The eye also gets affected by diabetes. One of the silent problems with diabetes is that the person with the disease usually feels ﬁne, and there are no symptoms even when the glucose levels are in the 6 to 10 Mmol/l range. Therefore, it is easy to ignore diabetes. Eventually, there are symptoms, but often, they are due to diabetes-related complications. This is why it is crucial to managing diabetes responsibly and proactively.
Diabetic eye disease includes three conditions:
High glucose levels or high blood pressure can injure the cells lining the back of the eye on the retina. These tiny blood vessels nourish the nerves of the eye. The earliest visible abnormalities are pinhead red dots next to the blood vessels that may come and go—these are called microaneurysms or dot hemorrhages. If there is progression, the injured blood vessels get blocked and the areas of the retina supplied by these vessels become starved of nutrients causing the retina to respond by releasing chemicals, such as vascular endothelium growth factor (VEGF), that promote the growth of new blood vessels. This abnormality is called proliferative retinopathy. Unfortunately, these new blood vessels are fragile and can bleed easily. The hemorrhages from these new vessels can cause sudden loss of vision. The hemorrhages and growth factors can also develop scar tissue at the back of the eye. This scar tissue can pull on the retina, causing retinal detachment and vision loss. The injured blood vessels can also leak ﬂuid and cause swelling in an area of the retina called the macula—this condition, called macular edema, can cause the loss of central vision, making it difﬁ cult to read or drive. One way of protecting vision is to use lasers to destroy the parts of the retina that do not have adequate nutrition so that the new blood vessels prone to bleeding do not grow. Laser therapy is also used to treat macular edema by removing the areas with very leaky blood vessels. Laser therapy’s disadvantage is that it destroys part of the retina. People who have had extensive laser therapy frequently complain of difﬁculty with night vision.
A cataract is a clouding of the eye’s lens so that the person cannot see clearly. The symptoms of cataracts are
- Gradual blurring of the vision
- Glare in bright light or sunlight
- Poor color vision with fading or yellowing of colors
- Double or multiple images when one eye is closed
Cataracts occur as part of the natural aging process, but they occur earlier and more often in people with diabetes. High glucose level causes changes in the proteins inside the cells of the lens, altering the optical properties of the lens. The treatment for cataracts is surgery—the cloudy lens is removed and replaced with an artiﬁcial lens.
The inside of the eye is ﬁlled with ﬂuid. A new ﬂuid is constantly being made, and the ﬂuid that is being replaced leaves the eye by entering a drainage meshwork toward the front of the eye. Blockage of the drainage system can lead to increased ﬂuid pressure within the eye—a condition called glaucoma. This pressure increase can damage the nerves from the back of the eye to the brain and cause vision loss. Like cataracts, glaucoma occurs more frequently in people with diabetes. Glaucoma is treated with eye drops. If the drops do not work, an eye operation to allow the ﬂuid to drain (trabeculectomy) is performed. Rarely, glaucoma can occur in people with diabetes when blood vessel growth in the iris blocks the ﬂuid drainage channels (a condition called iridis rubeosis). This type of glaucoma is usually treated with lasers.