Retinal Burn Thresholds for the Helium-Neon Laser in the Rhesus Monkey

Validation of a computer model to predict laser induced thermal injury thresholds of the retina

“…A four-surface schematic eye with homogenous media is derived from the Le Grand full theoretical model for the relaxed human eye [9] for the young Rhesus monkey by scaling all elements by a factor 0.8 (for instance, 0.71 has been used in [10]). This scaling factor gives a nominal focal length of 13.35 mm at 590 nm which is corroborated within ±0.7 mm by several studies [11,12,13]. The schematic eye of the Rhesus monkey can be downscaled from the human one [14].…”

“…Although smaller spots at the retina close to the diffraction-limited image can be actually achieved after adjustment [22,88], the observed average minimum spot size (MSS) is rather in the order of 30 µm to 80 µm [10,51,89]. This can be due to several factors: i) uncontrolled inter-subject variability and small refraction errors, for instance a 0.25 D error can increase the spot size from 20 µm to 50 µm [2,64], ii) the retinal spot size is thought not to be constant for all exposure durations due to residual movements even in anesthetized subjects [11,88,90], iii) the size of the source term in the heat equation can be larger than the observed or "theoretical" spot size [91] for instance due to intra-retinal scattering [92]. In earlier models, values ranging between 35 µm and 70 µm for exposures in the visible spectrum have provided good agreement with ED 50 s [5,7,19].…”

Validation of a computer model to predict laser induced thermal injury thresholds of the retina

“…A four-surface schematic eye with homogenous media is derived from the Le Grand full theoretical model for the relaxed human eye [9] for the young Rhesus monkey by scaling all elements by a factor 0.8 (for instance, 0.71 has been used in [10]). This scaling factor gives a nominal focal length of 13.35 mm at 590 nm which is corroborated within ±0.7 mm by several studies [11,12,13]. The schematic eye of the Rhesus monkey can be downscaled from the human one [14].…”

“…Although smaller spots at the retina close to the diffraction-limited image can be actually achieved after adjustment [22,88], the observed average minimum spot size (MSS) is rather in the order of 30 µm to 80 µm [10,51,89]. This can be due to several factors: i) uncontrolled inter-subject variability and small refraction errors, for instance a 0.25 D error can increase the spot size from 20 µm to 50 µm [2,64], ii) the retinal spot size is thought not to be constant for all exposure durations due to residual movements even in anesthetized subjects [11,88,90], iii) the size of the source term in the heat equation can be larger than the observed or "theoretical" spot size [91] for instance due to intra-retinal scattering [92]. In earlier models, values ranging between 35 µm and 70 µm for exposures in the visible spectrum have provided good agreement with ED 50 s [5,7,19].…”

Comparative study of retinal injuries induced by a 420-750 nm supercontinuum source and a 532 nm laser

“…Thus, the overall effect would be a slight higher ED 50 value for the SC source than that for the 532 nm laser. For the exposure duration of 1.0 s, Ham et al determined the rhesus retinal damage thresholds as 9.7 mJ at the wavelength of 633 nm [34], Onda et al determined the ED 50 as 4.2 mJ at the wavelength of 514 nm [35], and Lund et al determined the ED 50 value as 8.0 mJ at the wavelength of 441.6 nm [31]. For comparison, the determined ED 50 value for the 420-750 nm SC source (12.1 mJ) was slightly higher than previous values for lasers, which also possibly resulted from the higher proportion of red light in the SC spectrum.…”

Eccentric Fixation Can Sometimes Be Useful: Unilateral Foveal Preservation in a Child with Bilateral Laser-Induced Maculopathy

“…According to the United States Food and Drug Administration, class 3B and higher lasers have been categorized as high power, emitting greater than 5 mW, and are hazardous to the eye. Experiments in monkeys have shown that even class 3A lasers (output power does not exceed 5 mW, beam power density may not exceed 2.5 mW/cm 2 ) may photocoagulate the retina after 10 seconds of exposure [8].…”

Validation of a computer model to predict laser induced thermal injury thresholds of the retina

“…A four-surface schematic eye with homogenous media is derived from the Le Grand full theoretical model for the relaxed human eye [9] for the young Rhesus monkey by scaling all elements by a factor 0.8 (for instance, 0.71 has been used in [10]). This scaling factor gives a nominal focal length of 13.35 mm at 590 nm which is corroborated within ±0.7 mm by several studies [11,12,13]. The schematic eye of the Rhesus monkey can be downscaled from the human one [14].…”

