The overall goal of this procedure is to observe the effects of scleral cross-linking using riboflavin and ultraviolet-A radiation to induce axial myopia in a rabbit model. This method can help answer key questions in the scleral cross-linking field, such as, how can UVA radiation be directed to specific scleral areas. The main advantage of this technique is that it uses UVA radiation, fiber optics, and surgery to reach sceral areas of interest.
Assisting the surgical procedure will be Orly Gal-Or, a resident in Rabin Medical Center Ophthalmology Department. Before beginning the procedure, confirm a lack of response to pain reflex and use a sterile cotton swab to apply a small amount of ophthalmic ointment to the non-operated eye. Then, apply topical anesthesia to each eye.
And placing the probe perpendicular to the central cornea, use an Ultrasound A scanner to perform three axial length measurements of the eyes. Next, under an ophthalmic operating microscope, use surgical ophthalmic forceps and scissors to make a 360-degree conjunctival peritomy. Use a muscle hook to locate the four extraocular rectus muscles.
Then, isolate the muscles with two zero braided silk non-needle sutures to create four quadrants. Using a skin marker, designate one irradiation zone at the equatorial sclera, and one irradiation zone at the posterior sclera in each quadrant. Then, load a three-to five-milliliter syringe with 0.1 percent dextran-free riboflavin 5 phosphate photo-sensitizer solution and attach a 26 gauge lacrimal cannula.
Now, turn on an irradiation device with a 370 nanometer UVA light source connected to a beveled down custom made fiber optic, and set the device to 57 milliwatts per square centimeter. Twenty seconds before beginning the irradiation, move the eyeball by pulling the silk sutures in the opposite direction of the quadrant to be treated, and apply photo-sensitizer solution onto the irradiation zone. Then, use the custom made fiber optic to irradiate the selected zone for 200 seconds, applying photo-sensitizer solution to the zone every 20 seconds.
After all four quadrants have been irradiated, trim the lid margins with scissors. Then, use four zero ivory colored braided silk to gently suture the upper and lower eyelids. Apply a small amount of ophthalmic ointment onto the lid margin, and place the rabbit under a heat lamp.
When the animal is fully recovered, place it into a clean cage with new bedding. Fifty-five days after the cross-linking, use surgical ophthalmic scissors to remove the tarsorrhaphy. Then, perform three axial length measurements on each eye as just demonstrated.
In animals that underwent scleral cross-linking and tarsorrhaphy, the mean axial length decreased after eyelid suture, compared to the unoperated eye. In animals that underwent only peritomy and tarsorrhaphy, however, the mean axial length increased in the experimental eye. Indeed, eyes that underwent scleral cross-linking exhibited a lower axial length increase overall, compared to eyes that were peritomized only.
While the between-group difference in the mean axial length of the eyes that did not undergo surgery was not statistically significant. While attempting this procedure, it's important to remember to prepare all the necessary equipment in advance. After its development, this technique paved the way for researchers in the field of myopia, who explored the effects of riboflavin and UVA radiation on the retina, choroid, and sclera.
After watching this video, you should have a good understanding of how to visualize specific scleral areas of interest, and to apply focused UVA radiation treatments. Don't forget that performing surgeries on such small eyes with delicate rectus muscles can be extremely challenging and that the learning curve for perfecting the technique should be accepted. The implications of this technique extend towards the prevention of pathological myopic complications.
Though this method can provide insight into the prevention of axial myopia, it can also be applied to other conditions such as thin scleral areas.
