Primary Open-Angle Glaucoma With Improved Visual Outcomes Following Audio-Luminous Biofeedback Training: A Case Report

Introduction

Glaucoma, characterized by progressive optic neuropathy and the loss of retinal ganglion cells and optic nerve fibers, remains the leading cause of irreversible blindness worldwide [1,2]. Based on the configuration of the iridocorneal angle, glaucoma is classified as either primary open-angle (POAG) or primary angle-closure (PACG), with POAG being the most prevalent subtype [1]. Its global prevalence is estimated at 3.05% in individuals aged 40 to 80 years for POAG and 0.5% for PACG, with incidence increasing alongside life expectancy [3].

Because POAG often remains asymptomatic until advanced stages, regular screening is critical for early diagnosis. Evaluation consists of fundoscopic evaluation of the optic nerve, assessment of intraocular pressure, and complementary exams such as visual field and optical coherence tomography (OCT) [4]. Current management focuses on lowering intraocular pressure – the only modifiable risk factor – through topical therapy, laser procedures, or surgery [5].

However, visual function loss in glaucoma extends beyond what is captured by standard visual field or acuity assessments [1,5]. Lorenzana et al [6] demonstrated that many patients experience difficulties with depth perception, contrast sensitivity, and daily activities despite stable clinical parameters. This highlights the importance of rehabilitative strategies that address visual performance and quality of life.

Visual biofeedback training is a rehabilitative approach designed to enhance visual function in patients with ocular disease or reduced vision by optimizing fixation behavior. In the presence of central or paracentral visual impairment, patients often develop a preferred retinal locus (PRL), an eccentric retinal area used habitually for fixation when the fovea is no longer functionally optimal. However, the spontaneously adopted PRL is not always located in the area of highest residual sensitivity. Biofeedback training utilizes microperimetry to identify a more advantageous retinal region, referred to as the trained retinal locus (TRL), and employs structured visual and auditory stimuli to direct the patient’s attention toward this area. Through repeated stimulation and feedback, patients learn to shift and stabilize fixation onto the TRL, thereby improving oculomotor control and fixation stability. Over time, this process promotes the functional adoption of a more efficient retinal locus, effectively optimizing the PRL [7]. These adaptations can lead to improved visual performance and enhanced binocular function by facilitating more coordinated and stable visual input between both eyes [8–10].

Nevertheless, audio-luminous stimulation has shown success in improving fixation stability and visual function in diseases affecting central vision, such as age-related macular degeneration (AMD), Stargardt disease, and hemianopsia [1,11]. Through microperimetry-guided training, patients can learn to relocate fixation to retinal loci with higher sensitivity – known as trained retinal loci (TRL) – thus improving visual performance [11]. Although BT is used worldwide, there is still no consensus regarding the optimal frequency and number of sessions [12].

Our group has previously published a case report demonstrating the efficacy of audio-luminous biofeedback training in improving visual function in a patient with epiretinal membrane. In that case, functional gains were achieved through microperimetry-guided fixation retraining and optimization of a TRL, supporting the concept that targeted visual rehabilitation can enhance residual visual capacity [13]. These findings suggest that the benefits of biofeedback training can extend beyond a single disease entity and could be applicable across different types of visual impairment.

Reports on BT in glaucoma are scarce. Despite increasing interest in non-pharmacological interventions for glaucoma, biofeedback training has been explored in only 1 study to date [14]. Most prior studies, including our previous report, have focused on conditions affecting central vision or neurological pathways, where the mechanisms of visual loss differ from those seen in glaucomatous optic neuropathy [5,12]. As glaucoma is primarily characterized by progressive peripheral visual field loss with relative central sparing until late stages, the applicability of biofeedback training in this context remains uncertain. This highlights an important gap in the literature and underscores the need to explore whether the functional benefits observed in other conditions can be extended to patients with glaucoma.

This report describes the case of an 82-year-old man with bilateral primary open-angle glaucoma with improved visual outcomes following audio-luminous biofeedback training.

Case Report

BASELINE EVALUATION:

BCVA measured 20/25 (right eye) and 20/100 (left eye) using the ETDRS charts. Reading performance with 100% contrast was 20/25, and with 10% contrast was 20/50, as measured with the Colenbrander mixed contrast test. Stereopsis was absent on the Titmus Stereotest (no fly recognition). Eye alignment presented orthophoria. Reading speed (MNREAD app) was 79 words/min (reduced) with a critical print size of 20/25.

