Strabismus Precipitated by Monovision
Zane F. Pollard *, Marc F. Greenberg, Mark Bordenca, Joshua Elliott, Victoria Hsu
James Hall Eye Center and the Section of Ophthalmology, Children’s Healthcare of Atlanta at Scottish Rite Children’s Hospital, Atlanta, Georgia
* Inquiries to Zane F. Pollard, 5445 Meridian Mark Rd, Suite 220, Atlanta, GA 30342 E-mail address: zanepollard@bellsouth.net
Purpose
To present patients who had the onset of strabismus or the recurrence of strabismus after converting to a monovision system of seeing.
Design
Retrospective interventional case series.
Methods
Clinical records of 12 patients from the private practice of the corresponding author of this paper (Z.F.P.) were reviewed. Patients obtaining monovision via contact lenses, LASIK, and cataract surgery with posterior chamber intraocular lenses were studied if their monovision produced a new strabismus or was related to the recurrence of a previous strabismus.
Results
All patients were first treated by converting the monofixing near eye to distance vision and then using reading glasses for near work. Of the 12 patients, 7 regained their fusion by doing away with monovision and 5 required surgery to reestablish motor or sensory control. All of the surgery patients obtained an excellent alignment but 1 did not regain sensory fusion.
Conclusion
Monovision is successful for the far majority of patients who try it. However, in patients with a previous history of strabismus or those with significant phorias, caution should be used in recommending monovision, and if monovision is elected, keeping the anisometropia to small levels such as 1.25 to 1.50 diopters (D) might lessen the chance of producing strabismus post monovision. The majority of our patients developed strabismus after 2 years of monovision, telling us that while a trial of monovision with a contact lens prior to surgery may suggest that the patient could tolerate monovision, it is not a guarantee.
Before planning to produce monovision for patients who want to be able to see at distance and near without glasses, the ophthalmologist must consider certain potential complications. The physician must evaluate each patient’s risk for developing a post-procedural onset of diplopia and/or strabismus. Historically, there have been 3 ways to produce monovision. An early protocol involved fitting the patient with 1 contact lens for distance and another for near. A second method was laser in situ keratomileusis (LASIK), in which 1 eye was corrected for distance and the other for near. A third method used bilateral cataract surgery to implant one intraocular lens with the power calculated for distance and the other for near vision. All these methods have worked well for most of our patients. However, in the occasional patient who has a weak lock on fusion, producing monovision might trigger diplopia and/or strabismus. In the patient with a history of corrected strabismus either in childhood or adulthood, the induction of monovision might cause a return to the strabismic state. This paper discusses several patients who, after the production of monovision, were either diagnosed with strabismus for the first time or experienced a recurrence of an earlier strabismus. Treatment options for alleviating the strabismus and diplopia are discussed.
Case Reports
Case 1
This 45-year-old female had been wearing hard contact lenses successfully for 30 years for the correction of myopia. At the age of 44, she became presbyopic and opted for monovision with 1 eye fit for distance and the other for near using gas-permeable hard contact lenses. After 1 year of wearing the lenses to produce monovision, she noted the onset of diplopia at distance and at near. There had been no history of strabismus or diplopia. She measured 14 prism diopters (D) of esotropia at distance and at near and in all fields of gaze. Ocular rotations were full, and visual acuity was 20/20 in the right eye and 20/70 in the left eye. The left eye corrected to 20/20 with a −1.25 D. The patient was given contact lenses that corrected both eyes for distance. She used +1.50 D reading glasses for near. Three months later, an examination showed orthophoria in all fields of gaze. A 3-year follow-up showed her to be stable with no strabismus and no diplopia.
Case 2
This 47-year-old female had been wearing soft contact lenses for 25 years to treat her myopia. She had a history of a bilateral medial rectus muscle recession for congenital esotropia at age 1 with no obvious strabismus noted by her family since that time. For 2 years, she had been treated successfully with monovision via soft contact lenses. She presented with crossed eyes for the first time since infancy. She had no diplopia. She measured 20 prism diopters of esotropia at distance and at near. Ductions and versions were full. With her contact lenses, which corrected her for monovision, her visual acuity was 20/20 in the right eye and 20/60 in the left eye. The left eye corrected to 20/20 with −1.50 D. Each eye had 5 D of myopia. She suppressed the left eye for distance and the right eye for near. She was refitted to enable both eyes to be in focus for distance, and she wore +1.50 D glasses for reading. After 3 months, she still measured 20 prism diopters of esotropia at distance and at near. She underwent a resection of the lateral rectus muscle in both eyes and a 2-year follow-up showed orthophoria. She still suppresses the left eye for distance and the right eye for near. While it is possible that she simply had a recurrence of her infantile esotropia, the fact that she had been without a noticeable strabismus for over 40 years suggests that the monovision played a part in the recurrence of her esotropia.
