15 - Growth and Development of the Eye

Question 1

% de la population ayant un oblique inférieur avec 2 bellies

Answer 1

Most inferior oblique muscles have a single belly, but approximately 10% have 2 bellies; in rare cases, there are 3

Question 2

2 principaux moyens utilisés pour quantifier l’AV chez un enfant pré-verbal

Answer 2

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.

Question 3

3 facteurs importants jouant un rôle de le dévéloppement d’une erreur réfractive

Answer 3

Race
Ethnicité
Hérédité

Question 4

Caractérisques du développement de l’orbite des annexes (volume de l’orbite, dimensions de l’orbite, fosse lacrymale, fissure palpébrale)

Answer 4

• 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

Question 5

Caractéristique de la PIO chez l’infant

Answer 5

• 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

Question 6

Caractéristiques (ex. âge et croissance de la longueur axiale) de la FIRST phase

Answer 6

• 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.

Question 7

Caractéristiques de la SECOND phase du développement de la longueur axiale

Answer 7

• Age 2 to 5 years
• Growth slows
• Axial length increasing by about 1 mm per phase.

Question 8

Caractéristiques du développement de la longueur la THIRD phase

Answer 8

The THIRD phase
- Age 5 to 13 years
- Growth slows
- Axial length increasing by about 1 mm per phase.

Question 9

Caratéristiques du développement de la cornée (diamètre, courbure, kératométrie).

Answer 9

• 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.

Question 10

Conjugate _______ gaze is present at birth, but _______ gaze may not be fully functional until 6 months of age.

Answer 10

Conjugate HORIZONTAL gaze is present at birth, but VERTICAL gaze may not be fully functional until 6 months of age.

Question 11

Dans quelle année de vie a lieu la majorité de la croissance de l’oeil?

Answer 11

Most of the growth of the eye takes place in the first year of life.

Question 12

Distance entre l’insertion des muscles rectus et le limbe selon l’âge.

Answer 12

• 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.

Question 13

Décrire les 3 phases de développement de la longueur axiale de l’oeil

Answer 13

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.

Question 14

Définir Agenesis

Answer 14

Developmental failure (ex. anophthalmia)

Question 15

Définir Hypoplasia

Answer 15

Developmental arrest (ex. optic nerve hypoplasia)

Question 16

Définir Hyperplasia

Answer 16

Developmental excess (ex. Distichiasis)

Question 17

Définir Dysraphism

Answer 17

• Failure to fuse (ex. choroidal coloboma)
• Failure to divide or canalize (ex. congenital nasolacrimal duct obstruction)
• Persistence of vestigial structures (ex. persistent fetal vasculature)

Question 18

Définition de l’emmétropisation

Answer 18

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

Question 19

Définir malformation

Answer 19

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.

Question 20

Définition de sequence (dans le contexte d’un abnormal growth and development)

Answer 20

A single structural defect or factor can lead to a cascade, or domino effect, of secondary anomalies called a sequence.

Question 21

Développement de l’épaisseur centrale de la cornée

Answer 21

• 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.

Question 22

Environ « de combien » plus minces sont les insertions des muscles rectus chez les enfants?

Answer 22

Muscle insertions, on average, are 2.3–3.0 mm narrower

Question 23

Est-il N d’avoir du corneal clouding chez le n-né?

Answer 23

• 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.

Question 24

L’astigmatisme est-elle plus commune chez les African American children, les Hispanic children ou les non-Hispanic White children?

Answer 24

L’atisgmatisme est plus fréquent chez les African American children et les Hispanic children.

Question 25

L’hypermétropie est-elle plus commune chez les African American children, les Hispanic children ou les non-Hispanic White children?

Answer 25

Hypermétropie plus commune chez les non-Hispanic White children

Question 26

L’épaisseur cornéenne centrale est-elle similaire chez les White, les Hispanic ou les African American children

Answer 26

• Central corneal thickness (CCT) is similar in White and Hispanic children, whereas African American children tend to have thinner corneas.

Question 27

La myopie est-elle plus commune chez les African American children, les Hispanic children ou les non-Hispanic White children?

Answer 27

Myopie est plus fréquente chez les African American children

Question 28

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?

