Original study: The clinical profile of childhood blindness in a tertiary South African hospital - a 12-year review

The clinical profile of childhood blindness in a tertiary South African hospital - a 12-year review

Z Alashhab MBCHB, FICO, FC Ophth (SA), Registrar- Groote Schuur Hospital, Cape Town, South Africa.

ORCID: https//orcid.org/ 0009-0000-1600-2447

D Minnies PhD, MPH, NHDMedTech, NDMedTech, Director of the Community Eye Health institute - University of Cape Town, South Africa.

ORCID: https//orcid.org 0000-0002-9173-782X

C Tinley MBCHB, FRCOphth (London), Paediatric Ophthalmologist - University of Cape Town and Atlantic Eye Centre, Cape Town, South Africa.

ORCID: https//orcid .org 0000-0001-5817-7122

Corresponding author: Dr Zakaria Alashhab. e-mail: zakariaalashhab@gmail.com

Abstract

Aims: To investigate the causes of blindness among children aged 0-13 years in Cape Town over a 12-year period.

Methods: A retrospective review was conducted of all children registered blind between 2011-2022 at the Red Cross War Memorial Children’s Hospital. The children were diagnosed as blind according to the WHO criteria and referred to local blind schools. Data on anatomical site, aetiology and avoidable causes were collected using the WHO/PBL Eye Examination Record. Descriptive statistics were used for analysis.

Results: A total of 182 blind children were identified. The most common anatomical sites of blindness were the optic nerve (27%), retina (23.6%) and normal globe (21.4%), followed by whole globe (18.7%), uvea (3.3%), lens (3.3%), and cornea (2.7%). Regarding aetiological causes, hereditary conditions were responsible for (23.5%), perinatal factors (15.3%), postnatal factors (9.3%), intrauterine factors (3.3%), but the largest proportion of cases (48.5%), fell under disorders of unknown aetiology. Avoidable causes accounted for (22.5%) of cases, and the majority of these were cerebral palsy/neonatal asphyxia (7.1%).

Conclusions: We found optic nerve (27%), retina (23.6%) and normal globe (21.4% - mainly cerebral visual impairment) to be the most common causes of childhood blindness in Cape Town. These proportions are more closely aligned with developed nations and indicate a different clinical profile when compared to prior, nationwide studies. This information may help guide future public health strategies to target the specific causes identified.

Keywords: Childhood blindness, visual impairment, paediatric ophthalmology, Cape Town, South Africa.

Conflict of interest: None of the authors have conflicts of interest related to this submission.

Introduction

Childhood blindness has been a priority area for the Vision 2020: The Right to Sight initiative of the World Health Organization (WHO), launched in 1999.1

According to estimates at that time, there were globally 1.4 million blind children, with twice this number having low vision, and approximately 500 000 new cases of childhood blindness occurring each year.1 Childhood blindness is important not only because these children face a lifetime of vision impairment, but also because it carries profoundly negative psychological, educational, and economic impacts for the affected individuals as well as their communities.2 The causes of blindness in children have been linked to higher rates of child mortality.3 Furthermore, many causes of childhood blindness are either preventable or treatable.3

The distribution of causes of childhood blindness differs markedly between regions according to socioeconomic factors. In the lowest-income countries, corneal scarring leading to vision impairment is most prevalent, whereas high-income nations report lesions of the central nervous system as being predominant. Middle-income countries present a mixed epidemiological picture. Retinopathy of prematurity has increasingly become an important avoidable cause of blindness in this setting, as survival rates of preterm infants have risen. Additionally, across all regions, cataract, retinal diseases, and congenital anomalies affecting the whole globe constitute significant contributors to childhood visual impairment.3,4 Data from one country can therefore not be extrapolated to another.5 Accurate data on the causes of blindness is needed for appropriate allocation of resources towards preventive and curative services.6 Some of the causes may require primary level public health interventions, such as immunisation and nutrition to prevent corneal scarring, whereas others need tertiary-level intervention, such as surgery and low-vision services for cataract, retinopathy of prematurity and glaucoma.7 Data on childhood blindness in South Africa is sparse. The most recent study looked at causes of blindness in a Johannesburg blind school and the other was a broader, cross-sectional survey conducted almost thirty years ago.8,9

The aim of this study was to provide current data on the clinical profile of childhood blindness in the Western Cape province of South Africa and compare the pattern of childhood blindness with local and international published literature. Hopefully, this will assist local authorities in planning appropriate strategies to implement preventive, curative, and rehabilitative services.

