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David Birch, Kirsten Locke, Travis Porco, Martin Klein, Austin Roorda, Weng Tao, Jacque Duncan; Long-term follow-up of patients with retinitis pigmentosa (RP) receiving sustained-release CNTF through intraocular encapsulated cell technology implants. Invest. Ophthalmol. Vis. Sci. 2013;54(15):640.
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In a multicenter Phase 2 study, ciliary neurotrophic factor (CNTF) was delivered to one eye via encapsulated cell technology implants (NT-501, Neurotech Pharmaceuticals, Inc.) in 68 patients with RP. Patients had the option of having the implant removed at 24 months. Here we report cone photoreceptor density and visual field sensitivity (VFS) changes from a subset of patients with or without implant for up to 54 months.
For 3 patients, high-resolution images of regions of interest (ROIs) with unambiguous cones were obtained with Adaptive Optics Scanning Laser Ophthalmoscopy (AOSLO) in CNTF-treated and control eyes at baseline, 3, 6, 12, 18, and 24 months post-implant. Patients 1 and 3 elected to have the devices removed after 24 months and patient 2 retained the implant. They were subsequently imaged at 36 and 48 months. For 16 patients who consented to post-30 month visual field testing, VFS was measured twice per eye at baseline and every 6 months through month 30. Of these, 10 chose to retain the implant and 6 chose to have the device explanted. They were subsequently evaluated at 42 and 54 months.
Cone density was measured within selected ROIs at baseline and at least one subsequent imaging session 12 to 35 months later. Overall, cone density decreased by 9% to 24% in 8 of 9 locations (89%) in sham-treated eyes but remained stable in 12 of 12 (100%) locations in the CNTF treated eyes, changing less than the range of estimated measurement error (6.3%). VFS showed greater loss in eyes treated with CNTF than sham treated eyes starting at 6 months. At 42 months, loss in the eyes with the high-dose implant (compared to baseline) was 370 ± 43 dB, which was significantly greater (p<0.05) than 266 ± 29 dB loss in sham-treated eyes. Implant removal slowed the rate of VFS loss. Consequently, explanted eyes showed comparable sensitivity loss (p = 0.23) to sham-treated eyes at 42 months and less total sensitivity loss than the sham-treated eyes at 54 months.
CNTF treatment preserved cone photoreceptors from degeneration in the RP patients but concurrently reduced VFS. The loss of VFS was reversible upon implant removal. Further follow-up will be necessary to determine whether CNTF exposure preserves photoreceptors and slows long-term field loss relative to sham-treated eyes.
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