Introduction

Cataract is a condition in which the lens of the eye becomes progressively opaque, obstructing the passage of light to the retina and resulting in a loss of transparency [1]. This condition is asymptomatic and can lead to preventable blindness, accounting for 51% of blindness cases worldwide [2]. A national survey of Ethiopia showed that cataracts are the primary cause of blindness and low vision, accounting for 49.9% of blindness cases and 42.3% of low vision cases [3]. The most effective cataract treatment is surgery, which is also the most common intraocular surgery in the world. Cataract surgery can restore patients’ vision, improve their functional abilities, and enhance their quality of life [4]. However, the visual outcomes of cataract surgery vary from country to country and within countries, posing a major problem for both developed and developing countries [5].

The World Health Organization (WHO) has recommended that the percentage of people with poor visual outcomes after cataract surgery should be less than 5% according to best corrected visual acuity (BCVA) [6]. However, studies have shown that in developing countries, 30–50% of patients undergoing cataract surgery have poor postoperative visual outcomes that do not meet their daily visual requirements [7, 8]. Previous studies conducted in Ethiopia have found that the proportion of poor visual outcomes after cataract surgery was 7.8% in Jimma [9],11.5% in Addis Ababa [10], (35.3%, 44.5%) in Gondar [11, 12], and 38.8% in Borumeda [13]. In previous studies conducted in Jimma, Gondar, and Borumeda, Ethiopia, visual outcomes of cataract surgery were assessed based on post-operative presenting visual acuity, and also they did not identify factors associated with the visual outcomes. This study aims to address this gap by determining the magnitude of visual outcomes based on best-corrected visual acuity and identifying associated factors.

Studies have shown that diabetic retinopathy, hypertension, diabetes mellitus, surgical complications, limited surgical skills, inadequate postoperative optical correction, and inaccurate preoperative biometric measurements can lead to poor visual outcomes of cataract surgery [14, 15]. In addition, older age, female gender, lower education level, and rural residence have also been associated with unfavorable visual outcomes of cataract surgery [5, 15].

Reducing cataract-related blindness is hampered by poor surgical outcomes and inadequate access to surgery, particularly in resource-poor settings. These issues also affect patients’ satisfaction with vision after surgery, vision-related quality of life, ability to perform daily activities, and overall productivity [16, 17]. To improve the visual outcomes of cataract surgery, surgical capacity needs to be increased by training additional surgeons, providing equipment, and monitoring surgical quality [18, 19].

Assessment of visual outcomes after cataract surgery is an essential benchmark for ophthalmologists to maintain quality and standardize patient care, ultimately reducing the likelihood of poor visual outcomes [20]. However, there is limited evidence on the proportion of poor visual outcomes after cataract surgery and associated factors in Ethiopia, and no study has been conducted in the study region. Therefore, the primary aim of this study was to determine the proportion of poor visual outcomes and associated factors among adult patients who had undergone cataract surgery at Debre Markos and Felege Hiwot Comprehensive Specialized Hospitals in northwestern Ethiopia, 2023.

Methods and materials

Study design, area, and period

A cross-sectional study was conducted from June 7 to August 7, 2023, at the Debre Markos and Felege Hiwot Comprehensive Specialty Hospitals in northwestern Ethiopia. Debre Markos Hospital is located in the East Gojjam Zone of Amhara Regional State, 299 km from the capital city, Addis Ababa. According to the hospital’s health information system, it provides comprehensive health services to an estimated population of five million people. In Debre Markos hospitals, there are two ophthalmologists with 2 and 4 years of surgical experience, a cataract surgeon with 6 years of surgical experience, eight optometrists, and three ophthalmic nurses providing ophthalmology services. On average, 250 adult patients undergo cataract surgery at Debre Markos Hospital every month. Ethiopian cataract surgeons are qualified ophthalmic nurses with two years of training in cataract surgery.

Felege Hiwot Hospital is located in the West Gojjam Zone of Amhara Regional State, 567 km from Addis Ababa. In Felege Hiwot Hospital, there are two ophthalmologists with 2 and 3 years of surgical experience, a cataract surgeon with 10 years of surgical experience, three optometrists, ten ophthalmic nurses, one ophthalmic officer, and three nurses providing ophthalmology services. On average, 200 adult patients undergo cataract surgery at Felege Hiwot Hospital every month.