Materials and methods

We reviewed the causes of childhood blindness over a 12-year period in the ophthalmology department of the Red Cross War Memorial Children’s Hospital in Cape Town, South Africa. The hospital is one of two large tertiary referral centers serving Cape Town and its surrounding areas. UNICEF defines a child as an individual aged less than 16 years; at this institution, children are treated until age 13, with limited adolescent services. The WHO International Classification of Diseases-10 definition of visual impairment was utilised.10 This classification defines blindness as a best corrected visual acuity of less than 3/60 or a visual field less than 10 degrees in the better-seeing eye.

We performed a retrospective folder review of all children diagnosed with visual impairment, who were referred to three blind schools in Cape Town, from January 2011 to December 2022. The primary source of information was the hospital referral forms to the local blind schools, in the minority of cases, where data on the referral forms were insufficient, clinical records were retrieved to investigate findings. All causes of blindness were recorded according to the WHO/PBL Eye Examination Record for Children with Blindness and Low Vision Instructions.11 This provides definitions and methods of classification for anatomical, aetiological and avoidable causes of visual loss. The anatomical classification marks the major site of abnormality leading to blindness. These include whole globe, cornea, lens, uvea, retina, optic nerve, and globe appears normal. The aetiological classification refers to the timing of the insult leading to visual loss. These include hereditary disease, intrauterine, perinatal/ neonatal factors, postnatal/infancy/ childhood factors and cannot determine/ unknown aetiology. Avoidable causes were also determined, either preventable or treatable. After examination, the major site of abnormality and aetiology were determined for each eye and individual. Ethical and institutional approvals were obtained from the University of Cape Town Human Research Ethics Committee and the Red Cross War Memorial Children’s Hospital. Descriptive statistical analyses were used and presented as frequencies and percentages.

Results

Between 2011 to 2022, 182 children were diagnosed as being blind according to WHO criteria. 96 (52.7%) were male, while 86 (47.3%) were female. The mean age of the children was 3.8 years, with a standard deviation of 3.2 years. And the median age was 2.69 years, with interquartile range 1.34-6.01.

Anatomical site of visual abnormality

The anatomical sites of abnormality in the children are shown in Table I. Optic nerve, retinal conditions, and ‘the globe appears normal’ were the three most common causes. Optic nerve conditions were the most common site of visual impairment, with 49 children affected (27%). These included optic nerve atrophy due to hydrocephalus, which impacted 20 children (11%) and optic nerve hypoplasia, affecting 16 children (8.4%). Retinal conditions were the second most common cause, present in 43 children (23.6%). Of these, 11 children (5.8%) had oculocutaneous albinism (OCA). Fourteen children had retinal dystrophies including Leber’s congenital amaurosis, retinitis pigmentosa, and Bardet-Biedl syndrome, while ROP and retinal detachment found in five (2.7%) and three (1.6%) children, respectively. One child had a history of bilateral retinoblastoma. Thirty-nine children (21.4%) had normal ocular examinations and most of these cases were attributed to cerebral visual impairment. Abnormalities of the whole globe were seen in 34 children (18.7%). Microphthalmia was the leading cause, present in 16 children (8.4%). Glaucoma was present in five children (2.7%) and corneal scarring found in five children (2.7%), with causes identified as Peter’s anomaly and other congenital corneal opacities. Uveal conditions were found in six children (3.3%); five had aniridia and one had bilateral chorioretinal colobomas. Cataract was the cause of visual impairment in six children (3.3%), mainly due to late diagnosis and severe amblyopia after cataract surgery.

Aetiology of visual loss

Hereditary diseases accounted for 23.6% of cases. Most of these conditions were oculocutaneous albinism and retinal dystrophies. Intrauterine factors such as congenital rubella syndrome and cytomegalovirus infection contributed to a smaller percentage, of 3.3%.

