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Binocular vision impairment after refractive surgery
Binocular vision impairment after refractive surgery Daisy Godts, CO, Marie-Jose´ Tassignon, MD, PhD, Laure Gobin, Sc, PhD Purpose: To illustrate the need for an accurate preoperative orthoptic examination to prevent postoperative changes in binocular vision. Setting: Department of Ophthalmology, University Hospital Antwerp, Edegem, Belgium. Methods: Five patients presenting major subjective complaints after refractive surgery were analyzed. Results: In 1 patient, a latent N IV palsy decompensated after laser in situ keratomileusis (LASIK) in the more myopic eye to achieve monovision. A second patient, operated on for N IV palsy 10 years earlier, presented a recurrence of the palsy after bilateral LASIK for myopia. The third patient complained of discomfort in binocular vision caused by aggravation of a preexisting intermittent esotropia that worsened after LASIK for hyperopia. The fourth patient complained of diplopia after LASIK in the highly anisometropic and exotropic eye. The fifth patient experienced a decrease in fusion and stereopsis at the time he became anisometropic after bilateral LASIK. Conclusions: Special care should be taken of patients who have a preoperative history of strabismus surgery, an overcorrection or undercorrection in 1 or both eyes, or anisometropia and of those who are unhappy with contact lenses. An orthoptic examination should be done with and without spectacle correction to detect underlying vertical phorias. Intended monovision should be examined initially using contact lenses. J Cataract Refract Surg 2004; 30:101–109 2004 ASCRS and ESCRS
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n technology-assessment reviews of the safety and efficacy of refractive surgery, monocular visual outcome without spectacle correction is the reference for success. Little is reported about the postoperative binocular vision balance, although some alteration in binocular vision is expected because of the change in the nodal point for far and near distance.1 It is not always clear whether the authors performed an accurate orthoptic
Accepted for publication March 19, 2003. From the Department of Ophthalmology, University Hospital Antwerp, Edegem, Belgium. Presented in part at the XXth Congress of the European Society of Cataract & and Refractive Surgeons, Nice, France, September 2002. None of the authors has a financial interest in any product mentioned. Reprint requests to Daisy Godts, University Hospital Antwerp, Department of Ophthalmology, Wilrijkstraat 10, 2650 Edegem, Belgium. 2004 ASCRS and ESCRS Published by Elsevier Inc.
examination before surgery, thereby excluding risk groups for binocular vision impairment. Because of the increasing popularity of refractive surgery, the surgeon may hazard himself in more dangerous fields of indication such as hyperopia, anisometropia, manifest or latent strabismus, abnormal retinal correspondence, and torticollis. In a recent review article,2 the preoperative evaluation for myopic laser in situ keratomileusis (LASIK) is based on a “complete” ophthalmologic examination that includes a medical and ophthalmologic history and careful refraction with and without cycloplegia. In addition, factors such as contact lens use, presence of corneal pathology and/or dry-eye syndrome, pupil size, corneal topography, and corneal thickness should be carefully evaluated. It is not clear whether the complete ophthalmologic examination included an orthoptic examination. 0886-3350/03/$–see front matter doi:10.1016/S0886-3350(03)00412-7
BINOCULAR VISION AND REFRACTIVE SURGERY
The aim of this paper is to stress the importance of an orthoptic evaluation before refractive surgery and to define risk groups for binocular vision impairment after refractive surgery. To avoid decentration after photorefractive keratectomy (PRK) and LASIK, it is important to detect preexisting vertical phorias. These patients have a fragile binocular vision balance that can easily be altered by changing the nodal point in both eyes. An orthoptic examination should therefore be performed with and without spectacle correction, especially in patients who have not been adapted or appear to be dissatisfied with contact lenses. Since the anisoprism effect is absent in contact lens wearers, latent phoria may become manifest.
Case Report Case 1 A healthy 36-year-old woman was referred to our department because of an unexplained complaint of intermittent vertical diplopia after uneventful LASIK in the more myopic left eye. She had postponed LASIK in the better right eye and was looking for a second opinion. She had no history of strabismus, diplopia, abnormal head position, orthoptic training, or eye surgery. The patient had not been adapted to contact lenses. The preoperative best corrected visual acuity (BCVA) was 20/20 in both eyes. The refractive error before surgery was –1.75 –0.75 ⫻ 145 in the right eye and –3.50 –1.00 ⫻ 25 in the left eye. The postoperative visual acuity in the treated left eye improved to 20/25 with –0.75 –0.25 ⫻ 50. The right eye remained dominant postoperatively. EyeSys topography showed slight superotemporal decentration of the laser-ablated zone in the left eye (Figure 1, a). Orthoptic examination showed right hyperphoria of 3.0 prism diopters (PD) in primary position, increasing at distance (5.0 PD) and at left gaze (8.0 PD). Ocular motility evaluation showed a V-pattern, underaction of the right superior oblique muscle, and a positive Bielschowsky head-tilt test. Accommodation measured with the RAF ruler was 10.0 D in the right eye and 5.0 D in the left eye. Cyclotorsion was not observed despite a fundus examination showing bilateral tilted discs and extorsion of both macula, although more pronounced in the left eye (Figure 1, c). Vertical fusion amplitude, measured with the synoptophore, was 7 degrees. The Lancaster test was suggestive of right superior oblique palsy (Figure 1, b). The patient was advised to have the right eye treated to recover the preoperative binocular balance. It was recommended that the surgeon pay special attention to the right hyperphoria, which might induce inferotemporal decentration of the excimer laser ablation. 102
Case 2 A healthy 42-year-old man was referred to our department because of complaints of unexplained visual discomfort and intermittent diplopia after uneventful simultaneous bilateral LASIK for myopia. In 1990, the patient had had strabismus surgery in both eyes for congenital right N IV palsy. The preoperative BCVA was 20/20 in both eyes. The refractive error before surgery was –5.25 diopters (D) in the right eye and –5.00 D in the left eye. The postoperative uncorrected visual acuity (UCVA) was 20/40 and 20/32, respectively, and the BCVA at distance was 20/25 and 20/20, respectively. The right eye needed additional correction of –1.00 –0.25 ⫻ 20 and the left eye, of –0.50 –0.25 ⫻ 170. The UCVA at near was 20/40 in the right eye and 20/25 in the left eye. Corneal topography showed a well-centered ablation in the right eye and a slightly decentered ablation superonasally in the left eye (Figure 2, a). Orthoptic examination showed right hyperphoria of 3.0 PD at near and 2.0 PD at distance, increasing slightly at down gaze and left gaze. The right eye was dominant. Ocular motility evaluation showed a V-pattern, underaction of the right superior oblique muscle, and a positive Bielschowsky head-tilt test. The vertical fusion amplitude was increased to 6 degrees with the synoptophore. The Lancaster test is shown in Figure 2, b. Excyclotorsion of 1 degree was measured in both eyes. Fundus examination showed more torsion of the macula in the left eye than in the right eye (Figure 2, c). Recurrent right N IV palsy was diagnosed. The patient was advised to have the right eye retreated to achieve emmetropia and restore right dominance.