Study population and eligibility criteria

All adult patients aged 40 years or older who had undergone cataract surgery at Debre Markos and Felege Hiwot Comprehensive Specialized Hospital with a surgery duration of 4 weeks to one year at the time of data collection were eligible to participate in this study.

However, patients who had undergone surgery for uveitic or traumatic cataracts and patients who were severely ill and unable to undergo slit lamp, retinoscopy, and visual acuity testing were excluded from the study.

Sample size determination and sampling procedure

The sample size required for the study was determined using a single population proportion formula with the consideration of the expected proportion of poor visual outcomes after cataract surgery of 44.5%, based on a previous study in Gondar, Ethiopia [12], a 95% confidence level and a maximum allowable error of 5% (d).

Based on these factors, a sample size of 380 was determined. To allow for a non-response rate of 10%, the final planned sample size was set at 418.

A proportional allocation of the desired sample was made between two hospitals based on the number of patients visited. The hospital logbook indicated that approximately 900 adult patients who had undergone cataract surgery within the last four weeks to one year visited the outpatient clinic each month. Of this total number, 500 patients visited the Debre Markos Comprehensive Specialized Hospital, while 400 patients visited the Felege Hiwot Comprehensive Specialized Hospital. Based on these statistics, the sample size was divided proportionally, 232 patients were included from Debre Markos Comprehensive Specialized Hospital, and 186 patients were included from Felege Hiwot Comprehensive Specialized Hospital.

Study participants were selected using systematic random sampling with an interval of 2. The first study participant was selected by drawing a single number using a lottery method and then selecting each K interval. The Kth interval was calculated by dividing the expected number of adult patients who underwent cataract surgery with a duration of 4 weeks to 1 year and visited the hospitals’ eye center during the data collection period by the calculated sample size (K = N/n, N = 900, n = 418).

Operational definitions

Post-operative visual acuity (either presenting or best corrected) was categorized into three groups. If the visual acuity was 6/12 or better, it was considered good vision. If the visual acuity was less than 6/12 but better than or equal to 6/60, it was considered borderline vision. If the visual acuity was less than 6/60, it was considered poor vision [21].

Poor visual outcomes after cataract surgery was defined as having a best corrected visual acuity of less than 6/60 [21].

Axial length was categorized as < 22 mm, 22–25 mm, and > 25 mm [22].

Corneal astigmatism was categorized into ≤ 2.00Dc and > 2.00Dc [10].

Pre-operative and Post-operative intraocular pressure (IOP) were categorized as normal if the IOP was ≤ 22 mmHg and abnormal if the IOP was greater than 22 mmHg [10].

Post-operative refractive error was defined by the spherical equivalent of post-operative refractive error, which was greater than ± 1.00D (sphere refractive error plus half of cylindrical refractive error) [23].

Data collection procedures (personnel and instrument)

The data was collected by four trained and experienced optometrists. They conducted face-to-face interviews and ocular examinations using various equipment, including a visual acuity chart, slit lamp bio-microscopy, 90-diopter Volk lens, I-care tonometry, retinoscope, and trial lens cases. The optometrists used a pre-tested semi-structured questionnaire, based on reviewed literature [10, 12, 24,25,26], to collect socio-demographic data and personal ocular and medical history. Additionally, biometric data such as axial length and keratometry reading, as well as information on the types of cataract surgery, position of the intraocular lens implantation, preoperative visual acuity, pre and post-operative intraocular pressure (IOP), maturity and types of cataract underwent cataract surgery, post-operative visual acuity in the first day and week, and presence of any ocular problem (pre-existing or intraoperative or early postoperative complications) were collected from the medical records of each study participant.

After determining who was a candidate for cataract surgery, biometric data such as corneal curvature and axial length were evaluated using a Keratometer and A-scan ultrasound to calculate the power of the intraocular lens (IOL) the day before surgery. In addition, the patient and their caregiver were asked to give their consent after a detailed explanation of the benefits and risks of cataract surgery. On the day of surgery, before entering the operating room, the patient’s blood pressure was measured, the patient’s clothes were changed, the eyelashes of the upper eyelid were trimmed and the operated eye was dilated with 1% tropicamide eye drops.

