Optical Coherence Tomography Studies Provides New Insights into Diagnosis and Prognosis of Infantile Nystagmus: A Review

Measurement of macular thickness with optical coherence tomography: impact of using a paediatric reference database and analysis of interocular symmetry

PURPOSE

Optical coherence tomography (OCT) software is used to classify abnormality of macular thickness by colour category based on reference data from adult series. We assessed the impact of using paediatric reference thickness values for macular thickness instead of adult reference values.

METHODS

Cross-sectional study. Primary and tertiary healthcare setting. Out of 140 healthy participants aged 5 to 18 years, 126 were eligible, 83% from European origin. Following a dilated eye examination and cycloplegic refraction, participants underwent macular scanning with OCT (Topcon 3D OCT-2000). Macular thickness paediatric reference values were recorded by spherical equivalent (SE) and sex, and the specific agreement between paediatric and adult reference values below or equal to percentile 5 and above percentile 95 was estimated. The absolute interocular differences for all macular parameters were determined.

RESULTS

Multivariate regression analysis confirmed statistically independent positive associations between SE and average thickness, total volume, and temporal and inferior outer quadrants (all p values ≤ 0.003). The analysis also revealed higher values in males for average thickness, central thickness, and all inner macula quadrants (all p values ≤ 0.039). The use of the adult database only detected 49% of the extreme values (≤ p5 and > p95) in our paediatric sample. The 95th percentile limits for absolute interocular differences for all macular parameters ranged from 12 to 17 μm.

CONCLUSIONS

OCT-based macular reference values for paediatric SE and sex improve detection of children with abnormal macular thicknesses. Interocular differences exceeding standard references for macular parameters should be considered for further examinations.

Nystagmus and optical coherence tomography findings in CNGB3-associated achromatopsia

PURPOSE

To describe the nystagmus characteristics of subjects with molecularly confirmed CNGB3-associated achromatopsia and report the spectral domain optical coherence tomography (SD-OCT) findings in these individuals.

METHODS

Adults and children with CNGB3-achromatopsia underwent visual acuity testing, ocular motility assessments, video nystagmography, and SD-OCT imaging. Qualitative assessment of foveal structure was performed by grading SD-OCT images into one of five categories.

RESULTS

A total of 18 subjects (11 adults) were included. The majority demonstrated a phoria, with manifest strabismus present in only 3 subjects. The predominant nystagmus waveform within the cohort was pure pendular. Nine individuals demonstrated a mixture of waveforms. Nystagmus frequencies were 4-8 cycles/second, with no notable differences in eye movements between adults and children. SD-OCT imaging revealed a continuous ellipsoid zone (EZ) at the fovea in 2 subjects (grade 1) and EZ disruption (grade 2) in the remaining 16. Retinal structure characteristics were symmetrical in both eyes in each subject.

CONCLUSIONS

In our study cohort, nystagmus in CNGB3-associated achromatopsia had distinctive features, and the majority of subjects had retinal abnormalities at the fovea on SD-OCT. Early use of SD-OCT in the clinical work-up may eliminate the need for more invasive investigations, such as neuro-imaging.

Genotype and Phenotype Spectrum of FRMD7-Associated Infantile Nystagmus Syndrome

Purpose

We investigate the genotype and phenotype spectrum of FRMD7-associated infantile nystagmus syndrome in Korean probands.

Methods

A total of 37 patients with infantile nystagmus syndrome were recruited prospectively for genetic analysis. We performed polymerase chain reaction (PCR)-based direct sequencing and haplotype analysis for FRMD7. Detailed ophthalmic examinations and eye movement recordings were compared between FRMD7 and non-FRMD7 groups.