Case 3 A healthy 40-year-old woman was referred to our department because of decreased visual acuity in the moderately amblyopic left eye, which had been treated with LASIK for hyperopia. She reported a history of intermittent esotropia since childhood. The postoperative BCVA was 20/20 in the right eye with ⫹1.50 and 20/63 in the left eye with ⫹1.25 –3.50 ⫻ 150. Corneal topography showed an inferotemporally decentered ablation zone in the left eye (Figure 3, a). With the prism cover test, performed with glasses, esotropia of 18.0 PD was found at near vision and of 10.0 PD at distance vision. Without glasses, the esodeviation increased to 25.0 PD at near and 18.0 PD at distance. Partial accommodative esotropia was diagnosed (Figure 3, b). Ocular motility showed a V-pattern with overaction of the left inferior oblique muscle. The objective angle of strabismus, measured with the synoptophore, was ⫹7 degrees and the subjective angle was –1 degree. These results were suggestive of an abnormal retinal correspondence with pe-
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Figure 1. (Godts) a: Postoperative corneal topography of both eyes in Case 1.The left eye had LASIK for myopia. The ablation zone is decentered superotemporally. b: Postoperative Lancaster test. c: A tilted disc and excyclotorsion of the macula are present in both eyes.
ripheral fusion on the subjective angle of strabismus. Suppression of the left eye was present in free space. Accommodation, measured with the RAF test, was 5.0 D in both eyes, a low but still acceptable value considering the patient’s age. Fundus examination showed extreme extorsion of both maculae (Figure 3, c). The Bielschowsky head-tilt test was negative. The patient was advised to have the left eye reshaped to correct for the decentered optical zone.
Case 4 A healthy 39-year-old man was referred to our department because of manifest diplopia after uneventful LASIK in the myopic right eye. The patient had been anisometropic for many years. The left eye was almost emmetropic. He presented significant exotropia in the myopic right eye. The preoperative BCVA was 20/25 in the right eye with –9.50 –0.75 ⫻ 80 and 20/20 in the left eye with –0.50 –0.75 ⫻ 15. The spectacle correction was –5.25 D in the right eye and –0.25 ⫻ 85 in the left eye, although this correction was seldom used. He had not been advised to try contact lenses before having refractive surgery. The postoperative UCVA was 20/25 in the right eye and 20/40 in the left eye. Corneal topography showed a decentered ablation inferonasally in the right eye (Figure 4). Orthoptic examination
revealed right exotropia of 50.0 PD and right hypertropia of 14.0 PD for distance and near vision, respectively. Ocular motility evaluation showed overaction of the right inferior oblique muscle, a V-pattern, and absence of convergence. The Bielschowsky head-tilt test was negative. Neither fusion nor suppression could be demonstrated. Fundus examination showed a peripapillary staphyloma in the myopic right eye and was without particularity in the left eye. The patient was advised to have supplementary ocular muscle surgery to correct the strabismus.
Case 5 A healthy 25-year-old male student was referred to our department because of difficulty reading for a prolonged period and glare at night after multiple refractive surgery procedures for myopia. Initially, he had bilateral PRK to correct –6.50 D in the right eye and –7.00 D in the left eye. One year later, the right eye was retreated with LASIK for residual myopia and after another year, the left eye was retreated for residual myopia using PRK and mitomycin. The patient’s ophthalmologic history was negative for strabismus, abnormal head posture, and orthoptic exercises. The postoperative BCVA was 20/25 in the right eye with –0.75 D and 20/32 in the left eye with ⫹1.50 D. The
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Figure 2. (Godts) a: Postoperative corneal topography of both eyes in Case 2. Bilateral LASIK for myopia was performed. The ablation zone is slightly decentered superonasally. b: Postoperative Lancaster test. c: Excyclotorsion of the macula is present in the left eye.
UCVA at near was 20/20 in the right eye and 20/100 in the left eye, which improved to 20/50 with ⫹2.00 D. Corneal topography showed a well-centered but extremely small optical zone in the right eye and a slightly inferiorly decentered ablation zone in the left eye. The optical power of both corneas differed by 2.0 D over the ablated zone. The dioptric power of the cornea in the area of the ablated zone varied from 43.5 D in the periphery to 36.6 D and 38.8 D in the central optical zone of the left eye and the right eye, respectively (Figure 5, a). The diameter of the optical zone was not larger than 2.5 to 3.0 mm. Orthoptic examination showed esophoria of 16.0 PD at near vision and 4.0 PD at distance vision with normal ocular motility (Figure 5, b). Horizontal fusion was in the normal range, although stereopsis, measured with the Titmus stereo test, was poor (200 seconds of arc). Accommodation was 5.0 D in both eyes, a poor result considering the young age of the patient. These measurements explained the patient’s difficulty in sustained reading conditions. Fundus examination was without particularity in both eyes. The patient was fitted with a contact lens in the left eye to correct the hyperopia. Although this resulted in subjective improvement in the binocular vision, the patient did not tolerate the contact lens well so it was abandoned. The patient was advised to have the optical zone in the left eye enlarged by first making him myopic using DTK and then correcting 104
the myopia. This approach was rejected by the patient. Therefore, a conservative approach consisting of spectacle correction with additional prismatic correction to support convergence at reading distance was proposed.
