Stereopsis and visual acuity: Bilateral trifocal versus blended extended depth of focus and diffractive bifocal intraocular lenses

Stereopsis Following Implantation of Presbyopia-Correcting Intraocular Lenses: A Narrative Review

Recent advancements in cataract surgery have broadened its scope from mere vision restoration to include correction of refractive errors and presbyopia. This evolution has introduced multifocal and extended depth-of-focus (EDOF) intraocular lenses (IOLs), allowing enhanced vision across multiple distances. However, the influence of these advanced IOLs on stereopsis remains controversial. Factors influencing stereopsis after surgery include visual acuity, interocular differences, residual astigmatism, and the type of IOL, etc. Binocular vision integration and neuroadaptation further affect stereopsis, especially in cases of presbyopia-correcting IOLs. It is widely acknowledged that bilateral implantation of presbyopia-correcting IOLs yield superior stereopsis compared to unilateral implantation. However, there remains no consensus on whether binocular implantation of multifocal or monofocal IOLs provides superior stereopsis. Most studies suggest no significant difference in stereopsis between these two types of implants. Among different types of multifocal IOLs, refractive multifocal IOLs may offer better stereopsis than diffractive multifocal IOLs when implanted bilaterally. Emerging EDOF and hybrid multifocal-EDOF IOLs also demonstrate promising postoperative stereopsis. Additionally, a mix-and-match strategy with different types of IOLs implanted in each eye may result in interocular differences in visual acuity at certain distances, potentially affecting stereopsis. Nevertheless, with appropriate selection, most patients can achieve satisfactory postoperative stereopsis. This review synthesizes current literature on the effects of presbyopia-correcting IOLs on postoperative stereopsis recovery following cataract surgery. Studies on stereopsis outcomes with different IOLs have yielded mixed results, urging further investigation for optimized surgical strategies and patient outcomes.

Comparison of visual outcomes of bilateral dual-technology diffractive intraocular lens vs blended enhanced monofocal with dual-technology intraocular lens

PURPOSE

To compare clinical outcomes after implantation of TECNIS Synergy (ZFR00V) intraocular lenses (IOLs) in both eyes and implantation of the TECNIS Synergy and TECNIS Eyhance (ICB00) combination in patients undergoing cataract surgery.

SETTING

Department of Cataract, Hospital Oftalmológico de Brasilia (HOB), Brasília, Brazil.

DESIGN

Prospective, interventional, randomized, parallel-group study.

METHODS

Patients were categorized into 2 groups: Group 1: ZFR00V IOL was implanted in both eyes. Group 2: An ICB00 IOL was implanted in the dominant eye, and a ZFR00V IOL was implanted in the nondominant eye.

RESULTS

Visual acuity was similar between the 2 groups (95% CI <0.1 logMAR). A superior visual acuity of ≥ 20/25 (at -2.00 to -2.50 diopters [D]) was achieved in Group 1 (bilateral ZFR00V) than in Group 2 (combination of ZFR00V/ICB00). The binocular defocus curve demonstrated better visual acuity at 40 cm (-2.00 D) and 50 cm (-2.50 D) in Group 1 than in Group 2 ( P < .05). Similar contrast sensitivity values were observed between the 2 groups. Patients in Group 1 reported higher satisfaction (completely satisfied) than those in Group 2 ( P < .05). However, halos and glare were more pronounced in Group 1 than in Group 2 ( P < .05).

CONCLUSIONS

Both presbyopia-correcting IOL combinations showed similar binocular visual acuity results. Group 1 demonstrated enhanced visual acuity in the defocus curve at 40 cm (-2.00 D) and 50 cm (-2.50 D). Comparable contrast sensitivity outcomes were observed in both groups. Patients were more completely satisfied in Group 1 than in Group 2, despite the higher frequency of postoperative nighttime halos and glare.

The influence of simulated visual impairment on distance stereopsis

The intricate interrelationships between visual acuity (VA) and stereopsis depend on an array of factors, incorporating the nature of vision impairment, its manifestation (monocular versus binocular), and the classification of stereopsis test symbols used. The objectives of this study were to methodically dissect these multifaceted interactions by simulating a diverse range of vision loss conditions. Thirty medical students with normal vision were subjected to simulated vision loss through opacification and blurring methodologies. Stereopsis was assessed at a distance using both contour-based and random-dot-based symbols under equal binocular and varied monocular VA conditions. In this study, opacification consistently affected stereopsis more than blurring at equivalent VA reductions. However, this difference was absent in contour-based symbols under binocular vision impairment conditions. Significant differences in stereopsis emerged between monocular and binocular vision within the opacification contour-based groups. These differences were less evident in the opacification and blurring groups using random-dot-based patterns. In terms of symbols, the contour-based test demonstrated superior results to the random-dot-based test, particularly under decreased VA. In sum, the method of VA reduction and the choice of stereogram significantly impact distance stereopsis outcomes. This understanding can guide clinical assessments of stereopsis in individuals with varying visual impairments.

Effect of changing mesopic and photopic light conditions on visual functions

AIM

To determine the effects of change in light conditions on refractive error and visual functions including visual acuity, stereopsis and contrast sensitivity.

METHODS

This cross-sectional study was conducted in the optometry clinic of the Shahid Beheshti School of Rehabilitation on 48 students in 2021-2022. All of them had eye health and normal visual function and could have refractive errors or not. Light intensity of 4 lx was considered equivalent to photopic light condition and light intensity of 1 lx was considered to be equivalent to mesopic light condition. The amount of refractive error was checked by auto refractometer and its changes in mesopic light condition were subjectively measured. Also, visual acuity, stereopsis and contrast sensitivity (in five spatial frequencies of 1.5, 3, 6, 12, and 18 cycles per degree), were measured first in photopic light condition and then in mesopic light condition, by Snellen control vision chart, stereo butterfly test and the M&S technology monitor test respectively.

RESULTS

In the 48 student subjects with an average age of 22.69±3.56y, mean of refractive error as sphere equivalent, visual acuity and stereopsis were -1.25±1.74 diopters, 0 logMAR, 44.37±13.03 seconds of arc, respectively in photopic light condition while in mesopic light was equal to -1.56±1.75 diopters, 0.12±0.09 logMAR and 50.62±33.35 seconds of arc, respectively. The mean of contrast sensitivity measured at spatial frequencies of 1.5, 3, 6, 12, and 18 cycles per degree in photopic condition was equal to 2.38±0.04, 2.37±0.07, 2.04±0.21, 1.27±0.32, 0.82±0.27 logarithm of contrast sensitivity, respectively and in mesopic lighting condition was equal to 2.34±0.12, 2.30±0.16, 1.84±0.28, 1.02±0.28, 0.63±0.24 logarithm of contrast sensitivity, respectively. Statistical analysis showed a significant difference between the two lighting conditions in all evaluated variables [refractive error (P<0.001), visual acuity (P<0.001), stereopsis (P=0.008) and contrast sensitivity (P<0.001)].

CONCLUSION

The refractive error of the student subjects in mesopic light condition change towards myopia, and its amount is clinically significant. Also, the examination and comparison of the factors of visual acuity, stereopsis and contrast sensitivity in these two lighting conditions show that the decrease in brightness level to the mesopic level causes a decrease in the aforementioned visual functions.