Optical systems that emit radiation between the visible and near-infrared wavelength region pose a potential hazard to human vision as the radiation is imaged on the retina. The radiation interacts with the retinal tissue in a photomechanical, photothermal, and photochemical manner that can result in irreversible injuries. To ensure an eye safe system, it is important to correctly apply the laser safety standard IEC 60825-1:2014 or the lamp safety standard IEC 62471:2006. We aim to provide a general calculation procedure for both coherent and incoherent sources, which are compliant with the respective safety standards. An air-equivalent eye model generates retinal images. Two software-based calculation methods are introduced, which are referred to as image analysis. The first method calculates the angular subtense of the apparent source needed for photomechanical and photothermal limits. The second method applies to photochemical limits. Using exemplary optical systems, the image analysis is investigated. The proposed image analysis gives guidance for missing aspects in the standards and reduces ambiguity and complexity. The proposed method can be used for eye safety evaluations since it follows the concept of the safety standards with conservative approaches.
Peripheral vision not only plays a vital role in daily visual tasks, such as locomotion and detection but there is also the hypothesis that peripheral refraction could influence eye growth and myopia development. In 1971 Hoogerheide et al. suggested an increased risk for humans to become myopic if the peripheral refractive errors tend to be hyperopic, i.e., positive relative peripheral refraction (RPR). The hypothetical link discovered between peripheral refraction and myopia development has opened a series of scientific investigations to confirm the theory and understand the underlying foundations. In this way, high-quality peripheral refractometry has gained importance in the study of myopia. Clinical aberrometers are efficient and robust instruments for measuring wavefront error for central vision; however, to measure aberrometry in the peripheral field, several difficulties arise that prevent standardization for clinical use. In the present work, we develop a new type of scanning aberrometer to improve and simplify the system for the analysis of peripheral refraction. Four physical eye models were made to provide a stable sample resembling a human eye and validate the new methodology. The purpose of this study is to investigate the characteristics of the current system to determine the factors that limit the employability of the instrument, and it is aimed at the development of the gold standard technology for peripheral refraction measurement, making the instrument more economical, simple to use and offering the highest possible measurement quality. The validation has been done by a comparative analysis between theoretical and experimental results showing good correlation. The results of this study will provide us with helpful information when conducting studies in human eyes using this new apparatus.
Significance: A validated biophysical computer model simulating retinal thermal damage thresholds is used to investigate elongated retinal images. The International Commission on Non-Ionizing Radiation Protection Guideline and the laser safety standard IEC 60825-1:2014 include a method for averaging non-uniform extended sources, however, there are no studies that have examined the applicability in detail. Our study represents a method that can also support future research in the field of eye safety.
Aim: As there is currently no experimental data available for non-uniform irradiance profiles, the calculation procedure given in the laser safety standard is derived from symmetric retinal images. We aim to verify this calculation procedure for such profiles on the retina in the thermal hazard regime.
Approach: A three-dimensional computer model, which solves the heat transfer equation and the Arrhenius equation describing the denaturation of the proteins in the retina, is used to simulate the threshold values for the retinal thermal injury. Three different non-uniform irradiance profiles, elliptical Gaussian, elliptical top-hat, and rectangular top-hat distributions, are investigated for a wavelength of 530 nm. The profiles are varied in their sizes and simulated for different single-pulse durations. By applying the laser safety standard, the maximum allowed energies are calculated and divided by the corresponding threshold values to obtain the reduction factor (RF) which is a crucial parameter.
Results: Due to the thermal behavior in the retinal tissues, the Gaussian irradiance profiles yield larger threshold values than both top-hat profiles. Furthermore, the ratio between the threshold values and the maximum allowed energies are found to be the lowest for the Gaussian profiles.
Conclusion: The simulated retinal thermal injury thresholds for the three investigated non-uniform irradiance profiles show larger RFs than the minimum RF found for symmetric profiles. This supports the applicability of the evaluation scheme of the laser safety standard for non-uniform retinal images.
Laser systems emitting radiation in the visible and near infrared region are potentially hazardous for the retina of the human eye. This can result in irreparable injuries due to photomechanical, photothermal or photochemical light-tissue interactions. This investigation focuses on the photothermal interaction for which a computer model is used to simulate the thermal behavior of the retina and to predict the injury threshold values. The most important factors are the wavelength of the radiation, the exposure time and the irradiance profile on the retina. For performing safety evaluations and classifications the laser safety standard IEC 60825-1:2014 has to be considered. These evaluations are based on emission limits which depend on the same above mentioned factors. According to the IEC 60825-1:2014, non-uniform retinal images are treated by an image analysis where an averaged spot size is used. This averaged size is calculated by the extent of the irradiance profile along two orthogonal directions. Unlike the laser safety standard, the computer model predicts the injury thresholds for an irradiance profile on the retina without averaging the spot size. In this investigation, a broad variety of non-uniform retinal images is investigated with regard to the injury thresholds predicted by the computer model and to the classifications according to the laser safety standard.
Optical systems emitting radiation in the visible and near infrared wavelength range represent a potential hazard for the retina of the human eye. This can result in irreparable damages due to photochemical, photothermal, photomechanical or thermomechanical interactions. To perform an eye safety evaluation a distinction must be made between coherent light sources and broadband light sources. For both types of light sources the corresponding safety standards, namely the IEC 60825-1:2014 and the IEC 62471:2006, provide accessible emission limits which depend on the angular subtense of the apparent source. This parameter is not a characteristic of the light source but must be determined by the irradiance distribution of the retinal image in case of coherent radiation and by the spectral radiance distribution of the retinal image in case of broadband radiation. This investigation introduces software-based methods investigating the retinal image in order to calculate the angular subtense of the apparent source. The results can be used to perform an eye safety evaluation in conformity with the laser safety standard IEC 60825-1:2014 as well as with the lamp safety standard IEC 62471:2006. However, the procedures given by the standards are not clearly defined. For this reason different implementations are discussed and compared to each other for a broad variety of exemplary retinal images.
In the visually challenging situation of microsurgery with many altered depth cues, digitalization of surgical systems disrupts two further depth cues, namely focus and parallax. Although in purely optical surgical systems accommodation and eye movements induce expected focus and parallax changes, they become statically fixed through digitalization. Our study evaluates the impact of static focus and parallax onto performance and subjective 3D perception. Subjects reported decreased depth realism under static parallax and focus. Thus surgeons’ depth perception is impacted further through digitalization of microsurgery, increasing the potential of artificial stereo-induced fatigue.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.