Correlation between electroretinography, foveal anatomy and visual acuity in albinism

Quantitative Foveal Structural Metrics as Predictors of Visual Acuity in Human Albinism

Purpose

To assess the degree to which quantitative foveal structural measurements account for variation in best-corrected visual acuity (BCVA) in human albinism.

Methods

BCVA was measured and spectral domain optical coherence tomography (SD-OCT) images were acquired for 74 individuals with albinism. Categorical foveal hypoplasia grades were assessed using the Leicester Grading System for Foveal Hypoplasia. Foveal anatomical specialization (foveal versus parafoveal value) was quantified for inner retinal layer (IRL) thickness, outer segment (OS) length, and outer nuclear layer (ONL) thickness. These metrics, participant sex, and age were used to build a multiple linear regression of BCVA. This combined linear model's predictive properties were compared to those of categorical foveal hypoplasia grading.

Results

The cohort included three participants with type 1a foveal hypoplasia, 23 participants with type 1b, 33 with type 2, ten with type 3, and five with type 4. BCVA ranged from 0.08 to 1.00 logMAR (mean ± SD: 0.53 ± 0.21). IRL ratio, OS ratio, and ONL ratio were measured in all participants and decreased with increasing severity of foveal hypoplasia. The best-fit combined linear model included all three quantitative metrics and participant age expressed as a binary variable (divided into 0-18 years and 19 years or older; adjusted R2 = 0.500). This model predicted BCVA more accurately than a categorical foveal hypoplasia model (adjusted R2 = 0.352).

Conclusions

A quantitative model of foveal specialization accounts for more variance in BCVA in albinism than categorical foveal hypoplasia grading. Other factors, such as optical aberrations and eye movements, may account for the remaining unexplained variance.

Subretinal gene therapy delays vision loss in a Bardet-Biedl Syndrome type 10 mouse model

Blindness in Bardet-Biedl syndrome (BBS) is caused by dysfunction and loss of photoreceptor cells in the retina. BBS10, mutations of which account for approximately 21% of all BBS cases, encodes a chaperonin protein indispensable for the assembly of the BBSome, a cargo adaptor important for ciliary trafficking. The loss of BBSome function in the eye causes a reduced light sensitivity of photoreceptor cells, photoreceptor ciliary malformation, dysfunctional ciliary trafficking, and photoreceptor cell death. Cone photoreceptors lacking BBS10 have congenitally low electrical function in electroretinography. In this study, we performed gene augmentation therapy by injecting a viral construct subretinally to deliver the coding sequence of the mouse Bbs10 gene to treat retinal degeneration in a BBS10 mouse model. Long-term efficacy was assessed by measuring the electrical functions of the retina over time, imaging of the treated regions to visualize cell survival, conducting visually guided swim assays to measure functional vision, and performing retinal histology. We show that subretinal gene therapy slowed photoreceptor cell death and preserved retinal function in treated eyes. Notably, cone photoreceptors regained their electrical function after gene augmentation. Measurement of functional vision showed that subretinal gene therapy provided a significant benefit in delaying vision loss.

Structural, Microvascular, and Functional Findings Associated with Fovea Plana

PURPOSE

To analyse structural (OCT), microvascular (OCTA), and functional changes (BCVA, mfERG) associated with fovea plana and to compare it to healthy controls.

METHODS

A retrospective observational study was performed on 13 patients (26 eyes; aged 34.46 y ± 20.26) with a clinical picture of fovea plana and 15 controls (30 eyes; aged: 41.47 y ± 14.03).

RESULTS

In fovea plana, BCVA ranged from 0.25 to 1.0, with a spherical error of - 5.5 to + 18.0 dpt. Posterior segment changes included elevated papillomacular retinal fold, uveal effusion syndrome, crowded optic discs, and hypopigmented fundus. OCTA imaging of the superficial (FAZ-S), intermediate (FAZ-I), and deep foveal avascular zone (FAZ-D) confirmed absence of foveal avascular zone (FAZ-S in 13 eyes, FAZ-I in 21 eyes, and FAZ-D in 10 eyes). Fovea plana patients had a significantly smaller FAZ-S, FAZ-I, and FAZ-D than controls (p < 0.001). Within the fovea plana group, a smaller FAZ-S correlated with reduced BCVA (p = 0.004) and with reduced mfERGs in zones 1 and 2 (p = 0.001 and p = 0.017). Also, a smaller FAZ-D showed positive correlations with the mfERG, with statistically significant values in zones 1 and 2 (p = 0.003 and p = 0.017).

CONCLUSION

In conclusion, our results confirm an altered structural, microvascular, and functional pattern in patients with a clinical picture of fovea plana. As documented by the functional microvascular interactions in our study, the developmental arrest in foveation reflects the functional maturation by means of visual acuity and central retinal function.

