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ORIGINAL ARTICLE
Year : 2019  |  Volume : 26  |  Issue : 3  |  Page : 123-126  

Has spectral-domain optical coherence tomography retinal nerve fiber layer assessment become the method of choice for glaucoma evaluation in clinical practice?


1 Department of Ophthalmology, Alluri Sitaramaraju Academy of Medical Sciences, Eluru, Andhra Pradesh, India
2 Department of Ophthalmology, Father Muller's Medical College, Mangalore, Karnataka, India
3 Department of Ophthalmology, Kasturba Medical College, Manipal, Karnataka, India

Date of Submission08-Mar-2018
Date of Decision18-Jan-2019
Date of Acceptance24-Aug-2019
Date of Web Publication30-Sep-2019

Correspondence Address:
Dr. Sarita Gonsalves
Department of Ophthalmology, Father Muller's Medical College, Mangalore, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/meajo.MEAJO_62_18

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   Abstract 


AIM: The aim of the study was to assess the role of spectral-domain optical coherence tomography (SD-OCT) as a method of choice for early glaucoma diagnosis in glaucoma suspects.
DESIGN: This was a retrospective cross-sectional study.
MATERIALS
AND METHODS:
After a comprehensive ophthalmic examination and visual field analysis, 20 patients were included in each of the three groups: Normal group, possible glaucoma, definitive glaucoma, respectively. The optic nerve head (ONH) and peripapillary retinal nerve fiber layer parameters of participants were analyzed using SD-OCT optic disc cube protocol scans. Data was analyzed using one-way analysis of variance test.
RESULTS: ONH RNFL defects in possible glaucoma patients were frequently found in superior, inferior, and temporal quadrants.
CONCLUSION: Diagnostic capability of SD-OCT parameters for detection of structural changes in the ONH and retinal nerve fiber layer differed in three groups significantly. Hence, using SD-OCT has become an imperative and quick way of timely diagnosis of glaucoma in private practice.

Keywords: Glaucoma, retinal nerve fiber layer defects, spectral-domain optical coherence tomography


How to cite this article:
Undrakonda V, Gonsalves S, Bhat SS. Has spectral-domain optical coherence tomography retinal nerve fiber layer assessment become the method of choice for glaucoma evaluation in clinical practice?. Middle East Afr J Ophthalmol 2019;26:123-6

How to cite this URL:
Undrakonda V, Gonsalves S, Bhat SS. Has spectral-domain optical coherence tomography retinal nerve fiber layer assessment become the method of choice for glaucoma evaluation in clinical practice?. Middle East Afr J Ophthalmol [serial online] 2019 [cited 2019 Dec 12];26:123-6. Available from: http://www.meajo.org/text.asp?2019/26/3/123/268250




   Introduction Top


Normally, in our day-to-day clinical practice, we come across situations where we have to diagnose whether an individual optic disc is glaucomatous or not. Traditionally, four specific subtypes of glaucomatous disc appearance have been described in the text books, which include focal ischemic disc, myopic disc, senile sclerotic, and concentrically enlarging disc.[1] Spectral-domain optical coherence tomography (SD-OCT) technology has enabled a more precise structural assessment of the optic nerve head (ONH), peripapillary retinal nerve fiber layer (pRNFL), and macular region.[2],[3] Hence, we tried to assess whether SD-OCT RNFL assessment could be used as a tool for quick method of glaucoma evaluation in private practice.


   Materials and Methods Top


This was a retrospective analysis of medical records of patients. Patients who were either diagnosed or suspected to have glaucoma were included in this study. After obtaining ethical clearance from institutional ethics committee, informed consent was obtained in local language from all the patients included in this study. All these patients had undergone a comprehensive ophthalmic examination including a detailed review of ocular and medical histories, measurement of visual acuity, Goldmann applanation tonometry, gonioscopic examination, dilated stereoscopic examination of the ONH, central corneal thickness measurement, automated perimetry using the Swedish Interactive Threshold Algorithm standard program (Humphrey Visual Field [VF] Analyzer; Carl Zeiss Meditec, Inc, Dublin, CA), and SD-OCT scans (Topcon 3D OCT-2000 System) for the measurement of ONH parameters and pRNFL thicknesses.

All the patients included in the study had best-corrected visual acuity of 6/9 and above.

Four criteria's were used to diagnose patients to have glaucoma. These included:

  1. Dilated stereoscopic examination and evaluation of ONH
  2. Intraocular pressure >21 mmHg
  3. Those with open angles on gonioscopy
  4. Those with at least two reliable VFs test results with a false-positive error <15%, a false-negative error <15%, and a fixation loss <20% were included in the study.


Patients with coexisting retinal pathology; previous history of intraocular surgery or ocular trauma; and medications both topical and systemic, optic nerve pathologies other than glaucoma were excluded from the study. Except for definitive glaucoma group patients, none of the other patients in normal and possible glaucoma were on antiglaucoma medications. After performing a clinical evaluation of ONH in all cases, patients were subjected to the remaining criteria mentioned above. If patients had a suspicious disc, they were subjected to criteria 2, 3, and 4. When only two of four above criteria were satisfied, such patients were grouped under “possible glaucoma,” and when all the four criteria were satisfied, such patients were included in “definitive glaucoma” group. In addition to the above two groups, healthy control eyes with normal optic disc, intraocular pressure <21, and normal VFs were included in “normal group.” A total of 20 patients were included in each group, respectively. The ONH and four-quadrant pRNFL parameters of participants were analyzed using SD-OCT optic disc cube protocol scans.

