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Eye Strain, Depth Perception, and Focus Problems

Headache, nausea, dizziness, vertigo, fatigue, and depth perception difficulties after Lasik, Bladeless Lasik, PRK, LASEK, Epi-Lasik, RLE, and P-IOL

Image of woman with both hands on the sides of her head and a distressed expression.  
Many seemingly unrelated temporary problems may be caused by the sudden optic changes of Lasik.  

After Lasik and similar laser eye surgery, patients sometimes experience temporary problems with focusing, perception of distances, eye strain, headaches, fatigue, vertigo, even nausea and dizziness. These normally temporary symptoms may be related to the sudden change of optics created by Lasik or Lasik dry eye.

An issue often related to these symptoms is Lasik dry eye.

When the eye is in a relaxed state, it is myopic (nearsighted, shortsighted), hyperopic (farsighted, longsighted), or emmetropic (no refractive error). When emmetropic, the optimum depth of focus is about 20 feet and beyond.

A complicating factor to these optic states is astigmatism. Astigmatism most often refers to the cornea not being spherical like the top of a ball, but being elliptical like the back of a spoon. Astigmatism would cause some - but not all - light passing through the cornea to be focused off-center. For purposes of discussion we will assume there is no astigmatism.

Accommodation and Convergence

Accommodation is when the natural crystalline lens in the eye changes shape to manipulate the focus of light entering the eye. Accommodation dynamically changes the optic state of the eye. As an example, if an emmetropic patient wanted to see an object within about 20 feet, the natural lens would change shape to make the patient myopic, thus allowing clear focus on a near object. If a person was myopic and wanted to see an object more than about 20 feet away, the natural lens would change shape to make the patient plano. Up to about age 40 we have a significant amount of accommodation.

An often overlooked part of seeing objects near is convergence. When looking at a distant object, the dominant eye looks directly at the object and the nondominant eye looks at the object from a slight angle. This difference between straight on and slight angle helps provide depth perception. When looking at an object near, the eyes converge toward each other to keep the relative angles of the dominant and nondominant eye the same as with distance and provide good depth perception. This convergence, which can look like a person is cross-eyed, is performed with the muscles outside the eye that control eye direction.

Presbyopia is when the natural lens of the eye becomes less able to change focus. Presbyopia is a natural part of the aging process that actually starts at around age 8-10, but is not very noticeable until around age 40 when it becomes difficult to read a newspaper and otherwise see objects close. This is when we need reading glasses or bifocals.

It is important to remember that there are two ways to describe myopia. One is that you cannot see things far away very well, the other is that you can see things close very well. Reading glasses are actually regular spectacles designed to make the wearer more myopic. If you are naturally myopic and presbyopic, it is probably possible to just remove your glasses to see objects near. Even with glasses on, myopia provides a mechanical advantage and can “mask” the effects of presbyopia.

If you have Lasik or similar refractive surgery and remove your myopia, you remove any advantage that myopia provided for near vision and are suddenly hit with the full effects of presbyopia. We call this “sudden presbyopia” and it catches Lasik patients in their early 40’s off guard all too often. Before surgery seeing things close was not much of a problem, now they need reading glasses to see objects near.

In addition to removing any advantage myopia may have provided, refractive surgery changes the range of accommodation and convergence necessary to see objects near. For the sake of demonstration (and these numbers are only for demonstration) let's say that the range of focus of your eyes is 1-10. The range 1-3 is for near focus, like your computer. Range 4-7 is for mid-range, like your TV, and 8-10 is for distance vision. In the 8-10 range your eyes are almost or totally relaxed with no accommodation and no convergence. To achieve clear vision in the 4-7 range, you must accommodate. To achieve clear vision in the 1-3 range, you must accommodate and converge.

Before surgery, myopia provided a mechanical advantage (gross over-simplification but you get the idea) for the 1-3 range. You actually had to accommodate and converge less before surgery than after. Before surgery your myopia would have provided a slight advantage in the 4-7 range. Not much, but a little. Now that you don't have myopia, your accommodation and convergence must work full time, not part time.