Case 3
This 48-year-old female with high myopia of −12 D in each eye had been wearing glasses for correction of her myopia since infancy. For the past 20 years, however, she had worn soft contact lenses to correct her myopia. She underwent a 12-incision radial keratotomy on her left eye, which corrected 10 D of myopia. Because of contact lens intolerance after radial keratotomy in her left eye, she used her right eye for distance with the soft contact lens, and her −2.00 D left eye uncorrected for near vision. She presented 3 months later with a large esophoria of 12 prism diopters at distance and at near with asthenopic symptoms. Rotations were full and normal. It was recommended that she undergo radial keratotomy of the right eye. Following this procedure, her result showed −1.00 D in the right eye and −2.00 D in the left eye. She elected to go without contacts, using glasses while driving. Her esophoria was no longer present, and she has been stable for the past 20 years.
Case 4
This 66-year-old female, hyperopic in both eyes, had undergone a recession of her left medial rectus muscle combined with a resection of her left lateral rectus muscle 2 years prior to this examination. The history revealed that she had been esotropic for 1 year prior to her surgery. Her strabismus was secondary to a sixth cranial nerve palsy precipitated by a car accident. She had been orthophoric since her surgery. At this visit she complained that she had experienced a recurrence of her crossing for 3 months. She also remarked that she now could read without reading glasses. She had been wearing contact lenses for 40 years, which corrected her hyperopia of +3.00 D in the right eye and +5.00 D in the left eye. Wearing her contact lenses, she measured 14 prism diopters of esotropia at distance and near in the primary position and in all fields of gaze. There was full abduction in each eye. Visual acuity was 20/80 in the right eye and 20/20 in the left eye. She could read J1 with the right eye. Cycloplegic refraction over her contact lens showed −2.00 D in the right eye and plano in the left eye. She remarked that she had lost the lens for the right eye and had replaced it 4 months previously. Apparently, she was wearing a left lens for both eyes. The proper lens was dispensed, and she returned 3 months later, orthophoric again. An 18-month follow-up showed her still to be orthophoric. She had fusion on the Worth 4-dot at distance and at near, and she had 40 seconds of near-stereo acuity. She wears +2.25 D reading glasses over her contact lenses for near work. She had essentially self-produced monovision by wearing 2 left contact lenses.
Case 5
This 70-year-old male had undergone bilateral cataract surgery 2 weeks apart with implantation of a posterior chamber lens in each eye. The right eye was designated for distance vision, and without correction he was 20/25. His refraction in the right eye was −0.25 D, giving 20/20. The left eye was 20/100 and was designated to be used for near work, as it had a refraction of −1.75. The monovision worked very well for 2 years until he presented with 16 prism diopters of esotropia at distance and at near and in all fields of gaze. Ductions and versions were normal. He did report wearing glasses for crossed eyes as a child until age 13, but he had outgrown the glasses. He had no strabismus until 2 years after the bilateral cataract surgery. Glasses were prescribed that were a −0.25 D for the right eye and −1.75 D for the left eye with an add of +2.50 D for each eye. Four months later, he presented with orthophoria in all fields of gaze. He fused the Worth 4-dot at distance and at near.
Case 6
This 46-year-old male had worn glasses for myopia since age 8, having 4.75 D in each eye. He underwent LASIK surgery with a planned monofixation. The postoperative refraction in the right eye was plano +0.50 axis 090 and the left eye −1.50 D. Monovision was functioning for 3 years until he presented with 20 prism diopters of esotropia at distance and at near in the primary position and in all fields of gaze. Ocular rotations were full in both eyes. He denied having any strabismus as a child, but had remembered going to see an eye doctor as a teenager with a complaint of eye fatigue. No treatment had been given. He did report horizontal diplopia at this time. He was treated with a contact lens for the left eye and was given reading glasses of +1.50 OU for near work. He was unable to regain his fusion, and 4 months later underwent a recession of his left medial rectus muscle combined with a resection of his left lateral rectus muscle. After only a month, he regained his sensory and motor fusion. He was orthotropic at distance and at near and fused the Worth 4-dot at distance and at near. A 2-year follow-up showed him maintaining his sensory and motor fusion at distance and at near.