Results

In 13 (35%) of 37 patients, five different mutations of FRMD7 were detected: start codon mutation c.1A>G, splice site mutation c.162+6T>C, and three missense mutations (c.575A>C, c.722A>G, and c.875T>C). The latter mutation was identified in seven unrelated patients, and always was accompanied with two single nucleotide polymorphisms of exon 12 (rs6637934, rs5977623). Compared to non-FRMD7 groups, a cup-to-disc ratio was significantly decreased in FRMD7 groups (P < 0.001), and a disc-macula distance to disc diameter ratio markedly increased in the FRMD7 group (P = 0.015). Most patients in the FRMD7 group had at least two types of the nystagmus waveforms, and the most common type was unidirectional jerk nystagmus (75%), such as pure jerk and jerk with extended foveation, followed by pendular (25%), bidirectional jerk (19%), and dual jerk (6%) nystagmus. No significant differences were observed between FRMD7 and non-FRMD7 groups in terms of the nystagmus waveform, presence of periodic alternating nystagmus, and mean foveation time.

Conclusions

We identified five FRMD7 mutations in 35% of our infantile nystagmus syndrome cohort, expanding its mutational spectrum. The missense mutation c.875T>C may be a common mutation arisen from the founder effect in Korea. Optic nerve dysplasia associated with FRMD7 mutations suggests that the abnormal development of afferent visual systems may affect neural circuitry within the oculomotor system.

Retinal microstructures are altered in patients with idiopathic infantile nystagmus

PURPOSE

To compare segmented retinal layer thicknesses between patients with idiopathic infantile nystagmus (IIN) and controls.

METHODS

This retrospective case-control study included 66 patients with IIN and 66 age-matched controls. The retinal layers were examined using spectral domain optical coherence tomography with autosegmentation. Central foveal thickness (CFT), outer nuclear layer (ONL), and outer segment length (OSL) thickness were measured at the fovea center. Mean values for retinal nerve fiber layer, ganglion cell inner plexiform layer (GCIPL), inner nuclear layer, outer plexiform-outer nuclear layer (OPNL) thicknesses were calculated at two measurement points (nasal and temporal hump points at the macula area).

RESULTS

There were no significant between-group differences in age, gender, or refraction error. The CFT was thicker in the IIN group compared with the control group (225.0 μm vs. 217.8 μm, P = 0.017) and OSL was shorter in IIN than in controls (40.0 μm vs. 43.7 μm., P < 0.001). The ONL thickness at the central fovea was not statistically different between the two groups. At the nasal and temporal position where the ganglion cell density was thickest, the GCIPL thickness was thinner in the IIN group compared to the controls (99.5 μm vs. 102.8 μm, P = 0.010). The GCIPL thickness was negatively correlated with logMAR visual acuity (Spearman's rho = -0.502, P < 0.001).

CONCLUSIONS

The foveal pit was shallower, OSL was shorter, and the GCIPL thicknesses at macular humps were decreased in the patients with IIN compared with that of controls. The faulty development of the macula may be related to unknown pathophysiologic mechanism during fovea maturation in IIN or continuous eye movement itself interrupt fovea development.

Optical coherence tomography angiography of foveal hypoplasia

AIMS

To discuss foveal development in the context of detailed retinal vasculature imaging in foveal hypoplasia using optical coherence tomography angiography.

METHODS

In this case series, the optical coherence tomography angiography results of four patients with idiopathic foveal hypoplasia and two patients with foveal hypoplasia secondary to oculocutaneous albinism are presented.

RESULTS

Cases with intact visual acuity demonstrated lower grades of foveal hypoplasia on optical coherence tomography, while those with poor vision demonstrated high grades of foveal hypoplasia. The superficial retinal capillary plexus was intact in the foveal area in all cases, with no demonstrable foveal avascular zone. The deep retinal capillary plexus was absent to variable degrees in most cases, but was most persistent in those cases with reduced vision.

CONCLUSIONS

The superficial retinal capillary plexus is present in cases with foveal hypoplasia, while the deep retinal capillary plexus is absent to varying degrees. Our findings support the hypothesis that an intact foveal avascular zone of the deep capillary plexus allows for outer retinal photoreceptor specialisation to occur unimpeded, resulting in preserved visual acuity, while this process may be inhibited by an absent deep capillary foveal avascular zone with resultant poor vision.