If you have been overcorrected into hyperopia, your range is now -3 to 10 and your eyes must first accommodate an additional 3 steps.

All this attempted accommodation and convergence can cause more than just poor vision. Accommodation and convergence deficiency can cause headaches, nausea, vertigo, and dizziness.

Since we are going into great detail, let’s throw in anther complicating matter. If one eye does not have the same refractive error - especially if one eye is hyperopic and the other is myopic - then the accommodation and convergence is imbalanced and one eye is always working harder than the other. Also, the size of the images hitting the retinas may be different, causing the eyes to be constantly trying to focus away the resulting blur.

All of these issues may combine into the “perfect storm” to cause problems with focusing, perception of distances, eye strain, headaches, vertigo, nausea, and/or dizziness. If you are experiencing these problems after Lasik or similar surgery, there are some options you may consider. What is most appropriate will depend upon the exact nature of the problem.

If the refractive error is different between the two eyes, contact lenses, glasses, or enhancement surgery to provide full and balanced correction may be the appropriate solution. If the issue is accommodation and convergence, the brain and eyes tend to become acclimated to the new range of vision correction with enough time.

Looking For Best Lasik Surgeon?

If you are ready to choose a doctor to be evaluated for conventional or custom wavefront Lasik, Bladeless Lasik, PRK, or any refractive surgery procedure, we recommend you consider a doctor who has been evaluated and certified by the USAEyes nonprofit organization. Locate a USAEyes Evaluated & Certified Lasik Doctor.

Personalized Answers

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Recent Lasik Eye Strain Medical Journal Articles...

Related Articles

Relationship between Induced Spherical Aberration and Depth of Focus after Hyperopic LASIK in Presbyopic Patients.

Ophthalmology. 2014 Oct 29;

Authors: Leray B, Cassagne M, Soler V, Villegas EA, Triozon C, Perez GM, Letsch J, Chapotot E, Artal P, Malecaze F

OBJECTIVE: To evaluate to what extent the modification of corneal asphericity to induce spherical aberration (SA) can improve the depth of focus and to determine whether preoperative adaptive optics assessment (Voptica SL) can predict an optimal SA value for each patient.
DESIGN: Comparative, prospective clinical trial with paired eye control.
PARTICIPANTS: Patients ≥45 years old who are hyperopic from +1.00 to +2.50 diopters (D), with eyes suitable for LASIK surgery.
INTERVENTION: Bilateral hyperopic LASIK surgery using a 200-Hz Allegretto excimer laser. The dominant eye was operated using a conventional profile. The nondominant eye was programmed with an aspheric ablation profile and -0.75 D monovision.
MAIN OUTCOME MEASURES: Primary outcome was the correlation between postoperative SA and depth of focus, defined as the pseudo-accommodation value (PAV = [1/reading distance {m}] - minimum addition [D]). Main secondary outcome was the comparison of depth of focus between patients with an induced SA close to the optimal one (group 1), patients with an induced SA far from the optimal one (group 2), and patients for whom SA induction did not increase the depth of focus (control group).
RESULTS: We included 76 patients. Between preoperative and postoperative assessment, the mean increase of distance-corrected PAV for near vision was +0.25±0.64 D (P < 0.001) for dominant eyes and +0.63±0.55 D (P < 0.001) for nondominant eyes. As the level of negative or positive postoperative SA increased, PAV for intermediate and near vision increased. Among the 37 eyes that followed the preoperative adaptive optics assessment, the mean PAV increase at near was significantly higher (P < 0.05) in group 1 (0.93±0.50 D) than in group 2 (0.46±0.42 D) and than in the control group (0.35±0.32 D). The mean optimal SA value determined by the dynamic simulation procedure to optimize the depth of focus was -0.18±0.13 μm at 4.5 mm.
CONCLUSIONS: Aspheric hyperopic LASIK can increase the depth of focus without impairing far vision, but this benefit would be maximal and reproducible if we could define and achieve an optimal SA value determined by preoperative assessment using an adaptive optics instrument.

PMID: 25444348 [PubMed - as supplied by publisher]


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