ABSTRACT
PURPOSE: To compare the effects of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) on corneal sensation. SETTING: Ohshima Hospital of Ophthalmology, Fukuoka, Japan. METHODS: Corneal sensation was measured with a Cochet-Bonnet esthesiometer in 35 patients before and 3 days, 1 week, and 1 and 3 months after correction of myopia by PRK (22 patients) or LASIK (13 patients). RESULTS: After PRK, corneal sensitivity was decreased slightly at 3 days, began to recover at 1 week, and returned to preoperative values at 3 months; none of the changes was statistically significant (P >.05). After LASIK, corneal sensation was significantly decreased at 3 days, 1 week, and 1 month; it recovered slightly at 3 months, although it remained significantly less than preoperatively. CONCLUSIONS: Laser in situ keratomileusis was associated with a negative effect on corneal sensation, which was markedly greater than the effect with PRK and was evident for at least 3 months after surgery.
Subject(s)
Corneal Diseases/etiology , Keratomileusis, Laser In Situ/adverse effects , Myopia/surgery , Photorefractive Keratectomy/adverse effects , Sensation Disorders/etiology , Adolescent , Adult , Corneal Diseases/diagnosis , Corneal Diseases/physiopathology , Diagnostic Techniques, Ophthalmological , Female , Humans , Lasers, Excimer , Male , Middle Aged , Sensation Disorders/diagnosis , Sensation Disorders/physiopathology , Time FactorsABSTRACT
The electrogenic Na+ -K+ pump current (Ip) in carp bipolar cells was investigated under voltage-clamp conditions. The Ip was activated in a concentration-dependent manner by adding external K+ (Ko+) and was completely suppressed with 10(-4) M ouabain (EC50=1.23 mM; Hill coefficient=1.36). The Ip was suppressed in a concentration-dependent manner by ouabain (IC50=1.90 mM; Hill coefficient=0.93). The Ip did not show a distinct voltage dependency either with or without Na(o)+. A large outward shift of the holding current was observed by completely removing Na(o)+. In the presence of Na(o)+, a steady Ip was observed even in the absence of internal Na+ (Na(i)+). These results suggest that continuous Na+ influxes exist across the membrane. When external and internal Na+ was removed, a transient Ip was observed (half decay time (t1/2) was 5.0+/-0.6 s), thus indicating that the transient Ip was activated by the residual Na(i)+. In the absence of Na(o)+, the transient Ip was also observed with lower than 8 mM Na(i)+. The t1/2 depended on Na(i)+. However, a steady Ip was observed with 10 mM Na(i)+ or more. The functional properties of the Ip are discussed.
Subject(s)
Carps/metabolism , Retina/metabolism , Sodium-Potassium-Exchanging ATPase , Animals , Carps/anatomy & histology , Cell Polarity , Electrochemistry , Enzyme Inhibitors/pharmacology , Ouabain/pharmacology , Patch-Clamp Techniques , Potassium/pharmacology , Retina/cytologyABSTRACT
The electrogenic Na+-K+ pump current in horizontal cells acutely dissociated from the carp retina was investigated using a nystatin-perforated patch recording configuration under voltage-clamp conditions. In the presence of suitable blockers for known voltage-dependent Na+, K+ and Ca2+ conductances, the pump current was activated in a concentration-dependent manner by adding K+ ions to external solution. The EC50 value and Hill coefficient for the external K+ concentration were 0.66 mM and 1.39, respectively. The pump current did not show any significant voltage dependency at the physiological potential range between -90 and 20 mV either with or without external Na+ ions. In the presence of 120 mM external Na+ concentration, the addition of 3 mM K+ to the external solution induced a steady outward pump current even when the patch-pipette (internal) solution did not contain Na+. A large outward shift of the holding current was observed by removing external Na+. The result thus suggests that continuous Na+ influxes exist across the plasma membrane in the presence of external Na+. When Na+ was removed from both external and internal solutions, a transient outward pump current was observed by adding K+ to the external solution, thus indicating that the transient pump current was activated by the residual intracellular Na+ ions. The pump current was suppressed by ouabain in a concentration-dependent manner, and the ouabain-sensitive inhibition curve was fitted by two components. The IC50 values of high- and low-sensitive pump currents for ouabain were 20 nM and 10.4 microM, respectively, indicating the existence of at least two isoforms of the pump in the horizontal cells.
