Purpose
To compare the differences in retinal vessel density (VD) between topical administration of latanoprostene bunod (LBN) ophthalmic solution 0.024% and timolol maleate 0.5% in patients with open-angle glaucoma (OAG) or ocular hypertension (OHT) and normal subjects.
Design
Randomized, single center, crossover clinical trial.
Methods
Eligible subjects were examined during 6 study visits over 12 weeks. All subjects were randomized in a 1:1 ratio to LBN dosed once daily or timolol dosed twice daily in both eyes (OU) for a duration of 4 weeks each, separated by a 2-week washout period. A comprehensive eye examination OU was performed at each visit. Testing was performed with optical coherence tomography and optical coherence tomography angiography (optic nerve and macula), as well as visual field examination, on the study eye at baseline and before and after each treatment.
Results
One eye from each of 50 patients was enrolled (10 healthy patients, 26 patients with OHT, and 14 patients with OAG). After administration of LBN there was significantly increased macular VD (0.76% [0.20%-1.33%], P = 0.009) and a trend in increasing peripapillary VD in patients with OAG and patients with OHT. In contrast, after administration of timolol, there were no differences in macular VD, and a decrease in peripapillary VD only was observed in the nasal inferior sector (−0.56% [−1.08% to −0.03%], P = .04) in patients with OAG and patients with OHT. No change in peripapillary or macular VD was observed in the normal subjects ( P > .05 for all).
Conclusions
Topical administration of LBN enhanced macular VD in patients with OAG or patients with OHT. In contrast, timolol administration did not have any effect on VD.
G laucoma, a multifactorial optic neuropathy, is a leading cause of irreversible blindness worldwide. Elevated intraocular pressure (IOP) is considered a major risk factor for the pathogenesis of glaucomatous visual field (VF) loss. Lowering IOP slows the progression of VF loss in patients with open-angle glaucoma (OAG) and reduces the risk of onset of OAG in patients with ocular hypertension (OHT). To date, reduction of IOP is the only proven method to treat glaucoma, and pharmacologic reduction of IOP is the most common initial treatment in patients with OAG or OHT.
Several classes of topical ocular hypotensive agents are used for the treatment of OAG and OHT. One class of drugs is β-adrenergic receptor antagonists that includes timolol maleate. The administration of timolol lowers IOP by decreasing the production of aqueous humor. Another class of ocular hypotensive agents is the prostaglandin analogs, including latanoprost. This class of agents increases aqueous humor outflow through the uveoscleral pathway and possibly the trabecular meshwork. Latanoprostene bunod (LBN) is a prostaglandin analog similar to latanoprost that also has a nitric oxide (NO)–donating moiety. Both latanoprost acid and NO lower IOP in humans. Moreover, NO activates a signaling cascade that results in the relaxation of smooth muscle cells and contributes to basal retinal vascular tone in humans.
In addition to IOP, there is increasing evidence that abnormalities in retinal vasculature and blood flow are involved in the pathogenesis of glaucoma. , It has been proposed that high IOP or other risk factors (eg, vascular dysregulation) can diminish ocular blood flow, particularly in susceptible individuals. , Previous studies have investigated the effect of topical ocular hypotensive medications on microcirculation and observed an improvement in the perfusion of the optic disc and retina in patients with OAG. Kiseleva and associates reported the effects of topical latanoprost and a combination of dorzolamide/timolol on the optic nerve head (ONH) and retinal and choroidal microcirculation. They observed an improvement of ocular hemodynamics using latanoprost in patients with POAG, which was related to its IOP-lowering effect. No changes were observed using the combination of dorzolamide/timolol. Conversely, Takusagawa and associates reported that topical beta-blocker administration caused lower macular VD (3.3%) compared with prostaglandins, carbonic anhydrase inhibitors, and alpha agonists.
Several studies using optical coherence tomography angiography (OCT-A) have reported that alterations in the microvasculature, including vessel density (VD), are detectable in the optic nerve and macula of glaucomatous eyes. Moreover, some topical ocular hypotensive medications, but not all, previously have been shown to influence VD. For instance, ripasudil, a topical Rho-assisted coiled-coil forming protein kinase inhibitor, improved VD in the peripapillary retina of patients with POAG and patients with OHT, while brimonidine, an alpha 2 agonist, had no effect. Similarly, a recent study evaluated the response of VD to topical brimonidine, dorzolamide, and carteolol in patients with normal-tension glaucoma and did not find any change in the microcirculation with brimonidine. In this study, however, topical dorzolamide and carteolol, a beta-blocking agent similar to timolol, had different effects on VD of the peripapillary retina; dorzolamide enhanced VD and carteolol decreased VD. Therefore, there is considerable interest in understanding the potential ocular hemodynamic effects of available ocular hypotensive drugs and whether this might influence glaucoma progression.
