Naka-Rushton Equation Parameters in Normal Pigmented Rabbit ERG

The Naka-Rushton equation, R=R(max) I(n)/(I(n)+K(n)), has been used to describe the luminance-response function of the scotopic electroretinogram. R(max) is the asymptotic value of the b-wave amplitude as a function of stimulus luminance, K is the intensity that produces a b-wave amplitude that is one-half R(max) and n is a dimensionless contant that controls the slope of the function and represents the degree of homogeneity of retinal sensitivity. These three parameters are often used in experimental laboratories, since it can show selective changes in each parameter. The present study describes and compares the parameters of Naka-Rushton equation obtained by using ganzfeld stimuli(R(max)=363+/-32 uv, n=0.86+/-0.06, log K=-2.39+/-0.19 log cd.sec/m2) and direct flash stimuli(R(max)=354+/-28 uv, n=0.80+/-0.06, log K=-2.26+/-0.15 log cd.sec/m2) in 20 eyes of the normal pigmented rabbits respectively. The n values were significantly increased by the ganzfeld light stimuli than by the direct flash stimuli(p<0.05).

Safety of intravitreally injected ciprofloxacin in phakic rabbit eyes

This study was designed to determine the maximal safe drug concentration of intravitreal ciprofloxacin in phakic rabbit eyes. Twenty-two eyes of New Zealand pigmented rabbits received midvitreal ciprofloxacin of 100, 200, 400, 600 or 800 microgram in BSS Plus, or BSS Plus only. Retinal toxicity was dose-dependent as determined with electroretinography, light microscopy, and transmission electron microscopy. At a dose of greater than 400 microgram, disorganization of the outer segments was a main pathological finding in transmission electron microscopy. We evaluated retinal function by measuring the electroretinograms for a graded series of flash intensities and by fitting electroretinogram b-wave amplitudes to the Naka-Rushton equation. At a dose of greater than 600 microgram, Rmax was significantly decreased and log K was significantly increased. N-value tended to decrease. A decrease of b-wave amplitudes caused by retinal toxicity could be detected very sensitively with lower luminance stimuli. Determination of retinal toxicity with lower luminance electroretinography revealed a significant decrease of b-wave amplitudes at a dose of greater than 400 microgram. We concluded that a safe dose of intravitreal ciprofloxacin in phakic rabbit eyes was 200 microgram in phakic eyes.

Safety of Intravitreal Ciprofloxacin in Phakic Rabbit Eyes Determined with Electroretinography

This study was conducted to determine the safe intravitreal dosage of ciprofloxacin. Twenty-four phakic eyes of New Zealand pigmented rabbits were used. Each group(4 eyes) received midvitreal ciprofloxacin of 100, 200, 400, 600, 800 micro gram in 0.1ml BSS Plus, or 0.1ml BSS Plus only as control. We evaluated retinal function by measuring the electroretinograms for a graded series of flash intensities and fitting b-wave amplitudes to the Naka-Rushton equation. At a dose of greater than 600 micro gram, Rmax decreased signifantly and log K increased signifantly. N-value decreased slightly. B-wave amplitude decreased as a toxic response of intravitreal ciprofloxacin in a dose dependent manner, and this response was best detected using lower luminance stimuli. Lower luminance electroretinography revealed a significant decrease in b-wave amplitude in eyes injected with a dose of 400 micro gram or more. We concluded that 200 micro gram will be the safe intravitreal dosage of ciprofloxacin in phakic rabbit eyes.

The luminance-response function of the dark-adapted rabbit electroretinogram

The Naka-Rushton equation of the form, R = R(max) I(n)/(I(n)+K(n)), has been used to describe the b-wave luminance-response function of the scotopic electroretinogram. Rmax is the asymptotic value of the b-wave amplitude as a function of stimulus luminance I, K is the luminance that produces a b-wave amplitude that is one-half R(max), and n is a dimensionless constant that controls the slope of the function. These three parameters are often used in research laboratories, since it can show selective changes in each parameter. The present study describes these parameters (R(max) = 354 +/- 28 uV, n = 0.80 +/- 0.06, log K = -2.26 +/- 0.15 log cd. sec/m2) and the values obtained from the derivative analysis of Naka-Rushton equation (Anastasi et al) in 20 normal pigmented rabbit eyes. However, Naka-Rushton equation accurately describes the function only at low to moderate flash luminances. At high flash luminances, a second amplitude increase appears in the function.

The luminance-response function of the dark-adapted rabbit electroretinogram

The Naka-Rushton equation of the form, R = R(max) I(n)/(I(n)+K(n)), has been used to describe the b-wave luminance-response function of the scotopic electroretinogram. Rmax is the asymptotic value of the b-wave amplitude as a function of stimulus luminance I, K is the luminance that produces a b-wave amplitude that is one-half R(max), and n is a dimensionless constant that controls the slope of the function. These three parameters are often used in research laboratories, since it can show selective changes in each parameter. The present study describes these parameters (R(max) = 354 +/- 28 uV, n = 0.80 +/- 0.06, log K = -2.26 +/- 0.15 log cd. sec/m2) and the values obtained from the derivative analysis of Naka-Rushton equation (Anastasi et al) in 20 normal pigmented rabbit eyes. However, Naka-Rushton equation accurately describes the function only at low to moderate flash luminances. At high flash luminances, a second amplitude increase appears in the function.