Other Cases
We saw 6 additional patients who had decompensated after switching to monovision. All were aged 45 to 50. Four became esotropic and 2 became exotropic. One patient decompensated within 2 months after the onset of monovision via contact lenses, and a second after 3 years of monovision with contact lenses. Four others decompensated after 3 years of monovision, 2 after LASIK and 2 after cataract surgery, all with planned monovision. Three regained fusion after eliminating the monovision optically, but the other 3 required surgery. In all of these 6 cases, there was no history of strabismus. All have done well regaining motor and sensory fusion.
All 12 patients were in good health. Several had hypertension, which was controlled at the time of the onset of strabismus.
This series of patients lost their control of alignment because of the onset of monovision. Most did not decompensate until 3 years after starting monovision. However, 1 decompensated after only 2 months of monovision. The response to eliminating monovision was variable, with some regaining the ability to fuse, while others required surgery. While monovision is an excellent way of handling presbyopia in patients not wanting to wear glasses, it can disrupt fusion in patients who have a weak lock on binocularity. All of our patients eventually did well, but only 7 of the 12 regained sensory and motor fusion by optically eliminating monovision. The other 5 required surgery to align the eyes. Four of the 5 who required surgery obtained both motor and sensory fusion, while 1 obtained straight eyes but continued to suppress 1 eye.
Discussion
Fixation-switch diplopia might occur with monovision. This occurs when certain patients with strabismus who have a strong fixation preference for 1 eye are treated with monovision.1 When they fixate with the nondominant eye, diplopia occurs. This type of patient can be diagnosed prior to refractive surgery and should be warned against having surgery. Fixation-switch diplopia can occur with fourth cranial nerve palsy. Normally, fixating with the nonparetic eye might not cause diplopia, as the small deviation is within the range of fusional reserves for the patient. However, with monovision, while fixating with the paretic eye, the secondary deviation is larger than fixating with the nonparetic eye, and diplopia might be experienced as the deviation has exceeded fusional reserves.2 A thorough preoperative examination looking for a prior use of prisms, aniseikonia, and strabismus should become routine as a way of screening patients who need to be cautious of having refractive surgery.3 A decompensated fourth cranial nerve palsy after LASIK for monovision as well as a patient with a decrease in fusion and stereopsis after becoming anisometropic from bilateral LASIK have been reported.4, 5 Prisms may have to be used if fusion is not obtained after discontinuation of the monovision. This may be practical if the residual deviation is small.
Patients with a history of strabismus should be advised that the use of monovision as treatment for presbyopia might precipitate a recurrence of previous strabismus or asthenopic symptoms. Patients who are diagnosed with a significant exophoria or esophoria should be informed that monovision might cause strabismus to appear. This condition might occur in as soon as 2 months’ time or as late as 3 years after the onset of the monovision.
Photorefractive keratectomy (PRK) was a popular method of producing monovision prior to LASIK in myopic eyes. An intentional undercorrection of 1.25 in the nondominant eye was chosen in 1 large series. Mean stereopsis in the monovision group was 218 seconds of arc for distance and 160 seconds for near. Binocular fusion convergence amplititude was normal in 16 of 21 patients. Five had less than 20 prism diopters of fusional convergence amplititude, but none experienced a significant phoria or misalignment after surgery. One patient had 3.13 D of anisometropia postoperatively and had reduced stereopsis. This individual had the lowest patient satisfaction in the group. It is advisable not to induce more than 2 D of anisometropia without a pretreatment trial with contact lenses, as this might disrupt fusion.6
Stereoacuity and foveal fusion can be affected in adults with long-standing surgical monovision. One study reported on 32 adults with monovision induced by LASIK or PRK.7 They measured sensory fusion and stereopsis by correcting the myopic eye with a contact lens for distance and using reading glasses for near vision. Median stereoacuity values were 40 seconds of arc for age-matched controls, 100 seconds in those with less than 1.5 D of anisometropia, and 150 seconds of arc for patients with 1.5 D or greater of anisometropia. Seventy-eight percent of patients with 1.5 D or less of anisometropia and 50% of patients with more than 1.5 D of anisometropia passed the Worth 4-dot at distance. All passed the Worth 4-dot at near. Those that suppressed 1 eye at distance and fused at near on the Worth 4-dot examination had developed the monofixation syndrome with less-than-perfect stereopsis. Therefore, the authors concluded that long-term monovision can cause deficient foveal binocular vision.