The purpose of this investigation was to compare the effect of topical LBN ophthalmic solution 0.024% dosed once daily and timolol maleate ophthalmic solution 0.5% dosed twice daily on the peripapillary and macular VD.
METHODS
All research conformed to the tenets of the Declaration of Helsinki and the Health Insurance Portability and Accountability Act and was authorized by the institutional review boards at the University of California, San Diego. Informed consent was obtained from all study subjects. The registration information for this human clinical trial is available at http://www.clinicaltrials.gov (identifier NCT03931317).
STUDY POPULATION
Forty subjects with OAG (n = 14) or OHT (n = 26) and 10 healthy participants were evaluated in this randomized, single-center, investigator-masked treatment, crossover study. Subjects were randomized in a 1:1 ratio to 1 of 2 treatment sequences: LBN 0.024% once daily and timolol maleate 0.5% twice a day, which were dispensed by 1 technician. The investigator who performed the examination and imaging was masked to treatment. Each treatment sequence consisted of two 4-week treatment periods, separated by a 2-week washout period.
Inclusion criteria at study entry were age >40 years, open angles on gonioscopy, diagnosis of OAG (including primary, pigmentary, or pseudoexfoliative glaucoma) or OHT in 1 or both eyes, intraocular pressure ≥22 mm Hg in ≥1 eye, and ≤36 mm Hg in both eyes in treatment-naïve subjects at the screening visit (visit 1) and pretreated subjects at the end of the washout period (visit 2). Patients with no ocular diseases were included in the normal group.
Subjects with a central corneal thickness >600 µm in either eye, significant corneal surface abnormalities, such as severe dry eye, angle-closure, advanced or secondary glaucoma, active optic disc hemorrhage, nonglaucomatous optic neuropathy, coexisting retinal diseases, any intraocular infection, inflammation, laser, incisional ocular surgery, or trauma in either eye within 3 months before the screening visit were excluded from the study.
Glaucomatous eyes were defined as having repeatable glaucomatous VF loss that was consistent with glaucomatous structural damage (ie, neuroretinal rim thinning, cupping, and/or retinal nerve fiber layer [RNFL] loss on ONH stereophotography). Glaucomatous VF damage was defined as glaucoma hemifield test and pattern standard deviation outside 95% normal limits confirmed on a minimum of 2 consecutive reliable tests with fixation losses and false-negatives ≤33% and false-positives ≤15%. Patients with OHT were required to have a postwashout IOP ≥22 mm Hg, a normal-appearing optic disc with intact neuroretinal rim and RNFL, and ≥2 normal reliable VF tests. Healthy subjects were required to have IOP ≤21 mm Hg and no structural abnormalities or functional loss.
STUDY VISITS
Eligible subjects were seen for ≤6 study visits over the course of approximately 12 weeks for treatment-naïve subjects and approximately 12 to 19 weeks for pretreated subjects, who required a minimum 28-day washout period.
All subjects were screened before treatment randomization to confirm that they met the subject selection and preliminary eligibility criteria during the first visit (screening visit; visit 1, performed by M.S.). During the same visit, subjects underwent a comprehensive ophthalmic examination, including refraction (visit 1 only), best-corrected visual acuity using an Early Treatment of Diabetic Retinopathy Study logarithm of the minimum angle of resolution chart, slit-lamp biomicroscopy, IOP using Goldmann applanation tonometry, gonioscopy (visit 1 only), pachymetry (visit 1 only), and dilated fundus examination. In addition, vital signs (resting blood pressure and heart rate) were recorded in a sitting position.
Eligible pretreated subjects were asked to discontinue their current IOP medication 28 to 56 days before starting the randomized treatment depending on the pharmacologic class of their IOP-lowering therapy. IOP was measured at the end of the washout period for these subjects (visit 2). For patients with OAG/OHT, the study eye was the eye with the highest IOP value at visit 1 (treatment-naïve subjects) or visit 2 (pretreated subjects). If both eyes had the same IOP value, the right eye was chosen to be the study eye. For normal subjects, the study eye was the one with the highest IOP value at visit 1. Both eyes of each subject were treated for the duration of the study.
During the remaining visits (visits 3-6), all subjects underwent a comprehensive ophthalmic examination for both eyes. In addition, they all had optic disc and macula OCT-A (Avanti Angiovue [performed postdilation]), OCT (Avanti Angiovue [postdilation]), stereophotography (postdilation), Humphrey Field Analyzer SITA standard 24-2 and 10-2 (Carl Zeiss Meditec), and Swedish Interactive Thresholding Algorithm VF testing (predilation) for the study eye. ONH and macula OCT-A were repeated 2 hours after the initial OCT-A measurement for all subjects. Any adverse systemic and ocular events and vital signs were recorded on each visit. All measurements were made around the same time of the day.
