keratometry front (AKf).This prospective comparative study was done at Ophthalmology Dep. of Al Azhar university hospitals throughout the interval from March 2021 to Sept 2021.
Results: .Highly statistical significant (p-value < 0.001) increased Δ K1(0.47 ± 0.09) , Δ K2(0.86 ± 0.18) and Δ astigmatism (1.32 ± 0.13) in group A when compared with Δ K1 (0.22 ± 0.09), Δ K2 (0.46 ± 0.08), Δ astigmatism (0.69 ± 0.1) in group B. Non significant change was found among groups A & B regarding Δ (Avg K and AKF).
Conclusion: Induced astigmatism can responsible for a decrease in unaided visual acuity in the earlier post-operative times post glaucoma operations. SST persuade further astigmatism than NPDS.

Keywords


INTRODUCTION

Glaucoma is  the second most common cause of worldwide blindness following cataract, and is the main reason of non-reversible visual disability ,mainly because of POAG.1 Elevated intra-ocular pressure (IOP) is the main risk factor of glaucoma and present glaucoma treatments are entirely pointed to decreasing IOP. 2

Surgery is offered in POAGif there is advanced glaucoma at presentations, especially in younger patients, or if glaucoma is progressing despite 2-3 classes of drugs or after laser trabeculoplasty. Surgery may be offered earlier in the developing world because of lack of availability or affordability of medications, and lack of regular long term access medical care as in remote communities. 3

The golden standard in glaucoma operation still the SST. It is a penetrating filtration operation that efficiently decrease IOP by permitting aqueous drainages via a sclerostomy, with  complete penetrations of the  anterior chamber creating a linking with the sub-conjunctival space.4  Following decrease in IOP as well depend on sub-conjunctival bleb formation.5 Non penetrating deep sclererectomy

 

 

 

 

(NPDS) is another, nonpenetrating filtration operation, that preserve the trabeculo‐Descemet membrane.6 The former is conventionally accompanied with an elevated rate of complications.7

The influence of glaucoma  operations on refraction, predominantly astigmatism, aren’t entirely explained. It is frequent for cases experiencing glaucoma operations to have a shorter time of decreased visual acuity in the earlier post-operative time, and for some cases, this may persevere longstanding. While the variation in vision may be because of the reduction in IOP, numerous reports have investigated the direct impact of glaucoma surgeries on astigmatism, signifying that variations in corneal topography and refractive conditions may have a function. 8

PATIENTS AND METHODS

A randomized prospective observational study was carried out from March 2021 to Sept 2021.The study was conducted on 30 eyes of 30 patients suffering from POAG with uncontrolled IOP by maximum tolerable antiglaucoma therapy and operations has been done in in the departments of ophthalmology at Al- Azhar University hospitals.

All patients had normal corneal topographic parameters before operation. The research excepted cases with neo-vascular glaucoma, congenital and juvenile glaucoma, ocular pathology rather than glaucoma such as (corneal dystrophies and uveitis), history of ocular trauma, history of intraocular surgeries, or any systemic diseases that could affect the eye such as uncontrolled diabetes and hypertension. Patients who failed to complete the follow-up examinations after the surgery were also excluded.

Informed agreement was attained from all cases pre any operation. The dangers, profits, substitutes and restrictions of the intervention were explained to them .

Patients were allocated into 2 similar groups:

Group A:15-eye of 15 cases who had SST with adjuvant intra-operative usage of 0.2 mg/ml (MMC) for 2 mins.

Group  B:15 eyes of 15 cases who had NPDS with adjuvant intra-operative usage of 0.2 mg/ml (MMC) for 2 mins.       

Preoperative Assessment

A detailed medical and surgical history,including: history of prior ocular inflammation ,trauma or infection  and  history of bleeding disorders and medications.

Complete ophthalmological examination, including: measurement of  BCVA, slit-lamp  bio-microscopy  , IOP measurements with Goldman applanation tono-metry, dilated fundoscopy and corneal topography by SIRIUS Topographer® (CSO, Firenze, Italy).

Surgical Techniques

All operations have been done underneath Peri bulbar anesthesia. The site of the operation, whether for trabeculectomy or deep sclerectomy was be at superior half of the globe for all eyes. A corneal traction suture was taken  using a silk 8/0 and a conjunctival fornical based flap was made .

