The influence of congenital corneal opacity on ERGs obtained using an abbreviated protocol

ABSTRACT

Background

Visual electrophysiology may be used to assess visual potential in infants with congenital corneal opacities (CCO). It is essential to recognize confounding effects from these opacities on the flash electroretinogram (ERG).

Methods

ERGs were recorded in awake children employing skin electrodes placed at the lower eyelid crease, both referred to a midfrontal electrode (Fz). A hand-held stimulator was used to present a mixed rod-cone and a dim white stimulus. Recordings were carried out before and after penetrating keratoplasty (PK), when performed.

Results

Five infants under the age of 12 months with visually significant CCO were evaluated. In all cases, initial ERGs employing the mixed rod-cone stimulus showed well-defined a-wave with reduced amplitude b-wave. Reduction of stimulus intensity resulted in an increase in the b-wave and normalization of the b:a ratio from 1.1 (range 0.7 to 1.3) to 2.8 (range 1.5 to 4.3). In three cases who underwent PK, the postoperative ERGs recorded with a mixed rod-cone stimulus were normal in waveform shape with a mean b:a ratio of 2.0 (range 1.7 to 3.0).

Conclusion

Selective reduction of the scotopic bright flash ERG b-wave is typically caused by retinal dysfunction that is post-phototransduction or inner retinal. In infants with CCO, scotopic ERGs to bright flashes can show a reduced b:a ratio that improves or normalizes either after PK or stimulus intensity reduction. The study highlights that media opacity can contribute to the generation of an ERG with reduced b-wave in the absence of inner retinal dysfunction.

KEYWORDS:

• Electroretinogram
• congenital corneal opacities
• b-wave

Author contributions

K.K.N. and A.L. designed the study; A.L. performed the electrophysiology tests; K.K.N. performed surgery; A.L., S.H., and H.S. collected the data; A.L. generated the figures; K.K.N., A.L., E.F., S.H., and H.S. drafted and revised the manuscript; and all approved the final manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are not publicly available because they contain information that could compromise the privacy of research participants but are available from K.K.N. upon reasonable request.

Statement of ethics

The study was conducted ethically in accordance with the World Medical Association Declaration of Helsinki. This study protocol was reviewed and approved by the University of Pittsburgh Institutional Review Board (approval number STUDY21070059).

Supplemental data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/13816810.2022.2149817.

Additional information

Funding

P30 CORE award EY08098 from the National Eye Institute, NIH, and unrestricted supporting funds from The Research to Prevent Blindness Inc, NY, the Eye and Ear Foundation of Pittsburgh and the Children's Foundation.