Aqueous Humor Dynamics Changes and Predictors of IOP Response to Latanoprost in Healthy Subjects

In our study of the factors predictive of latanoprost response, we found that normotensive subjects with higher intraocular pressure, lower uveoscleral outflow, and higher body mass index had a greater response to 1-week treatment.

To evaluate relationships between variable intraocular pressure (IOP) responses to latanoprost and participant characteristics, baseline values and changes in aqueous humor dynamics (AHD) parameters.

We assessed 226 eyes from 113 healthy participants. AHD parameters measured at baseline and after 1-week treatment with latanoprost included: IOP by pneumatonometry, episcleral venous pressure (EVP) by venomanometry, aqueous humor flow rate by fluorophotometry, outflow facility by 2-minute pneumatonography, and uveoscleral outflow calculated using the modified Goldmann equation. IOP responses were categorized into 4 groups: nonresponders (<10% reduction), all-responders (≥10% reduction), medium-responders (10%-20% reduction), and high-responders (≥20% reduction). Generalized estimating equation models were used to analyze treatment effects and compare groups.

Baseline IOP was higher in high-responders than medium-responders and nonresponders ( P =0.007 and P <0.001, respectively). Body mass index (BMI) was significantly higher in high-responders and all-responders compared with nonresponders ( P =0.02 and P =0.03, respectively). Responders had lower baseline uveoscleral outflow ( P =0.03). There were no significant differences in other baseline characteristics including EVP, outflow facility, and aqueous flow rate between the 4 groups. IOP decreased while outflow facility and uveoscleral outflow increased after latanoprost treatment in all responder groups but did not change in nonresponders. EVP and aqueous flow rate did not change significantly in any group. The change in uveoscleral outflow was greater in high-responders than in nonresponders ( P =0.004).

In healthy subjects, higher baseline IOP, lower uveoscleral outflow and higher BMI are predictors of a greater IOP reduction by latanoprost. A greater increase in uveoscleral outflow is responsible for this larger response.