Discussion Few reports of binocular vision impairment and diplopia after refractive surgery have been published. Marmer3 reports 1 patient with a history of strabismus surgery who developed esotropia between a 2-step radial keratotomy (RK) procedure. One case presenting diplopia due to decompensated exotropia 9 months after unilateral PRK is described by Mandava et al.4 Chaduteau and Kohane5 report a case of Duane retraction syndrome, diagnosed after bilateral RK and PRK, and Schuler and coauthors6 describe a patient with vertical and torsional diplopia caused by decompensated congenital superior oblique palsy immediately after bilateral LASIK aiming at monovision. Holland and coauthors7 report persisting diplopia after bilateral LASIK in a patient with high anisometropia and amblyopia. Finally, Yap and Kowal8 describe a patient who presented exo-
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Figure 3. (Godts) a: Postoperative corneal topography of both eyes in Case 3. The left eye had LASIK for hyperopia. The ablation zone is decentered inferotemporally. b: Postoperative Lancaster test in both eyes. c: Excyclotorsion of the macula is present in both eyes.
phoria preoperatively and developed vertical diplopia after LASIK surgery that was decentered. In this paper, we emphasize the importance of a detailed anamnestic and orthoptic examination before refractive surgery to prevent decentration of the ablation due to preexisting abnormal patterns of fixation. Since all cases involved patients looking for a second opinion, very little is known about the preoperative orthoptic situation. The postoperative examinations, however, were sufficient for us to understand most of the patients’ complaints. In addition, we tried to explain the complaints, focusing on some basic principles of optics and binocular vision. The first principle we want to emphasize concerns the influence of the prismatic effect of spectacles on binocular vision by applying the following formula9: Pprism (PD) ⫽ 100 tan
冦 40c ⫺ 冪冢 40c 冣
2
⫺1
冧
where c is the spectacle correction in diopters, assuming the index of refraction of the spectacles is 1.5.
The spectacle vertical prismatic effect, expressed in prism diopters (PD ⫽ ⌬), was calculated before and after refractive surgery in all cases (Table 1). The prismatic effect equals zero in emmetropic patients or patients with equal ametropia in both eyes but will be substantial in anisometropic patients. This is called the anisoprism effect.9 In patients with anisometropia, muscular effort is needed to maintain binocular single vision and compensate for the anisoprism effect of the spectacle correction. This leads to new muscular effort repartition with overaction on 1 side and compensatory inhibition on the contralateral side (Haring effect). In addition to anisometropia, some patients have vertical or horizontal compensatory phoria. If this muscular balance is suddenly disturbed, eg, by suppression of the anisometropia or induction of inverse anisometropia, the heterophoria will decompensate, leading to a serious disturbance in binocular fusion, even diplopia. Some patients may develop alterations in their binocular vision fusion when they are adapted with contact lenses. Case 1 illustrates the vertical anisoprism influence of spectacles on the patient’s binocular vision. Preopera-
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Figure 4. (Godts) a: Preoperative and postoperative corneal topography of the right eye in Case 4, which had LASIK for myopia. The ablation zone is decentered inferonasally. b: Postoperative Lancaster test in both eyes.
tively, this patient presented an anisometropia of 1.75 D, inducing a vertical anisoprism of 2.2⌬ (Table 1). She also presented right hyperphoria of 3.0 PD. After excimer laser surgery in the more myopic left eye, anisometropia was induced in the opposite direction. The total postoperative change in prismatic vertical balance between the right and left eyes was as high as 4.06⌬. As a result, the preoperative latent hyperphoria became manifest postoperatively. This situation was also seen in Case 4, although at a more extreme level. This patient had hypertropia of 14.0 PD corresponding to 12.4⌬, as calculated in Table 1. Besides extreme hypertropia, the patient presented extreme exotropia of 50.0 PD in primary position. The question of which correction should have been taken care of initially, refractive or strabismic, can be raised. We will not discuss this since it is outside the scope of this paper. Fusion was absent in this patient, as expected in a case of undercorrected anisometropia.10,11 Dominance is the second principle in binocular vision that should be carefully evaluated preoperatively. Fixed dominance allows less compensatory mechanisms than alternate dominance. In Case 1, the right eye had absolute dominance. Moreover, this dominant eye became undercorrected postoperatively to achieve monovision. Only patients with normal binocular vision and their dominant eye corrected optimally for distance12,13 should be considered for monovision. Undercorrection of the dominant eye also occurred in Cases 2, 4, and 5. 106
Refractive surgery in patients with a fragile balance in binocular vision is possible if all parameters are well known in advance. Previous strabismus was positive in Cases 2 and 3. The patient in Case 2 had a well-known history of congenital right N IV palsy. The right eye was dominant but became undercorrected postoperatively, which resulted in a recurrence of the right N IV palsy, confirmed by the Lancaster test (Figure 2, b). Fixation of the right eye caused a small deviation, downward and inward, in the left eye. This deviation caused a slight decentration of the excimer laser superonasally, as shown in Figure 2, a. Decentration of the ablation zone is not a hazard but can often be explained by the preoperative imbalance in binocular vision. Decentration of the ablation zone was also found in Cases 1, 3, and 4, ie, in 4 of the 5 cases described. Decentration in Cases 1 and 2 was caused by the presence of preoperative hyperphoria of the contralateral dominant eye, causing a decentration superiorly (Figures 1, a, and 2, a) in the nondominant eye. In addition, in Case 1, both eyes presented a tilted disc and macular excyclotorsion (Figure 1, c), which should alert the surgeon to postoperative problems even when no binocular vision problems are observed. The Lancaster test (Figure 1, b) measured an 8.0 PD deviation in the vertical axis. We propose the relationship between the decentration (H) and the PD deviation (P) of the eye, based on the angular deviation of the visual versus the optical axis,1 as illustrated in Figure 6.
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Figure 5. (Godts) a: Postoperative corneal topography of both eyes in Case 5 after LASIK for myopia. The ablation zone is not decentered, but the zones are extremely small. b: Postoperative Lancaster test in both eyes. c: Fundoscopy of the right eye.
