Abstract
Purpose: :
To compare the juxtapapillary retinal nerve fiber layer (RNFL) thickness in naïve and chronic experimental glaucomatous cynomolgus monkeys with Spectral Domain Optical Coherence Tomography (SD-OCT).
Methods: :
Chronic ocular hypertension (OHT) of various durations (0.7-12 y) was induced in the right eye (OD) of 40 cynomolgus monkeys by argon laser trabeculoplasty. The left eye (OS) was untreated with normal intraocular pressure (IOP). An additional 19 naïve animals served as controls. The juxtapapillary RNFL thickness in the normal and experimental eyes was evaluated with Spectralis SD-OCT (Heidelberg Engineering, Germany) and was divided into six sections: temporal (T), temporal-superior (TS), nasal-superior (NS), nasal (N), nasal-inferior (NI), and temporal-inferior (TI) for comparative analyses.
Results: :
In the 19 naïve 4-yo monkeys, there was no difference in RNFL thickness between OD and OS. In 14 OHT 4-yo monkeys (OHT duration = 0.7 y), significant thinning of OD RNFL (-15 ± 7 µm, -11.5%, p < 0.05) was detected compared to the OS in the NI section. In a second group of 26 OHT monkeys (age = 7-16 y; OHT duration = 2-12 y), mean RNFL thickness of OD (87 ± 3 µm) was significantly thinner (-9.3%, p < 0.001) than the contralateral control eyes (96 ± 2 µm). RNFL thickness was negatively correlated with elevated IOP (r2 = 0.39). Significant (p < 0.05) thinning of OD RNFL was detected in TS (-10 ± 4 µm, -6.8%), NS (-14 ± 6 µm, -10.4%), N (-8 ± 3 µm, -11.2%), and NI (-29 ± 7 µm, -22.4%) sections, but not in TI (-9 ± 6 µm, -4.4%) and T (3 ± 2 µm, 4.7%) sections.
Conclusions: :
Initial thinning of juxtapapillary RNFL was detected in the NI section of the eyes with 0.7 y of OHT. With longer duration of IOP elevation, this and other sections continued to become thinner. However, the temporal section which corresponds to the papillary-macular bundle was not affected by OHT. Progressive thinning of RNFL observed in monkey eyes with different duration of chronic OHT is likely indicative of continuous death of retinal ganglion cells, and is similar to the disease progression in POAG in humans.
Keywords: nerve fiber layer • intraocular pressure • imaging/image analysis: non-clinical