Invasive surgery on cats eyes to test retina implants with limited pain relief

Villalobos, J, Nayagam, D, Allen, P, McKelvie, P, Luu, C, Ayton, L, Freemantle, A, McPhedran, M, Basa, M, McGowan, C, Shepherd, R & Williams, C 2013, ‘A Wide-Field Suprachoroidal Retinal Prosthesis Is Stable and Well Tolerated Following Chronic Implantation’, Investigative Ophthalmology & Visual Science, vol. 54, no. 5, pp. 3751-3762.

Associated Institution(s): Royal Victorian Ear and Eye Hospital, the Bionics Institute, and The University of Melbourne


The aim of the study was to test the safety and reliability of a retinal electrode implantation as a treatment option to improve the sight of visually challenged people.

The Experiment

A total of seven cats with normal vision were used to test the implants over a three-month period. The prosthesis containing 21 platinum electrodes was implanted during surgery, with the cats intubated and anaesthetised. The invasive surgical procedure involved incisions to the skin surrounding the eye, manipulations to expose the back of the eyeball, and incisions to the eyeball itself. The electrode was then situated inside the back of the eyeball and stitched into place with a cable protruding from the eye and then fixed to the cheek bone.

The cats received medication in the weeks following the surgery, including antibiotics for one week, and other eye medication given twice daily for two weeks and tapered off as required. The eye medication that was given was a combination of anti-inflammatory medication (prednisolone), antibiotic medication (chloramphenicol) and pupil dilators (atropine). The atropine medication is also known to produce common side effects of stinging pain when the drops are administered as well prolonged mild eye pain. The cats were administered with pain relief as they were waking up from surgery, but after this initial dose the cats received no pain relief for the days following. Two weeks post surgery the cats were anaesthetised again for the sutures to be removed. No mention of further medication or pain relief was made in the study publication.

There were a number of health issues recorded during the study. All the cats suffered from post-surgery swelling due to accumulation of excess fluid. Two cats suffered further postoperative complications. The first was observed to have developed an abnormal region of cells at the back of the eye and the other had extended haemorrhage of the retina that took 7 weeks to recoverAll of the cats suffered from subretinal hematomas (solid swelling of clotted blood) within the two weeks after surgery as well as chronic mild inflammation associated with the body’s response to the foreign implant. In one case the implanted device protruded out of the eye due to the pressure from the attached cable, which was associated with greater inflammation.

Electroretinography was performed first at two weeks then at three months after the initial implantation. This test is used to detect abnormal functioning of the retina. Electroretinography procedures usually involve numbing of the eye followed by the eyelids being forced open with a metal clamp and an electrode being placed on the eye with a contact lens. Following the electroretinography, the cat was then exposed to different light levels and the response of the retina was recorded. There is no mention of the cats being sedated during this procedure, however with the eye being propped open and expensive equipment being placed on the cat then there would need to be restraint methods for the procedure to be successful. This would potentially be very stressful for the cats involved.

Lastly the cats were anaesthetised for an electrophysiologic experiment that lasted two days, and involved the electrodes in the eye being stimulated with an electrical charge. The methods and findings of this part of the experiment were not published in nor referenced in the study publication.

At completion of the last experiment, the cats were killed via overdose and their eyes removed for further analysis.


The retinal prosthesis implant was considered successful as there was mild tissue reaction and no significant changes to retinal function in cats with normal vision. The study recommends development of the implant device.

Unanswered Questions

There are a number of questions that remain unanswered, concerning the unnecessary suffering placed on the cats. There is also an issue of logic in terms of the experimental subjects chosen.


  • Why was pain medication not given in the days/weeks following the surgical procedure?
  • Why were cats not sedated during the electroretinography when this would not have affected the results but reduced the stress level of cats involved?
  • Why were the cats killed at the termination of the experiment?
  • What does this procedure tell us about humans with affected vision when it was performed on cats with functional vision?



The experiment was supported by the Ian Potter Foundation, John T. Reid Charitable Trusts, and the Australian Research Council through its Special Research Initiative in Bionic Vision Science and Technology grant to Bionic Vision Australia (BVA).

The Centre for Eye Research Australia (CERA, University of Melbourne) receives Operational Infrastructure Support from the Victorian Government and is supported by the National Health and Medical Research Council (NHMRC) (#529923; $2,552,356). The Bionics Institute (at St Vincent’s Hospital) receives support from the Victorian Government through its Operational Infrastructure Support Program.

What You Can Do

Please write to the following to ask for the explanations to the unanswered questions above:

Vice Chancellor, University of Melbourne


Please also write to the following funding bodies to ask why they are funding the use of animals in experimental procedures when these animals do not appropriately model humans.

Professor Anne Kelso
National Health and Medical Research Council
GPO Box 1421
Canberra ACT 2601


Australian Research Council
GPO Box 2702
Canberra ACT 2601


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