Perinatal factors, which included cerebral palsy and retinopathy of prematurity, resulted in visual impairment in 15.3% of children. Postnatal childhood infections and trauma resulted in 9.3% of cases. However, the largest proportion of cases, 48.5%, fell under disorders of unknown aetiology. These included conditions such as hydrocephalus, microphthalmos, anophthalmos, glaucoma and optic nerve hypoplasia, which could not be clearly attributed to hereditary, intrauterine, or perinatal risk factors. (Table II).

Avoidable causes

The term ‘avoidable blindness’ is used to encompass the conditions causing blindness which can be prevented or treated. Avoidable causes of visual impairment are shown in Table III. Forty-one children (22.5%) had underlying causes that could have been avoided. These comprised 25 (13.7%) with conditions amenable to primary prevention, such as cerebral palsy, neonatal infections, and trauma, as well as 16 (8.8%) with visual impairment secondary to treatable conditions, including cataract, glaucoma, and retinopathy of prematurity.

Discussion

The WHO has reported a notable variation in childhood blindness prevalence according to socioeconomic development levels across regions. Specifically, they found higher rates of visual impairment in lower-income areas, and the estimated global prevalence of blindness among children was approximately 0.75/1000 children in 1999.12 This study contributes novel insights into the causes of childhood blindness among children in Cape Town. O’Sullivan et al. provided a comprehensive overview of childhood blindness across South Africa in 1997 and in 2020, Esra reported on visual impairment in children in a school for the blind in Johannesburg.8,9

These studies found different leading causes of childhood blindness when compared to ours. Esra reported retinal conditions as the primary cause of blindness in school children in 42% of cases, followed by whole globe abnormalities in 16% of cases. Similarly, O’Sullivan found retina to account for 38.5% of childhood blindness, with optic nerve being the second highest at 15.2%.8,9

The high prevalence of retinal disorders in these earlier studies was attributed to high rates of retinopathy of prematurity, aligning them more closely with developing country profiles. Additionally, the O’Sullivan et al. study identified cornea as a major cause (11.2%), consistent with typical patterns across sub-Saharan Africa. (Table IV)

In Cape Town, the top three anatomical sites contributing to blindness were the optic nerve, retina, and cases where the globe appeared normal. This clinical profile is more closely aligned to that of childhood blindness in the developed nations. When compared to other provinces in South Africa, the Western Cape is known to perform better in terms of health care delivery. It scored amongst the highest of several clinical, management and financial indicators, including provincial expenditure on the district health system in 2011-12 (DHB 20112012). In the 2019-2020 financial year, the Western Cape recorded the second highest proportion of “Ideal Clinics” (a measure of adherence to high quality performance) and “Core essential medicines availability”, after Gauteng, the province with the highest gross domestic product in Africa. (https://www.gov.za/provinces). The Western Cape Province also reported the highest ratio of medical practitioners per 100 000 population in the public sector in the same period. (DHB 2019-2020). Hence the clinical profile of childhood blindness found here may not be generalisable to the rest of the country, or indeed the larger African continent.

The leading anatomical site of childhood blindness found in this study was optic nerve disease in 27% of cases. This proportion is significantly higher than reported in previous South African studies. The Johannesburg school for the blind study recorded optic nerve disease in just 10% of children, while the O’Sullivan et al. study reported it at 15.2%.8,9 Our figure of 27% is more aligned with data from established market economy (EME) countries,12 where optic nerve conditions have been attributed to approximately 25% of visual impairment. (Table IV ) Retinal pathology also represented a significant proportion of visual impairment cases in our study (23.6%). It included two prominent aetiologies - retinal dystrophies and oculocutaneous albinism, accounting for 8.2% and 5.6% of cases respectively. The third highest cause was where the globe appeared normal (21.4%), the majority of these cases were attributed to cerebral visual impairment (20.3%), these data match closely to data on the anatomical causes of blindness for EME countries.

Congenital anomalies affecting the whole globe were also common, affecting 15.3% of cases. Genetic diseases and intrauterine factors are the likely underlying reasons for these conditions, although the causes remain unknown in most cases. There seems to be large regional differences in the percentages of blind school children with congenital anomalies. Data shows the rates ranging from 1.4% of blind students in Cuba to as high as 33.2% in Sri Lanka.13 This wide range suggests that factors that influence the prevalence of such anomalies may vary significantly between locations.

