Intra-Subject Variability and Diurnal Cycle of Ocular Perfusion Pressure as Characterized by Continuous Telemetry in Nonhuman Primates

Ocular examination findings and selected ophthalmic diagnostic tests in African green monkeys (Chlorocebus aethiops sabaeus)

OBJECTIVE

To document ocular lesions and establish ophthalmic diagnostic test reference values in a colony of African green monkeys (Chlorocebus aethiops sabaeus).

ANIMALS STUDIED

Fifty one geriatric (GAGM, 19-30 years old), 10 adult (AAGM, 5-9 years old) and 10 juvenile (JAGM, <2 years old) African green monkeys housed in a single Caribbean research colony.

PROCEDURES

Ocular biomicroscopy, indirect fundoscopy, Schirmer tear test (STT), rebound tonometry (TonoVet®) and corneal fluorescein staining were performed. Mixed ANCOVA tests were performed to compare STT and IOP between groups.

RESULTS

Common ocular lesions in GAGM included vitreal degeneration (27/51, 51/102 eyes) and cataracts (21/51, 32/102 eyes). Vitreal degeneration was also common in AAGM (8/10, 16/20 eyes) and infrequent in JAGM (3/10, 6/20 eyes). Cataracts were not present in any JAGM or AAGM. All eyes in all three groups had perilimbal corneal pigmentation and faint lace-like anterior corneal stromal opacification. Median (range) STT values were 16.0 (18) mm/min in GAGM. Mean (SD) STT values were 14.2 (4.6) mm/min in AAGM, and 8.9 (3.4) mm/min in JAGM. Median (range) IOP values were 16.5 (27) mmHg in GAGM. Mean (SD) IOP values were 18.0 (2.8) mmHg in AAGM, and 14.1 (2.2) mmHg in JAGM. JAGM had significantly lower STT and IOP values compared to AAGM (p = .0449, .0057, respectively) and GAGM (p = .0002, .0130, respectively).

CONCLUSIONS

Spontaneous ocular lesions were common in geriatric monkeys in this research colony. IOP and STT values were lower in juvenile African green monkeys relative to adult or geriatric animals.

Diurnal Variation and Effects of Dilation and Sedation on Intraocular Pressure in Infant Rhesus Monkeys

PURPOSE

Intraocular pressure (IOP) is an important factor in numerous ocular conditions and research areas, including eye growth and myopia. In infant monkeys, IOP is typically measured under anesthesia. This study aimed to establish a method for awake IOP measurement in infant rhesus monkeys, determine diurnal variation, and assess the effects of dilation and sedation.

METHODS

Awake IOP (iCare TonoVet) was measured every 2 h from 7:30 am to 5:30 pm to assess potential diurnal variations in infant rhesus monkeys (age 3 weeks, n = 11). The following day, and every 2 weeks to age 15 weeks, IOP was measured under three conditions: (1) awake, (2) awake and dilated (tropicamide 0.5%), and (3) sedated (ketamine and acepromazine) and dilated. Intraclass correlation coefficient (ICC) was used to determine intersession repeatability, and repeated measures. ANOVA was used to determine effects of age and condition.

RESULTS

At age 3 weeks, mean (±SEM) awake IOP was 15.4 ± 0.6 and 15.2 ± 0.7 mmHg for right and left eyes, respectively (p=.59). The ICC between sessions was 0.63[-0.5 to 0.9], with a mean difference of 2.2 ± 0.3 mmHg. Diurnal IOP from 7:30 am to 5:30 pm showed no significant variation (p=.65). From 3 to 15 weeks of age, there was a significant effect of age (p=.01) and condition (p<.001). Across ages, IOP was 17.8 ± 0.7 mmHg while awake and undilated, 18.4 ± 0.2 mmHg awake and dilated, and 11.0 ± 0.3 mmHg after sedation and dilation.

CONCLUSIONS

Awake IOP measurement was feasible in young rhesus monkeys. No significant diurnal variations in IOP were observed between 7:30 am and 5:30 pm at age 3 weeks. In awake monkeys, IOP was slightly higher after mydriasis and considerably lower after sedation. Findings show that IOP under ketamine/acepromazine anesthesia is significantly different than awake IOP in young rhesus monkeys.

Development of Primary Open Angle Glaucoma-Like Features in a Rhesus Macaque Colony From Southern China

Purpose

To describe the ocular phenotype of spontaneous glaucoma in a non-human primate colony.

Methods

In total, 722 Rhesus macaque monkeys aged 10 to 25 years underwent optical coherence tomography (OCT), fundus photography (FP), and intraocular pressure (IOP) measurements. Monkeys with baseline cup-to-disc ratio (CDR) <0.5 were used to establish baseline ocular features. A subset was followed longitudinally for three years and compared to glaucoma suspects on the basis of OCT/FP criteria.

Results

The average IOP under ketamine sedation and average CDR for the entire colony was 13.0 ± 4.3 mm Hg and 0.38 ± 0.07, respectively. The mean baseline conscious IOP of glaucoma suspects (N = 18) versus controls (N = 108) was 16.2 ± 3.5 mm Hg and 13.9 ± 2.3 mm Hg, respectively (P = 0.001). All glaucoma suspects had unremarkable slit lamp examinations and open angles based on anterior segment OCT. Baseline global circumpapillary retinal nerve fiber layer (RNFL) thickness was 91.5 ± 11.0 µM versus 102.7 ± 8.5 µM in suspects and controls, respectively (P < 0.0001). All sectors on the baseline circumpapillary OCT showed a significant reduction in RNFL thickness versus controls (P ≤ 0.0022) except for the temporal sector (P ≥ 0.07). In three-year longitudinal analysis, neither CDR nor OCT parameters changed in controls (N = 40; P ≥ 0.16), whereas significant increase in CDR (P = 0.018) and nominally significant decreases in two OCT sectors (nasal, P = 0.023 and nasal inferior, P = 0.046) were noted in suspects.

Conclusions

Members of a nonhuman primate colony exhibit important ophthalmic features of human primary open-angle glaucoma.

Translational Relevance

Identification of a spontaneous model of glaucoma in nonhuman primates represents an unprecedented opportunity to elucidate the natural history, pathogenesis and effective therapeutic strategies for the disease.