Utilizing Göttingen Minipigs in Ocular Research – Review and Current Perspectives Stephanie Shrader, DVM, DACVP and William Greentree, DVM, DACVO. Charles River Laboratories, Spencerville, OH, USA

1 ABSTRACT Göttingen minipigs were developed in the 1960’s at the University of Göttingen in Germany for use in biomedical research. Since then, they have become a popular alternative to other non-rodent animal models, especially for ocular studies, because of their ease of handling, smaller size (compared to other miniature swine breeds), rigorous genetic maintenance, and ocular anatomy that is similar to humans. Although Göttingen minipigs are commonly used in ocular research, there is a paucity of literature available to researchers, ophthalmologists, and pathologists regarding their overall use in such research endeavors. To date, the Göttingen minipig has been used for a variety of ocular studies, including those evaluating the safety and efficacy of ocular therapeutics (delivered via various routes of administration), glaucoma etiopathogenesis and treatment, novel biomaterials and implantable devices, and novel surgical procedures. Additional diagnostics tools that are often utilized during the course of ocular studies include in vivo procedures (e.g. electroretinography, optical coherence tomography, fundoscopic imaging, and fluorescein angiography) and histopathologic evaluation of enucleated globes. This review provides an understanding of porcine ocular anatomy, human ocular therapeutic needs, surgical procedures, feasibility of implantable biomaterials, useful adjunctive diagnostic tools, and demonstrated uses of this animal model in ocular research which are critical for the appropriate design of future studies.

4 CONCLUSIONS Ocular research utilizing the Göttingen minipig is an important and rapidly-growing research niche; however, there is a paucity of aggregated information available regarding this topic for researchers, ophthalmologists, and pathologists. Compared to other laboratory species, the Göttingen minipig has an eye that is more comparable in anatomy and size to humans, allowing for the study of specific disease states (esp. retinal diseases), administration of clinically relevant drug volumes, the testing of comparable surgical techniques, and the study of full-sized medical devices. As more ocular diseases, therapeutic agents, surgical techniques, and implantable materials/devices are studied in the Göttingen minipig, knowledge of this animal model’s ocular anatomy, utility in specific study settings, and available adjunctive diagnostic techniques is imperative to facilitate informed decisions on study design and evaluation.

Closed orbit 6 extraocular muscles Round cornea and pupil No Harderian gland Plica semilunaris Bowman’s membrane Variations in iris color Annulus of Zinn present Macula and fovea present

Orbit open laterally

7 extraocular muscles Horizontally ovoid cornea and pupil

Harderian gland present Transparent nictitating membrane

Bowman’s membrane absent Iris color usually blue or brown

Annulus of Zinn absent Fovea absent

Area centralis present (similar to macula)

HUMANS PIGS

BOTH

Binocular vision Color vision

Meibomian glands present Descemet’s membrane present

Holangiotic retinal vessels Similar photoreceptor densities

Similar viscoelastic vitreous Tapetum lucidum absent

Figure 1. Basic comparison of human and pig ocular anatomy and physiology.

5 REFERENCES 1. Ehall, H. (2011) Ocular examination and background observations. In: The Minipig in Biomedical Research. McAnulty, P.,

Dayan, A. D., Ganderup, N .C., Hastings, K. L., eds. Boca Raton, FL: Taylor & Francis. 293-303. 2. Nielsen, L. S., and Lind, N. M. (2005) Measurements of Three Ocular Parameters in the Gottingen Minipig. Scand J Lab

Anim Sci 1, 9-16. 3. Swindle, M. M. (2007) Swine in the Laboratory: Surgery, Anesthesia, Imaging, and Experimental Techniques. 2nd ed. CRC

Press, Boca Raton, FL. 4. Swindle, M. M., Makin, A., Herron, A. J., Clubb, F. J., Frazier, K. S. (2012) Swine as Models in Biomedical Research and

Toxicology Testing. Vet Pathol 49, 344-56.

How are Göttingen minipigs

used in ocular research?

Develop novel ocular

therapeutics

Topical administration Traditionally delivers drugs to ocular surface and anterior

segment

Intravitreal administration Delivers drugs to the posterior ocular structures

Subretinal administration Delivers gene therapy

vectors, stem cells, steroid implants, antimicrobials, etc.

Study ocular disease

pathogenesis

Glaucoma

Vascular disturbances

Retinal vein occlusion

Retinal arterial ischemic stroke

Retinitis pigmentosa

Presbyopia

Diabetic macular edema

Develop corneal biomaterials

Porcine collagen and co-polymer systems

Fish-scale derived collagen matrix

Study ocular surgical

techniques

Suture patterns

Ptosis repair

Corneal grafts

Laser usage

Femtosecond laser cataract surgery

Femtosecond laser assisted in situ keratomileusis

(fs-LASIK) Transconjunctival sclerotomy

Ocular medical devices

Epiretinal and retinal implants

Lens implants

Pseudophakic intraocular lens

Phakic intraocular lens Intravitreal drug delivery

systems

Figure 3. Examples of diagnostic modalities that are useful in Göttingen minipig ocular research.

Ocular Diagnostic Modalities

Fluorescein angiography

Slit lamp biomicroscopy

Indirect ophthalmoscopy

Tonometry

Electroretinography Optical

coherence tomography

Fundoscopic imaging

Corneal confocal microscopy

Histopathology

Scheimpflug analysis

Figure 2. Examples of how the Göttingen minipig is used in ocular research.

3 COMPARATIVE ANATOMY AND CURRENT USES

2 AIM The intent of this poster is threefold: to compare human and pig ocular anatomy/physiology, review the various ways in which the Göttingen minipig is utilized in ocular research, and introduce diagnostic modalities that are important in these research endeavors.