The Importance of Family Screening in Glaucoma
Dr Aparna Rao, Consultant - Glaucoma Services, L V Prasad Eye Institute, Bhubaneswar
Glaucoma constitutes an important cause for irreversible blindness,mostly due to obstruction of intraocular aqueous outflow passage resulting in raised intraocular pressure and optic nerve damage. This is predominantly seen in two forms in adults, namely, open (POAG) and closed angle (PACG) glaucoma, referring to the anatomic configuration of the inside of the eye which defines the mechanism of outflow obstruction.
POAG is estimated tobe hereditary in 1/4th-1/5th of cases. Though autosomal dominant and autosomal recessive mode of inheritance has been reported, exact mode of transmission remains unclear. Family history is a relative risk factor to raised IOP, early optic nerve damage or both. The prevalence of POAG in first degree relatives ranges from 2.8-13.5% in different studies. Rosenthal and Perkins have reported that the risk of raised IOP in patient with family history of POAG is 3-5 times more than the general population. So it is important to understand that glaucoma does not affect only individuals but also affects families. Various landmark trials have established the importance of early diagnosis and IOP control in preventing glaucomatous damage.
Similar observations have been made regarding angle closure glaucoma with most of the anterior segment parameters or “configuration’ of the eye being hereditary. The observed ethnic differences in prevalence of angle closure, and their underlying anatomic basis, have led to considerable interest in identifying a genetic basis of the disease. A positive family history has long been recognized as predisposing to angle-closure. The similarity of ocular biometry in first-degree relatives of patients appears to suggest that these anatomic characteristics of the “angle of the eye” are heritable.
Glaucoma in younger individuals termed as Juvenile open angle glaucoma is also known to be hereditary. Hence siblings and other family members need to be screened for glaucoma.
So screening of family members is of utmost importance in early diagnosis of glaucoma in first-degree relatives to avoid preventable blindness.
There is a strong familial inheritance of childhood glaucoma and the prevalence is very high among communities where consanguineous marriages are accepted socially, as seen in many parts of southern India. Hence screening of children is mandatory in such families. Also genetic counseling and planning the family helps in preventing this serious disease.
Who should be screened?
All first-degree relatives, parents, siblings, children should undergo detailed ophthalmological examination atleast once with specific emphasis on diagnosing glaucoma. While family history of glaucoma is a definite risk factor for adult glaucoma, similar risk holds true for another child if one child has glaucoma at birth-3 years (congenital or developmental glaucoma)or between 3-25 years (juvenile open angle glaucoma) of age. So screening of children along with genetic counseling of parents is essential for those with one or more children with glaucoma in the family.
When should they be screened?
While there is no set age at which screening should start, all patients should have their eyes tested atleast once beyond the age of 40 years if they have a family history of glaucoma. Children may also be screened at any age to rule out juvenile onset glaucoma or diagnosing steroid responders which are common in family members of patients with POAG.
What if they have glaucoma?
Various studies have established that reduction of IOP by early intervention can help prevent blindness and long term progression of glaucoma. So early diagnosis is a key for initiating early treatment which goes a long way in preventing further damage.
What if they are normal?
A normal examination at baseline does not rule out glaucoma and periodic screening atleast yearly in all family members. Such evaluations would include IOP assessment, gonioscopy and fundus evaluation. There is no cut off age beyond which screening should be stopped and risk can be deemed to be absent in a particular individual.