Corneal tomography should be performed before other tests that require the instillation of fluorescein or mydriatics, according to a study published in Cornea. 

Researchers investigated the impact of instilling 1% fluorescein and mydriatics (0.8% tropicamide + 5% phenylephrine) on tomographic imaging. They also obtained measurements of corneal shape (maximum keratometry and best fit sphere of anterior and posterior corneal surfaces), pachymetry (at the pupil center, corneal apex, and thinnest location), and anterior chamber parameters (depth, volume, and angle of anterior chamber and corneal volume) using the Pentacam® HR (OCULUS) before and after the instillation of fluorescein and mydriatics. 

A total of 131 eyes of 131 patients were included. Participants were subdivided into 3 groups: 87 in group A, 28 in group B, and 16 in group C. Baseline measurements were performed in all groups. They were repeated 1.5 hours after the instillation of fluorescein and mydriatics in group A, 10 minutes following fluorescein only instillation  in group B, and 1.5 hours after mydriatic only instillation in group C. The researchers noted significant differences in corneal pachymetry and anterior chamber parameters among all 3 groups. They observed the highest range of differences in pachymetry at the pupil center (17±53.5 μm) and in anterior chamber volume (26.7±69.8 mm3). Fluorescein or mydriatic instillation did not significantly affect anterior and posterior corneal surface measurements. 


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“Our study shows significant differences in measurements taken by the Pentacam after the instillation of 1% fluorescein or when the pupil is dilated,” the researchers note.  “For accurate information and planning purposes, the measurements with the Pentacam must be taken before any other test is performed.“ 

Study limitations include its small sample size.

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.  

Reference

Padmanabhan P, Belin MW, Sudhir RR, Mukundan D, Chidambaram H, Ambrósio R. Implications of diagnostic drops on Scheimpflug tomography: The proper order for clinical testing. Cornea. Published online November 11, 2021. doi:10.1097/ICO.0000000000002927