Introduction

Cat eye syndrome (CES) is an extremely rare genetic disorder that affects roughly one in 50,000 to one in 150,000 live births, according to literature.¹ Despite being named after its most prominent characteristic, iris coloboma (IC) (figure 1), which results in a noticeably enlarged pupil that resembles a cat's eye, the effects on the retina and optic nerve² can cause much more severe complications. Although retinal colobomas (RC) occur less frequently than iris abnormalities, greater detrimental effects on vision can raise the likelihood of retinal detachment, which can result in secondary issues like glaucoma^.2,3

Understanding coloboma in cat eye syndrome 

 Coloboma is derived from the Greek word Koloboma,⁴ which means "cut short" or "missing." The iris, lens, retina, choroid, and optic nerve⁴ are all parts of the eye that may be impacted by this congenital disorder. Iris coloboma is the most prevalent type of coloboma in CES, occurring in one or both eyes and occurs in 50–60% of cases.⁵ 

Table 1. A comparison of vision impact between iris coloboma and retinal coloboma.

Pathophysiology of coloboma in CES

CES is brought on by partial trisomy or tetrasomy of chromosome 22's long and short arms during embryogenesis.^7,8 The eye develops from an optic vessel that folds in to form the optic cup during the first five to seven weeks of pregnancy. An embryonic optic fissure at the bottom of this cup enables blood vessels to supply the developing eye.³ By the seventh week of pregnancy,³ this fissure often resolves. Coloboma, on the other hand, results in a gap or missing tissue in that area of the eye because the fissure does not completely close. The risk of visual loss increases with the amount of missing tissue.

Vision issues linked to CES

IC mainly causes cosmetic changes, such as the “cat-eye” appearance and photophobia. It rarely causes severe vision loss but can affect a person's self-esteem, especially in children and young adults.⁹ 

Those who have RC are more likely to experience significant vision loss because the back of the eye is affected, where light is processed: 

Table 2: Summary of retinal coloboma and its management options. 

Diagnosis and eye evaluation 

Prenatal diagnosis of CES

CES is frequently suspected during standard ultrasound scans. Findings like anal atresia, heart problems, or kidney anomalies at the 20-week anomaly scan may result in specific diagnostic procedures like Chorionic villus sampling (first trimester) or amniocentesis (second trimester). By using karyotyping or FISH,² it can be confirmed whether chromosome 22 has a partial trisomy or tetrasomy.

Postnatal diagnosis of CES

CES is commonly identified after birth if it is not discovered during pregnancy by its distinctive characteristics. This includes IC, anal abnormalities and preauricular skin tags.² Diagnosis of CES is confirmed through genetic testing, and a thorough multisystem evaluation aids in the assessment of the heart, kidney, hearing, and neurodevelopmental functions.²

Assessment for coloboma 

Once CES has been confirmed, a comprehensive eye evaluation is conducted. 

• Slit lamp examination: To examine the iris and other front parts of the eye² 
• Fundoscopy and OCT imaging: To evaluate the retina, macula, and optic nerve²
• Visual acuity testing: Age- Age-appropriate methods, such as preferential looking for infants or letter charts for older children¹⁴
• Electroretinography: Used when retinal function is unclear or when vision loss is unexplained¹⁵ 

Management and treatment strategies 

Due to coloboma being a congenital anomaly, it has no definitive cure.² Treatment focuses on maximising vision, preventing or managing complications, and addressing cosmetic and psychosocial concerns. Given the multisystem nature of CES, a coordinated approach involving eye specialists, paediatricians, surgeons, and cardiologists is essential.² 

The severity of vision loss depends on the location and extent of the coloboma. Early intervention leads to better diagnosis and improved prognosis, and quality of life for affected children. Treatment should be personalised to each patient’s needs and regularly reviewed through comprehensive follow-up.

Clinical management: 

• Optical Correction: When there are refractive problems, using prescription glasses or contact lenses can significantly improve vision. Tinted lenses can help people with coloboma who experience photophobia, reducing light sensitivity and improving comfort and visual function¹⁵

• Surgical Intervention: When conditions like cataracts, retinal detachment, or major iris defects cause functional or cosmetic problems, surgery is the only treatment available. For example, removing a cataract can restore clear vision, while laser therapy or vitrectomy can be used to repair a detached retina and preserve remaining vision.^16-17 In some cases, cosmetic repair of the iris may also be considered to enhance the appearance and support psychological well-being

• Visual Rehabilitation: In certain situations, eye exercises and treatments that improve binocular vision and eye movement coordination may be beneficial. Low-vision aids can help with daily activities and education, such as using electronic devices, large-print materials, and magnifiers¹⁸

• Frequent Ophthalmic Monitoring: To detect and treat progressive conditions like glaucoma or retinal tears early, paediatric ophthalmologists need to conduct ongoing monitoring. Early detection and treatment can prevent irreversible vision loss

Full-rounded, effective care is more than just prescribing drugs or administering treatments to patients with CES. Psychological and social support are crucial in the care of patients with CES. Further, children with coloboma will often have to face challenges associated with visual impairment and appearance. This may affect their self-esteem and their interactions with friends. Providing access to vision rehabilitation, educational support, and counselling services is essential for comprehensive care.

Guardians of patients with CES should also be supported and educated on protective strategies. For instance, making home environments more visually accessible, using appropriate eye protection, and ensuring regular eye appointments. This will enable families to follow treatment plans and identify any changes in vision. 

Living with CES - psychosocial dimensions 

Lastly, parents and caregivers of children with coloboma should also receive support. This enables them to provide sensitive and specific care for their children. They should be encouraged to attend regular eye check-ups, use protective eye wear when appropriate, create visually accessible homes, and monitor any changes in their child's vision.

FAQs

Is coloboma curable?

No. Coloboma is a congenital condition where parts of the eye are missing and cannot be replaced. However, vision problems related to coloboma can be managed with regular eye check-ups, glasses or contact lenses, tinted sunglasses, and, in some cases, surgery or laser treatment if the condition leads to more serious eye issues, such as glaucoma, cataracts, or retinal detachment.

Will coloboma always cause blindness?

No. Iris coloboma usually has little or no effect on vision. However, those with retinal coloboma are at a higher risk of developing other eye conditions, such as glaucoma, which can lead to permanent vision loss. It is important for individuals with coloboma to have regular check-ups with specialists and monitor their vision to prevent the development of more serious eye conditions.

How often should people with coloboma have their eyes checked?

Children with coloboma should be seen by a paediatric ophthalmologist at least once a year.

More frequent visits may be needed if complications are found. Adults should have annual eye examinations and additional check-ups to test eye pressure for monitoring glaucoma risk.

Is coloboma always inherited?

No. Although coloboma may be part of a genetic condition like CES, it can also occur randomly due to developmental changes in the early stages of pregnancy.

Summary 

To summarise, CES is a complicated multisystem disorder with its main hallmark feature being coloboma. However, the impact it can have on vision can be drastic and life-changing, so patients with visual challenges due to CES must be monitored regularly by health care professionals. Effective management of CES should involve coordinated multidisciplinary care from various specialists, including ophthalmologists, cardiologists, and paediatricians.