Answer 28

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.

Question 29

Qu’est-ce qu’un syndrome?

Answer 29

• 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.

Question 30

Quel est le % de major congenital anomalies of live births?

Answer 30

Major congenital anomalies occur in 2%–3% of live births.

Question 31

Quel Tx a démontré une diminution significative du développement de la myopie chez les enfants asiatiques?

Answer 31

Low- dose (0.01%) atropine has been shown to significantly decrease myopic progression in Asian children.

Question 32

Quelle est la kératométrie N chez le newborn versus chez l’adulte?

Answer 32

Newborn : 52,00 D
Adulte : 42,00 - 44,00 D

Question 33

Quelle est la longeur axiale N chez le newborn versus chez l’adulte?

Answer 33

Newborn : 14,5 - 15,5 mm
Adulte : 23,0 - 24,0 mm

Question 34

Quelle est le D cornéen horizontal N chez le newborn versus chez l’adulte?

Answer 34

Newborn : 9,5 - 10,5 mm
Adulte : 12,0 mm

Question 35

Quelles sont les causes de major congenital anomalies?

Answer 35

Causes include
- Chromosomal abnormalities
- Multifactorial disorders
- Environmental agents
- But many cases are idiopathic

Question 36

Quelles sont les hypothèses expliquant l’augmentation de la prévalence de la myopie worldwide?

Answer 36

The etiology of increased myopia prevalence is unclear, but urbanization, increased near work, and decreased exposure to ultraviolet light are suggested influences.

Question 37

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)

Answer 37

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

Question 38

V ou F, la fonction des MEOs continue de se développer après la naissance.

Answer 38

Vrai, extraocular muscle function continues to develop after birth.

Question 39

V ou F, la macula est bien développée à la naissance.

Answer 39

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

Question 40

V ou F, la prévalence de la myopie augmente worldwide?

Answer 40

Vrai

Question 41

V ou F, les rectus muscles sont plus larges chez les enfants.

Answer 41

Faux.

The rectus muscles of infants are smaller than those of adults.

Question 42

V ou F, les tendons des muscles rectus sont thinner chez les enfants

Answer 42

Vrai, the tendons are thinner in infants than in adults.

Question 43

À combien estime-t-on la prévalence de la myopie worldwide en 2050?

Answer 43

It is estimated that by 2050, 50% of the world population will be myopic.

Question 44

À la naissance, l’oeil est-il hypermétrope ou myope?

Answer 44

• 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

Question 45

À partir de quel AG le réflexe pupillaire à la lumière est-il normalement présent

Answer 45

The pupillary light reflex is normally present after 31 weeks’ gestational age

Question 46

À quel AG débute le développement de la vascularisation rétinienne? Et où a/n de la rétine débute-t-elle?

Answer 46

Retinal vascularization begins at the optic disc at 16 weeks’ gestational age.

Question 47

À quel AG la vascularisation rétinienne atteint l’ora serrata en temporal?

Answer 47

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.

Question 48

À quel âge l’accomodation et la fusion de convergence est-elle présente chez l’enfant?

Answer 48

Accommodation and fusional convergence are usually present by age 3 months.

Question 49

À quel âge la stereo acuity atteint-elle le 60 seconds of arc?

Answer 49

Stereo acuity reaches 60 seconds of arc by about age 5–6 months

Question 50

À quel âge le développement de la myopie chez un enfant augmente son risque d’une progression éventuelle à - 6,00 D ou plus?

Answer 50

If myopia develops before age 10 years, there is a higher risk of eventual progression to myopia of 6.00 D or more.

Question 51

À quel âge le strabisme intermittent se résout-il spontanément souvent chez l’enfant?

Answer 51

Intermittent strabismus occurs in approximately two- thirds of young infants but resolves in most by 2–3 months of age.

Question 52

À quelle période de l’enfant la couleur de l’iris peut-elle changer? Et pourquoi?

Answer 52

Most changes in iris color occur over the first 6–12 months of life, as pigment accumulates in the iris stroma and melanocytes.

Question 53

À quoi ressemble le power du cristallin avec le développement?

Answer 53

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.