Abstract:
Purpose. To perform a descriptive investigation of the chimpanzee (Pan troglodytes) eye, conduct selected
ophthalmic diagnostic tests, document intraocular measurements and determine the intraocular lens (IOL)
power for this species.
Methods. Thirty-three anaesthetised captive chimpanzees (20 females with a mean age of 21.8 ± 7.06 years
and a median age of 15 years, 13 males with a mean age of 16.4 ± 17.48 years and a median age of 15
years) underwent ophthalmic examination as part of routine health examinations. Selected diagnostic tests
performed: intraocular pressure (IOP) by rebound tonometry (TonoVet®), central corneal thickness (CCT) by
ultrasonic pachymetry, keratometry using a handheld automatic keratometer, A- and B-mode ultrasonography.
IOL power was calculated using the Retzlaff and Binkhorst theoretical formulas.
Results. Most common ophthalmic findings (eyes): iridal melanosis (11), dyscoria (3) and mature cataracts
(2). IOP: 22.59 ± 5.34 mmHg (“d” setting), 14.34 ± 4.03 mmHg (“P” setting). Mean horizontal corneal radius:
7.35 ± 0.47, mean vertical corneal radius: 6.55 ± 0.55 mm. Mean horizontal and vertical corneal curvatures
were 46.19 ± 2.80 D and 51.74 ± 4.39 D respectively. CCT: 0.45 ± 0.04 mm. No significant differences were
found between right and left eyes, age or sex for any parameter evaluated except for a sex difference in IOP
where males had lower IOP than females. Ocular biometry: axial globe length: 21.41 ± 0.76 mm, anterior
chamber depth (ACD): 3.63 ± 0.47 mm, crystalline lens thickness (LT): 3.81 ± 0.68 mm, posterior segment
depth: 13.98 ± 1.00 mm. The estimated postoperative ACD (PACD) was calculated as ACD + 0.5 x LT. To
address the effect of IOL position on lens power, additional calculations using PACD +2mm and PACD -2mm
were performed. Calculated IOL powers (using the Retzlaff and Binkhorst formulas respectively): PACD:
21.86 ± 5.73 D and 22.81 ± 5.79 D; PACD +2mm: 27.67 ± 7.36 D and 28.83 ± 7.43 D; PACD -2mm: 17.71 ±
4.59 D and 18.51 ± 4.65 D.
Conclusions. Normal parameters described in this study will aid in the identification of ocular pathology in
chimpanzees. Determination of the IOL power will facilitate correct IOL selection for the phacoemulsification
candidate, although further studies evaluating pseudophakic refraction and determination of actual PACD are
required.
