15 - Growth and Development of the Eye Flashcards
% de la population ayant un oblique inférieur avec 2 bellies
Most inferior oblique muscles have a single belly, but approximately 10% have 2 bellies; in rare cases, there are 3
2 principaux moyens utilisés pour quantifier l’AV chez un enfant pré-verbal
Two major methods are used to quantitate visual acuity in preverbal infants and toddlers:
- Preferential looking (PL)
- Visual evoked potential (VEP)
VEP studies show that visual acuity improves from approximately 20/400 in newborns to 20/20 by age 6–7 months.
However, PL studies estimate the visual acuity of a newborn to be 20/600, improving to 20/120 by age 3 months and to 20/60 by 6 months.
Further, PL testing shows that visual acuity of 20/20 is not reached until age 3–5 years.
The discrepancy between measurements obtained by these 2 methods may be related to the higher cortical processing required for PL compared with VEP.
3 facteurs importants jouant un rôle de le dévéloppement d’une erreur réfractive
Race
Ethnicité
Hérédité
Caractérisques du développement de l’orbite des annexes (volume de l’orbite, dimensions de l’orbite, fosse lacrymale, fissure palpébrale)
- Orbital volume increases
- The orbital opening becomes less circular, resembling a horizontal oval
- The lacrimal fossa becomes more superficial
- The angle formed by the axes of the 2 orbits less divergent.
- The palpebral fissure measures approximately 18 mm horizontally and 8 mm vertically at birth.
- Growth of the palpebral fissure is greater horizontally than vertically = resulting in the eyelid opening becoming less round and acquiring its elliptical adult shape.
- Most of the horizontal growth occurs in the first 2 years of life
Caractéristique de la PIO chez l’infant
- Normal IOP is lower in infants than in adults
- A pressure higher than 21 mm Hg should be considered abnormal
- CCT influences the measurement of IOP, but this effect is not well understood in children
Caractéristiques (ex. âge et croissance de la longueur axiale) de la FIRST phase
- Birth to age 2 years
- Period of rapid growth
- The axial length increases by approximately 4 mm in the first 6 months of life and by an additional 2 mm during the next 6 months.
Caractéristiques de la SECOND phase du développement de la longueur axiale
- Age 2 to 5 years
- Growth slows
- Axial length increasing by about 1 mm per phase.
Caractéristiques du développement de la longueur la THIRD phase
The THIRD phase
- Age 5 to 13 years
- Growth slows
- Axial length increasing by about 1 mm per phase.
Caratéristiques du développement de la cornée (diamètre, courbure, kératométrie).
- The corneal diameter increases rapidly during the first year of life.
- The average horizontal diameter of the cornea is 9.5–10.5 mm in newborns and increases to 12.0 mm in adults.
- The cornea also flattens in the first year such that keratometry values change markedly, from approximately 52.00 diopters (D) at birth, to 46.00 D by age 6 months, to adult measurements of 42.00–44.00 D by age 12 months.
Conjugate _______ gaze is present at birth, but _______ gaze may not be fully functional until 6 months of age.
Conjugate HORIZONTAL gaze is present at birth, but VERTICAL gaze may not be fully functional until 6 months of age.
Dans quelle année de vie a lieu la majorité de la croissance de l’oeil?
Most of the growth of the eye takes place in the first year of life.
Distance entre l’insertion des muscles rectus et le limbe selon l’âge.
- In newborns, the distance from the rectus muscle insertion to the limbus is roughly 2 mm less than that in adults;
- By age 6 months, this distance is 1 mm less;
- And at 20 months, it is similar to that in adults.
Décrire les 3 phases de développement de la longueur axiale de l’oeil
The FIRST phase
- Birth to age 2 years
- Period of rapid growth
- The axial length increases by approximately 4 mm in the first 6 months of life and by an additional 2 mm during the next 6 months.
During the SECOND (age 2 to 5 years) and THIRD (age 5 to 13 years) phases
- Growth slows
- Axial length increasing by about 1 mm per phase.
