![]() 3,5 Although this would not replace a retinal exam or photo, it has the potential for patients to train and screen themselves to identify early changes in many retinal diseases. 3 Studies suggest that this is an effective, noninvasive and portable screening tool to detect retinal dysfunction in diabetic retinopathy, allowing practitioners to identify asymptomatic patients prior to the onset of central vision loss. Scanning laser entoptic perimetry is of particular interest to assess diabetic retinopathy, a leading cause of blindness where early detection is a key factor in visual preservation. More recent studies recognize this modality as the method to measure entoptic phenomena, as it can offer significant retinal detail as it pertains to foveal capillary detail, the size of the foveal avascular zone (FAZ) and macular blood flow, with greater accuracy than more invasive methods, such as fluorescein angiography. 1 It was also helpful in cases where significant media opacities existed, where-if the illumination of a closed eye induced shadows-it correlated with good retinal and macular function. Screening ApplicationsIn the late 1990s, the application of this afterimage was used clinically to grossly measure potential acuity, as patients’ lack of perception of their vessels correlates highly with poor macular function and markedly reduced acuity. Here, entoptic phenomenon is perceived as vitreous floater secondary to posterior vitreous detachment. ![]() 2 In fact, it is this observation, which led to the conclusion that there must be a rapid mechanism of image creation and erasure as the foundation of normal visual processing. 1 It differs from a real image, particularly in that it does not track with eye or retinal movement due to the direct and constant relationship with the photoreceptor layer. HistoryEntoptic phenomena were first described by Johann Purkinje in the early 1800s, to describe the fleeting, black afterimage of retinal vasculature, later coined the ‘Purkinje tree.’ 1 This phenomena occurs due to the location and pattern of the branching retinal vascular ‘tree’ in front of the photoreceptor layer, casting a shadow that is only induced when the anterior segment of the eye is illuminated. This month, let’s evaluate what significance, if any, these reflections hold to us as eye care practitioners. 1,2 The presence or absence of different entoptic phenomena can raise red flags for posterior and anterior abnormalities, and even refractive and convergence conditions-making them potential markers of disease presence and progression. The results of this study of two microvascular preparations strongly suggest that in the human eye the blue field entoptic phenomenon is produced by leukocytes flowing within the macular retinal microvasculature.Oftentimes, when our patients are sitting behind the slit lamp during a routine examination, we hear them cry, “Wow, I can see the reflection of my blood vessels!” The image that appears to them is an instance of entoptic phenomena (EP), a phrase derived from the Greek words ‘inside’ and ‘light’ or ‘vision’, which describes the ability of an individual to perceive substances endogenous to their own eye, such as retinal vessels or vitreous opacities. The particles were observed in terminal arteriols capillaries, and post-capillary venules where they were not obscured by red blood cells. Under higher magnification, the particles appeared brighter than the plasma gaps between red blood cells and were demonstrated to be leukocytes by morphology, by specific staining and by typical behavioral movement. The appearance of the particles and their movement simulated the blue field entoptic particle motion. In both preparations, low magnification video-microscopy using 430 nm illumination produced a field of particles, which were brighter than the background, flowing within a network of dark vessels. In the rat cremaster alternating observations were made using transmission illumination at 430 nm and epi-illumination fluorescence microscopy with leukocytes rendered fluorescent by intravenous Quinacrine. In the wing of the hibernating bat, microvascular flow was simultaneously videotaped under transmission illumination at 430 nm and under unfiltered illumination. ![]() The cellular source of the blue field entoptic phenomenon was investigated in two microvascular preparations using video-microscopy with lighting conditions similar to those under which the entoptic phenomenon is visualized within the human eye. ![]()
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