After administered topical tetracaine was into the eye, the periorbital area, eyelid margin, and eyelash were cleaned with 5% povidone-iodine solution before the surgery. Patients received either retro-bulbar anesthesia (RBA) or sub-tenon anesthesia (STA) with an injection of 2% lidocaine with or without adrenaline. The surgeon chose a surgical strategy depending on the patient’s preoperative conditions: manual small incision cataract surgery (MSICS) or extracapsular cataract extraction (ECCE) with or without intraocular lens (IOL) implantation. The surgeon implanted anterior chamber (AC) and posterior chamber (PC) IOLs made of polymethylmethacrylate. After surgery, a subconjunctival injection of gentamicin-dexamethasone was administered. Finally, the operated eye was covered after administration of topical ciprofloxacin 0.3% and dexamethasone 0.1% eye drops.

The post-operative presenting and best-corrected visual acuity of study participants with a period of 4 weeks to one year following cataract surgery were tested using a Snellen acuity chart (tumbling E Optotypes) under good room illumination at a distance of 6 m. For those who could not read letters at 6 m, their vision was tested by moving the portable chart closer to the patient at specified meters such as 5 m, 4 m, 3 m, 2 m, and one meter. Furthermore, for individuals who could not see any letter at 1 m, their vision was expressed as counting fingers, hand motion, light perception, and non-light perception.

Post-operative anterior and posterior segment examinations were carried out using slit lamp biomicroscopy with a 90-diopter Volk lens to diagnose any post-operative complications by the surgeon who operated the case. Both objective and subjective refraction were conducted by the senior optometrist to determine the best-corrected visual acuity after cataract surgery and the presence of postoperative refractive error.

Data quality assurance

To ensure the quality of the data, a pre-test was conducted on 5% of the total sample size at the University of Gondar tertiary eye care and training center before the actual data collection process began. The data collectors received training on how to collect the data, and a supervisor provided oversight during the data collection process.

Data processing and analysis

After checking the completeness and consistency of the data, the data was encoded and entered into EPI-info version 7 software and exported to Statistical Package for Social Science (SPSS) version 25 for analysis. Both descriptive and analytical statistics were applied in analyzing the data. Summary statistics such as mean, median, frequency, and cross-tabulation were used to describe the descriptive parts of the data. Multicollinearity was checked using the variance inflation factor and tolerance. To determine possible factors associated with poor visual outcomes of cataract surgery, binary logistic regression was fitted. Variables with a P-value of less than 0.2 in bivariable analysis were entered into a multivariable binary logistic regression.

The strength of association was expressed using an adjusted odds ratio with a 95% confidence interval. The model’s fitness was ensured by Hosmer and Lemeshow’s goodness of fit. A variable with a P-value of less than 0.05 was considered statistically significant. Finally, the study’s results were described in text forms and tables.

Ethical consideration

This study was conducted in accordance with the Declaration of Helsinki. Ethical approval was granted by the Ethical Review Committee of the University of Gondar, College of Medicine and Health Sciences, with approval number 666/05/2023. In addition, an administrative permission letter was obtained from the clinical directorate of Debre Markos and Felege Hiwot Comprehensive Specialized Hospital. Written informed consent was obtained from all study participants after explaining the purpose of the study. Participants were informed of their right to refuse or withdraw from participating at any time. Confidentiality was ensured by excluding any personal identifiers from the questionnaire and by coding and locking the data.

Results

Socio-demographic and systemic health characteristics of study participants

In the study, 408 participants took part with a response rate of 97.6%. The median age of the participants was 65 years, with an interquartile range of 18. Out of the 408 participants, 210 (51.5%) were male, 289 (72.8%) lived in rural areas, and 297 (72.8%) had not received formal education. Among the participants, 21 (5.1%) had a known history of hypertension, and 12 (2.9%) had a known history of diabetes mellitus (Table 1).