Définir Agenesis
Developmental failure (ex. anophthalmia)
Définir Hypoplasia
Developmental arrest (ex. optic nerve hypoplasia)
Définir Hyperplasia
Developmental excess (ex. Distichiasis)
Définir Dysraphism
- Failure to fuse (ex. choroidal coloboma)
- Failure to divide or canalize (ex. congenital nasolacrimal duct obstruction)
- Persistence of vestigial structures (ex. persistent fetal vasculature)
Définition de l’emmétropisation
Emmetropization in the developing eye refers to the combination of changes in the refractive power of the anterior segment and in axial length that drive the eye toward emmetropia.
Exemples :
- The reduction in astigmatism that occurs in many infant eyes
- The decreasing hyperopia that occurs after age 6–8 years
Définir malformation
A malformation implies a morphologic defect present from the onset of development or from a very early stage.
- A disturbance to a group of cells in a single developmental field may cause multiple malformations.
- Multiple etiologies may result in similar field defects and patterns of malformation.
Définition de sequence (dans le contexte d’un abnormal growth and development)
A single structural defect or factor can lead to a cascade, or domino effect, of secondary anomalies called a sequence.
Développement de l’épaisseur centrale de la cornée
- Central corneal thickness (CCT) decreases during the first 6–12 months of life
- It then increases from approximately 553 μm at age 1 year to about 573 μm by age 12 years and stabilizes thereafter.
Environ « de combien » plus minces sont les insertions des muscles rectus chez les enfants?
Muscle insertions, on average, are 2.3–3.0 mm narrower
Est-il N d’avoir du corneal clouding chez le n-né?
- Mild corneal clouding may be seen in healthy newborns and is common in premature infants.
- It resolves as the cornea gradually becomes thinner, decreasing from an average central thickness of 691 μm at 30–32 weeks’ gestation to 564 μm at birth.
L’astigmatisme est-elle plus commune chez les African American children, les Hispanic children ou les non-Hispanic White children?
L’atisgmatisme est plus fréquent chez les African American children et les Hispanic children.
L’hypermétropie est-elle plus commune chez les African American children, les Hispanic children ou les non-Hispanic White children?
Hypermétropie plus commune chez les non-Hispanic White children
L’épaisseur cornéenne centrale est-elle similaire chez les White, les Hispanic ou les African American children
- Central corneal thickness (CCT) is similar in White and Hispanic children, whereas African American children tend to have thinner corneas.
La myopie est-elle plus commune chez les African American children, les Hispanic children ou les non-Hispanic White children?
Myopie est plus fréquente chez les African American children
La taille de la pupille d’un infant est-elle plus petite ou plus grande comparativement à l’adulte? Quelles dimensions sont suggestives d’une anomalie?
Compared with the adult pupil, the infant pupil is relatively small.
A pupil diameter less than 1.8 mm or greater than 5.4 mm is suggestive of an abnormality.
Qu’est-ce qu’un syndrome?
- A syndrome is a recognizable and consistent pattern of multiple malformations known to have a specific cause, which is usually a mutation of a single gene, a chromosome alteration, or an environmental agent.
- An association represents defects known to occur together in a statistically significant number of patients.
- An association may represent a variety of yet- unidentified causes.
- Two or more minor anomalies in combination significantly increase the likelihood of an associated major malformation.
Quel est le % de major congenital anomalies of live births?
Major congenital anomalies occur in 2%–3% of live births.
Quel Tx a démontré une diminution significative du développement de la myopie chez les enfants asiatiques?
Low- dose (0.01%) atropine has been shown to significantly decrease myopic progression in Asian children.
Quelle est la kératométrie N chez le newborn versus chez l’adulte?
Newborn : 52,00 D
Adulte : 42,00 - 44,00 D
Quelle est la longeur axiale N chez le newborn versus chez l’adulte?
Newborn : 14,5 - 15,5 mm
Adulte : 23,0 - 24,0 mm
Quelle est le D cornéen horizontal N chez le newborn versus chez l’adulte?
Newborn : 9,5 - 10,5 mm
Adulte : 12,0 mm
Quelles sont les causes de major congenital anomalies?
Causes include
- Chromosomal abnormalities
- Multifactorial disorders
- Environmental agents
- But many cases are idiopathic
Quelles sont les hypothèses expliquant l’augmentation de la prévalence de la myopie worldwide?
