Indian Journal of Clinical and Experimental Ophthalmology

Print ISSN: 2395-1443

Online ISSN: 2395-1451

CODEN : IJCEKF

Indian Journal of Clinical and Experimental Ophthalmology (IJCEO) is open access, a peer-reviewed medical journal, published quarterly, online, and in print, by the  Innovative Education and Scientific Research Foundation (IESRF) since 2015. To fulfill our aim of rapid dissemination of knowledge, we publish articles ‘Ahead of Print’ on acceptance. In addition, the journal allows free more...


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Bharathi N, Kumari C, Sadananda, Khanapur, Neetu N, and Shree B V: Comparitive study between normal tension glaucoma and primary open-angle glaucoma


Introduction

Glaucoma is progressive optic neuropathy that causes characteristic changes of the optic nerve and visual field in relation to intraocular pressure (IOP).1

Primary open angle glaucoma (POAG) has normal-appearing anterior chamber angle, increased intraocular pressure (IOP) with glaucomatous optic nerve damage and characteristic visual field loss.2 NTG differs from POAG only in that the IOP is consistently <21mmHg.

This study aims at determining the differences in functional and structural deficits in NTG and POA and rate of progression of NTG into POAG.

Materials and Methods

Patients attending the department of Ophthalmology at Minto Ophthalmic Hospital, screened during the period Nov 2016 – Aug 2019 & patients fulfilling the criteria like Gonioscopy showing open-angles, Optic nerve cupping and corresponding visual field defects were taken into study. Diurnal IOP was recorded and subjects divided into two groups based on the readings. Patients with <21mmHg IOP (56) were put in NTG group and those of >21mmHg (56) were grouped into POAG group. Written informed consent was taken. Ethical committee clearance was obtained.

Ocular hypertensives, patients with Primary angle-closure glaucoma, Secondary glaucoma, Corneal disorders, Posterior-segment pathologies and Non-glaucomatous optic neuropathy were excluded from the study.

Detailed history was taken from all the patients and ocular examination of both eyes was done, which included visual acuity with Snellen’s chart, Slit-lamp biomicroscopy, IOP was measured using Goldmann applanation tonometer, Indirect Gonioscopy using Goldmann three mirror lens, optic disc evaluation was done with slit-lamp biomicroscopy using by 78 D, Time domain OCT (Zeiss Cirrus HD OCT) done to asses RNFL parameters, Pachymetry was done and Visual fields assessment were done using Zeiss Humphrey field- analyser. Each patient was followed-up till 34 months.

Results

Statistical software namely SAS 9.2, SPSS 15.0, Stata 10.1, MedCalc 9.0.1, Systat 12.0 and R environment ver.2.11.1 are used for the analysis of the data. Student t test, Chi-square test / Fisher Exact test were used to study the significance of study parameters. Leven’s test was performed to assess the homogeneity of Variance. P-value of 0.05 was considered as significant.

Mean age was found to be 58.96 yrs in NTG and 55.07 in POAG. NTG was more common in females (58.9%), whereas POAG was more common in males (73.2%). Systemic involvement was more common in NTG (71.4%) with diabetes in 42.9% (24), hypertension in 25% (14), bronchial asthma and migraine in 1.8% each (1).

There was no significant difference in CDR between two groups.

Temporal (32.1%) and inferior (39.3%) NRR thinning was more common in NTG, whereas bipolar thinning (57.1%) was more common in POAG. Retinal Nerve Fiber Layer (RNFL) was significantly thinner in POAG in all four quadrants.

There were no significant changes in MD and PSD values of Visual fields (VF) between NTG and POAG. NTG showed localized field defects which were closer to centre of fixation, while it was diffuse and denser in POAG.

Table 1

Demographic comparision between the two groups of patients

Character

NTG

POAG

P value

Mean age

58.96 Yrs

55.07 Yrs

0.002

Sex

58.9% (33) Female

41.1% (23) Male

26.8% (15) Female

73.2% (41) Male

0.001

Systemic involvement

71.4% (40)

50% (28)

0.020

Table 2

Mean disc CDR comparison of patients in two groups of patients

Mean Disc CDR

NTG

POAG

Right Eye

0.69±0.11

0.73±0.09

Left Eye

0.71±0.11

0.76±0.11

[i] Chi-square test/Fisher Exact test

[ii] CDR – Cup Disc Ratio

Table 3

Disc NRR distribution of patients in two groups of patients studied

NTG

POAG

Disc NRR

Right Eye

Left Eye

Disc NRR

Right Eye

Left Eye

WNL

8(14.3%)

4(7.1%)

WNL

1(1.8%)

1(1.8%)

Temporal thinning

17(30.4%)

18(32.1%)

Temporal thinning

13(23.2%)

4(7.1%)

Bipolar thinning

6(10.7%)

8(14.3%)

Bipolar thinning

23(41.1%)

32(57.1%)

IR Thinning

21(37.5%)

