Laserclasses

The classification of a laser is based on the concept of accessible emission limits (AEL) that are defined for each laser class. This is usually a maximum power (in W) or energy (in J) that can be emitted in a specified wavelength range, exposure time that passes through a specified aperture at a specified distance. Main characteristics and requirements for the classification system, specified by the IEC 60825-1 standard, is listed.

A Class 3R laser is considered safe if handled carefully, with restricted beam viewing. With a class 3R laser, the MPE can be exceeded, but with a low risk of injury. Visible continuous lasers in Class 3R are limited to 5mW. For other wavelengths and for pulsed lasers, other limits apply.

Class3Rlaser

Class2laserpointer

Using pinhole visual acuity can offer the clinician a great deal of important information. It functions as a rapid tool to screen for best-corrected visual acuity without having to employ refractive techniques. It also suggests that if and when a pinhole fails to improve vision, the reduced vision is likely a result of pathology, whether a structural defect or functional change. Additionally, it is a readily available and cost-effective alternative to determine postoperative visual endpoints for patients undergoing cataract surgery.

Pupil constriction is also involved in the near triad of accommodation, convergence and miosis. A balance of these factors is essential to increase depth of focus and aid in providing a clear near image. The effect of pupil constriction, or use of a pinhole, is such that the subsequent increase in depth of focus lessens the accommodative demand required.3

Another worthy application is in the context of measuring potential visual acuity post cataract extraction. Potential acuity pinhole (PAP) is a monocular test using a pinhole occluder to view a near target amidst bright illumination to predict visual status postoperatively.

4. Marcos S, Moreno E, Navarro R. The depth-of-field of the human eye from objective and subjective measurements. Vision Research. 1999;39:2039-49.

As professional laser module manufacturer, IADIY standard laser modules all fit eye safety requirements and support customers to apply for FDA accession number.

Pinhole occluders are inexpensive and readily available tools that consist of multiple, small apertures amidst a dark background. They are available for purchase or, in some cases, can even be fashioned from punching approximately 1mm to 2mm holes in a dark card.1

The patient is first dilated so that they are able to search for a subjectively clearer area that may be less obstructed from lenticular opacities. Patients are then instructed to read the letters on a near card brightly lit with a transilluminator. The importance of using direct, bright lighting is to compensate for the reduced illumination from both the reduced viewing size and the cataract itself. The intensity of the light also helps to diminish the light scattering effect innate to cataracts.2,3 The best-corrected visual acuity measured using PAP correlates to the expected post cataract surgery visual outcome.

Class 1 laser is safe under all conditions of normal use. This means the maximum permissible exposure (MPE) cannot be exceeded when viewing a laser with the naked eye or with the aid of typical magnifying optics (e.g. telescope or microscope). To verify compliance, the standard specifies the aperture and distance corresponding to the naked eye. For example, a high-power laser with a very large beam or highly divergent beam may be classified as Class 1 if the power that passes through the apertures defined in the standard is less than the AEL for Class 1. Often, devices such as optical drives will be considered class 1 if they fully contain the beam of a more powerful laser, such that no light escapes under normal use.

Class 2m laserpointer

A patient may present to your office with reduced vision for any number of reasons, ranging from something as benign as uncorrected refractive error to serious pathology. Even in cases in which a combination of factors affect vision, the ability to distinguish between contributory ocular pathology and a refractive error is a must. Despite today’s high-tech tools—such as autorefractors or the potential acuity meter (PAM), to name a few—many ODs turn to a tried-and-true low-tech option: the pinhole occluder.

Class1Mlaser

The “pinhole effect” is an optical concept suggesting that the smaller the pupil size, the less defocus from spherical aberrations is present. When light passes through a small pinhole or pupil, all unfocused rays are blocked, leaving only focused light to land on the retina to form a clear image.1,2 In contrast, patients who have very large pupils, whether it is physiological or from pharmacological dilation, experience image “ghosting,” or a blurring halo around an otherwise sharp image.3

6. Sun JK, Aiello LP, Cavallerano JD, et al. Visual acuity testing using autorefraction or pinhole occluder as compared with a manual protocol refraction in individuals with diabetes. Ophthalmology. 2011;118(3):53-542.

