🔍 The Hidden Geometry of Vision: Understanding Concentric Macular Rings
In the intricate world of retinal imaging, few signs are as visually striking—and diagnostically powerful—as the Concentric Macular Rings (CMR) sign. First described in patients with foveal hypoplasia, this pattern of alternating bright and dark rings around the fovea has emerged as a noninvasive beacon for clinicians navigating the complexities of pediatric and genetic eye disorders.
🌀 What Are Concentric Macular Rings?
CMRs appear as circular bands around the fovea on ultra-widefield fundus photography, often resembling a fingerprint. These rings are not visible in standard fundus exams but become apparent at the Henle fiber layer, a retinal zone composed of obliquely oriented photoreceptor axons. Their presence reflects a distinctive retinal geometry, often linked to arrested foveal development.
🧬 The Developmental Backstory
Normal foveal maturation involves three key processes:
- Centrifugal displacement of inner retinal layers
- Cone photoreceptor specialization
- Centripetal migration of cones
Disruption in any of these stages results in foveal hypoplasia, a condition marked by poor visual acuity and often accompanied by infantile nystagmus. The CMR sign is a visual echo of this developmental arrest, offering clues about the severity and timing of the disruption.
🧪 Diagnostic Power
In a landmark study of 32 patients, researchers found that the horizontal diameter of the largest outer ring strongly correlated with the grade of foveal hypoplasia:
- Grade 1: ~1.5 mm
- Grade 2: ~2.4 mm
- Grade 3: ~3.3 mm
- Grade 4: ~4.4 mm
This correlation allows clinicians to estimate visual prognosis even when OCT imaging is not feasible, such as in young children or patients with unstable fixation30124-X/fulltext).
🧠 Multimodal Imaging Insights
The CMR sign is best appreciated through:
- Ultra-widefield fundus photography (Optos)
- En face OCT at the Henle fiber layer
- Fundus autofluorescence (loss of central attenuation)
- Near-infrared reflectance (absence of bowtie reflex)
These tools together paint a comprehensive picture of retinal architecture, especially in conditions like albinism, aniridia, Hermansky-Pudlak syndrome, and prematurity.
In addition to the Concentric Macular Rings (CMR) sign, several other diagnostic indicators can help identify foveal hypoplasia and related retinal conditions—especially when OCT imaging is challenging. Here’s a breakdown of key signs and tools:
🔍 Structural OCT Features
These are considered the gold standard for diagnosing foveal hypoplasia:
- Absence of foveal pit: No central depression in the retina.
- Persistence of inner retinal layers: Layers like the ganglion cell layer remain at the foveal center.
- No outer segment lengthening: Cone photoreceptors don’t elongate properly.
- Lack of outer nuclear layer widening: Indicates poor cone packing density.
These features are graded from Grade 1a (mild) to Grade 4 (severe) hypoplasia, with increasing structural disruption and decreasing visual acuity.
🧪 Fundus Autofluorescence (FAF)
- Loss of central attenuation: Normally, the fovea appears darker due to reduced autofluorescence. In hypoplasia, this attenuation is absent.
- Useful in patients with nystagmus or poor fixation where OCT is hard to obtain.
🌑 Near-Infrared Reflectance (NIR)
- Absence of bowtie reflex: A normal fovea shows a bowtie-shaped reflectance pattern. Its absence suggests structural abnormality.
- Not as sensitive as OCT but helpful in multimodal imaging.
🧫 En Face OCT at Henle Fiber Layer
- Reveals alternating hyper- and hyporeflective bands forming concentric rings.
- These correlate with the CMR sign and are exclusive to the Henle fiber layer.
👁️ Clinical Signs
- Infantile nystagmus: Often co-occurs with foveal hypoplasia.
- Reduced best-corrected visual acuity (BCVA): Severity correlates with hypoplasia grade.
- Poor foveal reflex on standard fundus exam.
👁️ Beyond the Rings
While some researchers have speculated that CMRs might be imaging artifacts caused by nystagmus, recent evidence shows they occur even in patients without nystagmus, reinforcing their anatomical origin. The rings are exclusive to the Henle fiber layer and reflect vertical orientation of photoreceptor axons, a hallmark of underdeveloped foveal structure.
📚 Citation:
Ramtohul, P., Comet, A., & Denis, D. (2020). Multimodal Imaging Correlation of the Concentric Macular Rings Sign in Foveal Hypoplasia: A Distinctive Henle Fiber Layer Geometry. Ophthalmology Retina, 4(9), 946–953. Read the full study
🧬 Case Overview
- A 5-year-old girl with Turner syndrome—specifically the isochromosome Xq karyotype [46,X,i(X)(q10)]—was referred for an ophthalmic exam.
- Her genetic profile shows a deleted short arm (Xp) and duplicated long arm (Xq) of the X chromosome.
👁️ Ophthalmic Findings
- Wide fundus photography revealed a concentric macular rings sign, a rare retinal pattern.
- Optical Coherence Tomography (OCT) showed a well-developed fovea with dentate-like alternating hyperreflective and hyporeflective bands in the Henle’s fiber layer.
🔍 Clinical Significance
- Although this sign is most commonly linked to foveal hypoplasia, it can also appear in:
- Normal retinas
- Inherited retinal diseases
- Tractional retinal disorders
👁️ Clinical Case Overview
- A 5-year-old boy presented with reduced visual acuity (20/40 in both eyes) and nystagmus.
- His medical history included recurrent infections and a bleeding tendency.
🧬 Diagnostic Findings
- Color Fundus Imaging: Revealed retinal hypopigmentation and a distinctive concentric macular rings sign.
- Infrared Reflectance Imaging: Showed absence of the typical “bow-tie” foveal reflex.
- Spectral Domain OCT: Indicated bilateral grade 3 foveal hypoplasia.
- Peripheral Blood Analysis: Identified giant azurophilic inclusions in neutrophils—hallmark of Chediak-Higashi Syndrome.
🔍 Clinical Significance
- The concentric macular rings sign is a notable feature of foveal hypoplasia.
- It can aid diagnosis, especially when OCT imaging is not feasible.