It's perfect if you're in a dark restaurant and forgot your glasses. While most folks seem to know about the flashlight option on the iPhone, the magnifying feature, which uses the phone's camera to zoom in on text, seems a little less well known. That's because it's buried in the settings menu.
You likely know how to turn your iPhone's flashlight on, but how do you turn it off when you're done using it? Thankfully, it's just as simple. Here's what you need to know (along with a nifty trick to make going dark again even quicker).
Eye flashlight (Android)
1. Wake up your iPhone's screen by tapping the screen, pressing the lock button, or pressing the home button. Note that you do not need to unlock it or go to the home screen where all of your apps are visible in order to use the flashlight app.
Swiping fully left on your screen opens the iPhone's camera. In this case, you're not swiping far enough to open the camera, but your phone doesn't know that, so it turns off the LED flashlight anyway. Pretty cool, huh?
Perhaps you don't really use things like Wi-Fi calling or NFC, but like having the ability to set your phone to vibrate, toggle Location on/off, or access the flashlight with a single tap. Open quick settings and find the Edit button, then push unused settings to a second page or remove them completely.
The idea to use smartphone for fundus photography was put forward in 2010. Over the last decade, there has been a dramatic development in this field. This narrative review focuses on the principle of smartphone fundus photography, how to master this technique, problems encountered by the beginners, camera applications/devices designed for this purpose and the safety profile of smartphone flashlights for retinal photoreceptors.
Smartphone fundus photography using a condensing lens is based on the same principle as indirect ophthalmoscopy. Smartphone flashlight serves the purpose of light source or illuminating system. Real and inverted image of the retina is focused by the smartphone camera after adjustment of the filming distance. Beginners can face difficulties like adjustment of the filming distance, glare from condensing lens and reflection from the ceiling lights. Mobile camera applications and holding devices designed for this purpose can help the beginners to address these difficulties. There have been safety concerns about photo-biological risk for retinal photoreceptors by flashlight. Although the spectral irradiance on the retina, while using smartphone for fundus imaging is within the safety limits set by ISO 15004-2.2. The safety profile of latest model flashlights which deliver more power compared to older flashlights, need to be assessed.
Fundus cameras (mydriatic and non-mydriatic): The standard method for retinal imaging is by using a fundus camera. Fundus camera can be mydriatic, which requires pupil dilation and uses bright light flash, or non-mydriatic which is more advanced does not require pupil dilation and uses a flashlight of low intensity [7].
The beginners can face a few problems at the start, while they are learning to adjust the filming distance. One difficulty highlighted by Raju et al. is that the phone flashlight is not continuously on if the phone is in picture mode [12]. Also in picture mode, it often becomes difficult to capture the image in a few seconds the fundus is in focus. The author recommends that if the mode of the phone camera is switched to video mode and the flashlight is turned on then it will remain on continuously. The examiner can focus the fundus and while it is focused the video shoot is turned on to film the video for the time the retina remains focused. The best screen from the video can then be saved by taking a screenshot. The problem highlighted with this method of video mode is that the resolution of an image in video mode is not as high as taken in still photography mode [12]. The use of the latest model smartphone with high-resolution video features and screen tap to focus the area of interest can address this problem of image quality.
Another problem faced by beginners is the glare caused by the reflection of a smartphone flashlight from a 20D lens. Also, the ceiling lights in the examination room can be reflected in the image (Fig. 3).
The glare due to the flashlight can be managed by a slight tilting maneuver of the examiner's hand holding the lens and notice the position of the lens where glare is least present. The reflection from examination room ceiling lights can be avoided by performing the procedure in a dark room.
The flashlight of smartphones, which is used as a light source in smartphone-based retinal imaging systems, may be a risk factor for photobiological damage to the retinal photoreceptors [18]. Different types of flashlights which are used in smartphone cameras include single light-emitting diode (LED), dual-LED flash, and xenon flash. Among these, single and dual LED flashlights are more commonly used by smartphone manufacturers while xenon flash is used with professional cameras. The radiant power of xenon flash is greater when compared with single or dual-LED flash [18]. The flashlights of smartphones are safe for their use while still photography and videography. When used for the purpose of fundus imaging, the exposure time to retinal photoreceptors exceeds the time while the flashlight is being used for videography or still photography.
International Organization for Standardization (ISO 15004-2.2) sets the safety limits profile for ophthalmic instruments. According to ISO 15004-2.2, spectral irradiance (W/cm2/nm) on the retina is calculated separately for thermal and photochemical action. Kim et al. demonstrated that for 1-min retinal exposure to smartphone flashlight, the retinal irradiance was 150 times below the limit for thermal damage, and 240 times below the limit for photochemical action [19].
The latest models of smartphones developed recently can deliver 20 times more power compared to older flashlights. They can therefore pose an increased risk for biological damage to the retina [19]. The safety profile of these new flashlights should be assessed according to ISO 15004-2.2 before they are used for fundus imaging.
In summary, smartphone based fundus photography is a cheap, portable and a convenient method to image the retina. It can serve as an alternate to costly and high built conventional fundus cameras. The basic optical principle of smartphone fundus photography is that of indirect ophthalmoscopy. Ophthalmologists and young residents should master this art, which can be utilized for disease screening, educational and tele-medicine purposes. Beginners can face difficulties including adjustment of the filming distance, glare from condensing lens, ceiling lights reflection and adjusting the relative position of condensing lens in relation to the smartphone. With practice and noting the hand maneuvers while using your smartphone, these issues can be mastered. Holding devices and smartphone camera applications can also serve to address these issues. The risk of photo biological damage to retina by smartphone flashlight is very less if exposure time is about 1 min. The latest flashlights which are being developed by smartphone companies can deliver more power as compared to older flashlights. So their risk should be investigated before their use for fundus imaging. 2ff7e9595c
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