Test–retest reliability of scotopic full-field electroretinograms in rabbits

Biocompatibility of polyvinyl alcohol/trisodium trimetaphosphate as vitreous substitute in experimental vitrectomy model in rabbits

Synthetic hydrogels have been proposed as vitreous substitutes recently. This study aims to evaluate the biocompatibility of polyvinyl alcohol (PVA) crosslinked with trisodium trimetaphosphate (SMTP) hydrogel in rabbit vitrectomized eyes. Seven animals were submitted to pars plana vitrectomy and the vitreous was replaced by PVA/SMTP hydrogel. Optical coherence tomography, fluorescein angiogram, clinical, and electrophysiological (ERG) examinations were analyzed at baseline, on postoperative days 7 and 30. The fellow eye was used as the control group. Hydrogel opacification was observed and ERG recordings were reduced in the hydrogel group in rod response, b-wave cone response and flicker. A histological analysis showed retinal disorganization, presence of multinucleated cells, and intraretinal hydrogel particles. The PVA/SMTP hydrogel showed poor biocompatibility. Novel biomaterials compounds should be analyzed in vivo.

ERG shrinks by 10% when reducing dark adaptation time to 10 min, but only for weak flashes

PURPOSE

To compare dark-adapted (DA) ERG between 10, 15 and 20 min of dark adaptation (DA).

METHODS

In a counterbalanced random block design, 40 healthy adult subjects were dark-adapted for 10, 15 or 20 min before we recorded ERGs to nine flash strengths from 0.001 to 10.0 cd s/m2 (dilated pupils) with a DTL-like electrode. Before and between sessions, the room was lit. Apart from choosing a wider range of stimulus strengths, and adding shorter DA times, the recordings fully complied with the ISCEV ERG Standard, namely using corneal electrodes, mydriasis and a standard DA sequence.

RESULTS

The a-wave amplitude was not affected by any adaptation condition. For the b-wave amplitude, effects of reduced DA time are stronger for weaker flashes: Reducing DA from 20 to 10 min had no measurable effect on the DA 3 ERG, but reduced the DA 0.01 b-wave significantly (p < 0.0001) to 87 ± 2% (mean ± SEM). The DA 0.001 b-wave (not part of the ISCEV ERG Standard) was more affected (down to 72 ± 4%). There was a small, but significant, increase, only for weak flashes, in a- and b-wave peak times for 20 compared to 10-min dark adaptation time.

CONCLUSION

Reducing dark adaptation time from 20 to 10 min in normal participants has no effect on the ISCEV DA 3 and DA 10 ERG. The reduction in DA 0.01 ERGs to 87 ± 2% agrees with Hamilton and Graham (Doc Ophthalmol 133:11-19, 2016. https://doi.org/10.1007/s10633-016-9554-x ) who found 90 ± 2% and with Asakawa et al. (Doc Ophthalmol 139:33-44, 2019. https://doi.org/10.1007/s10633-019-09693-8 ) who found 83%. Pending verification in pathophysiological states, the current results suggest that one might be able to correct for the 10% amplitude loss when gaining 10 min through shortened DA.

Safety and tolerability evaluation after repeated intravitreal injections of a humanized anti-VEGF-A monoclonal antibody (PRO-169) versus ranibizumab in New Zealand white rabbits

Background

To evaluate the retinal toxicity after repeated intravitreal injections of a humanized anti-VEGF-A monoclonal antibody (PRO-169) versus ranibizumab in New Zealand white (NZW) rabbit eyes.

Methods

NZW rabbits were injected intravitreally with PRO-169 (n = 12), 1.25 mg/0.05 ml or ranibizumab (n = 12), 0.5 mg/0.05 ml into the right eye (OD), whereas the left eye (OS) of each rabbit was used as control. Three consecutive injections were administered at 30-days intervals. An electroretinogram (ERG) was recorded 30 days after each injection. Clinical examination was conducted before and after injections, including intraocular pressure determination and eye fundus exploration. Eyes were enucleated and retina, cornea, conjunctiva, ciliary body and optic nerve were prepared for histopathology assessment.

Results

ERG of the experimental and control eyes in PRO-169 and ranibizumab groups were similar in amplitude and pattern throughout the follow-up period. Clinical examination found no alterations of intraocular pressure (IOP). No retinal damage was observed in both, the experimental and control eyes, of all the rabbits. The histopathologic studies showed similar results in both groups, showing no signs of structural damage.

Conclusions

Our study did not find evidence of retinal toxicity from a repeated intravitreal injection of PRO-169 or ranibizumab (Lucentis^®) in NZW rabbits. These findings support intravitreal PRO-169 as a safe candidate to develop as a future alternative for the treatment of retinal neovascularization diseases.

The effects of intravitreal sodium iodate injection on retinal degeneration following vitrectomy in rabbits

We sought to develop and characterize outer retinal degeneration induced by intravitreal injection of sodium iodate (SI) after vitrectomy in rabbits. To determine the effective dose of SI, the right eyes of 19 male New Zealand white rabbits received an intravitreal injection of SI or sham. Based on the dose-dependence results, 0.4 mg of SI in 0.05 mL of total volume was injected into the right eyes of 10 rabbits at two weeks after vitrectomy. In the dose-dependence study, localized retinal atrophy was observed with 0.3- and 0.4-mg SI injections without vitrectomy. Severe and diffuse retinal atrophy was identified by spectral-domain optical coherence tomography (SD-OCT) at one month after a 0.5-mg SI injection following vitrectomy. In the second experiment, 0.4 mg of SI in 0.05 mL was injected, and the severity of outer retinal degeneration was graded as one of two types according to electroretinography (ERG) response change. There was no response on ERG in complete retinal degeneration, 30% of all 10 rabbits. Intravitreal injection of 0.4 mg of SI into vitrectomized rabbit eyes induces diffuse outer retinal degeneration, and the degree of retinal degeneration can be evaluated through in vivo ophthalmic examination.