In SST with MMC: a superficial scleral flap (6x4mm) half thickness of the sclera  was shaped. Afterward, MMC (0.2 mg/mL) has been utilized underneath the scleral flap and the conjunctiva for 2 mins, and then it was cleaned. A sclerostomy and marginal iridectomy  was created then suturing the scleral flap by 10/0 nylon sutures. Lastly, conjunctival closure with a 8/0 virgin silk sutures. 

In NPDS with MMC: a superficial scleral flap (5x5mm) one-third of the sclera was shaped. Afterward, MMC (0.2 mg/mL) was utilized underneath the scleral flap  and the conjunctiva for 2 mins, and then it was cleaned. The deep flap (4x4mm) was shaped after that it was excised. Schlemm’s canal was unroofed followed  by removal of juxtacanalicular trabeculum. Suturing the scleral flap by 10/0 nylon sutures then conjunctival closure with a 8/0 virgin silk sutures.

Post-operative Follow Up

All cases were inspected on the 1st day post-operatively, 7 days and then once-a-month for 3-mths. Examinations involved measuring the BCVA, slit-lamp examinations and IOP measurements with Goldman applanation tonometry. Furthermore, corneal topography was obtained using SIRIUS Topographer® (CSO, Firenze, Italy) 3 months post-operatively.

Topical corticosteroid was given heavily then reduced gradually as the clinical course dictated. Topical anti-biotics and  cycloplegic agents  were as well be utilized.

Statistical Analysis:

Collected data analysis was done via SPSS-24.  Quantitative data have been introduced as mean ±SD (data with normal distribution) and median (IQR) (data with abnormal distribution).Qualitative data have been introduced as frequency and percentages.

The next tests were performed:

Independent-samples t-testing: was utilized for comparison among 2 means (normal distribution).

Mann–Whitney U testing: was utilized for comparison among 2 means (abnormal distribution).

A one-way analysis of variance (ANOVA): was utilized for comparison among more than 2 means (normal distribution).

Kruskal Willis test (KW): was utilized for comparison among more than 2 means (abnormal distribution).

Chi-square test: was utilized for comparison among non-parametric data..     

Probability (P-value)

P < 0.05 result has significance.

P < 0.001 result has high significance.

P > 0.05 result has no significance.

 


RESULTS

This prospective observational  study was carried out from March 2021 to Sept 2021, patients were admitted to Ophthalmology department of Al-Azhar university hospitals at Cairo through the outpatient clinic scheduled for glaucoma filteration surgery.

In this study, 30 patients (with 30 eyes) were allocated into 2 similar groups: (Group A) comprised cases who  had SST with adjuvant intra-operative usage of 0.2 mg/ml Mito-mycin C (MMC) for 2-min, and (Group B) comprised cases who had NPDS with adjuvant intra-operative usage of 0.2 mg/ml MMC for 2 mins.

Corneal topography was obtained using SIRIUS Topographer® (CSO, Firenze, Italy) preoperatively and 3 months post-operatively.

Demographic data:

 

 

 

Group A

(N = 15)

Group B

(N = 15)

Stat. test

P-value

Age

(years)

Mean

53.4

52.4

T = 0.32

0.751 NS

±SD

9.06

8.01

Sex

Male

8

53.3%

8

53.3%

X2 = 0.0

1.0 NS

Female

7

46.7%

7

46.7%

T: independent sample T testing.                            

X2: Chi-square testing.

Table 1: comparing among the study groups regarding Age and Sex

This table shows nonsignificant change among the study groups regarding demographic data (age and sex).

Clinical data:

1. BCVA:

 

Group A

(N = 15)

Group B

(N = 15)

Pre-BCVA
(Log MAR)

Mean

0.66

0.59

±SD

0.29

0.28

Post-BCVA
(Log MAR)

Mean

0.54

0.49

±SD

0.26

0.26

Stat. test

T

1.18

1.08

p-value

0.244 NS

0.289 NS

T: independent sample T test.

Table 2: comparison of BCVA (pre & post) in studied groups.                           

This table shows nonsignificant change among Pre-BCVA and Post-BCVA in group A and group B. (p-value > 0.05)

2. Intraocular Pressure (IOP):

 

Group A

(N = 15)

Group B

(N = 15)

Pre IOP

Mean

28.13

26.93

±SD

4.26

3.95

Post IOP

Mean

14.07

13.33

±SD

2.91

2.89

Stat. test

T

10.5

10.7

p-value

< 0.001 HS

< 0.001 HS

T: independent sample T test.

