context: Your vision may change as you age. You'll know it's happening when have to hold your favorite book, the daily newspaper, or a restaurant menu farther away just to read it. This is called presbyopia. It's normal, and almost all of us get it as we reach middle age. Over-the-counter reading glasses can help. But if you've always worn glasses or contacts, then bifocals, trifocals, or progressive lenses may do the trick. They're also called multifocals. Bifocals and progressives have different vision strengths built into the same lens. As you look down to read, the lens helps you see things close up. As you look up at the horizon, it lets you see clearly far away. This helps when you walk or drive. You can buy reading glasses over the counter. But your eye doctor must prescribe multifocals or progressives. Children sometimes need these eyeglasses or lenses, too. There are a few types of multifocal lenses: Bifocals are two lenses in one. They're shaped differently at the bottom and top to help you see close up or far away. They come in both eyeglasses and contact lenses. Some bifocal glasses have a line across the middle that divide the two corrections. Trifocals correct your vision so you can see close up, middle distance, or far away. They may also may have lines or come in a progressive lens. Progressives have a gradual or progressive change in vision in different parts of the lens, so there's no line. You may need time to adjust to your lenses. Most people get used to them after a week or two, but it can take longer. A few people never like the changes in vision and give up on bifocals or progressives. At first, you may notice: Blurry vision Objects that seem to jump or move around Headaches Nausea Balance problems Bifocals or progressives may change the way you judge distance or depth as you look down through the bottom of the lens. You could trip or fall when you climb stairs or walk around new places. Older people are even more likely to trip when they wear these lenses. As you look up and down, your eyes quickly move from one vision strength to another. Objects may seem to jump around. This can make you feel unsteady. Your brain has to adjust to different strengths as your eyes move around the lenses. That's why you might feel dizzy. Older people who've never worn multifocals before may need lenses with a big change between the top and bottom of the lens. They may need a little longer to adjust. Don't give up on your new lenses. Take these steps to get used to them and enjoy clear vision: Try putting on your new glasses first thing in the morning and wear them for just an hour or two. The next morning, try a few more hours. Slowly build up your tolerance to adjust to them. Don't switch between your new pair and your old one. Make sure your eyeglasses fit properly and don't slide down your nose. When you walk, look straight ahead, not down at your feet. Also work on pointing your nose in the direction you want to look, not just looking left or right with your eyes When you read, hold items down and about 16 inches away from your eyes. Look through the bottom of your lenses. Don't move your eyes or head as you read. Move the page or paper instead. Set your computer screen just below eye level. You can adjust your desk or chair to make this happen. Talk to your eye doctor if your lenses still bother you after a few weeks. You may need to change your prescription strength.