This is a prospective comparative study conducted on 102 cataract patients across two surgical centers from 2023 to 2024. Because each group was treated at a single dedicated center by a single dedicated surgeon, the surgical approach variables — center, surgeon, incision site, and optic-haptic junction orientation—were completely linked and cannot be analysed independently.

All patients listed for routine cataract surgery at both centers were considered for participation. Patients aged less than 18, uncooperative, or who have any coexisting eye diseases affecting their visual function (retinal pathology, glaucoma, or other optic neuropathies with visual field defects) were excluded from the study. Patients without a history of non-phacoemulsification cataract surgery and who developed intraoperative complications were also excluded.

Patients were approached consecutively on the first postoperative day, informed about the study, and invited to participate by completing a self-administered questionnaire. Participation was voluntary, and patients were free to withdraw at any time; patients who declined were not separately recorded. Completing and returning the questionnaire constituted consent to participate, to the extraction of surgical data from medical records, and to phone follow-up on day 3 and week 4. Data were kept confidential and accessible only to the primary and co-investigators. This study was ethically approved by the Institutional Review Board (IRB), General Directorate of Health Affairs in Madinah (IRB log No. 23-067).

The 102 enrolled patients were divided into two equal groups (51 per group) according to the center at which they were admitted. One surgeon performed all surgeries at Center A (Group 1: supratemporal incision, vertical optic-haptic junction), and a second surgeon performed all surgeries at Center B (Group 2: superior incision, inferotemporal optic-haptic junction). All procedures followed the standard phacoemulsification technique.

Both groups received monofocal acrylic IOLs. Two models were used across the study population: RayOne Hydrophobic Aspheric BLF and Alcon AcrySof IQ. The distribution of IOL model across groups was not a study variable and was not recorded, so no conclusions regarding the effect of IOL model on ND incidence can be drawn from this study.

The RayOne Hydrophobic Aspheric BLF is a single-piece monofocal IOL made from hydrophobic acrylic with a blue-light-filtering chromophore. It features a 6 mm biconvex optic, a 360° enhanced square edge, an aberration-neutral posterior aspheric surface, 0° uniplanar haptic angulation, and a Cornerstone anti-vaulting haptic design. It is delivered through a 2.2 mm incision via a fully preloaded, single-use injector. Refractive index: 1.51; ABBE value: 43; UV cut-off: 385 nm.

The Alcon AcrySof IQ is a widely used single-piece monofocal IOL made from hydrophobic acrylic with a blue-light filter. It has a 6 mm optic, a square-edge design, and a posterior aspheric surface engineered to reduce spherical aberration. Refractive index: 1.55; designed for in-the-bag placement across a broad dioptric range.

The primary endpoint was ND incidence, defined as any patient-reported dark shadows or curtains in the temporal visual field, captured by the question: “Do you experience dark, temporal arcing shadows or curtains in your vision?” ND status was assessed on postoperative day 1 (in-person questionnaire), day 3 (phone call), and week 4 (phone call). A patient was classified as having ND if they reported the symptom at any of these time points.

The questionnaire comprised four sections: 1) responsible consultant details; 2) patient demographics (medical record number, age, gender); 3) medical and ocular history and ND symptom items; and 4) surgical data (incision site and location, IOL fixation site, optic-haptic junction location, and complications).

Participants’ agreement to fill the questionnaire was considered as their consent to participate, and their data was kept confidential, accessible only to the primary investigator and co-investigators. Participation was voluntary, and participants had the right to withdraw from the study at any time.

Data analysis was performed using SPSS version 27 (IBM Corp., Armonk, NY). Descriptive statistics summarised bio-demographic and surgical characteristics. Associations between categorical variables were assessed with the exact probability test. Variables examined included surgical technique versus bio-demographic characteristics (age, gender, comorbidities), surgical characteristics (operated eye, IOL fixation site, optic-haptic junction location), and ND prevalence and its associated factors. A p-value < 0.05 was considered statistically significant.

The study included 102 patients with a mean age of 63.7 ± 9.8 years in Group 1 and 63.9 ± 10.4 years in Group 2 (p = 0.924). Gender distribution differed significantly between groups (p = 0.001), with more females in Group 1 (60.8% vs. 27.5%). Diabetes mellitus was the most common comorbidity in both groups (52.9% in Group 1 and 60.8% in Group 2), followed by hypertension.

