Analysis of enucleated eyes has demonstrated histological features characteristic of nevi within the edges of malignant melanomas, suggesting that at least some melanomas may evolve from malignant transformation within pre-existing nevi.8 Nevertheless, the risk that a choroidal nevus may turn into a melanoma is generally considered extremely low.
Stages of Sleep. During sleep, we usually pass through five phases of sleep: stages 1, 2, 3, 4, and REM (rapid eye movement) sleep. These stages progress in a cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1. We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages. Infants, by contrast, spend about half of their sleep time in REM sleep. During stage 1, which is light sleep, we drift in and out of sleep and can be awakened easily. Our eyes move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember fragmented visual images.
There are 4 stages to NREM sleep that need to occur before REM sleep begins. (The following stages are found in the Quick Series Guide to Healthy Sleep) STAGE 1: Light sleep, lasts about 10 minutes. During this time, you feel calm and experience sudden arm and leg movement. Your heart rate lowers and the eyes open without awareness. If you are awakened you feel in a state of âhalf-sleepâ. STAGE 2: Begins a sleep that lasts about 30 â 45 minutes. During this time there is lack of movement, you become oblivious to your surroundings. If you wake up during this time, you do not remember your dreams. STAGE 3: Brief time before Stage 4.