ENTOPTIC PHENOMENA EXAMPLES PORTABLE
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. That clear space lets light pass through and we see a quickly moving dot of white.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 cells are nearly the width of those capillaries, so they cause a little bit of a traffic jam, where red blood cells pile up behind them and a clear plasma space builds up in front of them. These lights are caused by white blood cells coursing through the tiny capillaries on the retina’s surface. The second phenomena, "dots of light darting about," is called the blue field entoptic phenomenon because it's easiest to see against a uniform blue field. When the floaters drift close to the back of your eye, they cast a shadow on the retina that you can see against a uniform background. "They might be bits of tissue, red blood cells or clumps of protein," the narrator explains, all floating in the vitreous humor contained within your eyeball. The "small worms or transparent blobs" are eye floaters or muscae volitantes, Latin for "hovering flies," explains Michael Mauser in this TED Ed video ( via CasesBlog). If you’re reading this at night, try a blank computer screen. Any bright, uniform background should work. Whether it’s the clear blue of a sunny day or the overcast gray of winter, you should be able to see a familiar sight-slightly darker or fuzzy blobs that dip and float when you shift your gaze and sparkling dots that zig and zag.
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