Scleral rigidity at puberty

Ocular findings in central precocious puberty

PURPOSE

To evaluate ocular findings in central precocious puberty (PP).

METHODS

This prospective study included 38 children with PP and 34 healthy control children. All participants were evaluated in terms of refractive error, axial length (AL), and anterior segment parameters, including keratometry (K), corneal volume (CV), anterior chamber depth (ACD), anterior chamber volume (ACV), and iridocorneal angle (ICA). Central macular thickness (CMT), retinal nerve fiber layer (RNFL) thickness and central subfoveal choroidal thickness (ChT) were also analyzed. The correlation of these parameters with Tanner stage was also investigated in the PP group.

RESULTS

Compared with the control group, spherical refraction was less hyperopic (P = 0.017) and AL was significantly higher (P = 0.001) in the PP group. Spherical value and AL were significantly associated with the Tanner stage. None of the anterior segment parameters obtained by Pentacam was different in the PP group compared with controls. In PP cases, CMT and RNFL thicknesses in all sectors did not differ from controls. Subfoveal ChT was significantly higher in the PP group, regardless of Tanner stage (P < 0.001).

CONCLUSIONS

In our cohort of children with central PP, AL and ChT were higher than in children without PP.

The expandability of the eye in childhood myopia

PURPOSE

While intraocular pressure has been shown to have some influence on eye growth, the stress exerted on the outer wall of the eye and the rigidity of the outer coats of the eye may be of greater importance. No studies have assessed the significance of both of these variables in terms of childhood myopia and its progression.

METHODS

Twenty myopic and twenty non-myopic children aged 8 to 12 years participated in the study. Refractive error (including refractive error shift over the past year), ocular dimensions (anterior chamber, lens thickness, vitreous chamber, axial length), intraocular pressure, equatorial scleral rigidity, and outer wall thickness were measured for right eyes. Outer wall stress was calculated using the approximation, p = IOP*r/2t.

RESULTS

The myopic group was 3.43 D more myopic and had 1.43 mm longer eyes on average than the non-myopic group. The myopic children had experienced a mean refractive shift of -0.30 D/yr over the past year. Equatorial wall thickness was significantly less in myopes than non-myopes (difference of 0.09 mm, p = 0.02) and in the combined sample was correlated to refractive error (r = 0.312, p = 0.05), but not refractive error shift. Ocular rigidity and eye wall stress values were similar in the two groups. The refractive shift increased as wall stress increased both in the combined sample (r = -0.386, n = 35, p = 0.022) and the myopic group (r = -0.600, n = 16, p = 0.014).

CONCLUSION

We did not find large differences in wall thickness, ocular rigidity, or wall stress in myopic and non-myopic children. While reduced ocular rigidity, increased wall stress and scleral thinning may have a role in myopia progression in childhood we were not able to clearly show this in our study of 40 children.

The effect of intraocular gas and fluid volumes on intraocular pressure

Large increases in the intraocular pressure (IOP) of postoperative gas-containing eyes may require the removal of gas or fluid to reduce the IOP to the normal range. Application of the ideal gas law to Friedenwald's equation provides a mathematical model of the relationship between IOP, intraocular gas and fluid volumes, and the coefficient of scleral rigidity. This mathematic model shows that removal of a given volume of gas or fluid produces an identical decrease in IOP and that the more gas an eye contains, the greater the volume reduction necessary to reduce the pressure. Application of the model shows that the effective coefficient of scleral rigidity is low (mean K, 0.0021) in eyes with elevated IOP that have undergone vitrectomy and retinal cryopexy and very low (mean K, 0.0013) in eyes with elevated IOP that have undergone placement of a scleral buckle and band. By using the appropriate mean coefficient of rigidity, the volume of material to be aspirated to produce a given decrease in IOP can be predicted with clinically useful accuracy.