June-July 2020

ASCRS NEWS

Eyeworld Journal Club
Review of “Comparison of visual performance and satisfaction with a bilateral emmetropic vs. a bilateral mild myopic target using a spherical monofocal intraocular lens”


by Matthew Floyd, MD, Jeremy Jones, MD, Rebecca Neustein, MD, Kenneth Price, MD, Gina Shetty, MD


From the Emory Eye Center: top, from left: Kenneth Price, MD, Jeremy Jones, MD; middle, from left: Matthew Floyd, MD, Gina Shetty, MD; bottom: Rebecca Neustein, MD
Source: Emory Eye Center

Shouldn’t plano be our target for monofocal IOL patients who want to see in the distance without eyeglasses? I asked the Emory residents to review this June JCRS study that reaches a different conclusion.

—David F. Chang, MD EyeWorld Journal
Club Editor

In the modern era of cataract surgery, surgical approaches and options for IOLs have grown exponentially. Mirroring this growth, patient expectations for postoperative vision and spectacle independence are higher than ever before. Innovative IOL designs aim to accommodate these expectations with options ranging from traditional monofocal IOLs to premium lenses, including bifocal, trifocal, multifocal, and extended depth of focus IOLs. These premium lenses have been reported to deliver better uncorrected near vision and have allowed for a higher proportion of patients to achieve spectacle independence compared to monofocal IOLs. However, they carry a greater risk of unwanted visual phenomena in contrast to typical monofocal lenses.1 Despite the increasing prevalence and versatility of premium IOLs, monofocal lenses remain the most common IOLs utilized in cataract surgery around the world.
A drawback of bilateral monofocal IOLs is the requirement for spectacle correction to optimize vision at near or distance. This can be attributed to the loss of depth of focus (DOF) that occurs with intraocular lens implantation. Patients who want to minimize the use of glasses postoperatively may consider “mini-monovision,” where the surgeon targets the dominant eye for emmetropia and the non-dominant eye for mild myopia.2 Patients with mini-monovision acquire an increased DOF at the cost of losing a degree of stereopsis. As a result, a portion of patients cannot overcome this discrepancy between postoperative focal points and require refractive correction via spectacles, contact lenses, or LASIK/PRK.3 As such, the majority of patients aim for equal refractive outcomes in both eyes.
Cataract surgeons employing monofocal IOLs typically aim for emmetropia or mild myopia. The choice between these two refractive targets is often guided by the surgeon’s assumption, within the context of the patient’s refractive history, of what will provide the most functional postoperative vision. While some patients value hyperopic uncorrected visual acuity, an era of handheld technology places a premium on intermediate and near visual acuity for daily functioning. Identifying which refractive goal—emmetropia or mild myopia—can preserve the greatest depth of focus at intermediate and near focal points, without sacrificing sharpness of distance vision, remains a critical challenge in surgical planning for patients receiving bilateral monofocal IOLs.

Study review

The study by Vinciguerra et al. is a retrospective study of 60 patients who were recruited postoperatively after phacoemulsification with monofocal IOL implantation in both eyes. This study was conducted at a single center with all surgeries being performed by a single surgeon. Once recruited, the 60 patients were divided into two groups. Group 1 included 30 patients who received bilateral monofocal IOLs with a near emmetropic target (0 to –0.30 D), and Group 2 included 30 patients who received bilateral monofocal IOLs with a mild myopic target (–0.40 to –0.75 D). Exclusion criteria were previous ocular surgery (aside from cataract surgery), ocular pathology, corneal abnormalities, and endothelial cell count less than 2,000 cells/mm.
Patients were examined 1 month after cataract surgery in the second eye. Both groups underwent near (40 cm), intermediate (66 cm; 80 cm), and distance (4 m) visual acuity testing using a Snellen chart with 100% contrast. This was performed under monocular and binocular conditions with and without correction. Defocus curve testing was performed from –4.0 D to +1.5 D in 0.5 D increments using a distance target under photopic lighting conditions. Patients in both groups completed a subjective questionnaire assessing visual satisfaction at near, intermediate, and distance targets. Spectacle independence and hours of spectacle use were also assessed.
The mean age of the emmetropic group was 71.7±8.7, and the mean age of the mildly myopic group was 69.1±8.7. The mean postoperative spherical equivalent of the emmetropic group was –0.15±0.29 D, and the mean postoperative spherical equivalent of the mildly myopic group was –0.63±0.31 D. Uncorrected intermediate visual acuity (UIVA) and uncorrected near visual acuity (UNVA) were found to be significantly superior in the mildly myopic group when compared to the emmetropic group. However, there was only minimal reduction in uncorrected distance visual acuity (UDVA) in the mildly myopic group.
In their analysis of binocular UDVA, the mildly myopic group demonstrated significantly better vision than the emmetropic group at –4.0 through –0.5 D, and the emmetropic group had significantly better vision than the mildly myopic group at +0.5 through +1.5 D. The emmetropic target group exhibited a non-significantly superior binocular UDVA at 0 diopters on the defocus curve, with the mildly myopic target group remaining very close to 20/20 (logMAR 0.03±0.06). There was no significant difference in binocular corrected distance visual acuity at any point on the defocus curve.
The results of the quality of vision questionnaire found that the mildly myopic group had significantly superior visual satisfaction at near while the mildly emmetropic group had statistically significant visual satisfaction at distance. Regarding overall visual satisfaction there was not a statistically significant difference between the groups, although there was a non-significant trend in favor of the mildly myopic group. Non-significant trends toward the mildly myopic target group were also found in responses regarding spectacle independence and hours of spectacle use.

