[Effect of corneal hydration and dehydration of donor tissue on the precision of the thickness in lamellar refractive keratoplasty].

The influence of corneal hydration on the precision of plano lamellas and on the precision of lenticles modified with a "non-freeze" technique was studied in pig eyes. Ten pig eyes were dissected with a rotating lamellar microkeratome, and the discs were measured with a mechanical pachymeter. The hydration of the discs was measured in BSS and in dextran solution. A total of 160 corneal discs with different degrees of hydration were modified with a "non-freeze" technique on concave anf convex vacuum cylinders and measured with a photokeratoscope TMS. The discs increased in thickness within 3 h becoming 1.7 times as thick in BSS and 1.2 times as thick in dextran. After refractive dissection minor modifications were achieved with higher precision than were larger corrections. However, we achieved an undercorrection after all refractive dissections. Plano-discs for refractive modification should be taken from dehydrated corneoscleral discs or from intact eyes. Owing to mechanical factors during cutting and tissue hydration undercorrection of the intended change was observed.