Patricia M. Kiely

The Mean Shape of the Human Cornea

The anterior surface of the cornea is the major refracting element of the human eye. Knowledge of its shape and the variation of this shape throughout the population are important in calculations of the corneal contribution to ocular aberrations. Since the cornea is the surface on which a contact lens rests, the corneal shape is also of importance in contact lens design. This paper presents results of the fitting of a conicoid equation to corneal shape data derived from a precision photokeratoscope. Both rotationally symmetric and non-rotationally symmetric forms of the conicoid equation were developed. The results show that if the cornea is regarded as a rotationally symmetric conicoid, the conicoid is ellipsoidal but with insufficient asphericity to eliminate spherical aberration for distance vision. More importantly, the results show that the cornea is significantly asymmetric in both radius of curvature and asphericity.

Diurnal variations of corneal topography and thickness.

ABSTRACT Measurements of central and peripheral corneal thickness, corneal topography, and central corneal curvature were made for 21 subjects at hourly intervals for 12 hr of 1 day for each subject. Values for corneal radius and asphericity were obtained from keratometry and photokeratoscopy, and their stability throughout the day was evaluated. Corneal radius was observed to steepen during the day, whereas asphericity remained constant. Corneal thickness was measured by pachometry and was found to be at its thickest on first awakening. Corneal curvature and central corneal thickness were highly correlated; low correlation was found between corneal asphericity and central corneal thickness. Some subjects exhibited large fluctuations in one or all of the parameters considered.

Disease-associated visual image degradation and spherical refractive errors in children

ABSTRACT Retrospective clinical data from 496 eyes of 256 children attending a low vision clinic were analyzed to determine the relation between disease states which involve visual image degradation and refractive error. Refractive data from 1023 normal vision children were used as a control. The low vision children were grouped according to their disease classification and the acknowledged age‐of‐onset of their visual disability. It was found that there was an overall inability to emmetropize and a trend towards myopia. It was also observed that the diseases which led to myopia were associated with a peripheral or peripheral plus central impairment of vision and that those conditions in which foveal vision was primarily impaired showed a mild hypermetropic trend. Eyes in which the visual impairment was not congenital but occurred before the age of 3 years tended to develop hypermetropia. The deviation from emmetropia decreased with increasing age‐of‐onset of the visual impairment, as did the variation about the mean refraction. The plastic period for emmetropization is estimated to end at 8 to 9 years of age.

Menstrual cycle variations of corneal topography and thickness.

ABSTRACT Two studies were performed to investigate dimensional stability of the cornea throughout the female menstrual cycle. In the first study, changes of corneal curvature, topography, and thickness were measured for six women for one complete menstrual cycle. Steepening of horizontal and vertical curvatures occurred at the beginning of the cycle, and flattening occurred after ovulation. Corneal thickening occurred on the second day of the cycle and around the time of ovulation, then thinning and another slight thickening on day 21. In the second study, more detailed information was sought on the timing of corneal thickness changes throughout any cycle. Corneal thickness was studied for two subjects throughout three consecutive cycles. Both subjects showed a slight decrease in thickness toward the end of the menses; thickening occurred at ovulation followed by thinning. Thickening also occurred 4 days after ovulation. Consideration of changes in urine levels of estrogen and pregnanediol suggests that rises in estrogen are accompanied by increases in corneal thickness.

Referral rates for a functional vision screening among a large cosmopolitan sample of Australian children

The aim of this study was to investigate the incidence of functional vision problems in a large unselected cosmopolitan population of primary school‐age children and to investigate whether constant clinical criteria for functional vision problems would be implemented by the practitioners involved in the screening. Refractive errors, near point of convergence, stereopsis, strabismus, heterophoria and accommodative facility were assessed for 2697 children (3–12 years) of varying racial backgrounds living in Australia. The spherical component of the refractive error ranged from −7.75 to +9.50 D (mean +0.54 D, ±0.79) with a distribution skewed towards hypermetropia; astigmatism ranged from 0 to 4.25 D (mean −0.16 D, ±0.35). There was a trend towards less hypermetropia and slightly more astigmatism with age. Mean near point of convergence was 5.4 ± 2.9 cm, heterophoria at far and near was 0.12 ± 1.58Δ exophoria and 1.05 ± 2.53Δ exophoria, respectively, 0.55% of children exhibited vertical phoria at near >0.5Δ, accommodative facility ranged from 0 to 24 cycles per minute (cpm) (mean 11.2 cpm, ±3.7), stereopsis varied from 20 to 800 s (′′) of arc with 50% of children having 40′′ or better. The prevalence of strabismus was particularly low (0.3%).

Meridional variations of corneal shape.

ABSTRACT The corneal shape of 196 eyes was determined by photokeratoscopy and subsequent fitting of a conicoid equation to four individual corneal meridians. This conicoid was found in almost all instances to be ellipsoidal, with the asphericity not varying between meridians. The corneal radius of curvature did vary as expected between meridians. The radii of curvature of these corneal meridians also varied with the age of the subjects, resulting in reduced corneal astigmatism, while the asphericity of each meridian did not vary substantially with age.

The Australian optometric workforce 2005

Background:  This paper presents the findings of the Optometrists Association Australia 2005 optometric workforce study.

When /b/ill with /g/ill becomes /d/ill : evidence for a lexical effect in audiovisual speech perception.

Although the McGurk Effect is a well researched illusory phenomenon arising from discrepant auditory and visual speech information little is known about the influence of lexical processes on this phenomenon. Thus, we investigated the McGurk Effect using three letter consonant-vowel-consonant real word and pseudoword pairs with an audiovisual discrepancy positioned at either stimulus onset or offset. The results demonstrated that the frequency of illusions was similar for real words and pseudowords when the discrepancy was at stimulus onset but was significantly lower for real words when the audiovisual discrepancy was positioned at stimulus offset. Positioning of audiovisual discrepancy was not important for accurate auditory perception of pseudowords. These results suggest that the McGurk illusion is the result of audiovisual integration that occurs early in perception prior to word identification and that these early audiovisual integrative processes are modulated by lexical knowledge.

Is there an association between functional vision and learning to read

Background: Controversy exists about the role of visual parameters and vision in learning to read. This study aims to determine whether ocular parameters or performance on a dynamic test of visual function differs for children of differing reading ability.

Astigmatism occurring in association with pediatric eye disease

ABSTRACT Retrospective clinical data from 496 eyes of 256 children attending a low vision clinic were analyzed to determine the relation between different classes of disease that involve visual image degradation and astigmatism. Control data comprised refractions from 79 normal vision children. Children were classified into groups according to the category of disease (14 groups) and the reported age‐of‐onset of their visual disability (0 to 13 years, 5 groups). The mean astigmatism for all groups of children with low vision was larger than that of the normals and in most cases the difference was significant at the 95% level. Astigmatism was highest in children with albinism, retinitis pigmentosa, and idiopathic nystagmus. Increased prevalance of astigmatism compared to normals was noted in children having their onset of low vision as late as 13 years of age. In the low vision subjects with‐the‐rule astigmatism occurred more frequently than oblique or against‐the‐rule astigmatism and oblique astigmatism more frequently than against‐therule astigmatism.