Purpose
To evaluate binocular visual acuity (VA), contrast sensitivity, and stereopsis in myopic patients after laser in situ keratomileusis (LASIK)-induced monovision.
Design
Prospective, observational study.
Methods
We performed a prospective study of 37 consecutive patients older than 45 years who underwent bilateral myopic LASIK with planned monovision. At the 6-month postoperative visit, we evaluated distance and near binocular visual acuity, contrast sensitivity, and stereopsis. Binocular tests were done without spectacles (in monovision condition) and compared with the results obtained by repeating the same binocular tests with the same patients (serving as a control group) after spectacle correction of the residual myopic defect in the nondominant eye for distance tests (reverting monovision) and after spectacle correction of the presbyopia bilaterally for near tests (near best spectacle-corrected VA).
Results
By inducing a mean residual spherical equivalent defect of -0.97 diopter in the nondominant eye, the patients achieved a mean near binocular uncorrected visual acuity (UCVA) of 0.74, a mean reading test binocular UCVA of 0.88 using an acceptable spontaneous reading distance (48 cm), and a mean distance binocular UCVA of 1.08. A slight decrease in contrast sensitivity and stereopsis was observed in monovision compared to full distance correction.
Conclusions
Monovision is a valid option for myopic patients with presbyopia who are considering LASIK. Good distance and near UCVAs can be obtained with this procedure.
Monovision, a method of presbyopic correction whereby 1 eye is corrected for distance vision and the fellow eye for near vision, has been used successfully for years by contact lens (CL) wearers. More recently, surgeons have been performing this procedure on candidates for refractive surgery. Monovision relies on the principle of interocular blur suppression, ie, the ability to ignore the blurred image of 1 eye under binocular conditions, because 1 eye is focused for distance and generally the nondominant eye is focused for near.
A review of the contact lens literature shows that the success rate for CL-induced monovision varies from 50% to 76% and increases to 86% when patients who are CL intolerant are excluded. However, few reports have been published on refractive surgery–induced monovision, which seems to obtain a patient satisfaction rate ranging from 72% to 96%. Patient selection and information are critical to the success of monovision, and an accurate preoperative examination is needed to prevent postoperative disruptions in binocular vision.
Several studies have reported a slight reduction in binocular visual acuity (VA) and stereoacuity in patients with CL-induced monovision. Nevertheless, the limitations and disadvantages of the visual quality in patients with surgically induced monovision remain largely unknown. Only 1 study has evaluated the VA, contrast sensitivity, stereopsis, and convergence fusion amplitude in a small sample of patients with photorefractive keratectomy (PRK)-induced monovision. We are unaware of previous reports of the visual outcomes of monovision induced by laser in situ keratomileusis (LASIK) in myopic patients with presbyopia.
Methods
This was a prospective, observational study. The characteristics of the surgical procedure and the study were fully explained to all patients, and all signed the appropriate informed consent form before entering the study. In order to be included in the study, patients had to be older than 45 years and have less than 6 diopters (D) of myopia, and less than 3 D of astigmatism. We excluded patients with unstable refraction, previous ocular surgery (refractive or other surgical procedures), and suspicion of keratoconus, ocular diseases, and systemic diseases, such as diabetes mellitus or connective tissue disorders, possibly interfering with the wound-healing process. We also excluded patients with a history of amblyopia or any ocular motility disorder.
All study patients underwent the same full preoperative examination, which included general and ophthalmic anamnesis; measurement of distance uncorrected visual acuity (UCVA); best spectacle-corrected visual acuity (BSCVA) including manifest and cycloplegic refractions, corneal keratometry, and topography (CSO; Compagnia Instrumenti Oftalmici, Florence, Italy); ultrasound corneal pachymetry (DHG 5100 contact pachymeter; DGH Technology Inc, Exton, Pennsylvania, USA);mesopic infrared pupillometry (Colvard pupillometer; Oasis Medical Inc, Glendora, California, USA); slit-lamp biomicroscopy; tonometry (CT-80; Topcon, Tokyo, Japan); and funduscopy.
Ocular dominance was determined by the “finger pointing” test, whereby the patient, using binocular vision, points to an object using the index finger of his or her dominant hand. The eye in alignment with the object and the finger was considered to be the dominant eye.
The dominant eye was targeted for distance vision and the nondominant eye for near vision. The target refraction for the nondominant eye varied with age: -1.0 D in patients 46 to 50 years of age, -1.25 D in patients 51 to 55 years, and -1.50 D for patients older than 55 years. Full correction was attempted for the dominant eye in all cases. No preoperative monovision contact lens trial was performed in any patient.
The same surgeon (M.A.T.) performed all LASIK procedures using the Moria M2 microkeratome (Moria SA, Antony, France) and the Technolas 217 (Bausch & Lomb, Rochester, New York, USA) excimer laser using an optical zone larger than the mesopic pupil size. All treatments were conventional (nonwavefront technology).
Postoperative examinations were scheduled for 1 day, 1 week, and 1, 3, and 6 months after surgery. At each examination, 2 optometrists measured the UCVA. At the 3- and 6-month examinations, the optometrists refracted the patients and measured the UCVA and BSCVA of each eye. Laser enhancements to achieve the refractive correction desired were performed, if necessary, 3 months after the original procedure.
