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PubMed1977

Variation and heritability of ocular dimensions. A population study among adult Greenland Eskimos.

Adult Greenland Eskimos from Umanaq town (age 15+) and villages (age 40+) were examined. Optical pachymetry, ultrasonic oculometry, corneal diameter and curvature measurements, and subjective refraction were performed in 5-600 persons. Frequent occurrence of primary angle-closure glaucoma motivated the survey. Age-, sex- and family-variations were studied by linear regression analyses. Conspicuous age effect was found with respect to increase of lens thickness and forward displacement of the lens with age. Almost no age influence was found with respect to increase of lens thickness and forward displacement of the lens with age. Almost no age influence was found with respect to corneoscleral size, i. e. axial length, corneal size and corneal radius of curvature. Conspicuous heritability (h2=0.6-0.8) was found in corneoscleral size parameters as well as lens position, while refractive error showed a much smaller genetic influence.

Adolescent↗
PubMed1978

Refractive amblyopia: a differential diagnosis.

The diagnostic characteristics of refractive amblyopia are discussed and compared to those of strabismic amblyopia. Those characteristics which have appeared in the literature include refractive error type, suppression pattern, fixation type, crowding phenomenon, effect of illumination on visual acuity, color vision and electrodiagnostic tests.

Amblyopia↗
PubMed1994

Changes in refractive trends and optical components of Hong Kong Chinese aged 19-39 years.

The distribution of refractive errors and its relationship to the optical components in 105 Hong Kong Chinese aged 19-39 years was studied. Myopia was most frequent (71%) in this population. The mean spherical equivalent was -3.00 DS. The trend of changes of the direction of refractive and corneal astigmatism from with-the-rule to against-the-rule with increasing age was shown. Significant correlations were found between age and anterior segment distance. Ultrasound examination showed that an increasing axial length was associated with higher myopia. Men had flatter corneal radii, but longer axial length. The prevalence of myopia in the Chinese population seems to be a new trend for the younger Hong Kong Chinese when compared with adults aged over 40 years. Thus the importance of genetics in determination of myopia is called into question by these findings.

Adult↗
PubMed1994

Extended-wear RGP contact lenses: a viable alternative to refractive surgery.

The rigid gas-permeable (RGP) extended-wear lens offers a unique alternative to the hydrogel extended-wear lens as well as to refractive surgery. In suitable patients it can provide almost maintenance-free visual correction for a wide variety of refractive errors. With prudent patient selection, use of high-permeability RGP materials, sound lens design and fitting principles, and conservative follow-up procedures, RGP extended-wear lenses can have success rates exceeding those of either hydrogel extended-wear lenses or refractive surgery, with fewer complications. The complications that do occur are often predictable after a short period of daily wear, and the remainder can often be managed with small changes to lens design.

Contact Lenses, Extended-Wear↗
PubMed1996

Two infant vision screening programmes: prediction and prevention of strabismus and amblyopia from photo- and videorefractive screening.

Two infant vision screening programmes on total populations in the Cambridge Health District have been designed to identify manifest strabismus and strabismogenic and amblyogenic refractive errors at 7-9 months of age. The first, completed, programme used the isotropic photorefractor with cycloplegia together with a standard orthoptic examination. The second, current, programme uses the VRP-1 isotropic videorefractor to identify infants with accommodative lags which are followed up by refraction under cycloplegia. Both programmes show good agreement between infants identified at screening and retinoscopic refractions at follow-up, showing that photo- and videorefraction (with or without cycloplegia) can be effective methods for screening for ametropia in infants and young children. In each programme 5-6% of infants showed abnormal levels of hyperopia (> or = 3.5 D in any meridian), less than 1% showed anisometropia > or = 1.5 D; very few infants (0.25%) showed -3D myopia or greater. Less than 1% showed manifest strabismus. Hyperopic and anisometropic children entered a randomised controlled trial of partial refractive correction. All children identified at screening, alongside appropriate control groups, are extensively followed up to age 4 years. The first programme has found that children who were hyperopic in infancy were 13 times more likely to become strabismic, and 6 times more likely to show measurable acuity deficits by 4 years, compared with controls. Wearing a partial spectacle correction reduced these risk ratios to 4:1 and 2.5:1 respectively. The impaired acuity can be attributed, in part, to meridional amblyopia resulting from persisting astigmatism. Both hyperopic and myopic infants showed refractive changes in the direction of emmetropia between 9 months and 4 years. Wearing a partial spectacle correction did not affect this process of emmetropisation, but does provide the possibility of reducing the incidence of common pre-school vision problems.