P ≈ 100
H L
where H is the decentering height and L is assumed to be nearly constant and equal to 5.0 mm,1 which is the classic nodal point with a thinner cornea. L is the distance from the nodal point to the cornea. Table 2 is the numerical application of this formula. According to Table 2, these 8.0 PD correspond to a decentration of 0.25 mm. In Figure 1, b, one can see that the decentration of the ablation zone is about 0.25 mm in the vertical axis. As mentioned above, this postoperative decentration in the ablation zone is not a problem. In Case 3, the patient presented an inferotemporal decentration in the left eye. Esotropia of 18.0 PD was found as well as overaction of the left inferior oblique muscle. This means the left eye was oriented superonasally when the laser procedure was performed, causing external and inferior decentration of the ablation (Figure
3, a). On the Lancaster test (Figure 3, b), 16.0 PD were observed in the horizontal axis, corresponding to the patient’s dominant axis of motility deviation. Additionally, because of the anisometropia, the patient compensated with vertical anisoprism of 2.49 D. The corneal topography in Figure 3, a, shows temporal decentration of 0.5 to 1.0 mm as well as a small downward decentration of about 0.1 mm. The preexisting strabismus, mild amblyopia, and extreme extorsion of both macula should have alerted the refractive surgeon to possible postoperative binocular problems. Case 4 is another example of a risk-group patient. The patient presented significant exotropia and hypertropia in the right eye; ie, during treatment, this eye was oriented temporally and upward, resulting in inferonasal decentration of the ablation, as seen in Figure 4, a. Case 5 is slightly different from the other cases in that the optical zone was too small. The left nondominant eye became hyperopic postoperatively, and the
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Table 1. Vertical anisoprism before and after excimer laser expressed in PD. Preoperative
Postoperative
RE
LE
Balance
RE
LE
Balance
Induced Change in RE–LE Balance
1 SE (D)
⫺2.25
⫺4.00
⫹1.75
⫺2.25
⫺0.75
⫺1.50
⫺3.25
PD (⌬)
⫺2.80
⫺5.00
⫹2.20
⫺2.80
⫺0.94
⫺1.86
⫺4.06
2 SE (D)
⫺5.25
⫺5.00
⫺0.25
⫺1.00
⫺0.50
⫺0.50
⫺0.25
PD (⌬)
⫺6.55
⫺6.25
⫺0.30
⫺1.24
⫺0.62
⫺0.62
⫺0.32
Case
3 SE (D)
UK
UK
UK
⫺1.50
⫺0.50
⫹2.00
2.00
PD (⌬)
UK
UK
UK
⫺1.87
⫺0.62
⫹2.49
2.49
4 SE (D)
⫺10.00
⫺0.75
⫺9.25
0.00
⫺0.75
⫺0.75
10.00
PD (⌬)
⫺12.40
⫺0.94
⫺11.46
0.00
⫺0.94
⫺0.94
12.40
5 SE (D)
⫺6.50
⫺7.00
⫺0.50
⫺0.75
⫹1.50
⫺2.25
⫺2.75
PD (⌬)
⫺8.10
⫺8.50
⫺0.40
⫺0.74
⫹1.90
⫺2.64
⫺3.04
PD ⫽ prism diopter; SE ⫽ spherical equivalent; UK ⫽ unknown
right dominant eye became slightly myopic. The acquired anisometropia resulted in unequal nodal points in both eyes, resulting in poor stereopsis. Decreased stereopsis after monovision with anisometropia has been described.10,12,13 As a consequence, the patient’s convergence capability was severely decreased. This 25-year-old’s postoperative accommodation capability corresponds to that of a 40-year-old, explaining his reading problems. Risk groups for postoperative binocular vision impairment and minimal screening techniques have been suggested by Kowal.14 Our recommendations are as follows: 1. A positive history for previous strabismological therapy should encourage the surgeon to ask for an advanced orthoptic examination. 2. Patients with anisometropia who have not been adapted with contact lenses should have an advanced orthoptic examination to rule out the presence of latent vertical strabismus. 3. Patients who feel more comfortable with spectacles
Figure 6. (Godts) Geometrical versus optical axis. 108
than with contact lenses should have an orthoptic examination to rule out fragile binocular vision balance, especially in cases of anisometropia and decentered, overcorrected, or undercorrected spectacles. 4. It is important to determine dominance since it is not wise to undercorrect a fixed dominant eye. 5. Monovision should be proposed only in patients with equal visual acuity and normal binocular vision with good fusion capacity. Correction should be performed in the dominant eye. If there is doubt, simulation with contact lenses should be tried. 6. Overcorrections should be avoided in myopic patients as this will induce a decrease in convergence. Table 2. Prism diopter deviation versus degree of vertical decentration. Decentration (mm) 0
Prism Diopter Deviation (⌬) 0.0
0.1
2
0.2
4
0.3
6
0.4
8
0.5
10
0.6
12
0.7
14
0.8
16
0.9
18
1
20
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7. Macular extorsion should be looked for as this alerts the surgeon that vertical muscle imbalance may occur postoperatively.
