Solar eclipses glasses are almost impossible to buy in-store and online – and members of the public have been issued with an urgent warning over trying other techniques.On the high street and internet stores, eclipses glasses are largely sold out ahead of the celestial spectacle this week.But members of the public have been warned that counterfeit glasses and other alternative ways of seeing the eclipse could lead to harm.The caution follows warnings from eye doctors, who emphasise that looking straight at the Sun for even brief periods can cause permanent vision damage.On August 12, the Moon will obscure over 90 per cent of the Sun between 6.17pm and 8.06pm, representing the greatest coverage seen above the UK since 1999.Specialists stress that only ISO 12312-2 certified glasses offer safe protection. However, approved products are largely sold out, with remaining options requiring hefty delivery fees for timely arrival.Experts have warned that so-called eclipse glasses that do not carry the safety standards, or ordinary sunglasses, no matter how dark, should never be worn to view an eclipse, as they reduce glare, making it feel more comfortable to look at the Sun for longer, but still allow harmful solar radiation to reach the retina.Following the 1999 total solar eclipse, the Royal College of Ophthalmologists reported around 70 cases of people experiencing vision problems after watching the eclipse.Specialists stress that only ISO 12312-2 certified glasses offer safe protection. (AFP/Getty)Around 40% had looked at it for less than a minute.Mohamed Elalfy, a consultant ophthalmologist and president of the Royal College of Ophthalmologists, said: “The safest way to enjoy the eclipse is to observe it indirectly, such as by watching a live broadcast.“Looking directly at the Sun during a solar eclipse can cause damage to the retina, potentially damaging the cells responsible for sharp central vision.“Crucially, the retina has no pain receptors, so people will not feel the damage as it happens.“Symptoms may only become apparent several hours later and can include blurred vision, a central blind or dark spot, distorted vision, reduced colour perception and increased sensitivity to light.“While some people recover over weeks or months, others can be left with permanent visual impairment.”Kyla Black, Boots Opticians director of optical practice, urged parents to be “particularly careful” letting their children view the eclipse, and warned some DIY filters can also be dangerous.“If you’re purchasing specially made eclipse glasses, make sure to double check that they are undamaged before use as even a glimpse of damage could have an impact on your eyesight,” she said.“It’s a common myth that wearing multiple pairs of sunglasses can protect you from any harmful UV light – this is untrue and should be avoided at all costs as only purpose-built eclipse glasses can allow you to watch an eclipse.”Special glasses are needed for safely viewing the eclipse. (AFP/Getty)Ms Black added: “Although a fun idea for many may be to make DIY filters and pinhole projectors out of cereal boxes, this can also be dangerous.“Objects such as smoked glass, colour film, floppy disks, X-ray film, and dark sunglasses are unable to block invisible infrared and ultraviolet rays, potentially leading to damage to your eyesight.“Budding astronomers who will be looking through cameras, binoculars or telescopes at the eclipse must make sure they have approved solar filters attached.“If you’re not sure your telescope does, then contact the maker of the product to ensure you know you’ll be safe.”The Royal Observatory Greenwich also warned the public that regular sunglasses are not a safe enough method to view the cosmic phenomenon.Imo Bell, a planetarium astronomer at the observatory, previously told the Press Association: “It’s not a total eclipse, but over 90% is really exciting.“We’re not going to get one this good for a really long time.“So, it’s important not to miss it, and to be prepared.Celestron solar eclipse glasses on sale at the Royal Observatory Greenwich, south-east London, ahead of the solar eclipse on August 12 (Jordan Pettitt/PA)“You can’t just go out and expect to have a look, because it’s really dangerous for your eyes.“So, you can use solar eclipse glasses, which are very, very different from sunglasses – they block out so much light that you can’t see anything through them except the Sun, because that’s how much light they need to block for the damaging light of the Sun to be safe to view.“Ideally a solar telescope is an amazing way to witness it, and if you don’t have one of them then you can look into whether your local astronomy society is doing any events.“And if all else fails, you can project the image of the eclipse using a household item like a colander which has lots of holes in – point the colander towards the Sun with your back facing it, and in the shadow of the colander you’ll be able to see the eclipse in the holes, which is really cool.”In an added bonus for stargazers, the annual Perseid meteor shower reaches its peak on the night of August 12-13.The shower is produced as Earth ploughs through a stream of dust left behind by Comet Swift–Tuttle.Each tiny grain strikes Earth’s atmosphere at about 60 kilometres per second, burning up in a brief flash that takes the appearance of a shooting star.