The aim of this study was to map out the developmental curve of the orbital volume of Chinese children aged 1–15 years.

CT scanning was performed on 109 children and the orbital volume, interlateral orbital rim distance (IORD), and extent of exophthalmos were measured on the CT images and plotted against age.

The development of the orbit structure followed a biphasic pattern. The first growth phase was before 3 years and the second growth phase was between 7 years and 12 years of age. The growth speed in the first phase was about 3 times that of the second one (first vs second phase: 2.28 cm^{3}/year vs 0.67 cm^{3}/year for orbital volume, 5.01 mm/year vs 1.57 mm/year for IORD, 1.29 mm/year vs 0.42 mm/year for the exophthalmos). During development, there was no significant difference between the left and right orbits. There was no significant difference between boys and girls before 12 years of age. However, after 12 years of age, boys had significantly larger orbital volumes (22.16±2.28 cm^{3}/year vs 18.57±1.16 cm^{3}/year, p<0.001) and a greater IORD (96.29±3.18 mm/year vs 91.00±4.54 mm/year, p<0.001) than girls.

In Chinese children, the development of orbital volume follows a biphasic pattern and a sex difference becomes significant after the age of 12 years.

The dynamic development of orbital volume during childhood creates several challenges for paediatric surgeons in clinical work.

Although several studies have been done in this field, some important controversies still exist. It is not clear if the orbital volume development follows a linear pattern with an even speed at any age, or if the developmental process has a certain phase with fast development and a certain phase with a slower speed. Although boys tend to have a larger orbital volume than girls, at which age the sex difference becomes significant is still debateable.

Therefore, the aim of this study was to estimate the orbital volumes in Chinese children up to 15 years of age using a spiral CT scan that has high accuracy and good repeatbility. The collected data could help with answer to address the controversies in this field.

The subjects, all of Han ethnicity, were children from many different parts of China who visited the Department of Ophthalmology at Tianjin Medical University for various ophthalmic diseases. CT scans were performed on each child. Children who had conditions that may disrupt the normal development of orbital structures, such as orbital lesions, craniofacial deformity or orbital fractures were excluded from the study. A total of 110 children were recruited, including 76 boys (69.1%) and 34 girls. The detailed breakdown of age and sex information is shown in

Demographic information of the subjects

Age | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | Total |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|

Male | 3 | 4 | 2 | 7 | 4 | 3 | 3 | 5 | 4 | 11 | 4 | 5 | 5 | 9 | 7 | 76 |

Female | 3 | 1 | 1 | 2 | 1 | 2 | 2 | 1 | 1 | 2 | 2 | 4 | 3 | 6 | 2 | 33 |

Subtotal | 6 | 5 | 3 | 9 | 5 | 5 | 5 | 6 | 5 | 13 | 6 | 9 | 8 | 15 | 9 | 109 |

The CT scans were performed on a double spiral CT (Prospeed, General Electronics, Chicago, USA). The voltage was set at 120 kV and the current was set at 150 mA. Each slice was 2 mm thick with a pitch distance of 1.5 mm to form a matrix of 512×512 pixels with a 200 mm field of view. Scanning was done in a horizontal orientation with the line connecting the external wall of the orbit and the external auditory canal was the baseline.

CT images illustrating the method to estimate the orbital volume (A), interlateral orbital rim distance and the extent of exophthalmos (B).

The working window was set to 250×50 HU (width×height) to have high resolution. The level was set to the one having the largest diameter for both eyeballs, the centres of the crystal lens and the optic nerves showing the entire intraocular pathway, with the lateral orbital rim shown as the lowest points. All of the measurements were done on this level of scan. The

In this study, SPSS V.12.0 statistical software was used to perform related statistical analysis. Least-square polynomial fitting and piecewise linear fitting was used to identify the different phases in development. An analysis of variance (ANOVA) test was applied to compare the values from different phases of development and post hoc comparisons were conducted with a Bonferroni correction. A t-test was used to compare the values obtained from boys and girls of the same age. A paired t-test was used to compare the values measured from the left and right orbits. A p value less than 0.05 was considered statistically significant.

The orbital volume was plotted against age to show the trend of development. Visual inspection suggested that the relationship between orbital volume and age is not a linear one. We fitted polynomial functions from the order of 1 (linear) all the way to the order of 12 and plotted the normalised sum of residual squares. The analysis indicated that a polynomial of fifth order was the best fit (

Developmental trend of orbital volume. (A) Developmental data fitted into a polynomial function of the fifth order. (B) Fitting errors versus the order of polynomial functions.