References 1. Corbe´ C, Menu J-P, Chaine G. Traite´ d’Optique Physiologique et Clinique. Paris, Doin, 1993; 35–39; 142– 217 2. Sugar A, Rapuano CJ, Culberston WW, et al. Laser in situ keratomileusis for myopia and astigmatism: safety and efficacy. (Ophthalmic technologies assessment) A report by the American Academy of Ophthalmology. Ophthalmology 2002; 109:175–187 3. Marmer RH. Ocular deviation induced by radial keratotomy. Ann Ophthalmol 1987; 19:451–452 4. Mandava N, Donnenfeld ED, Owens PL, et al. Ocular deviation following excimer laser photorefractive keratectomy. J Catararct Refract Surg 1996; 22:504–505 5. Chaduteau GC, Kohane B. De la ne´cessite´ du bilan orthoptique avant chirurgie re´fractive. J Fr Orthopt 1998; 30:106–108 6. Schuler E, Silverberg M, Beade P, Moadel K. Decompensated strabismus after laser in situ keratomileusis. J Cataract Refract Surg 1999; 25:1552–1553
7. Holland D, Amm M, de Decker W. Persisting diplopia after bilateral laser in situ keratomileusis. J Cataract Refract Surg 2000; 26:1555–1557 8. Yap E-Y, Kowal L. Diplopia as a complication of laser in situ keratomileusis surgery. Clin Exp Ophthalmol 2001; 29:268–271 9. Pedrotti LS, Pedrotti FL. Optics and Vision. Upper Saddle River, NJ, Prentice Hall, 1998; 157–169 10. Brooks SE, Johnson D, Fischer N. Anisometropia and binocularity. Ophthalmology 1996; 103:1139–1143 11. Bagolini B, Dickmann A, Savino G, Muci A. Evaluation orthoptique dans la chirurgie re´fractive. J Fr Orthopt 1991; 23:131–134 12. Wright KW, Guemes A, Kapadia MS, Wilson SE. Binocular function and patient satisfaction after monovision induced by myopic photorefractive keratectomy. J Cataract Refract Surg 1999; 25:177–182 13. Jain S, Arora I, Azar DT. Success of monovision in presbyopes: review of the literature and potential applications to refractive surgery. Surv Ophthalmol 1996; 40: 491–499 14. Kowal L. Refractive surgery and diplopia. Clin Exp Ophthalmol 2000; 28:344–346
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I
n technology-assessment reviews of the safety and efficacy of refractive surgery, monocular visual outcome without spectacle correction is the reference for success. Little is reported about the postoperative binocular vision balance, although some alteration in binocular vision is expected because of the change in the nodal point for far and near distance.1 It is not always clear whether the authors performed an accurate orthoptic
Accepted for publication March 19, 2003. From the Department of Ophthalmology, University Hospital Antwerp, Edegem, Belgium. Presented in part at the XXth Congress of the European Society of Cataract & and Refractive Surgeons, Nice, France, September 2002. None of the authors has a financial interest in any product mentioned. Reprint requests to Daisy Godts, University Hospital Antwerp, Department of Ophthalmology, Wilrijkstraat 10, 2650 Edegem, Belgium. 2004 ASCRS and ESCRS Published by Elsevier Inc.
examination before surgery, thereby excluding risk groups for binocular vision impairment. Because of the increasing popularity of refractive surgery, the surgeon may hazard himself in more dangerous fields of indication such as hyperopia, anisometropia, manifest or latent strabismus, abnormal retinal correspondence, and torticollis. In a recent review article,2 the preoperative evaluation for myopic laser in situ keratomileusis (LASIK) is based on a “complete” ophthalmologic examination that includes a medical and ophthalmologic history and careful refraction with and without cycloplegia. In addition, factors such as contact lens use, presence of corneal pathology and/or dry-eye syndrome, pupil size, corneal topography, and corneal thickness should be carefully evaluated. It is not clear whether the complete ophthalmologic examination included an orthoptic examination. 0886-3350/03/$–see front matter doi:10.1016/S0886-3350(03)00412-7
BINOCULAR VISION AND REFRACTIVE SURGERY
The aim of this paper is to stress the importance of an orthoptic evaluation before refractive surgery and to define risk groups for binocular vision impairment after refractive surgery. To avoid decentration after photorefractive keratectomy (PRK) and LASIK, it is important to detect preexisting vertical phorias. These patients have a fragile binocular vision balance that can easily be altered by changing the nodal point in both eyes. An orthoptic examination should therefore be performed with and without spectacle correction, especially in patients who have not been adapted or appear to be dissatisfied with contact lenses. Since the anisoprism effect is absent in contact lens wearers, latent phoria may become manifest.
Case Report Case 1 A healthy 36-year-old woman was referred to our department because of an unexplained complaint of intermittent vertical diplopia after uneventful LASIK in the more myopic left eye. She had postponed LASIK in the better right eye and was looking for a second opinion. She had no history of strabismus, diplopia, abnormal head position, orthoptic training, or eye surgery. The patient had not been adapted to contact lenses. The preoperative best corrected visual acuity (BCVA) was 20/20 in both eyes. The refractive error before surgery was –1.75 –0.75 ⫻ 145 in the right eye and –3.50 –1.00 ⫻ 25 in the left eye. The postoperative visual acuity in the treated left eye improved to 20/25 with –0.75 –0.25 ⫻ 50. The right eye remained dominant postoperatively. EyeSys topography showed slight superotemporal decentration of the laser-ablated zone in the left eye (Figure 1, a). Orthoptic examination showed right hyperphoria of 3.0 prism diopters (PD) in primary position, increasing at distance (5.0 PD) and at left gaze (8.0 PD). Ocular motility evaluation showed a V-pattern, underaction of the right superior oblique muscle, and a positive Bielschowsky head-tilt test. Accommodation measured with the RAF ruler was 10.0 D in the right eye and 5.0 D in the left eye. Cyclotorsion was not observed despite a fundus examination showing bilateral tilted discs and extorsion of both macula, although more pronounced in the left eye (Figure 1, c). Vertical fusion amplitude, measured with the synoptophore, was 7 degrees. The Lancaster test was suggestive of right superior oblique palsy (Figure 1, b). The patient was advised to have the right eye treated to recover the preoperative binocular balance. It was recommended that the surgeon pay special attention to the right hyperphoria, which might induce inferotemporal decentration of the excimer laser ablation. 102
Case 2 A healthy 42-year-old man was referred to our department because of complaints of unexplained visual discomfort and intermittent diplopia after uneventful simultaneous bilateral LASIK for myopia. In 1990, the patient had had strabismus surgery in both eyes for congenital right N IV palsy. The preoperative BCVA was 20/20 in both eyes. The refractive error before surgery was –5.25 diopters (D) in the right eye and –5.00 D in the left eye. The postoperative uncorrected visual acuity (UCVA) was 20/40 and 20/32, respectively, and the BCVA at distance was 20/25 and 20/20, respectively. The right eye needed additional correction of –1.00 –0.25 ⫻ 20 and the left eye, of –0.50 –0.25 ⫻ 170. The UCVA at near was 20/40 in the right eye and 20/25 in the left eye. Corneal topography showed a well-centered ablation in the right eye and a slightly decentered ablation superonasally in the left eye (Figure 2, a). Orthoptic examination showed right hyperphoria of 3.0 PD at near and 2.0 PD at distance, increasing slightly at down gaze and left gaze. The right eye was dominant. Ocular motility evaluation showed a V-pattern, underaction of the right superior oblique muscle, and a positive Bielschowsky head-tilt test. The vertical fusion amplitude was increased to 6 degrees with the synoptophore. The Lancaster test is shown in Figure 2, b. Excyclotorsion of 1 degree was measured in both eyes. Fundus examination showed more torsion of the macula in the left eye than in the right eye (Figure 2, c). Recurrent right N IV palsy was diagnosed. The patient was advised to have the right eye retreated to achieve emmetropia and restore right dominance.
