Recent industrial developments have resulted in the production and use of a variety of chemicals, including pharmaceuticals, cleaning and disinfection products, solvents, pesticides, and fertilizers, that can cause chemical injury. Ocular chemical injuries, which comprise 11.5-22.1% of all ocular injuries [1]. These injuries are one of the most important and critical emergencies requiring prompt diagnosis and intervention, failing which may result in long-term visual impairment [2-5]. Moreover, these conditions typically result in significant economic burdens not only for individuals but also for families and countries, owing to temporary or permanent layoffs, hospital costs, and the need for care, long-term follow-up, visual rehabilitation, and ocular surgery [6]. Despite these issues, only a few studies to date have investigated the clinical characteristics of patients with ocular chemical injuries [2-4,7].

The Gachon University Gil Medical Center is a tertiary of patients hospital located in Incheon, the third-largest city in South Korea, and has the highest ratio of industrial areas among the urbanized areas of the five major cities. It has been designated as a regional emergency and trauma center that provides medical services to urban and rural populations in South Korea. Although some minor ocular chemical injuries may be treated at a primary medical institution, most patients visit this hospital and receive proper treatment. Therefore, the assessment of clinical characteristics of patients with ocular chemical injuries in this medical center has its importance.

In this study, we aimed to evaluate the clinical manifestations and outcomes of patients with ocular chemical injuries over 6 years, from January 2018 to December 2023.

This study was approved by the Institutional Review Board (IRB) of Gachon University Gil Medical Center (IRB number: GBIRB2024-332) and adhered to the Declaration of Helsinki. The requirement for informed consent from patients was waived by the IRB because the study was based on a retrospective review of medical records.

We performed a retrospective analysis of the data of patients who visited the Gachon University Gil Medical Center and were diagnosed with ocular chemical injuries between January 2018 and December 2023. The data in the medical records of all patients were reviewed, including age, sex, location of ocular chemical injury, and properties of the causative chemical agents. Among these patients, those with ophthalmic medical records, including visual acuity (VA), intraocular pressure (IOP), distribution and severity of injury, management methods, and complications were included. The VA was measured using the logarithm of the minimum angle of the resolution (logMAR) chart. The IOP was measured using non-contact tonometry (CT-80; Canon Inc., Tokyo, Japan). Elevated IOP was defined as an IOp > 21 mmHg. The severity of ocular chemical injury was graded according to the extent of corneal haze and limbal ischemia according to the Roper-Hall classification [8]. Briefly, grade I was defined as corneal epithelial damage without limbal ischemia; grade II as corneal haze and visible iris details with ischemia of less than one-third of the limbus; grade III as total corneal epithelial loss, stromal haze, and obscured iris details with ischemia of more than one-third but less than half of the limbus; and grade IV as opaque cornea and obscured iris and pupil with ischemia of more than half of the limbus. Management methods included immediate irrigation after injury, topical medication (e.g., corticosteroids and prophylactic antibiotics), autologous serum, lens-type amniotic membrane (AM) application, and surgery including temporary/permanent amniotic membrane transplantation (AMT). Ocular complications, such as the presence of corneal opacity, limbal stem cell deficiency, and symblepharon, were also recorded at the final examination. Finally, the VA outcome was evaluated according to the difference between the first and last logMAR VA values. Visual outcome was defined as follows based on the logMAR VA values: improvement, -0.1 or less; maintenance, between -0.1 and +0.1; and deterioration, +0.1 or more.

Statistical analyses were performed using SPSS for Windows (version 23.0; IBM, Chicago, IL, USA) and Prism 10.4 (GraphPad Software, San Diego, CA, USA). An independent t-test was used to analyze the two sex groups (male and female). One-way analysis of variance (ANOVA) was used to compare the three causative agent groups (alkali/acid/neutral). Statistical significance was set at p < 0.05.