Morphology of foveal hypoplasia: Hyporeflective zones in the Henle fiber layer of eyes with high-grade foveal hypoplasia

Background

Foveal hypoplasia is characterized by the persistance of inner retinal layers at the macular center. We evaluated using spectral-domain optical coherence tomography (SD-OCT) morphological parameters of the macular center of eyes with foveal hypoplasia and describe the presence of hyporeflective zones in the Henle fiber layer (HFL) of eyes with high-grade foveal hypoplasia.

Methods

Eyes with foveal hypoplasia were classified into two groups: high-grade foveal hypoplasia with thick inner retinal layers at the macular center (thickness above 100 μm; 16 eyes of 9 subjects) and low-grade foveal hypoplasia with thinner inner retinal layers at the macular center (thickness below 100 μm; 25 eyes of 13 subjects). As comparison, SD-OCT images of normal control eyes (n = 75) were investigated.

Results

Eyes with foveal hypoplasia displayed shorter central photoreceptor outer segments (POS), a thinner central myoid zone, and a thicker central HFL compared to control eyes. Eyes with high-grade foveal hypoplasia also displayed a thinner central outer nuclear layer (ONL) compared to eyes with low-grade foveal hypoplasia and control eyes. There was a negative correlation between the thicknesses of the central ONL and HFL in eyes with foveal hypoplasia; however, the total thickness of both ONL and HFL was similar in all eye populations investigated. Visual acuity of subjects with foveal hypoplasia was negatively correlated to the thickness of the central inner retinal layers and positively correlated to the length of central POS. In contrast to central POS, the length of paracentral POS (0.5 and 1.0 mm nasal from the macular center) was not different between the three eye populations investigated. The paracentral ONL was thickest in eyes with high-grade foveal hypoplasia and thinnest in control eyes. Hyporeflective zones in the HFL were observed on SD-OCT images of eyes with high-grade foveal hypoplasia, but not of eyes with low-grade foveal hypoplasia and control eyes. OCT angiography images recorded at the level of the HFL of eyes with high-grade foveal hypoplasia showed concentric rings of different reflectivity around the macular center; such rings were not observed on images of eyes with low-grade foveal hypoplasia and control eyes.

Conclusions

It is suggested that the hyporeflective zones in the HFL of eyes with high-grade foveal hypoplasia represent cystoid spaces which are surrounded by Henle fiber bundles. Cystoid spaces are likely formed because there are fewer Henle fibers and a thinner central ONL despite an unchanged thickness of both ONL and HFL. Cystoid spaces may cause the concentric rings of different reflectivity around the macular center in the HFL of eyes with high-grade foveal hypoplasia.

OCT Imaging in Infants

Optical coherence tomography (OCT) is widely applied in diagnosis and management of retina diseases particularly macular diseases in adult retina practices. However, it has been under-utilized in pediatric retinal diseases especially in neonates and infants. Utilization of OCT in primary macular diseases in this age group is also uncommon and is less reported. Challenges involved in image acquisition and limitations with available devices technique can explain the limited research and accurate data availability in the literature in this field. Purpose of this review article is to summarize the use of OCT and its importance in various infantile retinal pathologies such as vascular diseases, tumors, retinal dystrophies, and optic nerve pathologies with primary focus on neonates and infants, along with infant choroid. In addition, we also discuss about future directions including OCT angiography for infants.

Correlation between electroretinography, foveal anatomy and visual acuity in aniridia due to PAX6 mutations

BACKGROUND

Aniridia patients have poor visual acuity and iris malformation. The fovea in these patients is underdeveloped, but the relationship between structure and electrophysiologic function remains incompletely understood. This study correlates electrophysiology, visual acuity and optical coherence tomography (OCT) in patients with aniridia secondary to mutations in the PAX6 gene and compares with age-similar controls.

METHODS

Patients were recruited from clinical practice. The mfERG protocol was a 4-min 103-hexagon protocol covering approximately 40° in diameter of central retina. Diagnosys full-field ERG (ffERG) and VERIS multifocal ERG (mfERG) were obtained using standard International Society for Clinical Electrophysiology of Vision protocols. OCT central thickness was recorded, and an OCT foveal score was calculated. Nonparametric permutation testing was utilized to determine the statistical significance.

RESULTS

A total of 6 aniridia patients and 25 control patients were recruited. On mfERG, aniridia patients had significantly lower amplitudes in rings 1-3 (p = 0.0006, 0.0013, 0.0132), shorter latencies in ring 1 (p = 0.0312) and longer latencies in rings 5 and 6 (p = 0.0026, p = 0.0042) than controls. There was a significantly positive relationship in aniridia patients between logMAR visual acuity and mfERG amplitude in ring 4 (p = 0.0392) and ring 5 (p = 0.0489). On ffERG, there was no difference in amplitudes, though photopic 3.0 a- and b-wave latency, 30 Hz flicker latency and scotopic 0.01 b-wave latency were significantly longer in aniridia patients versus control (p = 0.0018, 0.0.0005, 1.00 x [Formula: see text], 0.0198). Thicker central macula on OCT correlated with lower mfERG amplitudes in rings 4-6 (p = 0.0369, 0.0292, 0.0255). There was no correlation between visual acuity and central macular thickness or foveal hypoplasia score as determined by OCT.

