Originally posted in Insidermedicine
The eye is very similar to a camera. Both are optical systems that have lenses in the front to focus light rays onto a film. The retina is the eye’s film. It is a tissue that consists of 10 layers and is about 500 microns thick—or, half a millimeter. The main function of the retina is to trap light rays, convert them into electrical impulses, and send those impulses through the optic nerve to the brain. The photoreceptors (called rods and cones) are the cells that both trap light rays and make the conversion into electrical impulses happen.
There are 2 parts to the retina: the macula, which is the central part of the retina, and the retinal periphery. The macula is important for central vision, and therefore is important for functions like reading, driving and facial recognition. Because the macular contains the eye’s cones, it is also the area that is important in color vision. The retinal periphery is where the retina’s rods are located. These cells, which function best in lower levels of illumination, are responsible for both nighttime vision and peripheral vision.
Posterior vitreous vs. Retinal Detachment
The vitreous is the jelly of the eye and it sits right in front of the retina. As we get older, the jelly increasingly turns more to fluid. With time, the fluid coalesces, and moves towards the back of the eye forcing the back of the vitreous forward. Ultimately, this causes a separation of the posterior vitreous from the retina–an event called a posterior vitreous detachment or PVD. A PVD is an age-related event that happens to most people by the age of 80 years. In some cases, when the jelly moves forward, it causes a tear in the retina that is a risk factor for retinal detachment. This usually happens in an area where the vitreous is tightly adherent to the retina, and occurs in 14% of patients. In a retinal detachment, fluid from the vitreous moves through the tiny retinal tear or hole and causes the retina to separate from the back of the eye. Conceptually, a retinal detachment can be thought of as wallpaper peeling away from the back of the wall.
How do patients with PVD or retinal detachment present?
Patients with a PVD will usually notice a new floater. They will describe it as seeing a new “spider web” or a “little mosquito flying” in their vision. They usually say that if they try to look at it moves. Patients may also notice flashing lights that last for a few seconds. Our research shows that in 14% of patients with PVD, a retinal tear or detachment will be noted. So in patients with a new floater or new flashing lights we have to be concerned about an associated retinal tear or detachment. If a retinal detachment is present patients may also notice peripheral visual loss. This is often noted as a black curtain now covering part of their vision. If the macula comes off, central vision is lost, and the patient may become blind in that eye.
What is seen on exam?
From the perspective of a family doctor, urgent referral should be considered for any patient with new onset floaters or new flashes of light, as these can be associated with retinal tear or detachment.
Our research, based on a review of nearly 200 papers and a synthesis of 17, shows that the key signs that are predictive of a retinal tear or detachment in the setting of PVD include: vitreous hemorrhage, and tobacco dust. Tobacco dust represent liberated retinal pigment epithelial cells and mean that the retina has been torn, until proven otherwise. These signs usually cannot be visualized on direct ophthalmoscopy; and can only be seen using more advanced techniques like slit lamp examination or indirect ophthalmoscopy.
With more sophisticated instruments, one can see a retinal detachment-which, once elevated, becomes whitish in nature and very billowy. We can also see a hole in the retina.
How are PVD and retinal detachment assessed?
A new onset of floaters does not necessarily mean a retinal detachment. Floaters can also represent vitreous synergisms- a normal age-related degeneration of the vitreous, or could represent the presence red blood cells or white blood cells in the jelly. Both of these are also very serious problems and so anyone with new floaters should be taken seriously.
Flashes of light a symptom that is seen in patients with migraine. These flashes are usually bilateral, last for 10-20 minutes and have a zigzag shape to them. They usually are associated with a headache, followed by nausea, vomiting and significant sensitivity to light.
The diagnosis of PVD, retinal tear and detachment is made on examination. Sometimes though, patients will present with new onset of floaters and loss of vision and we cannot see the retina because the jelly is full of blood. In these situations, we have to perform an ultrasound test to see if the retina is detached.
How are PVD and retinal detachment treated?
Posterior vitreous detachment doesn’t need to be treated. While the floater is initially annoying, with time it becomes less noticeable to the patient.
If a retinal tear is noted, we use a laser to tack down the retina around the hole, known as laser retinopexy. This procedure limits the spread of fluid under the retina surrounding the hole.
If the retina is detached, there are a few things that we can do. We can inject gas into the eye to act as a tamponade to flatten the retina down. We then use laser to seal the hole. If there is a lot of blood in the jelly of the eye, we have to make incisions into the eye and remove it to get access to the retina – this is called a vitrectomy. At other times, we operate on the outside of the eye and sew on a small piece of silicone to push the sclera up to the retina. Again, here too, we seal the hole with laser.
Any patients with new onset floaters or flashes should be emergently referred if they have monocular visual loss, a new monocular field defect, or either hemorrhage or “tobacco dust” is noted on clinical examination of the vitreous. In all cases of acute PVD one should always have a high index of suspicion for retinal tear or associated retinal detachment.