Structural and functional properties of the healed tympanic membrane: a long-term follow-up after laser myringotomy.

HYPOTHESIS

The short-term healing scar that forms after experimental laser myringotomy will revert to a normal lamina propria in the long run. The mechanical stiffness will stay normal.

BACKGROUND

Recent studies have shown severe structural changes in the fibrous layer in the early course after experimental laser myringotomy, whereas the scar quickly restored the strength of the tympanic membrane (TM). A reorganization of the fiber layer is expected to occur.

METHODS

Potassium titanyl phosphate laser myringotomy was made on one side of the TM in Sprague-Dawley rats. The ear of the other side was untouched and used for control. After half a year of observation, the stiffness and strength of the healed TMs were measured with moiré interferometry and examined with otomicroscopy and light and electron microscopy.

RESULTS

The interferometry readings showed a slightly reduced strength in the myringotomized and healed TMs. After half a year, still there were immense structural changes including increased thickness over a wide area of the pars tensa with increased amounts of fibers. An obvious reorganization of the fiber layer was lacking.

CONCLUSION

Laser myringotomy causes profound, long-standing, or permanent structural changes in the lamina propria of the pars tensa, whereas the strength of the TM may become slightly reduced.