Case 3 A healthy 40-year-old woman was referred to our department because of decreased visual acuity in the moderately amblyopic left eye, which had been treated with LASIK for hyperopia. She reported a history of intermittent esotropia since childhood. The postoperative BCVA was 20/20 in the right eye with ⫹1.50 and 20/63 in the left eye with ⫹1.25 –3.50 ⫻ 150. Corneal topography showed an inferotemporally decentered ablation zone in the left eye (Figure 3, a). With the prism cover test, performed with glasses, esotropia of 18.0 PD was found at near vision and of 10.0 PD at distance vision. Without glasses, the esodeviation increased to 25.0 PD at near and 18.0 PD at distance. Partial accommodative esotropia was diagnosed (Figure 3, b). Ocular motility showed a V-pattern with overaction of the left inferior oblique muscle. The objective angle of strabismus, measured with the synoptophore, was ⫹7 degrees and the subjective angle was –1 degree. These results were suggestive of an abnormal retinal correspondence with pe-
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Figure 1. (Godts) a: Postoperative corneal topography of both eyes in Case 1.The left eye had LASIK for myopia. The ablation zone is decentered superotemporally. b: Postoperative Lancaster test. c: A tilted disc and excyclotorsion of the macula are present in both eyes.
ripheral fusion on the subjective angle of strabismus. Suppression of the left eye was present in free space. Accommodation, measured with the RAF test, was 5.0 D in both eyes, a low but still acceptable value considering the patient’s age. Fundus examination showed extreme extorsion of both maculae (Figure 3, c). The Bielschowsky head-tilt test was negative. The patient was advised to have the left eye reshaped to correct for the decentered optical zone.
Case 4 A healthy 39-year-old man was referred to our department because of manifest diplopia after uneventful LASIK in the myopic right eye. The patient had been anisometropic for many years. The left eye was almost emmetropic. He presented significant exotropia in the myopic right eye. The preoperative BCVA was 20/25 in the right eye with –9.50 –0.75 ⫻ 80 and 20/20 in the left eye with –0.50 –0.75 ⫻ 15. The spectacle correction was –5.25 D in the right eye and –0.25 ⫻ 85 in the left eye, although this correction was seldom used. He had not been advised to try contact lenses before having refractive surgery. The postoperative UCVA was 20/25 in the right eye and 20/40 in the left eye. Corneal topography showed a decentered ablation inferonasally in the right eye (Figure 4). Orthoptic examination
revealed right exotropia of 50.0 PD and right hypertropia of 14.0 PD for distance and near vision, respectively. Ocular motility evaluation showed overaction of the right inferior oblique muscle, a V-pattern, and absence of convergence. The Bielschowsky head-tilt test was negative. Neither fusion nor suppression could be demonstrated. Fundus examination showed a peripapillary staphyloma in the myopic right eye and was without particularity in the left eye. The patient was advised to have supplementary ocular muscle surgery to correct the strabismus.
Case 5 A healthy 25-year-old male student was referred to our department because of difficulty reading for a prolonged period and glare at night after multiple refractive surgery procedures for myopia. Initially, he had bilateral PRK to correct –6.50 D in the right eye and –7.00 D in the left eye. One year later, the right eye was retreated with LASIK for residual myopia and after another year, the left eye was retreated for residual myopia using PRK and mitomycin. The patient’s ophthalmologic history was negative for strabismus, abnormal head posture, and orthoptic exercises. The postoperative BCVA was 20/25 in the right eye with –0.75 D and 20/32 in the left eye with ⫹1.50 D. The
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Figure 2. (Godts) a: Postoperative corneal topography of both eyes in Case 2. Bilateral LASIK for myopia was performed. The ablation zone is slightly decentered superonasally. b: Postoperative Lancaster test. c: Excyclotorsion of the macula is present in the left eye.
UCVA at near was 20/20 in the right eye and 20/100 in the left eye, which improved to 20/50 with ⫹2.00 D. Corneal topography showed a well-centered but extremely small optical zone in the right eye and a slightly inferiorly decentered ablation zone in the left eye. The optical power of both corneas differed by 2.0 D over the ablated zone. The dioptric power of the cornea in the area of the ablated zone varied from 43.5 D in the periphery to 36.6 D and 38.8 D in the central optical zone of the left eye and the right eye, respectively (Figure 5, a). The diameter of the optical zone was not larger than 2.5 to 3.0 mm. Orthoptic examination showed esophoria of 16.0 PD at near vision and 4.0 PD at distance vision with normal ocular motility (Figure 5, b). Horizontal fusion was in the normal range, although stereopsis, measured with the Titmus stereo test, was poor (200 seconds of arc). Accommodation was 5.0 D in both eyes, a poor result considering the young age of the patient. These measurements explained the patient’s difficulty in sustained reading conditions. Fundus examination was without particularity in both eyes. The patient was fitted with a contact lens in the left eye to correct the hyperopia. Although this resulted in subjective improvement in the binocular vision, the patient did not tolerate the contact lens well so it was abandoned. The patient was advised to have the optical zone in the left eye enlarged by first making him myopic using DTK and then correcting 104
the myopia. This approach was rejected by the patient. Therefore, a conservative approach consisting of spectacle correction with additional prismatic correction to support convergence at reading distance was proposed.