Table 3: comparison of IOP (pre & post) in studied groups                 

This table shows:

Highly statistical significant (p< 0.001) decreased post IOP (14.07 ± 2.91) when compared with pre IOP (28.13 ± 4.26) in group A.

Highly significant (p< 0.001) decreased post IOP (13.33 ± 2.89) when compared with pre IOP (26.9 ± 3.95) in group B.

Corneal parameters:

1.Flat K (K1) :

 

Group A

(N = 15)

Group B

(N = 15)

Pre K1

Mean

42.38

41.20

±SD

1.10

1.30

Post K1

Mean

41.91

40.98

±SD

1.10

1.29

Stat. test

T

1.17

0.47

p-value

0.248 NS

0.640 NS

T: independent sample T test.

Table 4: comparison of K1 (pre & post) in studied groups.                  

This table shows nonsignificant change (p > 0.05) among (pre) K1 and (post) K1  in group A and group B.

2.Steep K (K2):

 

 

Group A

(N = 15)

Group B

(N = 15)

Pre K2

Mean

43.43

42.81

±SD

0.46

0.95

Post K2

Mean

44.29

43.27

±SD

0.57

0.95

Stat. test

T

4.5

0.92

p-value

< 0.001 HS

0.192 NS

T: independent sample T test.

Table 5: comparison of K2 (pre & post) in studied groups.

This table shows:

Highly significant increased post K2 (44.29 ± 0.57) when compared with pre K2 (43.43 ± 0.46) in group A.

Nonsignificant change among K2 (pre) and K2 (post) in group B.

 3. Average Keratometry (Avg K):

 

Group A

(N = 15)

Group B

(N = 15)

Pre Avg K

Mean

42.90

42.00

±SD

0.75

1.10

Post Avg K

Mean

43.10

42.12

±SD

0.80

1.09

Stat. test

T

0.69

0.3

p-value

0.495 NS

0.763 NS

T: independent sample T test. 

Table 6: comparison of Avg K (pre & post) in studied groups.            

This table shows nonsignificant difference among AVG K (pre) and AVG K (post) in group A and group B.

4.Apical Keratometry Front (AKF):

 

Group A

(N = 15)

Group B

(N = 15)

Pre AKF

Mean

44.41

43.42

±SD

0.53

0.93

Post AKF

Mean

44.41

43.51

±SD

0.47

0.92

Stat. test

T

0.0

0.26

p-value

1.0 NS

0.792 NS

T: independent sample T test.

Table 7: comparison of AKF (pre & post) in studied groups.                               

This table shows nonsignificant difference among AKF (pre) and AKF (post) in groups A and B.

5.Corneal Astigmatism :

 

Group A

(N = 15)

Group B

(N = 15)

Pre Astigmatism 

Mean

1.06

1.61

±SD

0.75

0.62

Post Astigmatism

Mean

2.38

2.30

±SD

0.70

0.61

Stat. test

T

4.96

3.06

p-value

< 0.001 HS

0.005 S

T: independent sample T test.

Table (8): comparison of astigmatism (pre & post) in studied groups.                   

This table shows:

Highly significant increased astigmatism post (2.38 ± 0.7) when compared with astigmatism pre (1.06 ± 0.75) in group A.

Statistically significant (p-value = 0.005) increased astigmatism post (2.3 ± 0.61) when compared with astigmatism pre (1.61 ± 0.62) in group B.

6.Axis Of Flat k:

 

Group A

(N = 15)

Group B

(N = 15)

Axis Pre

Mean

66.40

105.53

±SD

75.89

79.16

Axis Post

Mean

66.33

106.73

±SD

76.44

77.86

Stat. test

T

0.002

0.042

p-value

0.998 NS

0.967 NS

T: independent sample T test.

Table 9: comparison of axis (pre & post) in studied groups.                

This table shows nonsignificant change among axis (pre) and axis (post) in group A and group B.

