Utility of off-axis rebound tonometry in children with glaucoma

Abstract Purpose To evaluate the validity and reliability of off-axis rebound tonometry (RBT) measurements in children with glaucoma, and the utility of these off-axis measurements in ocular and systemic conditions. Methods RBT measurements were taken at the optical centre (RBTon) and 3 mm temporally (RBToff) from one eye of children with glaucoma who visited the Eye Department of Birmingham Women’s and Children’s Hospital. Goldmann applanation tonometer (GAT) measurements were subsequently obtained. Co-existing factors were analysed including age, sex, ethnicity, type of glaucoma, treatment, general health, nystagmus, strabismus, corneal scars, spectacle prescription (Rx) and best corrected visual acuity (BCVA). Results Thirty-four children aged 4–15 years (mean age 9.2 (SD 3.5) years, 14 female) with glaucoma were evaluated. RBTon measurements (mean 20.0 (SD 9.1) mmHg) overestimated GAT IOP (mean 17.6 (SD 7.1) mmHg) by 2.4 (SD 3.0) mmHg (p = 0.000), with bias increasing above 28 mmHg. To a lesser extent, RBToff overestimated IOP by 1.7 (SD 3.5) mmHg compared to GAT (p < 0.01). In absolute terms, mean RBToffwas closer to GAT than the mean RBTon. Notably, RBTon agreed better with GAT in younger children (< 9 years old), while differences were independent of coexisting factors such as sex or ethnicity. Conclusions Rebound tonometry consistently overestimated IOP relative to GAT, particularly at higher pressures, but within clinically acceptable limits. Whilst the bias was more pronounced in older children, underscoring the need for paediatric-specific calibration, peripheral RBT measures were closer to GAT than those taken centrally. Although a useful measure in this population, these findings advocate for caution when interpreting rebound readings, to ensure appropriate glaucoma management in children.