Glaucoma is a neuropathy characterized by progressive degeneration of the optic nerve caused by the loss of ganglion cells in the retina. It is the leading cause of irreversible blindness worldwide.^(1,2) Early detection and intervention are crucial for preventing progressive vision loss. Currently, assessment of the retinal nerve fiber layer (RNFL) using optical coherence tomography (OCT) plays a central role in glaucoma diagnosis and management. The main alterations are the thinning of the RNFL and the progressive increase in the cupping of the optic disc.⁽³⁾ While studies have established typical RNFL thicknesses in glaucoma patients internationally, current data specific to South America, and Ecuador in particular, are lacking. Glaucoma diagnosis and monitoring in Ecuador currently relies on OCT device parameters derived from studies conducted primarily on European and North American populations. This raises concerns about the applicability of these norms to the Ecuadorian population due to potential ethnic variations. Therefore, characterizing the primary RNFL changes in this region is crucial for identifying any variations or patterns that could improve glaucoma diagnosis and management.

Currently, only one national study has investigated RNFL thickness in glaucoma patients. Carrión et al. found the average RNFL thickness to be 87.58 µm in the right eye and 87.51 µm in the left eye.⁽⁴⁾

Despite global advances in glaucoma imaging, there remains a significant gap in region-specific data from Latin America, particularly regarding RNFL thickness in glaucomatous eyes. Very few studies have evaluated RNFL thickness in Latin American populations, and the existing ones are primarily focused on healthy individuals. For example, a cross-sectional study conducted in Brazil by Zangalli et al.⁽⁵⁾ assessed peripapillary RNFL thickness in healthy participants of different ethnic backgrounds. They reported a mean global RNFL thickness of 99.59 μm (standard deviation [SD] ± 9.57) in individuals of European descent, 103.53 μm (SD ± 11.59) in African descent, and 103.52 μm (SD ± 9.64) in individuals of mixed ancestry. These findings demonstrate considerable interethnic variability and highlight how structural differences may influence baseline OCT measurements. Furthermore, these values differ from those observed in the United States and European cohorts, emphasizing the potential limitations of extrapolating normative data across diverse populations.

Given Ecuador's multiethnic composition and the scarcity of local research on glaucomatous RNFL changes, there is an urgent need to generate population-specific data. This study aims to characterize structural optic nerve changes in Ecuadorian glaucoma patients using optical coherence tomography data from 2015 to 2022. In doing so, it seeks to enhance diagnostic precision and inform more tailored clinical management strategies within this demographic context.

This retrospective, quantitative, descriptive, and observational study analyzed anonymized data from patients diagnosed with glaucoma who underwent OCT at the Ophthalmic Center Exilaser in Cuenca, Ecuador, between January 2, 2015, and July 31, 2022. Exilaser is a leading ophthalmological referral center in Cuenca, one of the few in the city equipped with OCT technology. Due to the limited availability of OCT in public Ecuadorian medical facilities and the surrounding region, this center serves a broad population from southern Ecuador.

The study population comprised patients aged 18 years or older who had a pre-existing diagnosis of primary open-angle glaucoma (POAG) meticulously documented in their medical records by the center's ophthalmology specialists. These diagnoses were established based on a comprehensive clinical evaluation, considering the presence of at least two of the following cardinal signs:

A gonioscopic study was routinely performed to classify the iridocorneal angle and definitively rule out angle-closure mechanisms, ensuring an accurate diagnosis of POAG. Records were excluded if they presented: insufficient data; an average nerve fiber count of fewer than 10 in any quadrant (indicating recording error); a signal strength ≤ 5; retinal diseases other than glaucoma; ametropia ≥ 4 D; or if the patient was not from South America.

The following variables were analyzed:

A total of 446 eyes were initially identified. After applying the exclusion criteria (figure 2), 301 eyes from 162 patients with POAG were included in the analysis.

This retrospective study examined peripapillary RNFL and optic disc changes in glaucoma patients, aiming to identify the most vulnerable areas and establish local reference ranges for glaucoma-related OCT parameters using the Nidek 330, thus informing future research. Our key findings include: a mean global peripapillary RNFL thickness of 72.97 µm ± 16.48 (range 34-116), with the superior, inferior, nasal, and temporal sectors affected in descending order; and clock-hour sectors 1, 5, 7, 11, and 12 as the most frequently altered. These results are significant as they highlight potential initial areas of glaucomatous damage in Ecuadorian patients, even prior to symptom onset.

The study population had a mean age of 64 ± 14.76 years, was predominantly female, and presented with a mean IOP of 17.43 ± 6.72 mmHg. These demographics align with previous research. Daneshvar et al. reported a mean age of 68 years and a female majority (53:42) in their glaucoma progression study.⁽⁶⁾ Similarly, Trenkić-Božinović et al.⁽⁷⁾ and Wong et al.⁽⁸⁾ reported mean ages of 65.49 ± 9.36 and 65.6 ± 12.2 years, respectively, in their studies of POAG. Wong et al. also reported a mean IOP of 14.38 ± 2.75 mmHg. The similarity in age and the controlled IOP in our study likely reflects the use of ocular antihypertensive medications. The higher proportion of women in our study is consistent with other research indicating a greater female prevalence of glaucoma.^(6,8,9) Our finding of the highest prevalence in the ≥ 65 age group (50.83%) echoes Kreft et al.⁽⁹⁾ German study, which identified the 70 to 74 age range (21.1%) as most affected, further supporting the link between advanced age and glaucoma.