Amount of Changes in studied parameters (Δ):

 

Group A

(N = 15)

Group B

(N = 15)

MW

p-value

Δ BCVA

Mean

0.12

0.11

91.5

0.389 NS

±SD

0.05

0.06

Δ IOP

Mean

14.07

13.60

101

0.653 NS

±SD

1.91

1.88

Δ K1

Mean

0.47

0.22

10

< 0.001 HS

±SD

0.09

0.09

Δ K2

Mean

0.86

0.46

1

< 0.001 HS

±SD

0.18

0.08

Δ AVG K

Mean

0.20

0.12

71.5

0.089 NS

±SD

0.12

0.07

Δ Astigmatism

Mean

1.32

0.69

0.0

< 0.001 HS

±SD

0.13

0.10

Δ AKF

Mean

0.00

0.09

81.5

0.202 NS

±SD

0.25

0.05

MW: Mann Whitney U testing.

Table 10: comparing among the study groups regarding changes in studied parameters.                     

This table shows:

Highly statistical significant increased Δ K1 (0.47 ± 0.09) in group A when compared with Δ K1 (0.22 ± 0.09) in group B.

Highly statistical significant (p-value < 0.001) increased Δ K2 (0.86 ± 0.18) in group A when compared with Δ K2 (0.46 ± 0.08) in group B.

Highly statistical significant (p-value < 0.001) increased Δ astigmatism (1.32 ± 0.13) in group A when compared with Δ astigmatism (0.69 ± 0.1) in group B.

Nonsignificant change among group A and group B regarding Δ (BCVA, IOP, AVG K and AKF).

 


DISCUSSION

Surgery-induced astigmatism is one of the factors behind patients' complaints of   decrease of vision after uneventful glaucoma operation.9Various reports introduced dissimilar patterns of post-glaucoma operations induced-astigmatism.When studies defined those corneal topographic variations in few cases may last around 12 months, others defined that the persuaded variations vanish in 6 - 12 months.10 Moreover, other reports showed that keratometric readings has been stable after  2-3 months.11

As regard post SST persuaded astigmatism, Cunliffe et al.12, performed a study measuring refraction and kerato-metry in 16 cases having SST. Vertical radius of the cornea has been decreased from a pre-operative mean of 7.69 to7.56 mm at 1stwk . This with the rule (WTR) shift in corneal astigmatism persevered at 3rd wk and 8th wk of following-up but had resumed to pre-operative values at ultimate following-up at 10 mths. Horizontal radius of the cornea  was increased  at 1stwks and 3rd wk but, had normalized from 8th-wk onward. They stated no change in the axis of the vertical curvature of the cornea . Rosen et al. 13 protracted these results when compared corneal topo-graphy and kerato-metry in 8 eyes from 6 cases having SST.They established aWTR shift of 1.5 to 2.5 D of cylinder up to the 12th wks postoperatively. They as well revealed that the quantity of persuaded steepening was under-estimated via keratometry in comparison with topo-graphy. Kook et al.14 inspected 18 eyes of 16 cases having SST with 0.4 mg/mL MMC for 2-5 min at 1, 3, 6,and 12 mths.. Approving preceding reports, they revealed a mean WTR  shift in corneal astigmatism of 1.23 D at 3rd-mth post-operatively, trailed by a period of against the rule (ATR) shift .Strangely , persuaded astigmatism were still existing at 6th and 12th month (0.94 D and 0.65D resp), very longer than formerly documented without usage of MMC. 

In our study,we measuered corneal topographic changes 3 months post-operatively  in 15 eyes of 15 patients having SST with 0.2mg/ml MMC for 2 mins  (group A),we found:

No statistical significant difference in K1.

Highly statistical significant increased post K2  (44.29 ± 0.57) when compared with pre K2 (43.43 ± 0.46).

Highly statistical significant increased post astigmatism (2.38 ± 0.7) when compared with pre astigmatism (1.06 ± 0.75)

 WTR  shift in corneal astigmatism of  1.32 ± 0.13 .

 Nonsignificant change in axis.

In a larger report measuring  corneal topography in 29 cases having SST, Claridge and colleagues found more multifaceted variations. While they established an general tendency to vertical steepening and WTR astigmatism, they recognized 3 sub-groups characterized by a) superior corneal steepening, b) superior corneal flattening, and c)irregular changes . They as well confirmed that in some cases, the topographic variations persuaded by operation last for up to 12 mths.9

Egrilmez et al. 15 inspected 10 eyes having NPDS with a nonabsorbable implants. In comparison to SST controls, NPDS group  had lesser persuaded WTR  shift followed  by lesser ATR shift (0.62 D vs. 1.06 D at 3 mths; 0.62 D vs. 1.24 D at 6 mths)..This was in line with results in the current work we compared 15 eyes  having SST with MMC to 15 eyes having NPDS with MMC. We found the two groups showed a significant WTR  shift in astigmatism of (1.32 ± 0.13) in  SST group and (0.69 ± 0.1) in NPDS group at 3 months post-operatively.

