Primary angle closure glaucoma (PACG) is an aggressive type of glaucoma, accounts for just 26% of the total glaucoma cases but carries 3 times more risk of blindness than primary open angle glaucoma (POAG).1 PACG remains significantly under-diagnosed, in developing countries especially, leading to a substantial burden of blindness in these countries.2

They are also very commonly misdiagnosed as POAG, as found in almost 2/3rd of the cases of PACG.3 PACG being more severe that POAG, causes more visual loss than POAG, if left untreated.4 About 30% patients with PAC and Peripheral Anterior Synechiae go on to develop PACG within a period of about 5 years.5 Use of Mydriatic agents can precipitate a severe angle closure attack in PAC and PACS patients.

The current gold standard in assessing anterior chamber angles is the gonioscopy which is subjective. More objective techniques like the Anterior Segment Optical Coherence Tomography (AS-OCT), pentacam, ultrasound biomicroscopy are being assessed for their reliability.6 Present study was aimed to compare gonioscopy versus anterior segment OCT for detecting angle closure in patients of angle closure glaucoma at a tertiary care center.

Present study was single-center, comparative study, conducted in department of Ophthalmology, at MIMER Medical College & Dr. BSTR Hospital, Yashwant Nagar, Talegaon Dabhade, Pune 410507, Maharashtra, India. Study duration was of 6 months (January 2024 to June 2024). Study was approved by institutional ethical committee.

Inclusion criteria

• Patients > 30 years of age, known case of PACG, PAC or PACS, either gender, willing to participate in present study

Exclusion criteria      

• Previous history of intraocular surgery.
• History of trauma in either eye.
• Anterior segment laser treatment for any cause.

Study was explained to participants in local language & written informed consent was taken. A thorough physical examination was carried out in all patients including assessment of other systems for any related contributory pathology. All patients undergone a complete ophthalmologic examination.

Detailed slit lamp bio microscopic examination will be carried out for the status of the anterior segment specifically to look for narrow anterior chamber angle. IOP measurement done by GAT. Fundus examination: Disc evaluation using 90 D lens. Gonioscopy to assess the anterior chamber angle using Sussman 4 mirror gonio lens. AS OCT to assess anterior chamber angle in 4 quadrants using TOPCON MAESTRO 2- 3D OCT.

Detailed slit lamp examination was performed with special attention to Anterior Segment morphology and IOP will be measured using Goldman Applanation Tonometry. Fundus examination and disc evaluation will be done using 90D lens on Slit Lamp Examination. Anterior Chamber Angles will be assessed using Sussman 4 mirror gonio lens. AS OCT will be done to assess anterior chamber angle in 4 quadrants using TOPCON MAESTRO 2- 3D OCT.

• AC Angle is considered closed on GONIOSCOPY if Posterior Trabecular Meshwork could not be seen in primary position without indentation.
• AC Angle is considered closed on AS OCT if any contact between peripheral Iris and anterior wall of Scleral Spur was noted.

Collected data was statistically analysed using SPSS version 23.0. The descriptive statistics was presented as mean with standard deviation for the continuous variables such as age and IOP. The categorical variables such as grades in the different quadrants of the anterior chamber with gonioscopy and anterior segment OCT were presented as frequency and percentages. The agreement between the two methods were assessed by comparing the angle grades in different quadrants and then applying the Kappa statistic.

In present study, total number of 60 Glaucoma patients were examined by Gonioscopy and AS OCT. Out of 60 patients of Glaucoma ratio of POAG: PACG was 1.94: 1. Male to female ratio was 1.14: 1. The majority of patients were in the age group of 51 to 60 years (58.33 %). Mean age of the study participants was 54.5 ± 7.92 years.

Table 1: General characteristics

Total 480 Angles were examined. Total number of Angles closed on Gonioscopy were 164 (34.17 %). Total number of Angles closed on AS OCT were 231 (48.13 %). The Anterior segment OCT turned out to be better than Gonioscopy & difference was statistically significant.

Table 2: Frequency distribution of angle closure in different quadrants.

The kappa statistic for the gonioscopy & AS-OCT was 0.734 showing ‘Moderate to Good’ agreement between Gonioscopy and AS OCT in diagnosing closed angle in all 4 quadrant angles.