22(39.3%)

IR Thinning

3(5.4%)

0(0%)

Superior thinning

1(1.8%)

2(3.6%)

Superior thinning

16(28.6%)

16(28.6%)

Superior notch

2(3.6%)

1(1.8%)

Superior notch

0(0%)

0(0%)

All rims thinned

1(1.8%)

1(1.8%)

All rims thinned

0(0%)

0(0%)

Inferior thinning

0(0%)

0(0%)

Inferior thinning

0(0%)

3(5.4%)

P value

<0.001** Right Eye

<0.001** Left Eye

[i] NRR – Neuroretinal Rim

[ii] Chi-square test/Fisher Exact test

Table 4

Distribution of RNFL thickness on OCT

RNFL

NTG

POAG

P value

Superior Quadrant

82.76±16.9

63.73±12.59

<0.001**

Inferior quadrant

88.05±14.55

59.98±7.14

<0.001**

Nasal quadrant

54.66±8.18

46.04±6.80

<0.001**

Temporal quadrant

54.11±5.58

45.09±5.96

<0.001**

Average thickness

69.90±6.61

53.71±6.31

<0.001**

[i] RNFL – Retinal Nerve Fiber Layer

[ii] OCT – Optical Coherence Tomography

[iii] Student t test (two-tailed, independent)

Figure 1

RNFL OCT showing bilateral inferior rim thinning

https://s3-us-west-2.amazonaws.com/typeset-prod-media-server/e8e98493-bc13-46bf-a9ba-5d6cc301c2a6image1.jpeg

Table 5

Visual fields- distribution of patients in two groups of patients studied

Visual Fields

NTG

POAG

P value

Right Eye

MD (dB)

-17.14±7.25

-18.79±8.08

0.261

Mean PSD

9.27±3.50

11.42±3.85

0.003**

Left Eye

MD (dB)

-16.22±6.88

-17.56±6.75

0.303

Mean PSD

9.38±2.80

11.07±3.52

0.006**

[i] MD – mean deviation; PSD – pattern standard deviation

On follow up, two patients of NTG had raised IOP and were converted to POAG. No significant changes were observed in VF and RNFL on follow up.

Discussion

NTG & POAG are two extremes of pressure-independent & dependent glaucomatous optic nerve damage. NTG is a condition with glaucomatous optic disc, visual field changes, an open-angle with normal range of IOP. IOP is a part of the pathogenic process in NTG & factors other than IOP may contribute to optic nerve damage by making the nerve susceptible to damage at lower IOP levels.

Figure 2

Gonisoscopic picture of open angle. All four structures are visible. (SL – Schwalbe’s line, TM – trabecular meshwork, SS – Scleral spur, CBB – ciliary body band)

https://s3-us-west-2.amazonaws.com/typeset-prod-media-server/e8e98493-bc13-46bf-a9ba-5d6cc301c2a6image2.jpeg

In our study, it was found that majority of the patients i.e., 48.2% in NTG and 62.5% in POAG, belonged to the age group between 51 and 60 years (mean age of 58.96 yrs in NTG and 55.07 yrs in POAG). NTG was found to be more common in females i.e., 58.9% (33 patients) and POAG more common in males i.e., 73.2% (41 patients).

The optic disc CDR & NRR was examined between NTG & POAG. There was no significant difference in CDR between two groups whereas in disc NRR inferior & temporal rim thinning was more common in NTG. While bipolar thinning & superior rim thinning was more common in POAG.

In our study, it was found that systemic association for NTG (40%) was more common than POAG (28%). This is similar to a study done by Kristy G et al, in which 38% of NTG patients were associated with Migraine, Raynaud’s and hypotension, while 42% of NTG were associated with cardiovascular disease.3 The optic disc drance hemorrhage was found in NTG (9%) patients, unlike POAG & it was found to be associated with Diabetes mellitus & Hypertension.

In our study, the Mean RNFL thickness in superior quadrant is 85.82 ± 15.84 (NTG), 64.18 ± 14.42 (POAG); Inferior quadrant 86.64 ± 16.10 (NTG), 60.55 ± 8.26 (POAG); Nasal quadrant 54.29 ± 8.38 (NTG), 46.27 ± 6.93 (POAG) and Temporal quadrant 53.32 ± 5.98 (NTG), 45.38 ± 6.17 (POAG). Average thickness was 70.02 ± 6.14 (NTG) & 54.09 ± 6.84 (POAG). RNFL thickness by OCT gives an objective & quantitative assessment of glaucomatous structural loss.

Mean RNFL values by OCT of subjects in different studies.

