Newborns’ eyesight
Many parents consider that their babies are able to see them after a few days of life.
“It seems that the baby is looking at us”, they say. In spite of the fact that infants learn to see since birth, the complexity of their sight requires some explanations.
At birth, all the morphological structure of the visual system is already formed. “Visual impulses exist before birth, even without a luminous stimulus. They are transmitted by chemical stimuli genetically determined, and they are responsible for the development of the nervous structures of the visual system, namely the lateral geniculate body and the primary visual cortex”, explains the ophthalmologist Dr. Augusto Magalhães.
Nevertheless, focusing capacity is little developed, not going beyond 30 centimetres.
“It is as if the newborn was myopic”, elucidates Augusto Magalhães. But this capacity is quickly improved till the age of 6 months, enabling then the baby to focus up to a distance of 3 metres.
The nerve cells of the central area of the retina (fovea) undergo important improvements in their organization and structure during the first months of life.
The ophthalmologist, interviewed by the Portuguese periodical “Mãe Ideal”, explained that “the optic nerve, which conducts visual information from the eye to the brain, improves its transmission speed during the first 2 years of life. Besides, after birth, the cerebral cortex undergoes a great evolution due to the visual stimuli it receives”.
What do newborns see?
Newborn babies see unclear forms and distinguish border lines between objects. “Images are black and white and grey shades blurs. At birth, visual acuity is very low, owing to the immaturity of the nerve cells of the retina and the cerebral cortex: it was estimated to be about 0.5/10.
Besides, the reactions to visual stimuli are very rudimentary: slow movements of the head and the eyes towards the visual stimulus enable spatial locating”, explains Augusto Magalhães.
Despite the opinion of some parents about their babies being able to see them, newborns’ behaviours are related to reflexes, which are transmitted “by sub-cortical mechanisms, that is to say, which do not involve the cerebral cortex. At birth, visual behaviour is no exception to this rule, what explains the rudimentary reactions to visual stimuli”.
But the visual function evolves very quickly during the first 2 or 3 months of life. “Ocular structures undergo rapid functional improvements and the performance of the visual cortex progresses rapidly due to the visual stimuli”, says the ophthalmologist.
New abilities and capacities
The visual stimulus enables the development of the various elements of vision. These include aspects related to movement, orientation, colour and binocular disparity. After acquiring these abilities connected with the visual cortex, “the baby is beginning to have the capacity to integrate all these aspects in order to create the cerebral representation of an object, and also the capacity to dissociate this information so that this object can be distinguished from the background and the other objects”, explains Augusto Magalhães. Look fixation and attention are integrated later in the visual phenomenon. The capacity to decide to gaze at a certain object, or to move the gaze towards another one, represents a new and more complex ability that requires a cortical development only acquired around 5 or 6 months of age. “All this evolution is integrated in a global development, which includes the evolution of motor aspects. Attention and gazing capacity enable the baby, in a first stage, to explore the near visual space, leading to the capacity to touch and to hold the objects within reach; in a second stage, when the infant acquires the capacity to crawl and to walk, they enable it to explore the far visual space”, explains the ophthalmologist.
Visual acuity and the capacity to distinguish contrasts are the final result of all these visual abilities acquired during the first months of life.
Augusto Magalhães specifies that “visual acuity is estimated to evolve from 0.5/10, at birth, to 2/10 or 3/10, around 1 year of age. Adult visual acuity is only attained between the ages of 4 and 6 years”.
Discrimination of colours
The capacity to discriminate colours is also developed during the first months of life. Initially, at 2 months of age, babies distinguish green and red. Only later, around the age of 3 months, they recognize the blue colour. “A curious fact is that children only name colours consistently after 3 or 4 years of age, despite being able to discriminate them during the first months of life and despite including primary colours among the first 200 words they learn”, remarks Augusto Magalhães.
Do babies recognize their parents?
With only a few days of life, babies already show a preference for familiar faces, particularly for their mothers’, whom they identify since birth, from suckling them. “Nevertheless, this preference is based only on the characteristics of the contour of the face or the profile of the hair. This phenomenon is known as externality effect. If the mother changes her hairstyle or uses a hat that modifies her profile, the newborn hardly recognizes her”, which is a curious fact.
A real recognition of facial features only occurs after the age of 3 months, when a specific area of the temporal cortex is integrated in the visual function. The recognition of human faces depends on the development of that particular zone of the cerebral cortex.
Newborn babies’ eye care
If the pregnancy and the childbirth elapse normally, there is no need for special care apart from the basic general health care. This includes medical assistance, adequate nourishment and good hygiene care.
“All newborns should be examined by a paediatrician, who knows how to investigate the morphological aspects of the baby’s eyes and to detect malformations of the eyeball. Besides, paediatricians observe the red reflection of the eye fundus in order to identify any serious cause for deficient sight, such as congenital cataract and some forms of ocular tumours”, explains Augusto Magalhães.
Hygiene care is important to prevent infections and possible sequelae affecting the visual system. In Portugal, severe infections are rare, but there exist regions in the world with endemic ocular infections (for example, trachoma) that can cause blindness.
“Nourishment is very important. Whenever possible, babies should be suckled: maternal milk ensures a balanced diet, at all levels, and its high content of polyunsaturated fatty acids favours a more rapid development of the baby’s visual function”, says the ophthalmologist.
All the babies presenting alterations in the morphology of the eyes or the reflection of the eye fundus should be referred to an ophthalmological consultation. Likewise, the babies with a familial history of ocular diseases, a neurological disease, a genetic disease, facial dysmorphies or a history of prematurity should also be examined by a specialist.
Definitive colour of the eyes: since when?
After the sex, the colour of the eyes is the most remarked characteristic of a newborn baby!
“The colour of the eyes is in fact the colour of the iris. The iris structure presents essentially two layers: a posterior layer, very pigmented in all individuals (pigmented epithelium of the iris), which filters the entrance of light into the eye, and an anterior layer, named stroma, in which the quantity of pigment varies with the person. It is precisely the pigment of the stroma that defines the colour of the eyes. The stroma pigment increases after birth by the action of light (as occurs in the skin). A 1 year old child has usually half of the final pigment of its iris, and only around 3 years of age is the pigment definitive”, elucidates Augusto Magalhães.
Thus, in children with dark iris at birth, the colour is practically definitive, but in newborns with light-coloured iris, the definitive colour is hardly defined before 1 year of age and its darkening is possible until the age of 3 years.
Even after infancy the colour of the eyes can change, and some diseases and medicines alter the colour of the eyes in any moment of life.
Possible development of visual diseases
The visual system of the newborn may be affected by a great number of diseases: some involve exclusively the eyes, but others are associated with general diseases that can inclusively jeopardize the baby’s general health and life.
“Besides congenital anomalies, which include alterations of the shape and size of the eyeball, it is important to point out ptosis (drooped eyelid) and congenital cataract, due to their significance and frequency. These two problems obstruct the visual axis and hinder the correct development of the visual function, requiring therefore an urgent solution. This type of cataract may be due to genes inherited from progenitors or it may be associated with other general diseases of the baby”, explains Augusto Magalhães.