VEP analysis methods in children with optic nerve hypoplasia: relationship to visual acuity and optic disc diameter

Use of sweep visual evoked potential in preverbal children with optic nerve hypoplasia

PURPOSE

To evaluate sweep VEP (sVEP) in preverbal children with optic nerve hypoplasia (ONH) and to assess associations between sVEP results, patient clinical characteristics and future recognition visual acuity.

METHODS

The medical records of children with ONH who had sVEP testing and documented recognition visual acuity at the University of Wisconsin from 2005 to 2013 were reviewed retrospectively. Optic nerve size, amblyopia treatment, and neurologic diagnoses were collected.

RESULTS

A total of 57 patients were included: 41 (71%) with bilateral ONH and 27 (47%) with neurologic abnormality. Mean age at initial sVEP was 13.3 months (range, 1-32). Mean duration between initial sVEP and final recognition acuity was 5.5 years (range, 3.5-7). Sweep VEP was associated with ONH severity (P < 0.05). Sweep VEP, and the combination of ONH severity and neurologic status, were significant predictors (P < 0.05) of logMAR optotype acuity, together accounting for 54%-61% of the variance in final recognition acuity.

CONCLUSIONS

Sweep VEP in preverbal children with ONH depends on ONH severity and correlates with final recognition visual acuity. Children with milder degrees of ONH without neurologic abnormalities had better final vision, and patients with severe ONH and neurologic diagnoses had worse vision outcomes.

Direct OPTOS Nerve Size Determination of Prevalent Optic Nerve Hypoplasia in Alaska

Background

Optic nerve hypoplasia (ONH), one of the most common causes of pediatric blindness in developed countries, has been difficult to directly quantify. We sought to measure optic nerve size in Alaskan pediatric patients with optic nerve hypoplasia using ultra-widefield fundus imaging.

Methods

Adult and pediatric patients underwent conventional ultra widefield fundus imaging (OPTOS, Dunfermline, Scotland) with manual image processing to determine optic nerve size validated against refractive error and nystagmus and compared to optical spectral domain tomography. De-identified cases were then compared relative to visual acuity and birth prevalence.

Results

In Alaska’s only pediatric ophthalmology outreach clinic, 108 cases of ONH less than 20 years old were clinically identified with 80 having ultra-widefield analysis. Median horizontal optic nerve diameter for 135 normals was 1.70 (95% C.I. 1.49, 2.14) whereas in patients clinically diagnosed with optic nerve hypoplasia was 1.23 (95% C.I 0.38, 1.45). Visual acuity (20/y) was related to horizontal optic nerve diameter (x) by y = 187 x^-4.1. Horizontal nerve diameter h could be estimated from vertical nerve diameter v by h = 0.73v + 0.3 even in nystagmus patients. From 108 with ONH, 6 had threshold retinopathy of prematurity, 12 profound nystagmus, 32 legally blind, 6 with septo-optic dysplasia, and 5 with fetal alcohol syndrome. ONH is very prevalent in Alaska occurring at least 8–10 per 10,000 births.

Conclusion

Compared to vertical diameter, horizontal diameter was more distinctive of optic nerve hypoplasia and more perturbed by nystagmus. Both were independent of refractive error. When hand-held, spectral domain OCT is not convenient, ultra-widefield fundus analysis is recommended for direct estimation of optic nerve size in children and adults. Optic nerve hypoplasia is prevalent in Alaskan children.

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Predictive value of N95 waveforms of pattern electroretinograms (PERGs) in children with optic nerve hypoplasia (ONH)

PURPOSE

As part of a long-term, prospective study of prenatal and clinical risk factors for optic nerve hypoplasia (ONH) at Children's Hospital Los Angeles, pattern ERGs (PERGs) were evaluated for prognostic value using an automated objective and robust analytical method.

METHODS

Participants were 33 children with ophthalmoscopically diagnosed ONH [disc diameter-to-disc macula ratio (DD/DM) less than 0.35 in one or both eyes on fundus photographs]. Using cycloplegia and chloral hydrate sedation in one session before 26 months of age, we recorded PERGs to checkerboard reversal using five check sizes. Participants were followed with clinical and psychometric testing until 5 years of age. PERGs were analysed using automated robust statistics based on magnitude-squared coherence and bootstrapping optimized to objectively quantify PERG recovery in the challenging recordings encountered in young patients. PERG measures in the fixating or better-seeing eyes were compared with visual outcome data.

RESULTS

PERG recording was complete to at least three check sizes in all eyes and to all five sizes in 79%. Probability of recording a PERG that is significantly different from noise varied with check size from 73% for the largest checks to 30% for the smallest checks (p = 0.002); smaller waveforms were associated with earlier implicit times. The presence of significant PERGs in infancy is associated with better visual outcomes; the strongest association with visual outcome was for the threshold check size with a significant N95 component (ρ = 0.398, p = 0.02).

CONCLUSIONS

Automated statistically robust signal-processing techniques reliably and objectively detect PERGs in young children with ONH and show that congenital deficits of retinal ganglion cells are associated with diminished or non-detectable PERGs. The later negativity, N95, was the best indicator of visual prognosis and was most useful to identify those with good visual outcomes (≤0.4 LogMAR). Although PERGs reflect function of the inner layers of the central retina, they lack the specificity required to determine prognosis reliably in individual cases.