For statistical analysis, variables such as age, cup-to-disc ratio (horizontal: CDR_H, vertical: CDR_V), and pRNFL were used. All the variables were expressed in mean ± standard deviation. Statistical analysis was performed using SPSS 22.0 software (SPSS Inc., Chicago, IL, USA), and P ≤ 0.05 was considered to indicate a significant difference. One-way analysis of variance test was used for comparison of CDR and RNFL thickness between the groups. After applying Levene's test for homogeneity of variances, a post hoc analysis (multiple group comparison) using Bonferroni and Tamhane tests was applied wherever equality of variance was assumed and not assumed, respectively.


   Results Top


A total of 60 patients, with 20 each in normal, possible glaucoma, and definitive glaucoma, respectively, were analyzed. The mean age of patients in normal, possible glaucoma, and definitive group was 42.5 + 12.82, 51.05 ± 5.52, and 50.03 ± 5.27 years, respectively. The male-to-female ratio in normal, possible glaucoma, and definitive group was 11:9, 9:11, and 8:11, respectively [Table 1].
Table 1: Age and sex frequency

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The vertical (CDR_V) and horizontal (CDR_H) cup-to-disc ratios, average pRNFL thickness of superior (RNFL_S), nasal (RNFL_N), inferior (RNFL_I), and temporal (RNFL_T) quadrants between all the groups have been summarized in [Table 2]. P ≤ 0.05 was found to be significant in all the groups.
Table 2: Cup-to-disc ratio and four-quadrant retinal nerve fiber layer thickness comparison between the groups

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On post hoc analysis, there was no significant difference in horizontal and vertical cup-to-disc ratios between the groups; there was statistically significant difference in pRNFL thickness in superior, inferior, and temporal quadrants.


   Discussion Top


Ophthalmoscopically visible defects in the RNFL, were first described by Hoyt et al., represent the visible loss of optic nerve axons from any form of optic atrophy.[4] In glaucoma patients, two patterns of nerve fiber loss have been described – localized wedge defects and diffuse loss – which could be alone or in combination. Localized loss is more easily and consistently recognized but is less common.

SD-OCT has been shown to reproducibly detect damage in tissue thickness with a sensitivity of approximately 10 μm. Several studies have reported differences in OCT-measured RNFL thickness between normal eyes and those with ocular hypertension and early open-angle glaucoma; this suggests that OCT may differentiate between healthy eyes and those with early pressure-related damage before other techniques. Hence, SD-OCT can be used to discriminate these early changes in ONH suspected to have glaucoma.[5]

In our study, although there was no statistically significant difference between CDR_V and CDR_H between normal and possible glaucoma groups, but when ONH pRNFL thickness was compared, a statistically significant difference was present between normal and possible glaucoma group in superior, inferior, and temporal quadrants after using SD-OCT [Table 3]. Hence, using SD-OCT in patients suspected to have possible glaucoma to diagnose the presence of definitive glaucoma could give an additional advantage. This could aid in implementing appropriate time of starting treatment of such cases. The subjects' OCT parameters, even apparently optimal parameters, should not be used alone to clinically diagnose glaucoma.
Table 3: Post hoc analysis to analyze intergroup variation

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   Conclusion Top


Diagnostic capability of SD-OCT parameters for the detection of structural changes in the ONH and retinal nerve fiber layer should not be disregarded. However, the clinical examination of the disc in the diagnosis of glaucoma cannot be overemphasized and cannot be replaced. Hence, it has become an imperative and quick way of timely diagnosis of glaucoma in clinical practice.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Kanski JJ, Bowling B, Nischal KK, Pearson A. Glaucoma. Clinical Ophthalmology: A Systematic Approach. Ch. 10. Edinburgh: Elsevier/Saunders; 2011. p. 323-7.  Back to cited text no. 1
    
2.
Mwanza JC, Durbin MK, Budenz DL, Sayyad FE, Chang RT, Neelakantan A, et al. Glaucoma diagnostic accuracy of ganglion cell-inner plexiform layer thickness: Comparison with nerve fiber layer and optic nerve head. Ophthalmology 2012;119:1151-8.  Back to cited text no. 2
    
3.
Mwanza JC, Oakley JD, Budenz DL, Anderson DR. Cirrus Optical Coherence Tomography Normative Database Study Group. Ability of cirrus HD-OCT optic nerve head parameters to discriminate normal from glaucomatous eyes. Ophthalmology 2011;118:241-80.  Back to cited text no. 3
    
4.
Hoyt WF, Frisén L, Newman NM. Fundoscopy of nerve fiber layer defects in glaucoma. Invest Ophthalmol 1973;12:814-29.  Back to cited text no. 4
    
5.
Leung CK, Cheung CY, Weinreb RN, Qiu Q, Liu S, Li H, et al. Retinal nerve fiber layer imaging with spectral-domain optical coherence tomography: A variability and diagnostic performance study. Ophthalmology 2009;116:1257-63, 1263.e1-2.  Back to cited text no. 5
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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