Table 6

Superior quadrant

Study

NTG

POAG

OHT

GS

Normal

This study

82.76 ± 16.9

63.73 ± 12.59

-

-

Satyaprakash S et al 4

77.8 ± 30.58

65.45 ± 27.86

-

106.75 ± 16.47

[i] RNFL – Retinal Nerve Fibre Layer

[ii]

[iii] Mean superior quadrant RNFL thickness in NTG and POAG was comparable to Satyaprakash S et al. 4

Table 7

Inferior quadrant

Study

NTG

POAG

OHT

GS

Normal

This study

88.05 ± 14.55

59.98 ± 7.14

-

-

Satyaprakash S et al 4

92.6 ± 30.42

65.68 ± 32.89

-

103.62 ± 16.47

-

[i] Mean inferior quadrant RNFL thickness of NTG and POAG was comparable to Satyaprakash S et al.4

Table 8

Nasal quadrant

Study

NTG

POAG   

OHT

GS

Normal

This study

54.66±5.58

46.04±6.80

-

-

-

Satyaprakash S et al4

49.6±13.99

44.91±23.79

-

63.95±11.12

-

[i] Mean nasal quadrant RNFL thickness of NTG was comparable with Satyaprakash S et al. POAG was comparable with Satyaprakash S et al.4

Table 9

Temporal quadrant

Study

NTG

POAG

OHT

GS

Normal

This study

54.11±5.58

45.09±5.96

-

-

-

Satyaprakash S et al

54.7±12.99

42.84±18.86

-

57±11.77

-

[i] OHT – Ocular Hypertension

[ii] GS – Glaucoma suspect

[iii]

[iv] Mean temporal quadrant RNFL thickness of NTG and POAG was comparable with Satyaprakash S et al.4

Table 10

Average RNFL Thickness

Study

NTG

POAG

OHT

GS

Normal

This study

69.90±6.61

53.71±6.31

-

-

-

Satyaprakash S et al 4

70.1±17.81

55.26±19.75

-

82.29±10.66

-

[i] OHT – Ocular Hypertension

[ii] GS – Glaucoma suspect

[iii]

[iv] Mean average RNFL thickness of NTG and POAG was comparable with Satyaprakash S et al.4

We compared the mean deviation (MD) & pattern standard deviation (PSD) in visual fields between NTG & POAG. There was no significant difference between the two, similar to previous studies. We found that field loss was near centre of fixation in NTG, compared to POAG, which was diffuse.

Table 11

Mean MD (dB) in visual fields of subjects in different studies

Study

NTG

POAG

HTG

PXFG

This study

-

-

Michele Iester et al 5

-6.31±13.2

-7.69±5.02

-

Oraorn Thonginnetra et al 6

-3.61±2.08

-4.47±2.60

-

[i] MD – Mean Deviation

[ii] HTG – High Tension Glaucoma

[iii] PXFG – Pseudoexfoliative Glaucoma

The mean MD of our study was not comparable with other studies.

Table 12

Mean PSD in visual fields of subjects in different studies

Study

NTG

POAG

This study

Michele Iester et al 5

7.08±4.16

7.52±3.38

Oraorn Thonginnetra et al 6

2.82±3.54

4.98±2.46

[i] PSD – Pattern Standard Deviation

The mean PSD of NTG was comparable to Michele Lester et al while that of POAG was not comparable to previous studies.

Patients were followed up for 34 months, where IOP, Visual fields (VF) and OCT for RNFL was done. We found no significant difference in VF and RNFL, but two patients of NTG were converted to POAG due to raised IOP on follow up.

The results of this study were comparable with the variables of other similar studies. Hence, our study plays a significant role in assessing the parameters which may be noticed in NTG and POAG, which can assess the risk and reduce the further progression of the disease. Further medical and surgical management can also be planned for the same.

Source of Funding

None.

Conflict of Interest

None.

References

1 

S Satyaprakash S Vinai SA Kumar S Shivangi S Kamaljeet R Jagriti A comparison of retinal nerve fibre layer thickness by spectral domain optical coherence tomography in primary open angle glaucoma, normotensive glaucoma and glaucoma suspectJ Ophthalmol201835163

2 

BJ Song J Caprioli New directions in the treatment of normal tension glaucomaIndian J Ophthalmol20146252937

3 

JJ Kanski Clinical ophthalmology8th editonElsevier Limited2016358

4 

KG Ahrlich CGV De Moraes CC Teng TS Prata C Tello R Ritch Visual field progression differences between normal tension and exfoliative high-tension glaucomaInvest Ophthalmol Vis Sci2010513145863

5 

M Iester F DeFeo GR Douglas Visual Field Loss Morphology in High and Normal-Tension GlaucomaJ Ophthalmol2012201232732610.1155/2012/327326

6 

O Thonginnetra VC Gareenstein D Chu JM Liebmann R Ritch DC Hood Normal versus high tension glaucoma: A comparison of functional and structural defectsJ Glaucoma20101931517



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© This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


Article type

Original Article


Article page

562-567


Authors Details

Bharathi N, Shwetha Kumari C, Ranjitha C Sadananda, Madhura M Khanapur, Neetu N, Sowmya Shree B V*


Article History

Received : 09-01-2021

Accepted : 20-01-2021

Available online : 30-09-2021


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