Table 3: Agreement between Gonioscopy and AS-OCT in detecting Angle Closure

Glaucoma is a progressive optic neuropathy marked by anatomical abnormalities in the optic nerve head and visual field defects.7 While the eventual route of functional and structural loss for many forms of glaucoma is similar, a thorough assessment of drainage angle is necessary for proper therapeutic management and diagnosis.6 Very few clinicians can expertly detect angle closure correctly leading to significant undiagnosed/ misdiagnosed cases and the problem becomes even worse especially in developing countries due to lack of skilled manpower.2 For all such reasons, there is a need of a better, more convenient and an accurate tool to improve detection of angle closure.

Detection of angle closure is done by assessment of anterior chamber structures for which Gonioscopy has been the Gold Standard till now. It is low-cost, can be done quickly using a slit-lamp, provides dynamic observation of whole angle quadrant, and allows the indentation to distinguish between the synechia and appositional angle closure.8 Anterior Segment Optical Coherence Tomography (AS-OCT) is light-based, non-contact imaging modality, non-invasive diagnostic technique that provides higher image resolution than the UBM (axial resolution of 18 μm in Visante-Optical tomography vs. 50 μm in ultrasound bimicroscopy).9

In study by, Jaseena K & Rekha PS10 mean age of participants was 52.11 ± 5.37 years. Five (15.15%) of nasal angles and 4 (12.12%) of temporal angles identified as closed by gonioscopy were called as open by AS‑OCT. The Kappa statistic (0.59), pairwise correlation (0.60), and Lin’s concordance correlation coefficient (0.59) showed only moderate agreement and concordance between AS‑OCT and gonioscopy. AS‑OCT had a moderate sensitivity (73%) and better specificity (86.4%).

Though it is possible that AS-OCT may be detecting sub-clinical stages of angle closure as Baskaran et al.,11 found that eyes with more quadrants of angle closure on AS-OCT at baseline had a greater risk of angle closure on gonioscopy in the next 4 years. They also found that the subjects who had open angles on AS-OCT at baseline did not develop gonioscopic angle closure during follow up.

In study by Lune A et al.,12 mean age of the participants was 58.64 years. Of the 212 eyes found to have narrow angles on gonioscopy, 206 eyes (97.2%, 95% CI: 94.0%-99.0%) also had narrow angles on AS-OCT, while six eyes (2.8%, 95% CI: 1.0%-6.1%) were found to have open angles. The chi-square test for association yielded a p-value of <0.001, indicating a statistically significant relationship between AS-OCT and gonioscopy grading.

In study by Gandhi Y & Solu TM,13 50 Glaucoma patients were examined by Gonioscopy and AS OCT. Total number of Angles examined were 400. Total number of Angles closed on Gonioscopy were 136 (34%). Total number of Angles closed on AS OCT were 190 (47.5%). Agreement between Gonioscopy and AS OCT in detecting angle closure in all 4 quadrants was ‘Moderate to Good’ by Kappa Value. However, Gonioscopy and AS OCT imaging does not always agree in the Angle Closure assessments, but have their own advantages (Gonioscopy can distinguish appositional versus synechial angle closure, OCT imaging is more objective and rapidly performed without patient discomfort) and should be used together and not exclusively.

In a systematic review and meta-analysis, Desmond T et al.,1 noted that the sensitivity of AS-OCT ranged from 46 to 100% (median 87%). Twenty-one studies identified parameters that showed sensitivity above 80%. The specificity ranged from 55.3 to 100% (median 84%). AS-OCT demonstrates good sensitivity for detecting angle closure. It may provide an avenue to address high rates of undiagnosed angle closure, such as found in developing Asian countries. However, AS-OCT is not yet able to replace gonioscopy. Clinicians should consider whether the diagnostic accuracy of AS-OCT is acceptable for their specific clinical use before adopting it.

Anterior segment OCT is more efficient for detecting angle closure in patients of angle closure glaucoma as compared to gonioscopy. Using anterior segment OCT to examine anterior chamber angle and surrounding tissues helps in diagnosing early stages of disease and directing therapy. Agreement between Gonioscopy and AS OCT in detecting angle closure to be ‘Moderate to Good’. Thus, Gonioscopy and AS OCT imaging should be used together and not exclusively.

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