The Healthy Eye Newsletter
Presbyopia: Putting Things Into Focus
Normal Vision vs. Presbyopia
Some of the primary organs involved in the healthy development of vision include the occipital lobe, rod and cone receptors (which line the back of the eye and change light energy into electrical energy), optic nerve fibers, and horizontal, bipolar, amacrine, and ganglion cells (Goldstein, 2014). These organs all work together to form visual acuity, which is the ability to see details, allowing us to see the very small letters on an eye chart, or the ability to focus on details from far away (Goldstein, 2015). Presbyopia gradually occurs as we age, and is a condition of losing the ability to focus on objects that are close to us (Giorgi, 2016). This is due to the eye lens becoming less flexible with age, meaning it will not re-shape itself, and is thus unable to bend the light as it should to focus it on the retina (Giorgi, 2016). Figure 1 highlights the functions involved in the normal visual process.
Perception of Vision
Perception occurs because of activity in the brain caused by a triggering of light, the stimulus for vision (Goldstein, 2014). Light energy can be transformed into electrical energy, known as transduction, and occurs in the rods and cones: the receptors for vision (Goldstein, 2014). In simpler terms, when light meets the retina, the process of vision and sight begins (Society for Neuroscience, 2012). Information from the retina is sent in the form of electrical signals via the optic nerve to other parts of the brain, which then process the image and allows us to see (Society for Neuroscience, 2012). Figure 2 is an illustration of a pathway of detection of vision.
Perceiving Objects and Scenes
There is an old saying there is more than one way to look at something, and the ‘something’ is referring to any object. This saying has been proven true, as objects look different from different viewpoints and angles, a process called viewpoint invariance (Goldstein, 2014). When it comes to what we see in our environments, it all comes down to how we group the objects in that environment. And when we perceptually group elements in any given environment, creating a perception of objects, it is called perceptual organization (Goldstein, 2014).
This also influences how we view objects in scenes. Even though there is a lot going on in any given scene, sometimes even complex imagery, we are usually able to identify most scenes after viewing them for just a fraction of a second (Goldstein, 2014). Oliva and Torralba claim that this process is possible due to information called global image feature, rapid perception associated with specific types of scenes (as cited in Goldstein, 2014). Furthermore, the Gestalt Approach plays an element in how scenes become grouped together. Gestalt psychologists suggested that perception is dependent on numerous organizing principles, which usually start in the environment (Goldstein, 2014).
The Vision Process of Presbyopia
In our youth, our crystalline lenses allow us to see very clearly across a range of distances (Black, Karpecki, & Brooker, 2015). This includes our focus on objects both near and afar. But as we get older, a natural process occurs in which the crystallines start to lose their accommodative function in which the range of vision decreases, thus making images blurry (Black et al., 2015). What is unique about this vision disorder is that we can’t stop it from gradually occurring since the eye lens does harden with age, but there are a couple different treatment options to help reverse it.
One form of treatment that has proven effective in correcting presbyopia is a topical treatment combining a parasympathomimetic agent with an NSAID in an oil-based formulation (Krader, 2015). This topical drop intervenes by changing the pupil size helping to improve both near and distant visual acuity. Of course an evaluation must first be made of potential candidates, in which a successful one “if they have no more than 1.0 D of myopia, astigmatism, or hyperopia, and are free of corneal or vitreous opacities, retinal pathology, or chronic general pathology” (Krader, 2015, p. 36). It should be noted that side effects are not common, but have been reported, including nausea and headaches (Krader, 2015).
Another form of treatment is a surgical option, called corneal inlays, and is relatively new in the U.S. The surgery only lasts about 10 minutes, but the recovery time is anywhere between three to four weeks for full visual recovery (Black, Karpecki, and Brooker, 2015). As shown in figure 3, a microperforated inlay (artificial pupil) is implanted into a small area of the cornea, and increases the eye’s depth of focus by blocking unfocused light (Black et al., 2015). An image of this inlay is shown below.
Black, S., Karpecki, P., & Brooker, E. (2015). New surgical options for presbyopia: the corneal inlay is the latest in vision correction surgery for presbyopic patients; here's what you need to know about it, including the different styles, expected results, comanagement tips and more. Review of Optometry, 152(6), 35-41. Retrieved from Health Reference Center Academic via Gale, http://tinyurl.com/jqypqaz
Giorgi, A. (2016). Presbyopia. Healthline. Retrieved from http://www.healthline.com/health/presbyopia#Overview1
Goldstein, E.B. (2014). Sensation and perception. (9th Ed.). Belmont, CA: Wadsworth.
Guttman Krader, C. (2015). Simple solution for presbyopia: parasympathomimetic agent/NSAID reduce pupil size to increase depth of focus. Ophthalmology Times, 40(15), 36. Retrieved from Health Reference Center Academic via Gale, http://tinyurl.com/zxzbl3m
Vision: processing information. (2012). Society for Neuroscience. Retrieved from http://tinyurl.com/kdfttpp