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Background Ophthalmological Changes Following Subretinal Injection in the Brown Norway Rat 1 Vézina , 1 Li , 2 Bussières M. C. M. 1Charles River, Senneville (Montreal), Canada; 2V&O Services, St. Lazare, Canada EVER: NICE, FRANCE Introduction 10/2015 Subretinal injection has become more common in recent years as it is the route of choice for cell and gene therapy products targeting the retina. A subretinal dose allows for localized placement and containment of the administered product. The purpose of the study was to evaluate the background changes associated with transscleral subretinal injection in Brown Norway (BN) rats. Brown Norway rats were chose since they are a common species used for ocular studies and their pigmented eyes facilitate the subretinal dosing procedure. Methods Fifteen Brown Norway rats, 12 weeks of age, received a bilateral subretinal injection of 0.9% sterile saline at a volume of 6 uL while under isoflurane anesthesia. The injection was performed using a 10 µL Hamilton syringe with a 32G, ½-inch needle. Prior to injection, a pilot hole was made in the sclera using a 30G needle to facilitate insertion of the dosing needle into the eye. The eyes were examined by slit lamp and indirect ophthalmoscope the day following injection and 1, 2, 3, 4, 8 and 12 weeks post injection. Results Results (cont.) A summary of results is presented in Table 1 Table 1: Incidence of Ophthalmological Observations N=30 eyes Observation Day 2 1 Wk 2 Wks 3 Wks 4 Wks 8 Wks 12Wks Total Incidence Corneal opacity 5 5 4 - - - - 5/30 Cataract 1 3 5 1 1 2 2 5/30 Vitreous hemorrhage 28 21 15 13 11 2 2 28/30 Irregular pigmentation in bleb 1 3 5 5 9 2 2 13/30 Retina / choroid hemorrhage at injection site 19 20 18 13 4 - - 20/30 Focal depigmentation at injection site - 12 12 12 12 7 7 12/30 Focal retinal opacity 6 14 13 13 16 9 9 18/30 Retinal elevation (bleb) 27 12 - - - - - 27/30 The bleb, described as retinal elevation, was observed in 27/30 eyes the day after dosing and in 12/30 up to 1 week post dose (it was observed in all eyes immediately post dose). Transient corneal opacities occurred in 5/30 eyes that were considered related to the anesthesia. Cataracts developed in 5/30 eyes and were associated with lens trauma at the time of dosing. Slight vitreous hemorrhages occurred post dose in 28/30 eyes, resolving in all but 2 eyes by 4 weeks. An area of focal depigmentation of the retina/choroid or white focal retinal opacity was seen at the needle insertion site in the retina in 12/30 or 18/30 eyes, respectively, resolving by 4 weeks in 50% of the eyes and persisting up to 12 weeks for the remaining eyes. In the bleb itself, there were focal areas of irregular pigmentation in 13/30 eyes resolving in all but 2 eyes by week 4. The remaining 2 persisted up to week 12. Slight retinal/choroidal hemorrhages were also seen at the injection site in most eyes up to week 4. The severity of the ocular changes also diminished from slight/moderate to very slight/slight over the course of the 12 week observation period. Conclusion Transscleral subretinal injection in BN rats generally resulted in slight ocular trauma that resolved in most eyes by 4 weeks post injection. It is important to take these changes into account when evaluating therapeutics administered by this dose route. Acknowledgements The authors wish to thank the technical staff of the Ocular and Neuroscience Department for their participation in generating data for this evaluation.