MAIA microperimetry (10-2 program, CenterVue, Padova, Italy) showed a reduced mean retinal sensitivity in the right eye (16.8 dB) with a superior paracentral scotoma, and severely reduced sensitivity in the left eye (2.0 dB) with a tubular pattern. A relatively preserved region 2° inferior to the PRL was identified in both eyes. A base-down prism with 3 prism diopters in each eye could improve his vision, and biofeedback training in the right eye could produce a similar effect. Therefore, biofeedback training was selected prior to prescribing prisms (Figure 1A, 1B).

Given the residual retinal sensitivity inferiorly, BT was initiated in the right eye targeting a TRL located 2° below the preferred retinal locus (PRL). The PRL refers to the retinal area that a patient habitually uses for fixation when the fovea is no longer functional, whereas the trained retinal locus (TRL) corresponds to a newly designated eccentric retinal area selected and trained to improve fixation stability and visual performance. Training the fixation stability and improving oculomotor functions lead to an optimized new PRL and better functional binocular vision. We conducted 4 weekly 20-min audio-luminous BT sessions (80 min total) with the patient.

POST-TRAINING OUTCOMES:

After BT, BCVA improved to 20/20 (right) and 20/60 (left) EDTRS. Binocular near vision reached 20/20, and stereopsis improved to 800 arc seconds on the Titmus Stereotest. Binocular contrast sensitivity improved to 20/20 (100% contrast) and 20/40 (10% contrast). Reading speed increased to 131 words/min with a critical print size of 20/20.

Microperimetry confirmed functional improvement: average retinal sensitivity increased to 18.2 dB (right eye) and 2.8 dB (left eye). Fixation stability improved (BCEA 63% decreased from 3.57 deg² to 2.9 deg²).

To maintain binocular perception, prism correction was refined to 1 base-down in the right eye and 1 base-down in the left eye, achieving binocular BCVA of 20/25. Figures 1–5 illustrate the micro-perimetric and functional improvements.

Discussion

Our case highlights the potential of audio-luminous BT as a rehabilitative adjunct in advanced POAG, particularly for patients with bilateral functional impairment and limited remaining treatment options.

In a previous report from our group, similar improvements in visual performance were observed following audio-luminous biofeedback training in a different clinical context. While that case involved a distinct underlying pathology, it provided early evidence supporting the role of biofeedback-guided rehabilitation in enhancing functional vision [13].

Subsequent studies have further explored the application of biofeedback training (BT) across a range of ocular and neuro-ophthalmic conditions. In patients with age-related macular degeneration, BT has been associated with visual function improvements, suggesting enhanced utilization of preferred retinal loci [7]. Similarly, in pediatric idiopathic infantile nystagmus, audio-visual BT has been reported to improve visual function and fixation control. Isolated case reports have also demonstrated functional gains following BT in children with nystagmus using audio-luminous stimulation paradigms [15].

Beyond retinal and oculomotor disorders, BT-based rehabilitation has been investigated in patients with hemianopia, where immersive audio-visual stimulation protocols have shown potential in improving visual field awareness and functional performance [16].

Several parallels can be drawn between the present case and our prior reports. In both instances, patients demonstrated improvements in visual acuity, fixation stability, and overall functional vision following biofeedback training. These outcomes were achieved through targeted use of residual retinal sensitivity and the establishment of a more effective trained retinal locus.

In this context, the present case gains relevance by contributing to an underexplored area and supporting a still emerging concept in visual rehabilitation.

Glaucoma, as previously noted, is a leading cause of acquired irreversible blindness. Patients often remain asymptomatic until advanced stages, when significant visual field loss has already occurred. This underscores the importance of exploring effective visual rehabilitation strategies aimed at maximizing residual function and improving patients’ quality of life, even in advanced disease stages [5].

