First, let us look at an absolutely normal retina. The image below is the right eye of a happy child. There is a certain sheen to it, i.e., wet-looking, which is lost in adults. Some landmarks: you can see the blood vessels coming out from one small oval area, known as the optic disc. To the left of the optic disc is the macula. And the rest is the whole retina. It looks like a well-tended garden, certainly a pristine landscape. After a few decades, things are bound to be different. If you see anything, either extra, missing, or changed, that can be bad news.
A few examples:1. Peripheral chorioretinal atrophy: a "window" appears at 4 o'clock position from old chorioretinitis causing loss of retinal pigment epithelium. You can see through the opening at the blood vessels underneath. This is usually regarded as a scar. Sometimes it can be an active infection; typically more central that can threaten vision.
2. Lattice degeneration: On the left periphery, a long patch of retinal degeneration with potentially troublesome holes in it. The holes may need to be lasered/sealed to avoid retinal detachment.
3. More retinal degeneration in the periphery: A common type of degeneration in the aging eye, usually benign.
4. Melanoma: a small yet dangerous cancer in the peripheral retina (the dark spot in the 7 o'clock position).
5. Retinoschisis: This is not a retinal detachment, only a separation of retinal layers. It can, however, lead to retinal detachment.
6. Leber's aneurysm: Notice in the middle of the image a microaneurysm which can rupture and result in vitreous hemorrhage. In this case, the patient does have a family history of such a problem. Blood of course must be removed or the iron in hemoglobin can be toxic to the retina.
Take-home lesson: Even when the visual acuity is 20/20, danger can and does lurk in the far periphery of the retina.
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