The etiology of increased myopia prevalence is unclear, but urbanization, increased near work, and decreased exposure to ultraviolet light are suggested influences.
Quels sont les dimensions N suivantes chez le newborn versus chez l’adulte :
- Longeur axiale (en mm)
- Diamètre horizontal de la cornée (en mm)
- Kératométrie/puissance réfractive de la K (en D)
NEWBORN
- Longeur axiale = 14.5-15.5 mm
- Diamètre horizontal de la cornée = 9.5-10.5 mm
- Kératométrie/puissance réfractive de la K = 52.00 D
ADULT
- Longeur axiale = 23.0-24.0 mm
- Diamètre horizontal de la cornée = 12.0 mm
- Kératométrie/puissance réfractive de la K = 42.00-44.00 D
V ou F, la fonction des MEOs continue de se développer après la naissance.
Vrai, extraocular muscle function continues to develop after birth.
V ou F, la macula est bien développée à la naissance.
Faux.
The macula is poorly developed at birth but changes rapidly during the first 4 years of life.
Most significant are changes in
- macular pigmentation
- development of the annular ring and foveal light reflex
- differentiation of cone photoreceptors.
Improvement in visual acuity with age is due in part to development of the macula, specifically, differentiation of cone photoreceptors, narrowing of the rod- free zone, and an increase in foveal cone density
V ou F, la prévalence de la myopie augmente worldwide?
Vrai
V ou F, les rectus muscles sont plus larges chez les enfants.
Faux.
The rectus muscles of infants are smaller than those of adults.
V ou F, les tendons des muscles rectus sont thinner chez les enfants
Vrai, the tendons are thinner in infants than in adults.
À combien estime-t-on la prévalence de la myopie worldwide en 2050?
It is estimated that by 2050, 50% of the world population will be myopic.
À la naissance, l’oeil est-il hypermétrope ou myope?
- The refractive state of the eye changes as the eye’s axial length increases and the cornea and lens flatten.
- In general, eyes are hyperopic at birth, become slightly more hyperopic until approximately age 7 years, and then experience a myopic shift until reaching adult dimensions, usually by about age 16 years (Fig 15-1).
DONC :
- Hypermétropie à la naissance
- Augmentation de l’hypermétropie ad 7 ans
- Shift myopique ad 16 ans
- Résultante : oeil emmétrope
À partir de quel AG le réflexe pupillaire à la lumière est-il normalement présent
The pupillary light reflex is normally present after 31 weeks’ gestational age
À quel AG débute le développement de la vascularisation rétinienne? Et où a/n de la rétine débute-t-elle?
Retinal vascularization begins at the optic disc at 16 weeks’ gestational age.
À quel AG la vascularisation rétinienne atteint l’ora serrata en temporal?
Retinal vascularization begins at the optic disc at 16 weeks’ gestational age and proceeds to the peripheral retina, reaching the temporal ora serrata by 40 weeks’ gestational age.
À quel âge l’accomodation et la fusion de convergence est-elle présente chez l’enfant?
Accommodation and fusional convergence are usually present by age 3 months.
À quel âge la stereo acuity atteint-elle le 60 seconds of arc?
Stereo acuity reaches 60 seconds of arc by about age 5–6 months
À quel âge le développement de la myopie chez un enfant augmente son risque d’une progression éventuelle à - 6,00 D ou plus?
If myopia develops before age 10 years, there is a higher risk of eventual progression to myopia of 6.00 D or more.
À quel âge le strabisme intermittent se résout-il spontanément souvent chez l’enfant?
Intermittent strabismus occurs in approximately two- thirds of young infants but resolves in most by 2–3 months of age.
À quelle période de l’enfant la couleur de l’iris peut-elle changer? Et pourquoi?
Most changes in iris color occur over the first 6–12 months of life, as pigment accumulates in the iris stroma and melanocytes.
À quoi ressemble le power du cristallin avec le développement?
The power of the pediatric lens decreases dramatically over the first several years of life
= important consideration when intraocular lens implantation is planned for infants and young children after cataract extraction.
Lens power decreases from approximately 35.00 D at birth to about 23.00 D at age 2 years.
Subsequently, the change is more gradual: lens power decreases to approximately 19.00 D by age 11 years, with little or no change thereafter.