Discussion Few reports of binocular vision impairment and diplopia after refractive surgery have been published. Marmer3 reports 1 patient with a history of strabismus surgery who developed esotropia between a 2-step radial keratotomy (RK) procedure. One case presenting diplopia due to decompensated exotropia 9 months after unilateral PRK is described by Mandava et al.4 Chaduteau and Kohane5 report a case of Duane retraction syndrome, diagnosed after bilateral RK and PRK, and Schuler and coauthors6 describe a patient with vertical and torsional diplopia caused by decompensated congenital superior oblique palsy immediately after bilateral LASIK aiming at monovision. Holland and coauthors7 report persisting diplopia after bilateral LASIK in a patient with high anisometropia and amblyopia. Finally, Yap and Kowal8 describe a patient who presented exo-
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Figure 3. (Godts) a: Postoperative corneal topography of both eyes in Case 3. The left eye had LASIK for hyperopia. The ablation zone is decentered inferotemporally. b: Postoperative Lancaster test in both eyes. c: Excyclotorsion of the macula is present in both eyes.
phoria preoperatively and developed vertical diplopia after LASIK surgery that was decentered. In this paper, we emphasize the importance of a detailed anamnestic and orthoptic examination before refractive surgery to prevent decentration of the ablation due to preexisting abnormal patterns of fixation. Since all cases involved patients looking for a second opinion, very little is known about the preoperative orthoptic situation. The postoperative examinations, however, were sufficient for us to understand most of the patients’ complaints. In addition, we tried to explain the complaints, focusing on some basic principles of optics and binocular vision. The first principle we want to emphasize concerns the influence of the prismatic effect of spectacles on binocular vision by applying the following formula9: Pprism (PD) ⫽ 100 tan
冦 40c ⫺ 冪冢 40c 冣
2
⫺1
冧
where c is the spectacle correction in diopters, assuming the index of refraction of the spectacles is 1.5.
The spectacle vertical prismatic effect, expressed in prism diopters (PD ⫽ ⌬), was calculated before and after refractive surgery in all cases (Table 1). The prismatic effect equals zero in emmetropic patients or patients with equal ametropia in both eyes but will be substantial in anisometropic patients. This is called the anisoprism effect.9 In patients with anisometropia, muscular effort is needed to maintain binocular single vision and compensate for the anisoprism effect of the spectacle correction. This leads to new muscular effort repartition with overaction on 1 side and compensatory inhibition on the contralateral side (Haring effect). In addition to anisometropia, some patients have vertical or horizontal compensatory phoria. If this muscular balance is suddenly disturbed, eg, by suppression of the anisometropia or induction of inverse anisometropia, the heterophoria will decompensate, leading to a serious disturbance in binocular fusion, even diplopia. Some patients may develop alterations in their binocular vision fusion when they are adapted with contact lenses. Case 1 illustrates the vertical anisoprism influence of spectacles on the patient’s binocular vision. Preopera-
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Figure 4. (Godts) a: Preoperative and postoperative corneal topography of the right eye in Case 4, which had LASIK for myopia. The ablation zone is decentered inferonasally. b: Postoperative Lancaster test in both eyes.
tively, this patient presented an anisometropia of 1.75 D, inducing a vertical anisoprism of 2.2⌬ (Table 1). She also presented right hyperphoria of 3.0 PD. After excimer laser surgery in the more myopic left eye, anisometropia was induced in the opposite direction. The total postoperative change in prismatic vertical balance between the right and left eyes was as high as 4.06⌬. As a result, the preoperative latent hyperphoria became manifest postoperatively. This situation was also seen in Case 4, although at a more extreme level. This patient had hypertropia of 14.0 PD corresponding to 12.4⌬, as calculated in Table 1. Besides extreme hypertropia, the patient presented extreme exotropia of 50.0 PD in primary position. The question of which correction should have been taken care of initially, refractive or strabismic, can be raised. We will not discuss this since it is outside the scope of this paper. Fusion was absent in this patient, as expected in a case of undercorrected anisometropia.10,11 Dominance is the second principle in binocular vision that should be carefully evaluated preoperatively. Fixed dominance allows less compensatory mechanisms than alternate dominance. In Case 1, the right eye had absolute dominance. Moreover, this dominant eye became undercorrected postoperatively to achieve monovision. Only patients with normal binocular vision and their dominant eye corrected optimally for distance12,13 should be considered for monovision. Undercorrection of the dominant eye also occurred in Cases 2, 4, and 5. 106
Refractive surgery in patients with a fragile balance in binocular vision is possible if all parameters are well known in advance. Previous strabismus was positive in Cases 2 and 3. The patient in Case 2 had a well-known history of congenital right N IV palsy. The right eye was dominant but became undercorrected postoperatively, which resulted in a recurrence of the right N IV palsy, confirmed by the Lancaster test (Figure 2, b). Fixation of the right eye caused a small deviation, downward and inward, in the left eye. This deviation caused a slight decentration of the excimer laser superonasally, as shown in Figure 2, a. Decentration of the ablation zone is not a hazard but can often be explained by the preoperative imbalance in binocular vision. Decentration of the ablation zone was also found in Cases 1, 3, and 4, ie, in 4 of the 5 cases described. Decentration in Cases 1 and 2 was caused by the presence of preoperative hyperphoria of the contralateral dominant eye, causing a decentration superiorly (Figures 1, a, and 2, a) in the nondominant eye. In addition, in Case 1, both eyes presented a tilted disc and macular excyclotorsion (Figure 1, c), which should alert the surgeon to postoperative problems even when no binocular vision problems are observed. The Lancaster test (Figure 1, b) measured an 8.0 PD deviation in the vertical axis. We propose the relationship between the decentration (H) and the PD deviation (P) of the eye, based on the angular deviation of the visual versus the optical axis,1 as illustrated in Figure 6.
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Figure 5. (Godts) a: Postoperative corneal topography of both eyes in Case 5 after LASIK for myopia. The ablation zone is not decentered, but the zones are extremely small. b: Postoperative Lancaster test in both eyes. c: Fundoscopy of the right eye.