Aging↗
PubMed1981

Cycloplegic refractions of premature infants.

Cyclopentolate refractions of 146 premature infants disclosed higher incidences of myopia and anisometropia than those reported for full-term infants. Also, more than 70% of the premature infants had I diopter or more of astigmatism; 83% of the astigmatism was against-the-rule. Infants with shorter gestational periods had more severe myopia and astigmatism. Infants born very prematurely should undergo follow-up refractions to determine whether they retain refractive errors large enough to interfere with visual function.

Age Factors↗
PubMed1989

Effects of chronic optical defocus on the kitten's refractive status.

Lid closure initiated early in life produces axial myopia in a variety of species. However, it is currently not known what aspects of the anomalous visual experience associated with lid closure disrupt the emmetropization process and cause abnormal ocular axial elongation. This study was designed to determine if a degradation in the quality of the spatial characteristics of the retinal image was sufficient to produce an experimental myopia. Optical rearing procedures were employed to defocus one eye of developing kittens, and retinoscopic and ultrasonic procedures were used to evaluate the effects of chronic optical defocus on the kitten's refractive status. Different defocusing lens designs and rearing protocols were included to evaluate variables that may have confounded previous investigations. The major finding is that early chronic optical defocus results in axial myopia. The prevalence and magnitude of the induced refractive errors were dependent on the magnitude of optical defocus, but they were not affected by the sign or form of the defocusing lens. The results demonstrated that the potential for a clear retinal image is important for regulating normal ocular growth and maintaining a near emmetropic refractive status.

Animals↗
PubMed1991

A practice based study of factors influencing intra-ocular pressure.

Many factors are claimed to influence the pressure measured by the tonometer. This study analyses intra-ocular pressure data collected over 10 years on 500 'normal' individuals using a non-contact tonometer. It attempts to analyse which patient variables are relevant and considers the effects of age, sex, laterality and refractive status on intra-ocular pressure, using various statistical techniques. No significant relationship was found for age, sex or refractive error, but axis of astigmatism and laterality were found to be significant factors.

Adult↗
PubMed1986

Ophthalmic applications of biofeedback.

Biofeedback therapy has been shown to be of value in the treatment of numerous psychological and physiological problems. In this paper, applications of biofeedback for correction of oculomotor abnormalities including strabismus, nystagmus and amblyopia, refractive error correction, reduction of intraocular pressure (IOP), and blepharospasm suppression are reviewed.

Amblyopia↗
PubMedDate not supplied

Changes in the aphakic refraction of children with unilateral congenital cataracts.

Forty-two infants who presented to the Children's Hospital in Boston with unilateral congenital cataracts and had cataract surgery by 6 months of age received serial refractions (N = 369) of their aphakic eyes during the first 4 years of life. The 14 patients followed most intensively (185 refractions) showed a rapid decrease in mean spherical equivalent during the first year of life from +30.75 D to +26.36 D, with a less rapid decrease thereafter (24 months, +23.02 D; 36 months, +21.19 D; 48 months, +20.86 D). The rate of change per month decreased from .43 D between 1 and 6 months, .37 D between 6 and 12 months, .30 D between 12 and 18 months, .24 D between 18 and 24 months, and less than .19 D per month thereafter. This study shows that the refractive error of the aphakic eye of patients treated for unilateral congenital cataracts decreases most rapidly during infancy and less rapidly during the next few years of childhood. This information will be helpful in facilitating the treatment of these infants by allowing an approximation of their future contact lens refractive power changes.

Aphakia, Postcataract↗
PubMed2004

Early predict the outcomes of refractive accommodative esotropia by initial presentations.

