PubMed · 14807416
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G T WARREN. 1951-02-15. Three interesting cases.. https://pubmed.ncbi.nlm.nih.gov/14807416/
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PURPOSE: To quantify and characterize higher order aberrations in children and to investigate the influence of refractive error and cycloplegia. DESIGN: Observational cross-sectional study. METHODS: setting: Clinical practice. patients: One hundred sixty-two eyes of 82 children were examined. The mean age of the children was 6.7 years (range, 4 to 14 years), and the mean manifest refractive spherical equivalent was 2.39 +/- 3.35 diopters (range, -8.98 to +8.45 diopters). Aberrometry was performed with a wavefront analyzer (after cycloplegia and mydriasis with cyclopentolate 1%). Aberrometry was also conducted on a subgroup of 52 eyes of 27 children, both before and 30 minutes after the instillation of cyclopentolate 1% to investigate the effect of paralysis of accommodation. RESULTS: Mean root mean square values of total-, third-, fourth-, and fifth-order aberrations were 0.37 +/- 0.13 microm, 0.23 +/- 0.12 microm, 0.16 +/- 0.11 microm, and 0.08 +/- 0.12 microm, respectively. Mean root mean square values of total coma (Z(3)(-1), Z(3)(1), Z(5)(-1), Z(5)(1)) and total trefoil (Z(3)(-3), Z(3)(3), Z(5)(-3), Z(5)(3)) were 0.27 +/- 0.31 microm and 0.21 +/- 0.29 microm, respectively. Myopes had statistically significant greater levels of total (P = .005) and fourth order (P = .002) aberrations and Zernicke terms (Z(3)(-3), Z(3)(-1), Z(3)(3), Z(4)(-4), and Z(4)(2)) compared with hyperopes. Cycloplegia had minimal influence on higher-order aberrations. CONCLUSION: Significant levels of higher-order aberrations were found in these children. They were influenced by refractive error, because myopes had significantly greater levels compared with hyperopes. Paralysis of accommodation with cyclopentolate appeared to have little effect on higher-order aberrations.
The behavior of the human crystalline lens during accommodation is analytically studied. The lens is modeled as a closed axisymmetrical membrane shell of varying thickness enclosing an incompressible liquid. To simulate zonular tension associated with lenticular accommodation, an axisymmetrical radial force or displacement is imposed around the shell equator. Two second-order, simultaneous, nonlinear governing differential equations are derived. Numerical results, obtained from the investigation of human lens profiles of three independently published MRI images and a drawing of a microphotograph, demonstrate that when zonular traction within the physiological force range of the ciliary muscle is exerted, both central lens thickness and central optical power increase. Qualitatively, these increases are independent of lens shape. However, the magnitude of these changes is dependent on the initial profile of the lens and is enhanced by the "natural" variation in capsular thickness. Only when a pulling force significantly exceeds the force capacity of the ciliary muscle does the lens flatten and its central thickness and optical power decrease.
Vergence eye movements were recorded with the scleral search-coil system in 32 healthy subjects (ages 19-73 years) to characterize the age-related effects on the dynamic parameters of vergence responses to step (transient components) and ramp or sinusoidal targets (sustained components) under natural viewing conditions. Transient vergence showed an age-related increase in latency and decreases in peak velocity and acceleration in the binocular stimulus condition but not in accommodative vergence. Sustained vergence showed no age-related effect in the binocular condition, but there was an age-related decrease in accommodative vergence steady-state velocity and an increase in latency. Age-related changes of the transient and sustained components were very similar to those reported for saccades and smooth pursuit; they thus might support a distinction between a sustained and transient vergence system. Furthermore, such age-related effects have to be taken into account when assessing eye movement disorders in neurodegenerative and cerebrovascular diseases.