P ≈ 100
H L
where H is the decentering height and L is assumed to be nearly constant and equal to 5.0 mm,1 which is the classic nodal point with a thinner cornea. L is the distance from the nodal point to the cornea. Table 2 is the numerical application of this formula. According to Table 2, these 8.0 PD correspond to a decentration of 0.25 mm. In Figure 1, b, one can see that the decentration of the ablation zone is about 0.25 mm in the vertical axis. As mentioned above, this postoperative decentration in the ablation zone is not a problem. In Case 3, the patient presented an inferotemporal decentration in the left eye. Esotropia of 18.0 PD was found as well as overaction of the left inferior oblique muscle. This means the left eye was oriented superonasally when the laser procedure was performed, causing external and inferior decentration of the ablation (Figure
3, a). On the Lancaster test (Figure 3, b), 16.0 PD were observed in the horizontal axis, corresponding to the patient’s dominant axis of motility deviation. Additionally, because of the anisometropia, the patient compensated with vertical anisoprism of 2.49 D. The corneal topography in Figure 3, a, shows temporal decentration of 0.5 to 1.0 mm as well as a small downward decentration of about 0.1 mm. The preexisting strabismus, mild amblyopia, and extreme extorsion of both macula should have alerted the refractive surgeon to possible postoperative binocular problems. Case 4 is another example of a risk-group patient. The patient presented significant exotropia and hypertropia in the right eye; ie, during treatment, this eye was oriented temporally and upward, resulting in inferonasal decentration of the ablation, as seen in Figure 4, a. Case 5 is slightly different from the other cases in that the optical zone was too small. The left nondominant eye became hyperopic postoperatively, and the
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Table 1. Vertical anisoprism before and after excimer laser expressed in PD. Preoperative
Postoperative
RE
LE
Balance
RE
LE
Balance
Induced Change in RE–LE Balance
1 SE (D)
⫺2.25
⫺4.00
⫹1.75
⫺2.25
⫺0.75
⫺1.50
⫺3.25
PD (⌬)
⫺2.80
⫺5.00
⫹2.20
⫺2.80
⫺0.94
⫺1.86
⫺4.06
2 SE (D)
⫺5.25
⫺5.00
⫺0.25
⫺1.00
⫺0.50
⫺0.50
⫺0.25
PD (⌬)
⫺6.55
⫺6.25
⫺0.30
⫺1.24
⫺0.62
⫺0.62
⫺0.32
Case
3 SE (D)
UK
UK
UK
⫺1.50
⫺0.50
⫹2.00
2.00
PD (⌬)
UK
UK
UK
⫺1.87
⫺0.62
⫹2.49
2.49
4 SE (D)
⫺10.00
⫺0.75
⫺9.25
0.00
⫺0.75
⫺0.75
10.00
PD (⌬)
⫺12.40
⫺0.94
⫺11.46
0.00
⫺0.94
⫺0.94
12.40
5 SE (D)
⫺6.50
⫺7.00
⫺0.50
⫺0.75
⫹1.50
⫺2.25
⫺2.75
PD (⌬)
⫺8.10
⫺8.50
⫺0.40
⫺0.74
⫹1.90
⫺2.64
⫺3.04
PD ⫽ prism diopter; SE ⫽ spherical equivalent; UK ⫽ unknown
right dominant eye became slightly myopic. The acquired anisometropia resulted in unequal nodal points in both eyes, resulting in poor stereopsis. Decreased stereopsis after monovision with anisometropia has been described.10,12,13 As a consequence, the patient’s convergence capability was severely decreased. This 25-year-old’s postoperative accommodation capability corresponds to that of a 40-year-old, explaining his reading problems. Risk groups for postoperative binocular vision impairment and minimal screening techniques have been suggested by Kowal.14 Our recommendations are as follows: 1. A positive history for previous strabismological therapy should encourage the surgeon to ask for an advanced orthoptic examination. 2. Patients with anisometropia who have not been adapted with contact lenses should have an advanced orthoptic examination to rule out the presence of latent vertical strabismus. 3. Patients who feel more comfortable with spectacles
Figure 6. (Godts) Geometrical versus optical axis. 108
than with contact lenses should have an orthoptic examination to rule out fragile binocular vision balance, especially in cases of anisometropia and decentered, overcorrected, or undercorrected spectacles. 4. It is important to determine dominance since it is not wise to undercorrect a fixed dominant eye. 5. Monovision should be proposed only in patients with equal visual acuity and normal binocular vision with good fusion capacity. Correction should be performed in the dominant eye. If there is doubt, simulation with contact lenses should be tried. 6. Overcorrections should be avoided in myopic patients as this will induce a decrease in convergence. Table 2. Prism diopter deviation versus degree of vertical decentration. Decentration (mm) 0
Prism Diopter Deviation (⌬) 0.0
0.1
2
0.2
4
0.3
6
0.4
8
0.5
10
0.6
12
0.7
14
0.8
16
0.9
18
1
20
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7. Macular extorsion should be looked for as this alerts the surgeon that vertical muscle imbalance may occur postoperatively.
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7. Holland D, Amm M, de Decker W. Persisting diplopia after bilateral laser in situ keratomileusis. J Cataract Refract Surg 2000; 26:1555–1557 8. Yap E-Y, Kowal L. Diplopia as a complication of laser in situ keratomileusis surgery. Clin Exp Ophthalmol 2001; 29:268–271 9. Pedrotti LS, Pedrotti FL. Optics and Vision. Upper Saddle River, NJ, Prentice Hall, 1998; 157–169 10. Brooks SE, Johnson D, Fischer N. Anisometropia and binocularity. Ophthalmology 1996; 103:1139–1143 11. Bagolini B, Dickmann A, Savino G, Muci A. Evaluation orthoptique dans la chirurgie re´fractive. J Fr Orthopt 1991; 23:131–134 12. Wright KW, Guemes A, Kapadia MS, Wilson SE. Binocular function and patient satisfaction after monovision induced by myopic photorefractive keratectomy. J Cataract Refract Surg 1999; 25:177–182 13. Jain S, Arora I, Azar DT. Success of monovision in presbyopes: review of the literature and potential applications to refractive surgery. Surv Ophthalmol 1996; 40: 491–499 14. Kowal L. Refractive surgery and diplopia. Clin Exp Ophthalmol 2000; 28:344–346
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