Glaucoma accounted for 2.7% of treatable visual loss cases in this study. This was lower than the value documented in the previous 1997 national study of childhood blindness in South Africa by O’Sullivan et al., which found glaucoma in 6.7% of cases.8 This study’s lower percentage is more similar to studies from developed world regions, such as 1.1% of cases in New Zealand and 5% of cases in the UK.14,15 The glaucoma prevalence observed here was also lower than values documented for other African countries. For example, glaucoma caused blindness in approximately 9% of paediatric populations in both Ghana and Nigeria.16,17 Our findings therefore indicate the glaucoma burden in Cape Town children appears more closely aligned to developed nations than other parts of the continent.

Congenital cataract is a leading cause of surgically correctable blindness worldwide, with a reported global incidence ranging from one to 15 per 10 000 live births.18 However, data on childhood cataract prevalence specifically in South Africa is limited. In this study, lens-related disorders accounted for 3.3% of visual impairment cases, which is lower than the 3.7% reported in the previous 1997 national study of childhood blindness in South Africa by O’Sullivan et al. and is less than percentages reported for EME countries (8%) and globally (12%). This study’s low rate approximates the 3.6% reported in New Zealand.12,14

ROP was an unexpectedly uncommon finding in our study, with only five identified cases accounting for 2.7% of all childhood blindness causes. This is significantly lower than what was found in the previous study from 25 years ago, which reported ROP accounting for 10.6% of childhood blindness cases.8 However, the epidemiology of ROP-induced blindness is changing. In developed nations, implemented screening protocols have proven highly effective at reducing ROP rates.19 But it is emerging as an increasingly important, yet avoidable, cause of vision impairment in middle-income countries. This shift reflects improvements in perinatal care that have raised survival rates of preterm infants who are most at risk of developing ROP.19

In the developing world, the main pathology leading to blindness is corneal scarring resulting from conditions such as vitamin A deficiency, measles infection, ophthalmia neonatorum, or harmful traditional remedies.20 However, there were no such cases recorded in this study. This result is much improved compared to 25 years ago in South Africa, when corneal scarring accounted for 11.2% of childhood blindness cases.8

A significant proportion of our cases, (22.5%) fell under the WHO classification of avoidable causes. Previous research suggests approximately two-thirds of childhood blindness in low-income countries is avoidable.21 We found 22.5% of causes were avoidable, through either prevention or treatment. The reduction in blindness due to avoidable causes in South Africa, from 38.8% in previous local study to the current 22.5%, reflects the successful implementation of large-scale primary healthcare initiatives. 8 Campaigns have facilitated wide distribution of measles and rubella immunisation through South Africa’s Expanded Program on Immunisation (EPI-SA), initiated in 1995. Additionally, programmes have supported newborn eye prophylaxis and vitamin A supplementation.22

While eradicating all preventable causes of blindness remains a priority, it is also apparent that confronting unavoidable conditions like microphthalmos, congenital exophthalmos and retinal dystrophies poses a significant, ongoing challenge. Further research is needed to better understand the genetic and pathological underpinnings of these disorders. Advances in technologies such as genetic testing and counselling may help reduce the incidence of blindness due to inherited diseases.

Limitations

The findings of this study relate to a cohort of children diagnosed at a tertiary eye care facility in an urban setting in South Africa and may not necessarily be generalisable to the country as a whole. Some limitations existed when reporting visual impairment rates from blind school application forms. However, missing data was minimised by retrieving patient clinical notes wherever the referral forms were incomplete. We only included children from birth to 13 years in our study and did not report on those aged 13 to 16, who are still defined as children under the UNICEF criteria.

Conclusion

We found optic nerve (27%), retina (23.5%) and normal globe (21.4% - mainly cerebral visual impairment) to be the most common causes of childhood blindness in Cape Town during the 12-year study period. These proportions are more closely aligned with the developed nations and indicate a different clinical profile when compared to prior, nationwide studies. This information may help guide future public health strategies to target the specific causes identified.

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