The obvious benefit of using this optical principle in clinical practice is to discriminate between reduced visual acuity secondary to refractive error and the presence of pathology. When a patient’s visual acuity is not 20/20 despite the use of pinhole, further investigation to determine an underlying cause is warranted.

Class3Blaser

A Class 1M laser is safe for all conditions of use except when passed through magnifying optics such as microscopes and telescopes. Class 1M lasers produce large-diameterbeams, or beams that are divergent. The MPE for a Class 1M laser cannot normally be exceeded unless focusing or imaging optics are used to narrow the beam. A laser can be classified as Class 1M if the power that can pass through the pupil of the naked eye is less than the AEL for Class 1.

1. Schiefer U, Michels R. Refractive errors: epidemiology, effects and treatment options. Dtsch Arztebl Int. 2016;113(41):693-702.

A Class 3B laser is hazardous if the eye is exposed directly, but diffuse reflections such as those from paper or other matte surfaces are not harmful. The AEL for continuous lasers in the wavelength range from 315 nm to far infrared is 0.5 W. For pulsed lasers between 400 and 700 nm, the limit is 30mJ. Class-3B lasers must be equipped with a key switch and a safety interlock. Class 3B lasers are used inside CD and DVD writers, although the writerunit itself is class 1 because the laser light cannot leave the unit.

Class1laser

The size of the pinhole aperture or pupil size is an important consideration. While there is great benefit, as mentioned, to limiting marginal and unfocused rays from reaching the retina using a small aperture, a pinhole or pupil that is too small may cause diffraction and loss of resolution.1 Diffraction occurs when a light wave is fractured by the edge of the aperture, which limits the amount of detail available to form a clear retinal image.4 Additionally, a pinhole too small reduces retinal illumination. A clinical study evaluating pinhole size concluded that a diameter between 0.94mm to 1.75mm is most effective, with most instruments on the market containing approximately 1.2mm apertures.5

A similar test is the PAM test, which requires additional and more costly equipment for projection. In a study comparing the accuracy of PAP and PAM testing, both methods were similar in determining visual outcome post cataract surgery, though PAM provided a slightly more accurate correlation.3

The pinhole occluder works along the same basis as pupil constriction in bright conditions causing an improvement in visual acuity. Through a smaller pupil, the effects of minor ocular irregularities—such as refractive error or paracentral cornea or lens opacities—are diminished.

A Class 2 laser is considered to be safe but may cause eye strain if one stares directly into the beam for a prolonged duration. This classification is only available for lasers which use visible light (400nm-700nm) thus it is not possible for infrared or ultraviolet lasers to obtain Class 2 (or 2M) classification. Class 2 lasers are limited to 1 mW continuous wave, or more if the emission time is less than 0.25 seconds.

Class4laser

3. Abdul N, van Bosch M, van Zyl A, et al. The effect of pinholes of different sizes on visual acuity under different refracting states and ambient lighting conditions. S Afr Optom. 2009;68(1):38-48.

Class 4 is the highest and most dangerous class of laser, including all lasers that exceed the Class 3B AEL. By definition, a class 4 laser can burn the skin, or cause devastating and permanent eye damage as a result of direct, diffuse or indirect beam viewing. These lasers may ignite combustible materials, and thus may represent a fire risk. Class 4 lasers must be equipped with a key switch and a safety interlock. Most industrial, scientific, military, and medical lasers are in this category. Medical lasers can have divergent emissions and require awareness of nominal ocular hazard distance (NOHD) and nominal ocular hazard area (NOHA).

A Class 2M laser is safe because of the blink reflex if not viewed through optical instruments. As with class 1M, this applies to laser beams with a large diameter or large divergence, for which the amount of light passing through the pupil cannot exceed the limits for class 2.

This is also a useful tool to check best-corrected visual acuity in patients for whom performing a refraction is unnecessary or difficult.6 In a practical setting, pinhole visual acuity may be used to document vision of a patient returning for a medical follow-up; routine refraction is not indicated, but sometimes the patient does not bring their up-to-date spectacle or contact lens correction to the appointment.