Comments

As the first study to investigate mildly myopic (–0.40 to –0.75 D) vs. emmetropic (0 to –0.30 D) targets in bilateral monofocal IOL implantation, compelling evidence is provided for a mild myopic aim to optimize uncorrected intermediate (66 cm; 80 cm) and near visual acuity (40 cm). While the emmetropic group did exhibit a mildly superior binocular UDVA at 0 D, it was not statistically significant. The mildly myopic group did not compromise UDVA as it remained very close to 20/20 at 0 D (logMAR 0.03±0.06). This is not surprising given the focal point of a Snellen chart located 4 meters away corresponds more closely to an eye with a refraction of –0.25 D. Furthermore, the preserved distance visual acuity is supported by the mildly myopic group having an average spherical equivalent of –0.63 D±0.31 and two-thirds of the remaining DOF being located distant to the targeted focal point.
This study was limited by its retrospective nature, single surgeon/center design, and small sample size. There is lack of control for variables such as pupil size and axial length that can influence a patient’s DOF, with hyperopia and smaller pupil size favoring expanded DOF.4 Thus, the generalizability of this study is limited. Future research could consider controlling for preoperative refractive expectations when addressing subjective satisfaction. However, with the increasing prevalence of near work in modern society, it is not surprising to see a non-statistically significant trend favoring the mildly myopic target group in overall patient satisfaction and spectacle independence. As alluded by the authors, future research into these areas in combination with multifocal lenses is needed to further customize these findings into patient-specific recommendations for effective preoperative counseling and improved postoperative satisfaction.
Overall, the principles highlighted in this study provide evidence that aiming for mild myopia confers an improved spectrum of vision. Targeting mildly myopic refractive outcomes can provide statistically better vision at near and intermediate focal points without sacrificing meaningful distance vision. The practitioner can now more effectively counsel patients regarding goals for refractive outcomes when utilizing solely monofocal lenses. The values and occupation of each patient should be considered when discussing targeted refractive outcomes. Patient satisfaction will heavily depend on an individualized preoperative discussion of visual goals with every cataract surgery candidate.

References

1. Khandelwal SS, et al. Effectiveness of multifocal and monofocal intraocular lenses for cataract surgery and lens replacement: a systematic review and meta- analysis. Graefes Arch Clin Exp Ophthalmol. 2019;257:863–875.
2. Zvornicanin J, Zvornicanin E. Premium intraocular lenses: The past, present and future. J Curr Ophthalmol. 2018;30:287–296.
3. Labiris G, et al. A systematic review of pseudophakic monovision for presbyopia correction. Int J Ophthalmol. 2017;10:992–1000.
4. Wang B, Ciuffreda KJ. Depth-of-focus of the human eye: theory and clinical implications. Surv Ophthalmol. 2006;51:75–85.

Contact

Jones: jjones2@emory.edu

Review of “Comparison of visual performance and satisfaction with a bilateral emmetropic vs. a bilateral mild myopic target using a spherical monofocal intraocular lens” Review of “Comparison of visual performance and satisfaction with a bilateral emmetropic vs. a bilateral
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