Table 1 Socio-demographic and systemic health characteristics of the study participants, Northwest Ethiopia, 2023 (n = 408)
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Clinical characteristics of the study participants

Out of 408 patients who underwent cataract surgery, 82.8% had presented with mature cataracts. Manual Small Incision Cataract Surgery (MSICS) was performed on 96.6% of the participants. Out of the 408 study participants, 95.3% had a visual acuity of ≤ 2/60 before cataract surgery. Out of 14 patients who underwent extracapsular cataract extraction, 8 (57.1%) had poor visual outcomes, whereas 97 out of 394 (24.6%) patients who underwent MSICS had poor visual outcomes (Table 2).

Table 2 Clinical characteristics of patients who underwent cataract surgery at Debre Markos and Felege Hiwot Comprehensive Specialized hospitals in Northwest Ethiopia, 2023 (n = 408)
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Preexisting ocular comorbidities and surgical related complications

Out of the 408 individuals who participated in this study, the most frequently observed preexisting ocular comorbidities were central corneal opacity (7.6%), glaucoma (6.4%), and pseudoexfoliation (5.1%). In this study, 15.1% of patients who had cataract surgery without pre-existing ocular co-morbidities experienced poor visual outcomes.

In addition, out of 408 patients who underwent cataract surgery, 28 (6.9%) presented with intraocular complications. Among these, 15 (53.6%) had poor visual outcomes.

Furthermore, posterior capsular tear (3.2%) and post-operative refractive error (57.8%) were the most commonly encountered complications during and after cataract surgery, respectively (Table 3).

Table 3 Preexisting ocular comorbidities, and surgical-related complications among patients who underwent cataract surgery at Debre Markos and Felege Hiwot comprehensive specialized hospitals, Northwest Ethiopia, 2023 (n = 408)
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Proportion of poor visual outcomes of cataract surgery from 4 weeks to one year

Out of 408 patients who underwent cataract surgery, 56.9%, 56.1%, and 50.5% had achieved the presenting visual acuity of 6/18 to 6/60 on the first day, first week, and from 4 weeks to one year respectively.

In this study, the proportion of poor visual outcomes of cataract surgery from 4 weeks to one year through best corrected visual acuity was 25.7% (95%CI: 21.6%, 30.3%) (Table 4).

Table 4 Postoperative visual acuity of patients who underwent cataract surgery at Debre Markos and Felege Hiwot Comprehensive Specialized hospitals Northwest Ethiopia, 2023 (n = 408)
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Factors associated with poor visual outcomes of cataract surgery from 4 weeks to one year

In bi-variable analysis, age, marital status, monthly income, types of cataract surgery, place of intraocular lens (IOL) implanted, preoperative intraocular pressure (IOP), postoperative IOP, preoperative corneal astigmatism, central corneal opacity, glaucoma, pseudoexfoliation, age-related macular degeneration (ARMD), striate keratopathy, and intraoperative complication were all found to be associated with poor visual outcomes. However, in multivariable binary logistic regression analysis, non-posterior chamber intraocular lens implantation, preexisting central corneal opacity, preexisting glaucoma, pseudoexfoliation, age-related macular degeneration, and striate keratopathy were found to be significantly and independently associated with poor visual outcomes of cataract surgery.

Participants who had intraocular lens implantation without a posterior chamber were 2.91 times (AOR = 2.91, 95%CI: 1.46, 5.80) more likely to have poor visual outcomes of cataract surgery than those who had posterior chamber intraocular lens implantation. Participants with preexisting central corneal opacity were 3.83 times (AOR = 3.83, 95%CI: 1.52, 9.69) more likely to have poor visual outcomes of cataract surgery than those without preexisting central corneal opacity. The odds of poor visual outcomes of cataract surgery were 3.11 times higher (AOR = 3.11, 95%CI: 1.06, 9.17) in participants with preexisting glaucoma than those without preexisting glaucoma.

Participants with pseudoexfoliation were 3.91 times (AOR = 3.91, 95%CI: 1.39, 11.88) more likely to have poor visual outcomes of cataract surgery than those without pseudoexfoliation.

The odds of poor visual outcomes of cataract surgery were 3.75 times higher (AOR = 3.75, 95% CI: 1.22, 11.88) in participants with preexisting ARMD than those without preexisting ARMD. Moreover, participants with striate keratopathy were 3.4 times (AOR = 3.4, 95%CI: 1.11, 10.88) more likely to have poor visual outcomes of cataract surgery than those without striate keratopathy (Table 5).

