Role of a Standardized Prism Under Cover Test in the Assessment of Dissociated Vertical Deviation

ABSTRACT

Background: Dissociated vertical deviation (DVD) is commonly measured using a prism and alternate cover test (PACT), but some providers use a prism under cover test (PUCT). The aim of this study was to compare a standardized PUCT measurement with a PACT measurement, for assessing the magnitude of DVD.

Methods: Thirty-six patients with a clinical diagnosis of DVD underwent measurement of the angle of deviation with the PACT, fixing with the habitually fixing eye, and with PUCT, fixing both right and left eyes. The PUCT was standardized, using a 10-second cover for each prism magnitude, until the deviation was neutralized. The magnitude of hyperdeviation by PACT and PUCT was compared for the non-fixing eye, using paired non-parametric tests. The frequency of discrepancies more than 4 prism diopters (PD) between PACT and PUCT was calculated.

Results: The magnitude of hyperdeviation was greater when measured with PUCT (range 8PD hypodeviation to 20PD hyperdeviation) vs. PACT (18PD hypodeviation to 25PD hyperdeviation) with a median difference of 4.5PD (range –5PD to 21PD); P < 0.0001. Eighteen (50%) of 36 measurements elicited >4PD hyperdeviation (or >4PD less hypodeviation) by PUCT than by PACT.

Conclusions: A standardized 10-second PUCT yields greater values than a prism and alternate cover test in the majority of patients with DVD, providing better quantification of the severity of DVD, which may be important for management decisions.

KEYWORDS:

• DVD
• hypertropia
• prism under cover test

Acknowledgments

This material was presented in part at the 2016 annual meeting of the American Association for Pediatric Ophthalmology and Strabismus in Vancouver, Canada, and the abstract can be downloaded from http://dx.doi.org/10.1016/j.jaapos.2016.07.133.

Disclosure statement

None of the authors have any potential conflicts of interest to disclose.

Additional information

Funding

Supported by National Eye Institute, National Institutes of Health, Grant EY024333 (JMH), Research to Prevent Blindness, New York, New York (unrestricted grant to the Department of Ophthalmology, Mayo Clinic) and Mayo Foundation for Medical Education and Research.