While BT has been extensively investigated in retinal disorders involving central vision loss, such as AMD and Stargardt disease [17], its utility in glaucomatous optic neuropathy remains poorly defined. In the early 2000s, Sabel et al [14] introduced a form of vision restoration therapy that uses structured visual stimulation targeted along the interface between intact and impaired visual fields. This approach, although questioned at the time, was shown to promote expansion of the sensitive visual field in patients with injuries affecting the brain or optic nerve. Their findings support the concept that biofeedback training can enhance functional vision, underscoring the potential of brain training as a rehabilitative approach in glaucomatous optic neuropathy. Our findings align with those of Sabel et al and indicate that even in predominantly peripheral field loss, fixation retraining can enhance residual retinal function due to the presence of central scotomata in these cases.

Biofeedback training has been applied across various ocular and neurological conditions as a rehabilitative strategy. Its proposed mechanism involves enhancing visual performance by improving neural transmission within the retina and along retinal–brain pathways, thereby supporting the concept of a “remapping phenomenon” described by several authors [18]. Andrade et al [19] reported that individuals with glaucoma often remain unaware of their scotomata. In cases of optic pathway injury, the cortical receptive fields corresponding to the damaged region are not completely inactive; rather, they may become more responsive to stimuli in adjacent areas. This increased sensitivity is thought to occur through horizontal cell interactions within the inner retinal layers, as well as through connections in the lateral geniculate nucleus and visual cortex.

This remodeling process is hypothesized to occur in 2 stages: an initial redistribution of receptive fields surrounding the damaged area, followed by a gradual expansion of neuronal projections into adjacent regions, resulting in a modified visual field. While growing evidence supports such adaptive reorganization, functional improvements during training are also thought to reflect changes within visual pathways, including increased synaptic efficiency, faster interneuronal signaling, and enhanced neurotransmitter turnover. However, the precise mechanisms that initiate and drive these neuroplastic changes remain incompletely understood [8].

Previous studies have shown that BT can enhance neural efficiency and promote visual cortex reorganization through neuroplastic mechanisms [18,19]. While such mechanisms can contribute to the overall visual improvements observed, the enhancement in the left visual functions in our case is more plausibly attributed to the more effective use of residual retinal sensitivity, rather than cortical reorganization per se. By training a residual higher retinal sensitivity area (TRL) that has a correspondent area in the right eye, BT enhanced the coordination between both eyes, promoting more efficient binocular integration. This functional alignment optimized use of residual retinal areas, improved binocular correspondence, reduced interocular rivalry, and improved fixation stability, which together contribute to measurable gains in visual performance [8–10]. These observations suggest that biofeedback training acts through multiple complementary mechanisms.

Moreover, in our case, post-training improvements were associated with a reduction in the required yoked prisms strength, indicating enhanced sensory fusion and fixation coordination. This enhancement likely reflects a relocation of the preferred retinal loci (PRLs) and strengthened binocular integration, as both eyes began utilizing retinal regions with higher residual sensitivity. As a result, interocular rivalry – defined as the perceptual alternation or suppression that occurs when dissimilar images are presented to each eye due to impaired binocular integration – was reduced [10], consistent with evidence that rivalry diminishes when visual acuity improves in the poorer eye and when fixation shifts to more eccentric, yet functionally adaptive, retinal areas. The findings in this case suggest that biofeedback training can also contribute to improved sensory fusion and interocular coordination. This highlights a potentially broader role for biofeedback training in enhancing binocular visual function, particularly in patients with asymmetric or bilateral disease [8–10].

Following BT, our patient demonstrated significant gains in visual performance, improved BCVA, contrast sensitivity, reading speed, fixation stability, and, notably, improvement in stereopsis. Our results highlight BT’s potential in glaucoma rehabilitation, warranting further controlled studies.

Taken together, our prior report, previous studies, and the present case support the emerging concept that audio-luminous biofeedback training can have broader applicability across different types of visual impairment. However, the extent and mechanisms of functional improvement likely depend on the underlying disease, the location of visual field loss, and the availability of residual retinal function. Further studies are needed to better define these relationships and optimize patient selection.

Conclusions

Audio-luminous biofeedback training has the potential to serve as an innovative, non-invasive adjunctive therapy with no adverse effects for patients with advanced glaucoma and limited conventional treatment options. In this case, BT resulted in measurable and clinically meaningful improvements in acuity, contrast sensitivity, fixation stability, reading speed, and stereopsis. These findings support that microperimetry-guided BT can enhance functional vision and binocular performance even in optic neuropathies. Future studies should investigate long-term outcomes and underlying neurophysiological mechanisms to better define its role in glaucoma rehabilitation.