The eyes have it - Part I

Phototherapy is a common, successful treatment for age-related macular degeneration and other retinal disorders among people. Laser treatment of the affected eye can help patients with such conditions, and the power of the laser treatment and lens employed are calibrated to the unique qualities of each patient’s eye – including axial length. Monkeys naturally have axial lengths shorter than those of people. Despite this, and the fact that there are already human data on this treatment, some still choose to experiment on animals.


Citation: Effect of axial length on laser spot size during photodynamic therapy: an experimental study in monkeys. M Kondo, Y Ito, K Miyata, N Kondo, K Ishikawa, and H Terasaki. Am J Ophthalmol, January 1, 2006; 141(1): 214-5.

Summary of experiment: Authors used some pediatric equipment because of the size of the monkeys' eyes. The authors indicate that they have not treated any patient with an axial length in the range of these monkeys.

“Although we have not performed PDT on patients with very short axial lengths, a reduction of the spot diameter should be considered for such cases.” P. 215

Three monkeys with healthy eyes received the laser treatment. After one week there was an unusually powerful response to the laser, so they cut the eyes out to examine them. Once they figured out how their equations for laser calibration had to be adjusted, they performed the experiment on one additional monkey, cut his eyes out and got the results they expected.

My Notes:

• Procedure tested on these monkeys has already been vetted through a variety of clinical trials in humans.
• Despite existing data on humans treated with phototherapy and their natural variation in axial length, AND the fact that experiments with a model eye have shown that there is an important relationship between axial length and how the eye responds to this specific form of phototherapy, investigators decided to conduct an experiment in monkeys.
• The authors did not indicate whether the animals were killed in addition to having their eyes removed.
• There was very little detail about the methods, as this was a short communication.

Author affiliation:
Department of Ophthalmology, Nagoya University School of Medicine, Nagoya, Japan

Funding acknowledged: Supported by a Grant-in Aid 16591747 (M.K.) and 16390497 (H.T.) from the Ministry of Education, Science, Sports and Culture, Japan