To evaluate the enhancing effects of scleral biomechanics and safety of collagen crosslinking by using minimally invasive riboflavin and ultraviolet A.

Fifty-six healthy New Zealand white rabbits were randomized into non-cosslinking group, post-crosslinking 1-day group, post-crosslinking 7-day group, post-crosslinking 15-day group, post-crosslinking 1-month group, post-crosslinking 2-month group and post-crosslinking 3-month group, eight for each group.Riboflavin solution at the concentration of 0.1% was dropped once per 2 minutes for 20 minutes, and then minimally invasive riboflavin and ultraviolet A was carried out in the right eyes by putting the lighting emitting diode (LED) probe end of microinvasive ultraviolet scleral crosslinking device to irradiate the posterior sclera for 30 minutes with the wavelength of 370 nm and radiation energy of 3 mW/cm², and the left eyes served as the normal controls.The scleral temperature was measured using clinical thermometer during the crosslinking period.The rabbits were sacrificed according to the grouping and the eyeballs were obtained.The scleral thickness was measured by callipers, the pretension and tensile failure tests of sclera strips were tested by micromaterial mechanics performance test system to measure the extreme stress, extreme strain and 8% elastic modulus.Hematoxylin-eosin staining was employed to examine the morphology of eye tissues.Retinal cell apoptosis was detected by TUNEL assay.

The scleral thickness was insignificantly different among the non-crosslinking group, post-crosslinking 1-day group, post-crosslinking 7-day group, post-crosslinking 15-day group, post-crosslinking 1-month group, post-crosslinking 2-month group and post-crosslinking 3-month group and between right eyes and left controls (F_eyes =0.02, P>0.05; F_group=1.71, P>0.05). Compared with the non-crossliking group, the extreme stress and 8% elastic modulus of the scleras were significantly increased, and the extreme strain of the scleras was significantly decreased in post-crosslinking 1-day group, post-crosslinking 7-day group, post-crosslinking 15-day group, post-crosslinking 1-month group, post-crosslinking 2-month group and post-crosslinking 3-month group (all at P<0.05). Not any morphological abnormalities were found in corneas, scleras, irises, ciliary bodies and choroids in various groups.The apoptosis rates of retinal cells were (11.00±0.33)%, (12.33±1.58)%, (12.02±0.45)%, (11.81±0.85)%, (12.15± 0.61)%, (12.14±0.25)% and (11.74±0.63)% in the non-crosslinking group, post-crosslinking 1-day group, post-crosslinking 7-day group, post-crosslinking 15-day group, post-crosslinking 1-month group, post-crosslinking 2-month group and post-crosslinking 3-month group, respectively, with no significant difference among the three groups (F=1.78, P=0.14).

Rabbit sclera collagen crosslinking by using the minimally invasive riboflavin and ultraviolet A can effectively enhance the biomechanical strength of the sclera, and this procedure is safe.

Minimally invasive; Riboflavin; Ultraviolet A; Sclera collagen crosslinking; Biomechanics