Most of our patients developed esotropia rather than exotropia with monovision. Two developed exotropia, and 1 had a history of exotropia surgery. One of our patients with esotropia had a history of surgery for a sixth cranial nerve palsy. As we do not have childhood histories on most of these patients, we assume that the majority probably had an esophoria, which decompensated with monovision. Since most of our patients did not report a history of strabismus, one might not be able to predict the increased risk for acquired strabismus. However, a history of strabismus should be a warning sign for all potential monovision patients. Most of our patients (67%; 8/12) developed strabismus after 2 years of monovision. This is important in the follow-up of our monovision patients and implies that while monovision may initially be working for the patient, one needs to be aware that strabismus might appear several years later. These patients most likely had a phoria that had been held in check by fusion for a long time prior to the onset of monovision. With reasonable fusional reserves, they were able to tolerate monovision for several years before becoming symptomatic.
All of our patients who did recover their ability to fuse after the elimination of their monovision did so within a 3− to 4-month period. We decided that after 4 months, patients who were still symptomatic and nonfunctional with their diplopia and/or strabismus would be treated with surgery (Table).
TABLE Clinical Characteristics of 12 Patients With Monovision-Induced Strabismus
Characteristic Number of Patients
History of strabismus 3
Time in monovision until onset of strabismus
2-6 months 4
2 years 2
3 years 6
Recovered orthotropia within 4 months after discontinuation of monovision
Yes 7
No 5
In patients with strabismus who desire monovision correction via LASIK, a trial with a contact lens or glasses to simulate monovision should be tried first. If diplopia occurs, then there is a very high risk for postoperative double vision. The absence of diplopia does not guarantee that there will not be postoperative diplopia, as this might not present for months or even several years after the surgical inducement of monovision. In non-strabismus patients, we have even seen successful monovision for several years before the onset of fusional or motor complications. It cannot be determined with absolute certainty how long the preoperative trial of monovision without diplopia and/or strabismus should be observed before safely proceeding with monovision via LASIK. The most significant caveat to emerge from this study is that it can take as long as 3 years for the fusional and motility problems to occur after the onset of monovision. The length of time before the onset of diplopia and/or strabismus is probably quite variable. Therefore, this possibility should be discussed preoperatively with the patient. Keeping the anisometropia at the lowest functional level will help in reducing the loss of stereopsis8 and possibly aid in lowering the incidence of decompensated strabismus after monovision surgery.
Publication of this article was supported by the James Hall Eye Center, Atlanta, Georgia. The authors indicate no financial relationships with any commercial company. Involved in design of the study (Z.F.P., M.F.G.); collection, management, analysis, and interpretation of the data (Z.F.P., M.F.G., V.H.); and preparation, review, and approval of the manuscript (Z.F.P., M.F.G., M.B., J.E., V.H.). Approval of this study was provided by the Children’s Healthcare of Atlanta Institutional Review Board.
References
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2 Kushner B.J.. Causes and prevention of diplopia after refractive surgery. Am Orthopt J 2008; 58 (1): 39-44.
3 Kushner B.J., Kowal L.. Diplopia after refractive surgeryOccurrence and prevention. Arch Ophthalmol 2003; 121 (3): 315-321.
4 Godts D., Tassignon M.J., Gobin L.. Binocular vision impairment after refractive surgery. J Cataract Refract Surg 2004; 30 (1): 101-109.
5 Shuler E., Silverberg M., Beade P., Moadel K.. Decompensated strabismus after laser in situ keratomileusis. J Cataract Refract Surg 1999; 25 (11): 1552-1553.
6 Wright K.W., Guemes A., Kapadia M.S., Wilson S.E.. Binocular function and patient satisfaction after monovision induced by myopic photorefractive keratectomy. J Cataract Refract Surg 1999; 25 (2): 177-182.
7 Fawcett S.L., Herman W.K., Alfieri C.D., Castleberry K.A., Parks M.M., Birch E.E.. Stereoacuity and foveal fusion in adults with long-standing surgical monovision. J AAPOS 2001; 5 (6): 342-347.
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