“…Although smaller spots at the retina close to the diffraction-limited image can be actually achieved after adjustment [22,88], the observed average minimum spot size (MSS) is rather in the order of 30 µm to 80 µm [10,51,89]. This can be due to several factors: i) uncontrolled inter-subject variability and small refraction errors, for instance a 0.25 D error can increase the spot size from 20 µm to 50 µm [2,64], ii) the retinal spot size is thought not to be constant for all exposure durations due to residual movements even in anesthetized subjects [11,88,90], iii) the size of the source term in the heat equation can be larger than the observed or "theoretical" spot size [91] for instance due to intra-retinal scattering [92]. In earlier models, values ranging between 35 µm and 70 µm for exposures in the visible spectrum have provided good agreement with ED 50 s [5,7,19].…”

Comparative study of retinal injuries induced by a 420-750 nm supercontinuum source and a 532 nm laser

“…Thus, the overall effect would be a slight higher ED 50 value for the SC source than that for the 532 nm laser. For the exposure duration of 1.0 s, Ham et al determined the rhesus retinal damage thresholds as 9.7 mJ at the wavelength of 633 nm [34], Onda et al determined the ED 50 as 4.2 mJ at the wavelength of 514 nm [35], and Lund et al determined the ED 50 value as 8.0 mJ at the wavelength of 441.6 nm [31]. For comparison, the determined ED 50 value for the 420-750 nm SC source (12.1 mJ) was slightly higher than previous values for lasers, which also possibly resulted from the higher proportion of red light in the SC spectrum.…”

Eccentric Fixation Can Sometimes Be Useful: Unilateral Foveal Preservation in a Child with Bilateral Laser-Induced Maculopathy

“…According to the United States Food and Drug Administration, class 3B and higher lasers have been categorized as high power, emitting greater than 5 mW, and are hazardous to the eye. Experiments in monkeys have shown that even class 3A lasers (output power does not exceed 5 mW, beam power density may not exceed 2.5 mW/cm 2 ) may photocoagulate the retina after 10 seconds of exposure [8].…”

Validation of a computer model to predict laser induced thermal injury thresholds of the retina

“…A four-surface schematic eye with homogenous media is derived from the Le Grand full theoretical model for the relaxed human eye [9] for the young Rhesus monkey by scaling all elements by a factor 0.8 (for instance, 0.71 has been used in [10]). This scaling factor gives a nominal focal length of 13.35 mm at 590 nm which is corroborated within ±0.7 mm by several studies [11,12,13]. The schematic eye of the Rhesus monkey can be downscaled from the human one [14].…”

“…Although smaller spots at the retina close to the diffraction-limited image can be actually achieved after adjustment [22,88], the observed average minimum spot size (MSS) is rather in the order of 30 µm to 80 µm [10,51,89]. This can be due to several factors: i) uncontrolled inter-subject variability and small refraction errors, for instance a 0.25 D error can increase the spot size from 20 µm to 50 µm [2,64], ii) the retinal spot size is thought not to be constant for all exposure durations due to residual movements even in anesthetized subjects [11,88,90], iii) the size of the source term in the heat equation can be larger than the observed or "theoretical" spot size [91] for instance due to intra-retinal scattering [92]. In earlier models, values ranging between 35 µm and 70 µm for exposures in the visible spectrum have provided good agreement with ED 50 s [5,7,19].…”

Comparative study of retinal injuries induced by a 420-750 nm supercontinuum source and a 532 nm laser

“…Thus, the overall effect would be a slight higher ED 50 value for the SC source than that for the 532 nm laser. For the exposure duration of 1.0 s, Ham et al determined the rhesus retinal damage thresholds as 9.7 mJ at the wavelength of 633 nm [34], Onda et al determined the ED 50 as 4.2 mJ at the wavelength of 514 nm [35], and Lund et al determined the ED 50 value as 8.0 mJ at the wavelength of 441.6 nm [31]. For comparison, the determined ED 50 value for the 420-750 nm SC source (12.1 mJ) was slightly higher than previous values for lasers, which also possibly resulted from the higher proportion of red light in the SC spectrum.…”

Eccentric Fixation Can Sometimes Be Useful: Unilateral Foveal Preservation in a Child with Bilateral Laser-Induced Maculopathy

“…According to the United States Food and Drug Administration, class 3B and higher lasers have been categorized as high power, emitting greater than 5 mW, and are hazardous to the eye. Experiments in monkeys have shown that even class 3A lasers (output power does not exceed 5 mW, beam power density may not exceed 2.5 mW/cm 2 ) may photocoagulate the retina after 10 seconds of exposure [8].…”