During visit 3 and after performing a comprehensive examination, baseline imaging, and VF tests, subjects were randomized to 1 of the 2 treatment sequences and were instructed to take LBN once daily in the evening at approximately 8 pm , or timolol twice daily in the morning at approximately 8 am and the evening at approximately 8 pm for 4 weeks. After performing the same required measurements at visit 4, subjects were instructed to stop the IOP-lowering medication for 2 weeks to wash out the effect of the current topical treatment. All measurements were repeated after the washout period during visit 5. At the end of that visit, the second study drug was dispensed, and administration instructions were given to each subject. The same examination and imaging protocols were repeated on the final visit (visit 6; Figure 1 and Supplemental Figure S1).
OCT-A IMAGING AND PROCESSING
OCT-A imaging was performed using the Avanti Angiovue system (OptoVue Inc,; software version 2017.1.0.151). This technique provides a noninvasive high-resolution visualization of the retinal capillary vasculature using the split-spectrum amplitude decorrelation angiography algorithm that detects red blood cell motion by measuring differences in the reflectance amplitude between consecutive B-scans. Vascular information is characterized as percentage VD, which is calculated as the percentage of measured area occupied by flowing blood vessels.
High-density (HD) 4.5- × 4.5-mm ONH and 6- × 6-mm macula OCT-A scans were acquired. The scans consisted of merged Fast-X volume of 400 horizontal B-scans of 400 A-scans per B-scan and Fast-Y volume of 400 vertical B-scans of 400 A-scans per B-scan. In the ONH OCT-A images, whole image (wi) and peripapillary capillary densities were derived. Macular wiVD, parafoveal VD (pfVD), and foveal avascular zone including area and perimeter were derived from the macula OCT-A images.
Due to the importance of superficial capillary plexus layer in glaucoma diagnosis and progression and its better diagnostic accuracy for detecting glaucoma than deep capillary plexus layer, , , , VD measurements were only evaluated in the superficial capillary plexus layer.
The image quality of all scans was reviewed by a trained grader (N.W.E.), who followed the standard protocol of the Imaging Data Evaluation and Analysis Reading Center at the University of California at San Diego. Scans with poor quality, which were defined as image quality <4 (1 = minimum, 10 = maximum), Signal Strength Index (SSI) <48, poor clarity images, residual motion artifacts, uncorrectable RNFL segmentation errors, or local weak signal, were excluded.
STATISTICAL ANALYSIS
Patient and eye characteristics were presented as mean (95% confidence intervals [CIs]) for continuous data and count (percentage) for categorical data. Significance across randomized groups was determined using 2-sample t tests and the Fisher exact test for continuous and categorical variables. Random allocation sequence was determined by generating a random drug list in R statistical software by a statistician (software available at http://www.R-project.org/ ).
Conjunctival hyperemia was also summarized using descriptive statistics for discrete variables for safety analyses.
The differences in VD, foveal avascular zone, retinal thickness, best-corrected visual acuity, and vital signs from the start to the end of the treatment period for each treatment group and between the 2 treatment groups (LBN 0.024% minus timolol maleate 0.5%) were compared using linear mixed-effects models, with fixed effect terms for treatment, period, and randomization sequence, and a within-participant random intercept. The 2-sided 95% CI for the difference and the P values were also calculated. P < .05 was considered statistically significant. All statistical analyses were performed using R statistical software.
RESULTS
The study included patients with OHT (n = 26, 52.0%) and OAG (n = 14, 28.0%; n = 12 POAG and n = 2 pseudoexfoliation), as well as healthy eyes (n = 10, 20.0%). Patient demographic data and ophthalmic measurements stratified by drug randomization are shown in Table 1 . There were no differences in any patient and eye characteristics among the stratified groups ( P values ranged from .05-1.00). Recruitment started between December 2018 and February 2021 and follow-up assessments ended in May 2021. We chose to include combined data from all subjects because the results were similar among the separate groups (diseased vs healthy eyes).
