Hyperopia (Farsightedness) Explained

After examining a two-year old nephew this week, I attempted to explain what it means to be farsighted to his worried mother. I've been in practice for nearly 12 years and I still struggle to explain hyperopia in lay terms. Its not that Hyperopia is complicated, but it is not as intuitively tidy as Myopia, or nearsightedness (where near things are clear and far things are blurry). Patients often exclaim, "Ah, Farsighted... so things far away are clear and things up close are blurry?" Well, sort of. Therein lies the problem with understanding Hyperopia. We collectively miss-apply the logic that so nicely fits nearsightedness, to farsightedness. And people often confuse presbyopia, or bifocal vision with farsightedness. Even a quick google search on the subject reveals very little for the lay person that isn't slightly off colored just enough to leave an element of confusion. This post is for you, Sis, so you'll grasp how your young son sees; and for me, as I work to conjure a solid explanation of Hyperopia.


The Normal Eye




First, to understand Hyperopia, you must understand how the normal eye functions. When viewing things in the distance (20 feet and beyond are optically equal), the normal eye is relaxed and focused. The light rays entering the eye are parallel, and the relaxed eye converges those parallel rays, bringing them into focus on the retina. When the eye shifts its gaze to anything inside 20 feet, the rays of light begin to diverge, or open up, which pushes the focal point to somewhere behind the normal relaxed eye. The eye then has to accommodate, or shift focus, to keep the near object in focus. This happens when an internal muscle called the cilliary body activates and changes the shape of the crystalline lens that sits behind your pupil. This accommodation pulls the long-focused rays back into focus on the retina. And it all happens faster, and more fluidly than you can perceive, without conscious effort on your part. The normal eye uses about 2.50 diopters of accommodative power to see things at the normal reading distance (approx 16 inches).


Hyperopia

Farsightedness is the condition where the natural relaxed eye focuses the normal parallel rays from the distance behind the eye. How the farsighted person sees is based on the complex interaction between the amount of farsightedness, the natural strength of the accommodative mechanism, the person's age, and the visual system's alignment mechanisms which keep the eyes on target (they happen to be tied to the focusing system). A young person with small to moderate amounts of Hyperopia can use their close focusing power to pull the distance into focus on the retina and see clearly. Near objects take an additional 2.50 diopters in focus power, and if they have the ability to do it, they can see close as well. Here are some examples of a small and a large amount of Hyperopia:

A person with +1.00 diopter Hyperopia needs 1.00 diopter of their close-focus power to see in the distance. Add another 2.50 of accommodation for close vision and they end up needing a total of 3.50 in close focusing power to see clearly at the reading distance.

A person with +7.50 diopters of Hyperopia needs 7.50 diopters of help to correct the distance (usually they can't contribute that much by themselves unless they are very young) and they need another 2.50 for near for a total of 10.00 diopters of focusing power.


Since the eye's close focusing power was not designed to remain constantly activated, just like your arms weren't designed to hold a bucket of water outstretched for long periods of time, uncorrected Hyperopes can get extra fatigued with the full time, extra-duty use of their close focusing power. Depending on the factors mentioned above, Hyperopes experience a range of symptoms from mild, imperceptible strain, to extreme fatigue, double vision, and completely blurry distance and near vision.


Correction

Hyperopia can be corrected with glasses, contacts, or surgery, using PLUS dioptric power. Unlike Myopic (nearsighted) corrections which are very exact and simple to derive, Hyperopic corrections depend on the practitioner's ability to measure the amount of Hyperopia and then integrate all the other complex factors involved like age, accommodative strength, eye alignment, and lifestyle needs. Generally, correcting Hyperopia relaxes the farsighted eye for focusing in the distance the way it was designed, so the eye can use the normal amount of close focusing power for reading.


Because Hyperopic eyes can contribute accommodation to the vision-equation, finding the amount of correction that makes his/her eyes comfortable can be a challenge, and that equation changes over time as the aging eye loses its natural accommodative ability. The older you get, the easier it becomes to find the right amount of correction because your accommodation interferes less. Sometimes younger eyes won't relax and accept plus powered lenses. Large amounts of Hyperopia are easier to correct because the visual benefit is so dramatic. Small to moderate amounts are tougher because the benefit is the delayed gratification of reduced fatigue--which benefit often comes at the end of the day, the end of the week, the end of the school year, etc. For the younger Hyperope, we don't always correct the full amount, but instead, the amount that makes the eyes most comfortable--especially for close work.


Children and Hyperopia

Hyperopia is the most missed eye condition at school and pediatrician screenings because small to moderate amounts don't usually blur the child's vision. Children's symptoms increase with age and amount of Hyperopia, but they often don't know that the discomfort they feel is abnormal and they get numb to it. Often, it plays out as near-task avoidance. If reading is uncomfortable or tiresome after extended periods, the child usually develops avoidance patterns, which can turn into habits, attitudes, labels, and a self perception that can often be difficult to correct as the child gets older. As a parent, you can watch for these avoidance patterns, afternoon headaches, or strange visual behavior like squinting, sideways looking, or looking closer than normal at books, TV, etc.


Some eye doctors use a blanket approach to correcting a child's hyperopia--relying strictly on numbers. It is very important to find a practitioner who is committed to using the more sophisticated approach of finding the correction that makes the farsighted child comfortable for near tasks (whether that amount is none, or something different from their full correction). If correction is needed, sometimes single vision lenses suffice, or sometimes it is more convenient to put it in the form of bifocals. These are all complexities that take time to sort through and you will do well to expect your doctor to explain and recommend what is best for your child.

Having your child examined before the age of two is the best way to make certain that problems aren't missed which can lead to poor school performance and delayed visual development. You did a wonderful service for your son by bringing him in early, Sis. Check this post about a little girl we took care of with farsightedness similar to your son: THE EYES HAVE IT.