Table 5 Factors associated with poor visual outcomes among patients who underwent cataract surgery at Debre Markos and Felege Hiwot comprehensive specialized hospitals, Northwest Ethiopia, 2023 (n = 408)
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Discussion

This study found that the proportion of visual outcomes after cataract surgery was 25.7% (95% CI: 21.6-30.3%), which is higher than the WHO recommended standard of < 5% [6], and the studies conducted in Addis Ababa, Ethiopia (11.5%) [10], Jimma, Ethiopia(7.8%) [9], Kenya(2.2%) [27], Liberia(5.2%) [28], Ghana(9.5%) [24], Nigeria(5.5%) [29], Pakistan(3.5%) [15], India (1.6%) [5], Nepal (8.0%) [30], Malaysia (0.5%) [31], China (11.1%) [25], and North America (12%) [14]. The variation in outcomes may be due to differences in surgical techniques. The studies conducted in Malaysia, Pakistan, India, Liberia, and Addis Ababa, Ethiopia used phacoemulsification, which is the most advanced surgical technique for cataract surgery. This technique offers early visual rehabilitation and minimal intraoperative complications [32] compared to ECCE and MSICS, which were used in this study. In addition, poor surgical skills for cataract surgery and inadequate adherence to post-operative medication and follow-up due to transportation issues, lack of funds, and poor awareness about the benefits of such follow-ups and medication can contribute to this difference [11, 33].

On the other hand, the proportion of poor visual outcomes after cataract surgery in this study was lower than in other studies conducted in Gondar, Ethiopia (35%, 44.5%) [11, 12] and Borumeda, Ethiopia (38.8%) [13]. This difference in outcomes may be due to variations in surgical skills and measurement of visual outcomes. In this study, senior ophthalmologists and a senior cataract surgeon performed the surgery, and the visual outcomes were measured based on the best corrected visual acuity whereas study done in Gondar, Ethiopia, the cataract surgery was performed by a senior ophthalmologist and a resident ophthalmologist, and the visual outcomes was measured based on the presenting visual acuity.

Participants who had intraocular lens implantation without a posterior chamber were 2.91 times more likely to have poor visual outcomes of cataract surgery than patients who had intraocular lens implantation in the posterior chamber. This result was supported by the studies conducted in Liberia [28] and Malaysia [26]. Possible reasons for this association could be due to participants who had an intraocular lens implanted in the non-posterior chamber being more likely to experience postoperative complications such as cystoid macular edema, ocular inflammations, loss of corneal endothelial cells, corneal decompensation, secondary glaucoma, and pupil decentration [34]. Intraocular lens implantation in the non-posterior chamber is indicated when there is an intraoperative complication that makes it impossible to place a posterior chamber intraocular lens, leading to reduced visual outcome [35].

According to this study, individuals who had preexisting central corneal opacity were 3.83 times more likely to experience poor visual outcomes following cataract surgery compared to those patients without central corneal opacity. This finding is consistent with similar studies conducted in Gondar, Ethiopia [11], Liberia [28], India [5] and Malaysia [31]. The reason for this increased risk could be that corneal opacity can obstruct the surgeon’s view during cataract surgery, leading to longer surgery times and more intraoperative complications [36]. Additionally, preexisting central corneal opacity can prevent the transmission of light to the retina after cataract surgery, resulting in suboptimal visual improvement [37].

In this study, individuals with preexisting glaucoma who underwent cataract surgery are 3.11 times more likely to experience poor visual outcomes than those without preexisting glaucoma. This finding is consistent with previous studies conducted in Liberia [28], India [5], Malaysia [31], and Trinidad and Tobago in North America [14]. The possible explanation for this association is that patients with glaucoma are more vulnerable to surgical-related complications such as posterior capsular tear, postoperative inflammation, and transient increase of intraocular pressure which can damage the optic nerve and result in less visual improvement after cataract surgery [38]. Furthermore, the stage of preoperative glaucoma is an important factor to predict the final visual acuity after cataract surgery. Patients with advanced glaucoma tend to have less visual acuity improvement after cataract surgery as compared to those with moderate or early-stage glaucoma [38].