To further quantify the growth speed of each phase, a piecewise linear fitting was established over the range of all ages. For all three measures (orbital volume (

Piecewise linear fitting showing the developmental trend of orbital volumes (A), orbital width (B) and orbital protruding (C). In each panel, each circle represents a subject. Black lines represent the developmental trend and blue diamonds represent the mean value±SD of subjects in each of the developmental phases, outlined by the grey vertical lines.

Over the first 15 years of age, the orbit grew a lot, with a significant increase in orbital volume, IORD and the extent of exophthalmos (one-way ANOVA, p<0.001 in all three tests). The development of the orbital volume was fastest in the first phase (<3 years of age) with a slope of about 2.28. In the second phase (3–6 years of age), there was not much development at all with the slope close to zero. During the third phase (7–12 years of age), the development accelerated again with the slope increased to 0.67. In the last stage (>12 years of age), the development slowed down again with the slope reduced to 0.11 (

Statistics of orbital volume, interlateral orbital rim distance (IORD) and exophthalmos in the four developmental stages

A | |||||||
---|---|---|---|---|---|---|---|

Age (years) | N | Volume (cm^{3}) | IORD (mm) | Exophthalmos (mm) | |||

Mean±SD | Mean±SD | Mean±SD | |||||

<3 | 11 | 14.72±1.76 | 2.28 | 78.73±4.96 | 5.01 | 11.80±1.33 | 1.29 |

3–6 | 22 | 16.79±1.15 | −0.08 | 84.54±2.91 | 0.44 | 12.77±1.42 | −0.07 |

7–12 | 44 | 18.82±2.27 | 0.67 | 90.41±4.35 | 1.57 | 13.95±1.76 | 0.42 |

>12 | 32 | 20.92±2.61 | 0.11 | 94.47±4.445 | −0.16 | 15.31±1.75 | 0.02 |

B | |||||||

Age groups (years) | p Value | Age groups (years) | p Value | Age groups (years) | p Value | ||

<3 vs 3–6 | <0.001 | <3 vs 3–6 | <0.001 | <3 vs 3–6 |
| ||

<3 vs 7–12 | <0.001 | <3 vs 7–12 | <0.001 | <3 vs 7–12 | <0.001 | ||

<3 vs >12 | <0.001 | <3 vs >12 | <0.001 | <3 vs >12 | <0.001 | ||

3–6 vs 7–12 | <0.001 | 3–6 vs 7–12 | <0.001 | 3–6 vs 7–12 | 0.0082 | ||

3–6 vs >12 | <0.001 | 3–6 vs >12 | <0.001 | 3–6 vs >12 | <0.001 | ||

7–12 vs >12 | <0.001 | 7–12 vs >12 | <0.001 | 7–12 vs >12 | 0.0014 |

(A) Values are presented in the format of mean±SD. (B) The p value indicates the results from the possible combinations of comparisons.

The values from the right and left orbits were highly correlated for both the mean orbital volume (r=0.98) and the extent of exophthalmos (r=0.96). In each developmental phase, a paired t-test revealed no statistically significant difference between the two sides (

Statistical comparison of orbits on the right side and left side

Age (years) | N | Volume (cm^{3}) | Width (mm) | ||||||
---|---|---|---|---|---|---|---|---|---|

OD | OS | OD-OS | p Value | OD | OS | OD-OS | p Value | ||

<3 | 11 | 14.76±1.77 | 14.67±1.77 | 0.09±0.41 | 0.905 | 11.68±1.31 | 11.91±1.375 | −0.22±0.41 | 0.696 |

3–6 | 22 | 16.91±1.19 | 16.67±1.19 | 0.23±0.61 | 0.522 | 12.77±1.34 | 12.77±1.602 | 0±0.82 | 1.000 |

7–12 | 44 | 18.80±2.30 | 18.85±2.27 | −0.04±0.52 | 0.923 | 14.01±1.77 | 13.90±1.80 | 0.11±0.58 | 0.767 |

>12 | 32 | 21.02±2.61 | 20.83±2.64 | 0.18±0.62 | 0.778 | 15.34±1.83 | 15.28±1.69 | 0.06±0.35 | 0.887 |

Values are presented in the format of mean±SD. The p value indicates the comparison between the two sides (paired t-test).

OD, right eye, OS, left eye.

The overall developmental trends were very similar in boys and girls. Both groups demonstrated a fast phase before 3 years of age, slow phases between 3 years and 6 years, another fast phase between 7 years and 12 years, and a final slow phase after 12 years of age. This developmental pattern was clear for orbital volume, IORD and the extent of exophthalmos.

