Spiculated Speculation: When RP and Glaucoma Collide

Retinitis pigmentosa (RP) and glaucoma are both progressive diseases that can lead to peripheral visual field loss, making differentiation between the two challenging. While RP is an inherited retinal dystrophy affecting the retina photoreceptors and leading to concentric field constriction,¹ glaucoma is an optic neuropathy causing characteristic nerve fiber layer damage and arcuate defects. Misdiagnosis or incorrect attribution of visual field loss can lead to inappropriate treatment strategies, particularly the overuse of IOP-lowering medications in patients with RP. Here, we present the case of a patient whose progressive RP helped lead us to the correct diagnosis and the most appropriate management plan.

CASE PRESENTATION

A 69-year-old male patient presented with complaints of frequently bumping into objects, increasing difficulty with night vision, and progressive peripheral awareness loss over several years. He also reported hearing loss. His medical history was not significant for any systemic conditions, and his family history was noncontributory. His ocular history was significant for myopia, without prior ocular surgery or trauma.

His BCVA was 20/20 OU. He did not have an afferent pupillary defect, his extraocular movements were full and unrestricted, and his IOP was within normal limits. Anterior segment examination showed a normal cornea, clear lens, and deep anterior chamber. Posterior segment evaluation showed optic nerve head (ONH) pallor, attenuated retinal vessels, and midperipheral bone spicule pigmentation.

On fundus photography, progressive ONH pallor and vessel attenuation was noted from 2019 to 2022 (Figure 1). OCT showed progressive thinning of the neuroretinal rim from 2021 to 2022 (Figure 2) and early macular atrophy without cystoid macular edema (Figure 3). Visual field testing showed concentric constriction of the visual fields from 2021 to 2022, consistent with RP (Figure 4).

Diagnosis and Management

Differential diagnoses included RP, Usher syndrome, glaucomatous optic atrophy, and late-onset cone-rod dystrophy. The clinical findings and ancillary testing led to a diagnosis of Usher syndrome type 2, characterized by progressive RP and hearing loss. The management plan included referral to a low vision specialist for mobility training, genetic testing for confirmation of Usher syndrome, coordination with audiology for a hearing assessment, nutritional counseling including vitamin A supplementation per guidelines, patient education on disease progression and support resources, and annual monitoring with OCT, fundus photography, and visual field testing.

DISCUSSION

Usher syndrome is a rare genetic disorder that results in combined vision and hearing impairment.² It can be classified into three main types based on the severity and onset of hearing and vestibular dysfunction:

Type 1

Profound congenital hearing loss, severe vestibular dysfunction leading to early balance issues, and early-onset RP typically manifesting in childhood.

Type 2

Moderate-to-severe congenital hearing loss, normal vestibular function, and RP that presents later in adolescence or early adulthood.

Type 3

Progressive hearing loss and variable vestibular dysfunction, with RP onset in adolescence or adulthood. This type is the rarest and varies in presentation.

Differentiation relies on genetic testing, audiological evaluations, and clinical progression of RP. Early genetic diagnosis can guide prognosis and support services for patients.

Differentiating RP From Glaucoma

Patients with RP who are also glaucoma suspects present a diagnostic challenge. Both conditions can lead to peripheral vision loss, but the underlying mechanisms differ. Visual field loss in patients with RP typically manifests as concentric constriction, with relative sparing of central vision until later stages.³ Peripheral scotomas increase gradually over time. Visual field loss in patients with glaucoma often presents as arcuate defects, nasal steps, or paracentral defects that respect the horizontal meridian.³

When differentiation is difficult, ONH OCT findings become crucial. RP-related damage primarily affects the outer retina and photoreceptor layers, leading to generalized retinal thinning. Glaucoma-associated damage primarily affects the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC), showing characteristic thinning patterns. Physicians should assess whether the visual field loss correlates with RNFL and GCC damage on OCT to determine whether RP or glaucoma is the primary driver of disease progression. Longitudinal monitoring of structural changes is essential in managing these complex cases.

OUTCOME OPTIMIZATION

Early detection and a comprehensive care plan, including genetic counseling and vision rehabilitation, are essential to optimize the patient’s quality of life.⁴ Misdiagnosing by assuming the visual field loss is solely due to glaucomatous damage could lead to unnecessary over-medication, exposing patients to potential side effects from IOP-lowering medications without clinical benefit. In such cases, physicians should rely heavily on ONH OCT findings to differentiate disease progression. If visual field defects do not correlate with characteristic RNFL or GCC damage, caution should be exercised before escalating glaucoma treatment. Longitudinal monitoring with multimodal imaging is critical to ensure an accurate diagnosis and appropriate management strategy.

Continued research into retinal gene therapies and neuroprotective strategies may help guide treatment for patients with inherited retinal dystrophies such as Usher syndrome.