| LBN → Timolol (Tx Sequence 1), n = 24 | Timolol → LBN (Tx Sequence 2), n = 26 | Overall, N = 50 | P Value a | |
|---|---|---|---|---|
| Patient characteristics | ||||
| Age (y) (95% CI) | 66.7 (63.4-70.1) | 68.4 (64.8-72.1) | 67.6 (65.2-70.1) | .48 |
| Gender, n (%) Female Male | 14 (60.9) 9 (39.1) | 19 (70.4) 8 (29.6) | 33 (66.0) 17 (34.0) | .56 |
| Ethnicity, n (%) African American Asian White Other | 1 (4.3) 0 (0.0) 17 (73.9) 5 (21.7) | 1 (3.7) 2 (7.4) 22 (81.5) 2 (7.4) | 2 (4.0) 2 (4.0) 39 (78.0) 7 (14.0) | .30 |
| Hypertension, n (%) No Yes | 16 (69.6) 7 (30.4) | 18 (66.7) 9 (33.3) | 34 (68.0) 16 (32.0) | 1.00 |
| Diabetes, n (%) No Yes | 22 (95.7) 1 (4.3) | 27 (100.0) 0 (0.0) | 49 (98.0) 1 (2.0) | .46 |
| Eye Characteristics (95% CI) | ||||
| 24-2 MD | −1.04 (−2.35 to 0.27) | −1.22 (−2.02 to −0.41) | −1.14 (−1.85 to −0.42) | .81 |
| 24-2 PSD | 2.59 (1.61-3.58) | 1.91 (1.74-2.08) | 2.22 (1.77-2.67) | .17 |
| 10-2 MD | −0.67 (−1.68 to 0.33) | −0.75 (−1.51 to 0.02) | −0.71 (−1.31 to −0.12) | .90 |
| 10-2 PSD | 2.08 (0.86-3.30) | 1.36 (1.23-1.48) | 1.67 (1.15-2.19) | .23 |
| Baseline IOP (mm Hg) | 22.3 (19.9-24.8) | 25.2 (21.3-29.1) | 23.9 (21.5-26.2) | .21 |
| Baseline CCT (µm) | 564.4 (552.2-576.6) | 548.5 (537.6-559.4) | 555.8 (547.6-564.0) | .05 |
| Eye classification, n (%) Glaucoma Healthy Ocular hypertension | 6 (26.1) 5 (21.7) 12 (52.2) | 8 (29.6) 5 (18.5) 14 (51.9) | 14 (28.0) 10 (20.0) 26 (52.0) | .94 |
Baseline systemic blood pressure for patients starting on timolol first was 126.1 mm Hg (119.0-133.2 mm Hg) (systolic) and 84.0 mm Hg (79.4-88.6 mmHg) (diastolic) and for patients starting on LBN first was 134.3 mm Hg (127.8-140.8 mm Hg) (systolic) and 87.1 mm Hg (82.4-91.8 mm Hg) (diastolic) ( P systolic = .09, P diastolic = .33). Baseline heart rate for patients starting on timolol first was 73.3 beats/min (70.0-76.7 beats/min) and for patients starting on LBN first was 74.2 beats/min (68.0-80.4 beats/min) ( P = .81).
Blood pressure did not change after timolol use (systolic: −0.5 mm Hg [−3.6 to 4.5 mm Hg], P = .81; diastolic: −1.1 mm Hg [−4.4 to 2.2 mm Hg], P = .51) or LBN use (systolic: −1.9 mm Hg [−5.9 to 2.1 mm Hg], P = .36; diastolic: −1.4 mm Hg [4.7-2.0 mm Hg], P = .42). Alternatively, heart rate (beats/min) significantly decreased after timolol use (−4.1 beats/min [−6.4 to −1.7 beats/min], P = .001) but not LBN use (0.6 beats/min [−1.7 to 3.0 beats/min], P = .60; Supplemental Table S1).
IOP was lower after timolol and LBN applications. The differences in IOP (95% CI) post-timolol and post-LBN were −5.3 mm Hg (−8.6 to −1.9 mm Hg; P = .002) and −7.2 mm Hg [−10.1 to −4.2 mm Hg, P < .001), respectively. Although not statistically significant, the IOP difference was larger after LBN use when compared with timolol (−1.9 mm Hg [−4.9 to 1.0 mm Hg; P = .2]). No worsening in best-corrected visual acuity was observed after either medication use (Supplemental Table S1).
The percentage of study or fellow treated eyes experiencing conjunctival hyperemia was slightly higher in the LBN group (study eye: 8.0 %, fellow eye: 6.0 %) compared with the timolol group (study eye: 4.0 %, fellow eye: 2.0%; Supplemental Table S1). All other ocular adverse effects, including stinging, eye irritation, dry eye, and/or eye pain, were similar between LBN and timolol ( P > .05). All ocular adverse effects were considered mild in severity and no systemic adverse effects were reported.
Although there was a general trend of peripapillary capillary density (CD) decrease post-timolol, the differences in CD did not reach statistical significance ( P > .05 for all; Table 2 ) in any region, except for the nasal inferior peripapillary sector (−0.56% [−1.08% to −0.03%], P = .04). There was a trend of peripapillary CD enhancement for most regions after LBN use ( P > .05 for all; Table 2 ). Moreover, there was a trend of increased peripapillary CD with LBN compared with timolol (wiCD: 0.37% [−0.03% to 0.77%], P = .07).
