Neutral Density Filters as a Tool for Cycloplegic Plusoptix-Photorefractor Measurements: An Explorative Study

Helena Maria van Minderhout1, *, Maurits Victor Joosse2, Nicoline Elisabeth Schalij-Delfos3
1 Department of Ophthalmology, Haaglanden Medical Centre, Westeinde, The Hague, The Netherlands
2 Department of Ophthalmology, Haaglanden Medical Centre, Postbox 432, 2501 CK, The Hague, The Netherlands
3 Department of Ophthalmology, Pediatric Ophthalmology, Leiden University Medical Centre, Leiden, The Netherlands

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© 2022 Maria van Minderhout et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Ophthalmology, Haaglanden Medical Centre, Westeinde, Postbox 432, 2501 CKThe Hague, The Netherlands; Tel: 0031650748760; E-mail:



The purpose of this study is to investigate the usefulness of neutral-density (ND) filters in cycloplegic-Plusoptix-photorefractor measurements.


No-filter and ND-filter 0.04, 0.1 and 0.2 cycloplegic-Plusoptix-photorefractor measurements were made in 42 hypermetropic eyes. Sphere, cylinder, spherical equivalent (SEQ), J0, and J45 values were compared.


Mean Plusoptix-photorefractor pupil sizes were 7.7±0.68 and 7.7±0.72 mm The no-filter failure rate was 16%, with 87% in pupils >7.8 mm. Mean no-filter sphere, cylinder, SEQ, J0 and J45 values were +0.34±0.35D, -0.29±0.22D, +0.20±0.36, -0.00±0.15, and +0.02±0.11, respectively. Only ND-filter-0.04 provided 5% more successful measurements and a clinically significant alteration in the percentage of values exceeding 0.5D for sphere and SEQ (-10% and -20%), but not for cylinder (+5%). Despite the increased accuracy, 21% of the spherical outcome exceeded 0.50D. Furthermore, the single-measure-intraclass-correlation-coefficient between no-filter and ND-filter-0.04 outcome was moderate (sphere 0.78 (0.62-0.87), cylinder 0.59 (0.35-0.75), SEQ 0.68 (0.48-0.82), J0 0.73 (0.54-0.84) and J45 0.57 (0.50-0.86)) and indicated significant individual variation. Bland-Altman-analyses indicated significant bias for sphere and SEQ; p=0.038 and p=0.030.


ND-filter-0.04 resulted in a larger proportion of successful measurements and an increased accuracy. However, an unacceptable percentage of inaccuracy was still present compared to retinoscopy. There could be validity issues with the ND-filter 0.04 or the baseline no-filter readings at the start. We conclude that cycloplegic Plusoptix-photorefraction, even with the use of a 0.04 ND filter, is not a suitable method for exact objective refraction purposes in children.

Keywords: Pediatric ophthalmology, Photorefractor screening, Cycloplegic plusoptix screening, Objective pediatric refraction, Density filters, Tools.