BACKGROUND: The differential diagnosis between fully and partially refractive accommodative esotropia (Ac-ET) depends on outcomes after intervention with refraction correction. Whether the differences exist in terms of initial clinical features between these two variants has not been fully explored. METHODS: Children between the ages of 6 months and 8 years with esotropia and spherical equivalent greater than +3.00 (D) were included in this study. After wearing diopters glasses for at least 2 years, children were classified according to the indexed criteria into the fully Ac-ET group (group A, N=28) partially Ac-ET (group or the B, N=17). Six clinical parameters, including age at onset, age at first visit, visual acuity, refractive error, angle of esodeviation, and presence or absence of inferior oblique overaction at initial presentation were compared between these two groups. RESULTS: The angle of esodeviation (31.4+/-11.6 PD vs. 42.6+/-12.6 PD, p = 0.004) was significantly different between the fully and partially Ac-ET groups, while refraction (+5.79+/-1.84 D vs. +4.79+/-1.40 D, p = 0.062) had borderline significance. On the contrary, the age at onset (2.35+/-1.74 yrs vs. 2.01+/-1.96 yrs, p=0.539), age at first visit (3.51+/-1.36 yrs vs. 3.01+/-1.70 yrs, p =0.285), inferior oblique overaction (32% vs. 47%, p =0.317), and visual acuity before (LogMAR: 0.40+/-0.25 vs. LogMAR: 0.34+/-0.25, p =0.544) and after treatment (LogMAR: 0.057+/-0.079 vs. LogMAR: 0.051+/-0.19, p = 0.088) were similar in the two groups. CONCLUSIONS: Children with a smaller angle of esodeviation and higher hyperopia were more likely belonging to fully Ac-ET, which can be treated with glasses without the need of surgical intervention. Early detection and early treatment of accommodative esotropia are needed to prevent strabismus and amblyopia.

Accommodation, Ocular↗
PubMed1999

Imposed retinal image size changes--do they provide a cue to the sign of lens-induced defocus in chick?

BACKGROUND: Young chicks can adjust their eye growth to compensate for both imposed hyperopia and myopia (using negative and positive spectacle lenses); the rate of eye elongation increases in the former and slows in the latter case. This emmetropizing behavior implies that the eye can distinguish the sign and magnitude of defocus, although the identity of the cue(s) involved is unknown. As the spectacle lenses used in these studies generally introduce significant retinal image size differences that are in opposite directions for negative and positive lenses (minification vs. magnification), we asked whether retinal image size might provide the required sign information. METHODS: This question was addressed by manipulating retinal image size while keeping lens power constant. We also investigated the effect of eliminating other potential cues, accommodation and chromatic aberration, under these conditions. Three negative "size" lenses of approximately -11 D optical power were used, with 2 of the lenses producing magnification rather than minification as typical of negative lenses (i.e. +1.9% and +6.9% compared to -2.9%). The lenses were fitted monocularly to 7-day-old chicks, which were subsequently measured at 9 and 11 days of age (refractive error and axial dimensions). The same lens-wearing schedule was applied to two other groups of chicks that had monocular ciliary nerve section surgery to prevent accommodation 2 days posthatching; one of these groups was reared under monochromatic yellow light instead of white light. RESULTS: Near-perfect refractive compensation was seen by the end of the treatment period with all three lenses, for all three treatment groups, and there was also little difference in the rate of compensation among the various groups. In all cases, the typical responses of axial (mainly vitreous chamber) elongation and myopia were observed. CONCLUSIONS: That manipulations to retinal image size, which either decrease or reverse the usual effects of negative lenses, did not disrupt compensation to the imposed hyperopic defocus, even in the absence of accommodation and chromatic aberration cues, argues against imposed retinal image size changes being the directional cue to defocus in experimental emmetropization.

Accommodation, Ocular↗
PubMed2006

Laser photocoagulation for retinopathy of prematurity: structural and functional outcome.