Between January 2018 and December 2023, 218 patients visited the Gachon University Gil Medical Center and underwent ophthalmological examination for ocular chemical burns. The patient demographics are presented in Table 1. Among these patients, 137 (62.8%) were male, with a male-to-female ratio of 1.7:1. The mean age of the patients was 41.8 ± 15.0 years (range, 7-77). The average follow-up duration was 12.3 ± 58.6 days. Loss to follow-up after hospital admission, a single visit, or follow-up at a primary hospital accounted for the largest proportion (154 patients, 70.6%). The longest follow-up duration was 687 days. A significant difference in age was found between the sexes (p = 0.018; independent t-test), with a mean age of 39.9 ± 14.4 and 44.9 ± 15.5 years among the male and female patients, respectively. Ocular chemical injuries occurred most often in people aged 20-39 years (n = 94, 43.1%). The highest proportion of male patients was found in the 20-39-year age group (n = 64, 46.7%), whereas female patients had similar distributions in the 20-39-year (n = 30, 37.0%) and 40- 59-year (n = 33, 40.7%) age groups (Fig. 1). Fig. 2 shows the seasonal distribution of the occurrence of ocular chemical injuries. The injuries showed a bimodal predominance in summer (n = 64, 29.4%) and winter (n = 64, 29.4%). This was mainly influenced by the large distribution of male patients reporting ocular chemical injuries in summer and winter. In contrast, the distribution of female patients with such injuries was similar in all four seasons.

The injuries were reported to be caused by a variety of chemicals. When classified according to chemical properties, 72 patients (33.0%) suffered damage from alkaline substances, 80 (36.7%) from acidic substances, and 66 (30.3%) from neutral substances. Among female patients, the proportion of injuries caused by various chemical agents was relatively similar; however, damage caused by alkalis (n = 29, 35.8%) was the most common. Among male patients, damage caused by acidic substances accounted for the highest number of cases of injuries (n = 55, 40.1%) (Fig. 3). The average pH for the alkaline and acidic substances that caused the reported injuries was 11.7 ± 1.9 (range, 8.0- 14.0) and 3.8 ± 2.1 (range, 1.0-6.5), respectively.

A total of 61 patients (28.0%) had injuries with right eye involvement, 72 (33.0%) had injuries with left eye involvement, and 85 (39.0%) had injuries with bilateral eye involvement. The initial VA in the affected eye was 0.23 ± 0.35 logMAR, and the IOP was 13.7 ± 3.2 mmHg. The final VA in the affected eye was 0.18 ± 0.33 logMAR, and the IOP was 13.1 ± 3.2 mmHg. When divided into three groups according to chemical properties (alkali/acid/neutral) of the causative agent for the injury, there was no significant difference between the initial and final values of VA and IOP (all p > 0.05; ANOVA). However, there was a difference in the initial IOP among the three groups (p = 0.012; ANOVA). Post-hoc analysis showed that the initial IOP was higher in the group with acidic causative agent than in the group with neutral causative agent (Table 2).

The ocular surface was clear in 10 eyes. Among 293 eyes with ocular surface damage, the most common severity or injury classification was grade I (262 eyes, 89.4%), followed by grade II (22 eyes, 7.5%) (Fig. 4). The most common setting for ocular chemical injury was home (n = 106, 48.6%), followed by the workplace (n = 96, 44.0%). When divided by sex, female patients showed a predominant occurrence of ocular chemical injuries at home (n = 55, 67.9%), whereas male patients showed a predominant occurrence of such injuries at the workplace (n = 79, 57.7%) (Fig. 5).

Irrigation before hospital visit was confirmed to have been performed in 130 patients (59.6%). As most patients had grade I disease, medical treatments (topical antibiotics and steroids) were the main treatment options. Seven patients (12 eyes) were prescribed autologous serum, and three of these patients (six eyes) additionally received lenstype AM and temporary/permanent AMT. Among the seven patients who received additional treatment, three had corneal opacity and limbal stem cell deficiency as final complication, and one of them developed symblepharon; no complications were observed in any other patients. In terms of VA outcome, improvement was observed in 61 eyes (20.1%), maintenance in 236 eyes (77.9%), and deterioration in six eyes (2.0%) (Fig. 6).

Ocular chemical injury is a critical emergency that requires immediate diagnosis and intensive intervention to preserve VA and minimize severe complications [2,6]. The grade of injury mostly depends on the type of causative agent, pH, and exposure time [2].