In the current study, participants with pseudoexfoliation were 3.91 times more likely to have poor visual outcomes of cataract surgery than those participants without pseudoexfoliation which was supported by the studies conducted in Malaysia [31, 39]. Pseudoexfoliation is a material that is deposited within the stroma of the iris, ciliary body, and zonules. This can make it difficult for the pupil to dilate and cause weakness in the zonules during cataract surgery. As a result, it can lead to complications during the surgery such as posterior capsule tear and vitreous loss, and post-operative complications such as inflammation, posterior capsular opacity, and dislocation of the intraocular lens. All of these can ultimately affect the visual outcomes of cataract surgery [40]. The main reason for poor visual outcomes among patients with pseudoexfoliation in this study was the occurrence of intraoperative and postoperative complications. For example, the study revealed that among patients with pseudoexfoliation, 20% of patients experienced Zonular dehiscence, 7.7% had posterior capsular rupture, 13.3% suffered from chronic uveitis, and 33.3% had cystoid macular edema, all of which contributed to visual reduction after cataract surgery in this study.

In this study, individuals with preexisting age-related macular degeneration (ARMD) are 3.75 times more likely to experience poor visual outcomes from cataract surgery. This finding is consistent with studies conducted in Addis Ababa [10], India [5] and Malaysia [31]. The reason behind this correlation is that age-related macular degeneration can lead to irreversible central vision loss due to the hypo or hyperpigmentation of the retina-pigmented epithelium, sub-retinal neovascularization, hemorrhage, and disciform scar on the macula. These factors contribute to poor visual improvement following cataract surgery [41].

In this study, individuals who had striate keratopathy are 3.4 times more likely to experience poor visual outcomes following cataract surgery compared to individuals who didn’t have striate keratopathy. This correlation has been supported by studies conducted in Liberia [28], India [5] and Nepal [42]. The reason for this association could be that striate keratopathy is characterized by the presence of corneal stromal edema and Descemet’s folds, which are often located close to or even at the incision site, resulting in a significant decrease in corneal clarity. The degree of intraoperative insult, as well as a history of prolonged or complicated surgery, can also contribute to poor visual outcomes associated with striate keratopathy. Overall, this condition can affect corneal transparency and the integrity of corneal endothelial cells, which can lead to poor visual outcomes following cataract surgery [43].

The study found that the proportion of intraoperative complications was 6.9% (95% CI: 4.4–9.6). This rate is similar to studies conducted in Addis Ababa, Ethiopia (9.2%) [10] and Malaysia(6.1%) [44] it is higher than the study done in Liberia(3.3%) [28]. The difference in complication rates could be due to variations in the surgeons’ years of experience, the surgical methods used, and the presence of ocular co-morbidities in the study population. Among the patients with intraoperative complications, 13 out of 28 (46.4%) had pre-existing ocular co-morbidities. The study found that the presence of pre-existing ocular co-morbidities was associated with intraoperative complications (x2 = 5.97, P-value = 0.015).

Implication of this study for stakeholders

The research emphasizes the importance of enhancing surgical techniques and conducting comprehensive preoperative assessments to deal with existing eye-related conditions, which have a significant impact on poor visual results following cataract surgery. These conclusions can guide healthcare policies and training initiatives focused on improving surgical standards and patient care in underserved areas such as Ethiopia.

Limitations of this study

The study was conducted in two Comprehensive Specialized Hospitals within a short time of data collection using various surgical techniques which may affect the generalizability of our study results to the overall population who underwent cataract surgery in Ethiopia.

Conclusion

This study found that the proportion of poor visual outcomes after cataract surgery is higher than the World Health Organization recommendations. This study identified several factors that are significantly associated with poor visual outcomes of cataract surgery, including non-posterior chamber intraocular lens implantation, pre-existing central corneal opacity, age-related macular degeneration, glaucoma, pseudoexfoliation, and striate keratopathy. We recommend that ophthalmologists and cataract surgeons prioritize the reduction of surgical complications and pre-existing ocular co-morbidities to enhance post-operative visual acuity. Improving pre-operative assessment and refining surgical techniques like phacoemulsification will aid in achieving this goal. Moreover, we encourage future researchers conduct prospective investigations into similar and/or related topics.