Scientists used an iPhone 4S to diagnose intestinal worm infections in schoolchildren in rural Tanzania. They attached an $8...ball lens to the handset camera lens, and used a cheap [flashlight] and double-sided tape to create an improvised microscope. Pictures were then taken of stool samples placed on lab slides, wrapped in cellophane and taped to the phone. They were studied for the presence of eggs, the main symptom of the parasites. When the results were double-checked with a laboratory light microscope, the device had managed to pick up 70% of the samples with infections present - and 90% of the heavier infections. [The inventor of the technique] told the BBC he had read about smartphone microscopes being trialled in a laboratory and decided to "recreate it in a real world setting". "Ultimately we'd like something like this to be a useful diagnostic test. We want to put it in the hands of someone who might be able to use it," he said."70% (accuracy) isn't really good enough, we want to be above 80% and we're not quite there yet," he added. "The technology is out there. We want to use materials that are affordable and easy to procure." ...."You need the ball lens to help with the magnification - but any mobile phone with a decent camera and a zoom function will be sufficient," he explained. The smallest eggs visible using the smartphone were 40-60 micrometres in diameter....."Intestinal worms are estimated to affect up to two billion people around the world, mainly in poor areas. "These parasitic infections cause malnutrition, stunted growth, and stunted mental development,"...."It's a big deal, a big problem."
So, tape a ball lens over the iPhone camera lens, use double-sided tape to mount a stool sample slide on the phone, and illuminate the field with a flashlight. Check for ova and parasites in the sample. Pretty simple, rather effective, but not yet perfect. I am sure that diagnostic accuracy of the system can be improved easily enough with an improved clip-on lens and some simple holder to mount and stabilize the glass slide to the iPhone. Also, and as the article mentions, any decent mobile phone with a camera and zoom lens will suffice. If you have an inexperienced observer or unusual findings, any images can be sent to a distant expert for further interpretation.