In this study, we described the characteristics and outcomes of 218 patients who visited Gachon University Gil Medical Center in Incheon, South Korea, over a 6-year period. A large number of patients presented to our hospital with chemical injuries as a large number of industrial facilities and residences are located nearby. Most patients had ocular chemical injuries with a clinical severity of grade I, which were resolved with medical treatment without specific complications; however, male and female patients showed slightly different characteristics: in female patients, ocular chemical injuries usually occurred at home, in those aged between 20 and 59 years, all year round, and were caused by various causative agents, whereas in male patients, such injuries mostly occurred at the workplace, in those aged between 20 and 39 years, in summer or winter, and were caused by acidic substances.

Previous studies have reported that the ocular chemical injuries most commonly occur in industrial settings [2,9,10], whereas other studies have reported that they predominantly occur in domestic settings [11-13]. In the United Kingdom, a study analyzing chemical burns between 1981 and 1987 reported that industrial causes accounted for 76% of the incidence; however, a subsequent study conducted between 2003 and 2011 reported an incidence of 35%, which was less than the 43% incidence of domestic chemical burns [14]. Our study also found that both domestic and industrial settings accounted for a high proportion of injuries, and although the difference was small, slightly more number of injuries occurred at home (Supplementary Fig. 1).

Among women, ocular chemical injuries occur mostly at home in those aged 20-59 years when they are engaged in household chores, which explains the absence of specific seasonal predominance or predominance of specific causative substances. Among men, the incidence of ocular chemical damage at home was similar to those reported among women; however, the incidence at work was much higher (Supplementary Fig. 2). This may be because men in the age range of 20-39 years tend to have occupational environments with a higher risk of chemical exposure [7] or because women are more concerned about chemical exposure accidents at work and protect themselves.

Among men, most cases of damage were caused by acidic substances during summer and winter. Previous studies have reported more alkali-induced ocular chemical injuries than those caused by acidic or neutral substances [2,6]; however, along with our study results, some papers have reported acidic substances as a common causative agent for chemical burns [15,16]. Consistent with previous studies, the representative acidic agents in our study were hydrochloric acid, sulfuric acid - an important industrial raw material, hydrogen peroxide, and cleaning and disinfection products. Alkaline agents accounted for a large proportion of injuries, at 31.4%. The main causative agents were bleach, sodium hydroxide, cement, thinner, dye, and paint.

Studies have also shown a seasonal trend, with most of them showing a higher occurrence of ocular chemical injuries in summer [6,12,17]. Studies have postulated that warmer temperatures and higher humidity may hinder the wearing of eye protection. They also noted greater exposure to chemicals used for cleaning and disinfecting swimming pools and refrigerators during summer [15,18]. Studies have also reported occurrence of ocular injuries in the winter from boiling liquids and flames [19,20]. Slips and falls, the most common cause of workplace injuries in winter [21], may result in ambient chemicals unintentionally splashing onto the ocular surface.

The distribution of chemical injury severity may vary regionally according to socioeconomic status. In Switzerland and the United Kingdom, low-grade injuries account for a major proportion (83-90%) of chemical injuries [22,23]. In contrast, severe injuries have been more frequently reported in India [24]. In the present study, almost 90% of the patients had grade I or no definite ocular surface damage. As most cases were those of minor ocular chemical injuries, they resolved well with medical treatment, with minimal VA outcome deterioration. Prompt irrigation at the accident site could be one reason for the low-grade damage.

This study has certain limitations. First, data were obtained from only one hospital in this area, and only patients admitted to the hospital were included. Second, owing to the retrospective nature of the study, the VA before the injury and short- or long-term changes in VA were not known. Additionally, some patients were lost to follow-up.

Despite the recent increase in social interest and improved safety education, ocular chemical injuries still occur, owing to various substances and situations. According to the present study, ocular chemical injuries mainly occurred in young men and women engaged in work or household chores, respectively, and had a clinical severity of grade I. Medical treatment alone was sufficient for recovery in most cases and complications that compromised visual outcomes rarely occurred. However, comprehensive education and provision of protective equipment should be strengthened to prevent and reduce future ocular chemical injuries.