Forty percent of our open-angle glaucoma patients presented with comorbidities. This aligns with Torabi et al.⁽¹⁰⁾ findings on glaucoma risk factors, in which 31% of hypertensive patients and 4.4% of diabetic patients also had glaucoma. Kreft et al.⁽⁹⁾ identified hypertension (28.83%), diabetes mellitus (23.69%), and other conditions as risk factors for glaucoma. Similarly, Sun et al.⁽¹¹⁾ found significant associations between glaucoma and hypertension (OR 1.36), diabetes (OR 2.5), and dyslipidemia (OR 1.75).

The mean global RNFL thickness in our study (72.97 µm) was derived from 301 eyes using spectral-domain OCT (Nidek 330) with strict image quality criteria and refractive error limits. A previous local study reported a mean global RNFL thickness of 87.54 µm in suspected glaucoma patients in 2016.⁽⁴⁾ No other similar studies from Cuenca, Ecuador, were found.

It is well-established that OCT studies worldwide consistently demonstrate a reduced RNFL thickness in individuals with glaucoma compared to those without the disease.^(12,13) Research has further indicated that the earliest and most sensitive indicators of glaucomatous damage are typically observed in the global average, inferior, and temporal sectors of the RNFL.⁽¹⁴⁾ A systematic review supports the high diagnostic accuracy of OCT, reporting ≥90% sensitivity and specificity in identifying glaucoma.⁽¹⁵⁾

While international studies have evaluated global RNFL thickness (Table 4), our mean RNFL thickness differs notably from some reported values. Indeed, studies worldwide have explored normal RNFL thickness, revealing variations potentially linked to ethnicity, location, and measurement methods. For instance, Jammal et al. found a mean RNFL thickness of 82.4 ± 17.0 µm in a US population, suggesting potentially thicker RNFLs compared to other groups.⁽¹⁶⁾ This difference could be due to genetics, environment, or how the measurements were taken. Conversely, studies in China (Hou et al.)⁽¹⁷⁾ and Germany (Heindl et al.)⁽¹³⁾ reported lower average RNFL thicknesses, 70.5 ± 11.8 µm and 70.03 ± 18.2 µm respectively, possibly attributable to anatomical differences between ethnic groups or variations in imaging techniques. These findings underscore the critical need for population-specific RNFL data for accurate diagnoses, which our study aims to address for the Ecuadorian context. These variations could also be attributed to differences in technology, equipment, and population characteristics. RNFL thickness is recognized as a highly sensitive parameter, with Arnould et al.⁽¹⁸⁾ reporting 80.9% sensitivity and 87.14% specificity.

Regarding RNFL quadrants and clock-hour sectors, our findings partially align with previous research. Kim et al.⁽¹⁹⁾, using Cirrus OCT, found the thinnest nasal and temporal quadrants in glaucoma, similar to our results. However, we found the inferior and superior sectors to be most frequently classified as pathological, despite having higher average thicknesses. This highlights the importance of considering both thickness and regional vulnerability in glaucoma, as different areas may have varying susceptibility to damage.⁽²³⁾ Our study confirmed the ISNT rule (inferior, superior, nasal, temporal) in healthy eyes⁽¹⁸⁾, but observed a deviation in the nasal and temporal sectors in our glaucoma patients, likely due to glaucomatous damage.

Our clock-hour sector analysis revealed sectors 1, 5, 7, 11, and 12 as most frequently pathological, while sectors 3, 4, 8, and 9 showed the lowest thicknesses. This partially aligns with Kim et al.,⁽¹⁹⁾ who also identified these sectors as thinned, although the specific sectors varied slightly. Trenkić-Božinović et al.⁽⁷⁾ also reported reduced thickness in similar clock-hour sectors. These variations likely reflect methodological differences and disease severity. Our findings are consistent with Hood ⁽²⁴⁾ description of vulnerable areas in the optic disc, corresponding to similar clock-hour sectors.

Our optic disc findings included horizontal cup-to-disc ratio of 0.79 ± 0.14, and vertical cup/disc ratio of 0.75 ± 0.13. These are similar to those reported by Wong et al.⁽⁸⁾ and Anton et al.,⁽²⁵⁾ who found increased cup-to-disc ratios in glaucoma. These findings emphasize the importance of optic disc parameters in glaucoma assessment.⁽²⁶⁾

This study characterized optic nerve parameters with optical coherence tomography in glaucoma patients from Cuenca, Ecuador, revealing a mean global retinal nerve fiber layer thickness of 72.97 µm, with over 75% classified as pathological. Clock-hour sectors 1, 5, 7, 11, and 12 were most frequently affected. The horizontal cup-to-disc ratio represented a higher percentage of damage. These findings provide valuable insights into glaucoma characteristics in this Ecuadorian - Latin American population.