At the 6-month postoperative visit, all patients underwent the same full examination that included distance binocular UCVA using the New ETDRS (logarithm VA chart 2000 for testing at 3 meters; Precision Vision Inc., La Salle, Illinois, USA), near binocular UCVA using the New ETDRS (for testing at 40 cm, Precision Vision Inc.), near binocular UCVA using a reading test chart (Precision Vision Inc.) and the spontaneous reading distance. The contrast sensitivity was measured at 3, 6, 12, and 18 cycles per degree (cpd) using the CSV-1000 ETDRS chart (Vector Vision Inc, Greenville, Ohio, USA) for distance vision and the 10% low-contrast-sensitivity ETDRS test (La Salle, IL) for near vision. Macular sensory fusion was measured using the Worth 4-dot test at 3 meters. To evaluate distance stereopsis, a polarized test composed of 2 lines was shown to the patients, who wore dissociative polarized spectacles that cause each line to be seen with a different eye. The subject described if 1 line appeared sharper than the other, in which case the patient had distance stereopsis. To evaluate near suppression, a polarized test composed of 2 concentric circles and 2 lines of letters (Acuity Suppression Rx Vectogram, Stereo Optical Company Inc, Chicago, Illinois, USA) was shown to the patients, who wore polarized spectacles; the patients passed the test if they saw a circle and a line of letters sharper than the others. Finally, near stereopsis was evaluated with the TNO test (Stereo Optical Company Inc).
All binocular tests were performed without spectacles (in monovision) and compared with the results obtained by repeating the same binocular tests with the same patients (serving as a control group) after correcting the residual myopia in the nondominant eye, with spectacles, for distance tests (reverting monovision to distance BSCVA), and after correcting the presbyopia in both eyes with spectacles for near tests (near BSCVA). Two observers performed all tests in the same room, and under the same illumination.
Statistical analysis was performed using Statview+Graphics software (Abacus Concept Inc, Cupertino, California, USA) using the 2-tailed unpaired Student t test. P < .05 was considered significant. Data are expressed as the mean ± standard deviation (SD). Although the minimum angle of resolution (logMAR) values of all VA tests were used for the statistical analysis, we converted them to the more conventional Snellen quotation (decimal scale) throughout the text.
Results
We performed a prospective study of 37 consecutive patients with presbyopia (22 women, 15 men) with monovision resulting from myopic bilateral LASIK performed 6 months previously. The average patient age was 54.1 ± 4.0 years (range, 47-64). The right eye was the dominant eye in 32 patients (86.5%). The mean preoperative spherical defect was -3.14 ± 0.6 D (range, -0.75 to -5.75 D) and the mean preoperative cylindrical defect was -0.98 ± 0.3 D (range, -0.00 to -2.50 D).
At the 6-month postoperative visit, the mean distance UCVA was 0.96 ± 0.2 in the dominant eye, with a mean residual spherical equivalent (SE) defect of +0.08 ± 0.6 D. In the nondominant eye, the mean distance UCVA was 0.65 ± 0.2, with a mean residual SE defect of -0.97 ± 0.46 D (range, -0.25 to -1.50 D).
Binocular Vision
The changes in distance and near binocular visual acuity in monovision compared to full distance correction (ie, spectacle correction of the refractive defect in the nondominant eye) and bilateral full near correction are shown in Table 1 . The mean near reading test binocular UCVA was 0.88 ± 0.4 (range, 0.4-1.0) using a mean spontaneous reading distance of 48 cms (range, 40-50). The binocular distance and near UCVAs in monovision conditions are shown in Figures 1 and 2 .
| Monovision | Full Distance Correction | P Value | Full Near Correction | P Value | |
|---|---|---|---|---|---|
| Distance binocular UCVA | 1.08 ± 0.1 (range, 0.7-1.25) | 1.20 ± 0.1 (range, 0.9-1.50) | .0001 | ||
| Near binocular UCVA | 0.74 ± 0.1 (range, 0.4-1.0) | 0.47 ± 0.1 (range, 0.05-0.6) | .0001 | 1.02 ± 0.2 (range, 0.8-1.25) | .0001 |
Contrast Sensitivity
The distance binocular contrast sensitivity decreased slightly with monovision compared to no monovision (nondominant eye corrected for distance) but within normal limits for the patients’ age. This reduction in distance contrast sensitivity was only statistically significant ( P = .001) at high spatial frequencies (18 cpd). The distance binocular contrast sensitivity is shown in Figure 3 .
The mean monovision low-contrast near VA was 0.50 ± 0.1 (range, 0.15-1); that improved to a mean 0.76 ± 0.2 (range, 0.32-1.2) with full bilateral near correction ( P = .0001).
Binocular Sensorial Function
Distance binocular sensorial function and distance stereopsis in monovision compared to full distance correction are shown in Table 2 . Near suppression and near stereopsis in monovision compared to full bilateral near correction are shown in Table 3 .
| Monovision (N = 37) | Full Distance Correction (N = 37) | P Value | |
|---|---|---|---|
| Distance binocular sensorial fusion (using the Worth 4-dot test) | 30 patients (81%) passed | 37 patients (100%) passed | .01 |
| Distance stereopsis (using a polarized test) | 27 patients (73%) passed | 29 patients (78%) passed | >.05 |
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