CONCLUSIONS

Higher amplitude on mfERG correlated with poorer visual acuity in rings 4 and 5 in patients with PAX6 mutations. The slope of the change in amplitude from central to peripheral rings on the mfERG is significantly different in aniridia patients compared to controls, with a slower drop-off of amplitude from center to periphery. Additionally, mfERG in aniridia showed lower amplitudes than controls in rings 1-3. These changes along with the lack of correlation between visual acuity and central macular thickness/OCT score suggest that changes in electrical topography may be important to visual deficits in patients with PAX6 gene mutations.

Foveal Differentiation and Inner Retinal Displacement Are Arrested in Extremely Premature Infants

Purpose

Children with a history of prematurity often have poorly developed foveae but when during development foveal differences arise. We hypothesize that the course of foveal development is altered from the time of preterm birth.

Methods

Eyes of 102 preterm infants undergoing retinopathy of prematurity screening examinations in the STudy of Eye imaging in Premature infantS (BabySTEPS) (NCT02887157) were serially imaged between 30 and 42 weeks postmenstrual age (PMA) using handheld optical coherence tomography systems. Total retinal thickness, inner retinal layer (IRL) thickness, and outer retinal layer (ORL) thickness were measured at the foveal center and parafovea. Foveal put depth, IRL thickness, and ORL thickness were compared between infants born at different gestational ages using mixed effects models.

Results

Foveal pit depth and IRL thickness were inversely related to gestational age; on average, the most premature infants had the thickest IRL and shallowest pits at all PMAs. Differences were evident by 30 weeks PMA and persisted through 42 weeks PMA. The foveal pits of the most premature infants did not progressively deepen, and the IRLs did not continue to thin with increasing chronological age.

Conclusions

Foveation in extremely preterm infants is arrested from the earliest observed ages and fails to progress through term equivalent age. The developmental displacement of the IRL from the foveal center into the parafovea does not occur normally after preterm birth. These observations suggest that foveal hypoplasia seen in children with history of prematurity is due to disturbances in foveal development that manifest within weeks of birth.

Ocular findings of albinism in DYRK1A-related intellectual disability syndrome

BACKGROUND

Pathogenic variants in DYRK1A are associated with DYRK1A-related intellectual disability syndrome (DIDS). Common features of this diagnosis include microcephaly, intellectual disability, speech impairment, and distinct facial features. Reported ocular features include deep-set eyes, myopia, and strabismus. We present a case of DYRK1A-related intellectual disability syndrome with ocular findings of albinism and explore the possible pathogenesis of this previously unreported manifestation.

MATERIALS AND METHODS

This is a single, retrospective case report of a child with DIDS who underwent an ophthalmic exam including detailed visual electrophysiology. Results: A 21-month-old female with microcephaly, failure to thrive, language delay, cleft palate, and cardiac defects had an ophthalmic exam showing myopia, strabismus, a hypopigmented fundus and crossed asymmetry on visual evoked potential (VEP), consistent with ocular findings of albinism. Whole exome sequencing identified a pathogenic DYRK1A variant; no albinism gene variants were reported. Her constellation of features is consistent with a diagnosis of DYRK1A-related intellectual disability syndrome; however, ocular features of albinism have not previously been reported in this condition.

CONCLUSIONS

This is, to the best of our knowledge, the first report of ocular findings of albinism in a case of DYRK1A-related intellectual disability syndrome. We propose that ocular albinism is a novel ocular phenotype of DYRK1A-related disease. Ophthalmic exams in patients with this diagnosis should include thorough evaluation for ocular albinism, including VEPs.

Retinal Ganglion Cell Axon Wiring Establishing the Binocular Circuit

Binocular vision depends on retinal ganglion cell (RGC) axon projection either to the same side or to the opposite side of the brain. In this article, we review the molecular mechanisms for decussation of RGC axons, with a focus on axon guidance signaling at the optic chiasm and ipsi- and contralateral axon organization in the optic tract prior to and during targeting. The spatial and temporal features of RGC neurogenesis that give rise to ipsilateral and contralateral identity are described. The albino visual system is highlighted as an apt comparative model for understanding RGC decussation, as albinos have a reduced ipsilateral projection and altered RGC neurogenesis associated with perturbed melanogenesis in the retinal pigment epithelium. Understanding the steps for RGC specification into ipsi- and contralateral subtypes will facilitate differentiation of stem cells into RGCs with proper navigational abilities for effective axon regeneration and correct targeting of higher-order visual centers.