Common visual symptoms of floaters and less common light flashes present in the office on a daily bases. First, let’s talk about floaters. Usually, the patient will comment about seeing little dots, lines, “worms” or “cells” in one or both eyes. When asked, patients will report seeing these whenever the lights are bright. They do not see them when the lights are dim. What is the patient seeing and what caused them to form? To understand floaters we need to discuss normal eye anatomy. The eye is a globe that has the optic nerve attached to the back of this globe. Inside the globe is a jelly-like subs-embedded tance called the vitreous. Towards the front of the globe, we find the lens.
While we are developing inside the womb the lens needs a blood supply to develop. There is an artery that forms from the optic nerve, passes through the vitreous gel and attaches to the back of the lens. This artery is called the hyaloid artery and it allows blood to flow to the lens providing the nutrients to allow the lens to develop. About 3 months after we are born the lens does not need blood anymore. The hyaloid artery that is attached to the optic nerve and to the back of the now developed lens degenerates into little pieces. The little pieces of the degenerated artery are embedded in the vitreous gel. When we are young the vitreous has the consistency of jello. As we all age the vitreous gel changes into a water type liquid. The little pieces of the degenerated artery that was once embedded in the jello will start to float around more. If you allow a lot of light into the eye, the light will cast a shadow of these little pieces of degenerated artery onto the retina and that is what the person is seeing. If you study the little pieces you can tell it was once a hollow tube. Sometimes they are curled like a pigtail.
When I am thinking about my own floaters and I look at the dark wall in my exam room I do not see my floaters. If I now look at my bright computer screen I see my floaters. I have more in one eye compared to the other. They will not do any harm to the eye but can be annoying. If a person is really annoyed a vitrectomy can be performed. This procedure involves removing the vitreous gel and replacing it with saline. When you remove the gel you also remove the degenerated artery remnants which will get rid of the floaters. This is considered a high-risk procedure because the retina can be torn which can lead to problems including blindness. So a person has to be very annoyed before considering having this done.
If a person presents with a complaint of suddenly seeing floaters, cobweb, vail or flashes of light, a dilated retinal exam needs to done as soon as possible. Most likely the patient has had a PVD (Posterior Vitreous Detachment) but a retinal tear or detachment needs to be ruled out. As we learned before, when we are young the vitreous gel has the consistency of jello and as we age the jello becomes more water-like. To understand a PVD we need to know a little more eye anatomy. Again, the eye is a globe-like structure or you can imagine it is shaped like a basketball. If I took the basketball and lined the inside of it with wallpaper, the wallpaper would represent the retina. The retina is made up of rods and cones which are specialized cells that are stimulated when exposed to light. The retina sends these signals to the visual cortex of the brain so we can see. Remember the eye is filled with the vitreous gel. Around the vitreous gel is a thin membrane called the hyaloid membrane. This membrane is around the gel and against the wallpaper or retina. Again, when we are young the vitreous is like jello and as we age it changes and becomes more water-like. When the vitreous is like jello and we move our eyes around the jello moves with the eyes. When the vitreous becomes more water-like and we move our eyes around we create a sloshing effect. You get the same effect if you open the lid of your washing machine and look down when it is running. You can see the water sloshing around. When the vitreous gel changes and becomes even more water-like and you move your eyes around enough you can create a force that can pull the hyaloid membrane off the wallpaper/retina. The hyaloid membrane will float around causing the patient to see a cobweb, veil or floaters. Again, the patient will see this more when a lot of light enters the eye which casts a shadow onto the retina. The flash of light is caused by the hyaloid membrane separating from the wallpaper/retina. If you look down with your eyes closed and lightly tap the top of your eye with your finger you will see a flash of light. The tapping mechanically stimulates the retinal cells causing the flash of light.
When the hyaloid membrane pulls away from the wallpaper/retina it mechanically stimulates the retina cells causing the light flashes. Usually, the patient will report a light flash in the form of an arch. This is because of the round globe. Usually, the hyaloid membrane pulls away from the wallpaper/retina and floats toward the bottom of the eye and the patient reports no more light flashes and does not notice the cobweb, veil or floaters anymore. Sometimes as the hyaloid membrane pulls away from the retina, it can cause a tear in the retina or it can cause the retina to detach. If I have a patient with an acute PVD, 10-15 % of these patients will develop a retinal tear usually within the first 3-4 weeks after the acute presentation. That is why when I see a patient with an acute PVD and the retina is OK, I will see the patient back for a follow-up visit 3-4 weeks later to check for a retinal tear. If the retina tears, the patient can have the following symptoms. Light flashes, like lightning streaks during the daytime. Increase in floaters or like a curtain coming over the eye. I tell my patients to return in 3-4 weeks unless they have any of the above symptoms. If they do I need to see them immediately. Statistically, if I look at 40% of 40-year-olds I will see a PVD in one or both eyes. 50% of 50-year-olds, 60% of 60-year-olds, 70% of 70 years, etc. The hyaloid membrane separates from the wallpaper/retina without causing retinal complications most of the time. It’s that 10-15% of patients we have to watch out for. If we catch the tear early it is easy to fix with a laser. If the retina detaches, then it becomes more difficult to fix and the prognosis of a permanent vision loss is higher.
BY: Dr. William Corkins, O.D.