While, a larger report proposed that both NPDS and SST persuaded substantial and comparable post-operative astigmatism. El Saied et al.16 matched 60 eyes  having NPDS with MMC to 60 eyes having SST with MMC. They concluded that the two groups showed a significant and comparable WTR shift  in astigmatism of 0.67 D in the NPDS group and 0.82 D in the SST group at the 6th month post-operatively.

The cause of the surgical persuaded postoperative astigmatism succeeding glaucoma operation still non identified. Maybe when a tissue piece is excised from under the scleral flap permits the unsubstantiated corneal edge of the trabeculectomy to slightly sink  causing a reduction in vertical radius of the cornea. 12 In deep scelerectomy, the thin layer of trabeculo‐Descemet membrane that is left intact in nonpenetrating operation can aid to decrease the quantity of persuaded reduction in vertical radius of the cornea.15

 

CONCLUSION

 

Both SST and NPDS induced a significant post-operative astigmatism.

An indicated glaucoma surgery, is recommended to be done first prior to an intended refractive or  cataract surgery to avoid refractive surprises; particularly in cases of multifocal or toric interaocular lens ( IOLs).

REFERENCES
1.Davison Z, Rose C, “The Pivotal Role Played by Device  Developers to Improve Patient Eye Care. ONdrugDelivery.  2021; pp 12–6.
2.Weisschuh N. Common Genetic determinants of intraocular pressure and POAG. Plos Genetics. 2012 ;8:126-50.
3. Weinreb RN, Khaw PT. Primary open-angle glaucoma. The lancet. 2004 ; 22;363(9422):1711-20.
4. Razeghinejad MR, Fudemberg SJ, Spaeth GL. The changing conceptual basis of trabeculectomy: a review of past and current surgical techniques. Survey of ophthalmology. 2012 Jan 2;57(1):1-25.
5. Amar N, Labbe A, Hamard P. Filtering blebs and aqueous pathway. An immunocytological and in vivo confocal microscopy  study. Ophthalmology. 2008; 112: 1979– 86.
6. Mendrinos E, Mermoud A, Shaarawy T. Nonpenetrating glaucoma surgery. Survey of ophthalmology. 2008 Nov 1;53(6):592-630.
7. Rulli E, Biagioli E, Riva I. Efficacy and safety of trabeculectomy vs nonpenetrating surgical procedures: a systematic review and meta analysis. JAMA Ophthalmol. 2013; 131: 1573– 82.
8. Chan HHL and Kong YXG. Glaucoma surgery and induced astigmatism: a systematic review.Eye Vis., 2017;4: 27-36.
9. Claridge KG, Galbraith JK, Karmel V, et al. The effect of trabeculectomy on refraction, keratometry and corneal topography. Eye. 1995;9:292–8.
10. Hornova´ J. Trabeculectomy with releasable sutures and corneal topography. Cesk Slov Oftalmol. 1998;54:368–72.
11. Cunliffe IA, Dapling RB, West J, et al. The effect of trabeculectomy on corneal topography [letter]. Ophthalmic Surg. 1993;24:135.
12. Cunliffe IA, Dapling RB, West J, et al. A prospective study examining the changes in factors that affect visual acuity following trabeculectomy. Eye.1992;6:618–22.
13. Rosen WJ, Mannis MJ, Brandt JD. The effect of trabeculectomy on corneal topography. Ophthalmic Surg. 1992;23:395–8.
14. Kook MS, Kim HB, Lee SU. Short-term effect of mitomycin-C augmented trabeculectomy on axial length and corneal astigmatism. J Cataract Refract Surg. 2001;27:518–23.
15. Egrilmez S, Ates H, Nalcaci S, Andac K, Yagci A. Surgically induced corneal refractive change following glaucoma surgery: nonpenetrating trabecular surgeries versus trabeculectomy. J Cataract Refract Surg. 2004;30:1232–9.
16. El-Saied HM, Foad PH, Eldaly MA, Abdelhakim MA. Surgically induced astigmatism following glaucoma surgery in Egyptian patients. JGlaucoma.2014;23:190–3.