A start codon mutation of the FRMD7 gene in two Korean families with idiopathic infantile nystagmus

Idiopathic infantile nystagmus (IIN) is the involuntary oscillation of the eyes with onset in the first few months of life. The most common form of inheritance is X-linked, and mutations in FRMD7 gene are a major cause. To identify the FRMD7 gene mutations associated with X-linked IIN, we performed PCR-based DNA direct sequencing in 4 affected subjects from 2 Korean families. We also assessed structural abnormalities of retina and optic nerve head using optical coherence tomography (OCT). Genetic analysis revealed a A>G transversion at nucleotide c.1, the first base of the start codon. This mutation leads to the loss of the primary start codon ATG for methionine, which is replaced by a triplet GTG for valine. The alternative in-frame start codon is not present around a mutation. OCT revealed the morphological changes within the optic nerve head, including shallow cup depth and small cup-to-disc ratio. In summary, we identified a novel start codon mutation within the FRMD7 gene of 2 Korean families. Our data expands the mutation spectrum of FRMD7 causing IIN. We also demonstrated abnormal developments of afferent system in patients with FRMD7 mutations using OCT, which may help to understand the etiological factor in development of nystagmus.

Incidence of fovea plana in normal children

PURPOSE

To characterize the prevalence and features of subclinical foveal hypoplasia detected by optical coherence tomography (OCT) in children.

METHODS

Fast macular OCT scans were performed on normal children with normal vision for the development of a normative OCT-3 database; from this data, eyes with no discernable foveal depression were identified. When possible, the ocular imaging was repeated 3 years later using both OCT-3 and spectral domain OCT (SD-OCT). SD-OCT results were compared to age-matched controls.

RESULTS

Of the 286 normal children (mean age, 8.6 ± 3.1 years) scanned, 9 (mean age, 8 ± 2.9 years; 6 males) were found to have bilateral shallow foveal depression on OCT-3 imaging, including 8 of 154 white children (5.4%) and 1 child of mixed ethnicity (white/black). Children with shallow foveas (n = 9) had larger average foveal thickness (FT) compared to the cohort of controls (n = 277) with a defined fovea (FT = 231.4 ± 8.8 vs 188.8 ± 25.0, resp. [P < 0.0001]). Mean macular volume did not differ from that of controls. SD-OCT performed 3 years later on 5 of the 9 children with shallow foveal depression showed persistence of the inner macular layers over the foveal center, corresponding to grades 1 or 2 of foveal hypoplasia. The FT was increased compared to 5 age-matched controls with a defined fovea (FT = 294.5 ± 5.1 vs 219.75 ± 5.68 μm, resp. [P = 0.029]).

CONCLUSIONS

Up to 3% of children with clinically normal eyes had an anatomically underdeveloped foveal pit bilaterally on OCT.

Isolated foveal hypoplasia with secondary nystagmus and low vision is associated with a homozygous SLC38A8 mutation

Foveal hypoplasia, always accompanied by nystagmus, is found as part of the clinical spectrum of various eye disorders such as aniridia, albinism and achromatopsia. However, the molecular basis of isolated autosomal recessive foveal hypoplasia is yet unknown. Individuals of apparently unrelated non consanguineous Israeli families of Jewish Indian (Mumbai) ancestry presented with isolated foveal hypoplasia associated with congenital nystagmus and reduced visual acuity. Genome-wide homozygosity mapping followed by fine mapping defined a 830 Kb disease-associated locus (LOD score 3.5). Whole-exome sequencing identified a single missense mutation in the homozygosity region: c.95T>G, p.(Ile32Ser), in a conserved amino acid within the first predicted transmembrane domain of SLC38A8. The mutation fully segregated with the disease-associated phenotype, demonstrating an ∼10% carrier rate in Mumbai Jews. SLC38A8 encodes a putative sodium-dependent amino-acid/proton antiporter, which we showed to be expressed solely in the eye. Thus, a homozygous SLC38A8 mutation likely underlies isolated foveal hypoplasia.