However, there were some subtle differences between boys and girls during the course of development. In the first two fast phases (up to 6 years of age), there was no difference in orbital volume (p=0.227 and p=0.62, respectively). In the second fast phase (7–12 years of age), the difference between boys and girls started to increase, with boys showing a larger orbital volume. The difference was not quite significant (p=0.075,

Statistics of orbital volume, interlateral orbital rim distance (IORD) and exophthalmos in the four developmental stages

Age (years) | N | Volume (cm^{3}) | IORD (mm) | Exophthalmos (mm) | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|

G | B | Girl | Boy | p Value | Girl | Boy | p Value | Girl | Boy | p Value | |

<3 | 4 | 7 | 13.84±1.49 | 15.22±1.80 | 0.227 | 77.50±4.65 | 79.43±5.35 | 0.563 | 11.75±0.96 | 11.82±1.57 | 0.936 |

3–6 | 6 | 16 | 17.00±0.88 | 16.71±1.26 | 0.62 | 84.33±3.08 | 84.63±2.94 | 0.839 | 12.42±1 0.07 | 12.91±1.54 | 0.485 |

7–12 | 12 | 32 | 17.83±2.20 | 19.20±2.22 |
| 89.42±5.62 | 90.78±3.82 | 0.361 | 13.92±2.01 | 13.97±1.70 | 0.932 |

>12 | 11 | 21 | 18.57±1.16 | 22.16±2.28 |
| 91.00±4.54 | 96.29±3.18 | <0.001 | 15.00±1.28 | 15.48±1.96 | 0.474 |

Values are presented in the format of mean±SD. The p value indicates the comparison between the boys and girls (t-test).

Line plots showing the developmental trend of the orbital volume (A), interlateral orbital rim distance (B) and extent of exophthalmos (C). In each panel, each blue circle represents a boy and each grey triangle represents a girl. Blue and black lines represent the developmental trend of boys and girls, respectively. Blue and black diamonds represent the mean value±SD of boys and girls in each of the developmental phases, outlined by the grey vertical lines.

For the subjects studied in this project, their orbital volumes, interlateral orbital rim distances and the extent of exophthalmos were significantly correlated with each other linearly (

Scatter plots showing the correlations among orbital volume, interlateral orbital rim distance and exophthalmos. Each dot represents a subject and the straight line represents the best-fit regression line.

Considering the development of structures close to orbits, the biphasic development of the orbital volume could potentially be explained in the following way. The first fast phase, before 3 years age, is mainly determined by the fast growth of facial bones, the eyeball and orbital bones. At birth, the

In the management of the nasolacrimal duct obstruction, one often has to choose between conservative medical therapy, probing and silicone intubation, and dacryocystorhinostomy (DCR).

Exenterated orbit in childhood often experiences growth retardation as a result of reduced volume stimulus.

Although Graves' disease is rare in children younger than 4 years old, it can seriously interfere with growth and development if not recognised and treated.

In our study, the strong correlation between the orbital volume and IORD may be attributed to the fact that both structures are primarily bony structures. In contrast, the correlations between exophthalmos and orbital volume were rather weak, although significant. The extent of exophthalmos is determined by the combination of several factors including orbital volume, soft content and the size of the globe. For exophthalmos seen in Graves' disease, it is the mismatch between increased orbital contents and normal bony orbital container. In non-syndromic exorbitism, it is the relatively small orbital capacity versus the normal volume of the orbital contents. High myopia is an aggravating factor due to the relatively larger size of the globe.

Our data revealed a biphasic development model of the orbital volumes, with most of the development happening within the first fast phase. Clinically, when considering the timing for any surgery involving craniofacial/orbital structures or orbital contents, it is important to reference the developmental phase. Since development of the orbit depends on the stimulation from the soft tissues located inside the orbit, in the fast phase, the surgery should be performed as early as possible to provide a sufficient implant. Hopefully the orbital bones can be adequately stimulated in order to preserve partial or even full development, with less risk of craniofacial deformation as an adult.

XQ had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: XQ, NW and BZ. Acquisition, analysis or interpretation of data: all authors. Drafting of the manuscript: BZ and NW. Critical revision of the manuscript for important intellectual content: all authors. Statistical analysis: BZ and NW.

None declared.

Guardian consent obtained..

This study protocol was approved by the Institutional Review Board of the Tianjin Medical University.

Not commissioned; externally peer reviewed.