Adjusting the slit-lamp oculars: an unnecessaryburden or a must?
Abstract
Adjusting the slit-lamp eyepiece rings is perceived by some to be insignificant for achieving adequate focus. Others assume that these rings should be set only to compensate for one's refractive error. Observations are presented concerning the eyepiece scale setting during routine examinations, slit-lamp mounted YAG and Argon laser procedures and during ophthalmic surgery. Diagrams illustrate the optical basis of these observations. Factors influencing optimal eyepiece ring setting, besides ametropia, include slit-lamp misalignment (variations in calibration) as well as unconscious accommodation. An inaccurate setting cannot be fully compensated by adjusting the slit-lamp joy-stick. When an incorrect setting is used, while using oblique illumination, it becomes impossible to focus on details placed at the center of the viewfinder . In addition, irrespective of joy-stick position, it is impossible to view an oblique slit transecting the cornea in perfect focus. An accurate setting, as a whole, results in sharper images throughout the slit-lamp examination. Differences between individual instruments make it necessary to reset the eyepieces for each eye and for each individual instrument. Methods are described for evaluating the need for readjustment, as well as a simple technique for calibration in the absence of a focusing rod.
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Laser photocoagulation spot-size errors stemming from the refractive state of the surgeon's eye
2000, OphthalmologyMeaningful errors in photocoagulation spot size may result from several factors. In this article we discuss one major factor, namely, fluctuations in the surgeon’s accommodative state, coupled with an inaccurate setting of the slit-lamp oculars.
Experimental study.
We analyzed and tested the optics of slit-lamp mounted lasers. Varying the ocular setting is correlated with measurements of the actual spot size obtained with each system.
The spot size obtained.
Three distinct, but related, phenomena that may lead to spot size errors are defined: (1) focusing the laser spot as opposed to focusing the retinal image; (2) instrument misalignment; (3) inadvertent accommodation.
The ocular setting must be meticulously calibrated to produce a true spot-sized burn. At the 50 μm setting, each diopter of induced accommodation, or erroneous ocular setting, almost doubles the actual spot size obtained. With large (500 μm) spot size settings, the defocused delivery system is more prone to spot-size errors in contrast with parfocal lasers.
On focusing the slit-lamp: Part I. An inaccurate ocular setting - What is there to lose?
1998, Survey of OphthalmologyAdjustments of the diopter rings on the slit-lamp oculars compensate for three independent factors: the observer’s refractive error, the observer’s state of accommodation, and any instrument misalignment. An inaccurate setting of these rings will significantly affect the slit-lamp image quality, as well as the precision and accuracy of slit-lamp mounted lasers, such as are used for retinal photocoagulation, YAG capsulotomy, and laser trabeculoplasty. For each slit-lamp and microscope-related examination technique, photographic technique, and laser procedure, the consequences of an incorrect ocular setting are discussed. Data are presented on the preferred ocular settings of several random observers, highlighting both interobserver and intraobserver variability. Finally, photographs demonstrate the image deterioration that occurs when an incorrect ocular setting is used. It is shown that for younger observers, one’s distance refraction is only seldom the correct setting of the slit-lamp oculars, and that on different instruments, one should not be surprised to find somewhat different settings. Examiners are urged to check the accuracy of their habitual setting, if only to find out whether the improvement in image quality is worth the extra bother. (Surv Ophthalmol 42:351–354, 1998.