As shown in Table 1, surgery was performed on the right eye in 62.7% of Group 1 patients and 49.0% of Group 2 patients (p = 0.163). Capsular bag fixation was used in 100% of Group 1 cases and 96.1% of Group 2 cases (p = 0.153). The main incision was done superiotemporal, with the optic-haptic junction vertical in all Group 1 cases and superior main incision with the optic-haptic junction inferotemporal in all Group 2 cases.

Table 1. Participants’ surgical characteristics.

As shown in Table 2, the overall ND incidence (any report of dark shadows or curtains at day 1, day 3, or week 4) was 2.9% (3/102 patients): 3.9% (2/51) in Group 1 and 2.0% (1/51) in Group 2 (p = 0.558). Among patients with ND, 50.0% in Group 1 and 100% in Group 2 reported worsening in bright light and improvement in dim lighting (p = 0.386). By week 4, symptom improvement was reported by the single Group 2 patient (100%) but by none of the two Group 1 patients (0%; p = 0.083). With only three ND events in total, no stable between-group inference can be drawn from these observations.

Table 2. Negative dysphotopsia incidence and characteristics.

As shown in Table 3, among patients who experienced ND, 66.7% (2/3) had a vertical optic-haptic junction and 33.3% (1/3) had an inferotemporal optic-haptic junction. Among patients who did not experience ND, 49.5% (49/99) had a vertical optic-haptic junction and 50.5% (50/99) had an inferotemporal optic-haptic junction. There was no statistically significant association between optic-haptic junction position and ND incidence (p = 0.558).

Table 3. Negative dysphotopsia and optic-haptic junction position.

The present study aimed to evaluate the effectiveness of different surgical strategies in reducing the incidence of ND after IOL implantation. Because center, surgeon, incision site, and optic-haptic junction orientation were inseparable within each group, the findings reflect differences between complete approaches rather than the independent effect of any single variable. This distinction is important when interpreting comparisons with studies that manipulated only one variable.

The overall ND incidence of 2.9% is lower than rates reported in several prior studies. Osher RH. reported that 15.2% of patients experienced ND on the first postoperative day, declining to 3.2% at one year and 2.4% at two to three years [3]. A study done by Davison JA. reported a range of 0.2% - 20% [4]. The relatively low rate observed here may reflect the surgical techniques used, the characteristics of the implanted IOLs, the timing of assessment, or a combination of these factors.

No statistically significant difference in ND incidence was found between the supratemporal-incision/vertical-junction approach (3.9%) and the superior-incision/inferotemporal-junction approach (2.0%) (p = 0.558). This is broadly consistent with a study done by Cooke DL., which demonstrated that ND could occur after both superior scleral tunnel and temporal corneal incisions [9]. Masket et al. suggested that temporal corneal incisions may contribute to early ND but also noted that symptoms can persist after lens exchange, indicating that the incision site is not the sole determinant [10].

Regarding optic-haptic junction orientation, Henderson et al. reported a 2.3-fold reduction in ND when the junction was placed inferotemporally versus vertically [6]. However, Safran (2017) noted that this reduction was apparent only on day 1 and week 1, not at 28 days [11]. Pamulapati et al. found a significant association between junction orientation and ND at four to six weeks in a randomised controlled trial, with the horizontal orientation performing best [12]. The absence of a significant difference in our study may be partly explained by the timing of assessment and by the very low absolute event count.

Several mechanisms have been proposed for ND. Holladay et al. attributed it to a gap in rays traversing the lens edge [7], while Masket et al. emphasised light reflection from the IOL edge. Identified risk factors include small pupil size, large positive angle kappa, IOL geometry, and anterior capsule position were reported in different studies [13][14].

Strengths of this study include its prospective design, equal group allocation, structured follow-up at three time points, and the use of a consistent IOL class (monofocal acrylic) across both groups. However, several limitations must be acknowledged. First, the sample size is relatively small (102 patients), yielding only three ND events; this severely limits statistical power and precludes stable between-group inference. Second, center, surgeon, incision site, and junction position were completely linked, so the independent contribution of each cannot be estimated. Third, important ND-related variables were not measured, including pupil size, angle kappa, anterior capsule overlap, and detailed IOL position; any of these factors may influence ND independently of the surgical approach and represent a relevant source of unmeasured confounding. Fourth, the follow-up period (four weeks) is relatively short for fully assessing long-term ND resolution.

For persistent ND cases, reported treatment options include bag-to-sulcus IOL exchange, reverse optic capture, secondary piggyback IOL, or nasal anterior capsulectomy [2][8].