BACKGROUND: To report the structural and refractive outcome after laser photocoagulation for retinopathy of prematurity (ROP). METHODS: Nineteen consecutive patients who had undergone photocoagulation for ROP between 1997 and 2002 at our clinic were examined for this non-comparative, consecutive, interventional, retrospective case series. A total of 37 eyes received either transscleral or transpupillary laser treatment. Data consisted of grade of ROP pre- and postoperatively, birth weight, perioperative and postoperative complications and refraction. Based on indirect ophthalmoscopy, independent observers graded the extent of ROP and determined the postoperative refraction by retinoscopy. RESULTS: A total of 97% of all eyes responded to laser treatment with regression of ROP. Only one eye out of 37 progressed to stage IV B despite photocoagulation and therefore an encircling procedure was performed. After further progression a vitrectomy was carried out. Perioperative complications included haemorrhages in 22% that resorbed spontaneously and cataract formation in one eye (3%). Postoperative refractive errors at mean ages of 23 +/- 12 months and 45 +/- 14 months were evaluated in 15/19 patients (79%). The spherical equivalents ranged between -8 D and +6 D at the first examination and between -12 D and +7 D at the second examination. In all only 14% of the refracted eyes were myopic. CONCLUSIONS: Photocoagulation for ROP in our patients resulted in regression of threshold ROP. In addition, the analyses of the refractive outcomes demonstrated a predominance of hypermetropia in our patients.

Birth Weight↗
PubMed1996

Effect of ablation profile on wound healing and visual performance 1 year after excimer laser photorefractive keratectomy.

BACKGROUND: Early photorefractive keratectomy ablations were of limited diameter and depth to maintain the integrity of the globe and to minimise postoperative haze. This study evaluated the effects of deeper, larger diameter wounds on refractive stability and corneal haze, and investigated the effects of ablation profile on wound healing and visual performance. METHODS: One hundred patients undergoing -3.00D and -6.00D corrections were randomised to receive 5 mm, 6 mm, or multizone treatments. The multizone treatment was 6 mm in diameter, but only the depth of the 5 mm treatment. Outcome was measured by Snellen visual acuity, residual refractive error, objective techniques for haze and halos, pupil diameter, subjective night vision, and requirement for retreatment. RESULTS: Overall, the results of 6 mm treatments were superior to those of 5 mm and multizone treatments: they had a smaller hyperopic shift (p < 0.01), a more predictable (p < 0.001) and stable refractive outcome, less haze (p < 0.05), smaller halos (p < 0.05), fewer subjective night vision problems, and fewer patients required retreatment. CONCLUSIONS: Analysis of these data and a literature review of corneal wound healing demonstrated that the improved outcome associated with the 6 mm beam did not relate to the depth of ablation. The factor with greatest apparent influence on the development of haze and regression was the slope of the wound surface over the entire area of the ablation. Tapering the wound edge provided no additional benefit, and contributed to night vision problems. It is, therefore, recommended that small diameter or multizone treatments should not be used in low and moderate myopia.

Adult↗
PubMed1991

The learning and fatigue effect in automated perimetry.

A visual field test was performed on 100 volunteers to study learning or fatigue effects during one session. The test was carried out with the help of the Octopus program J1, which measures the threshold 12 times at 3 test locations. In the majority of cases the sensitivity was quite stable during the session. We noted no difference between trained and untrained subjects or between normal and pathological eyes. However, patients with refractive errors, especially myopes, revealed a larger learning effect than did emmetropes.

Adolescent↗
PubMed1990

Effects of dioptric blur on Snellen and grating acuity.

We compared the effects of dioptric blur on Snellen acuity and grating acuity. Dioptric blur had a strong negative effect on Snellen acuity, consistent with previous studies, but had little effect on grating acuity. Between 1 and 12 D both types of acuity were reduced as a linear function of blur. However, 12 D of blur reduced grating acuity to only 6/24 (20/80), whereas letter acuity was worse than 6/300 (20/1000). We suggest that these differences are due to the presence of "spurious resolution" in which phase-reversed gratings are readily detectable. But the phase reversals so distort the relative positions of linear segments within the letters that the letters become unrecognizable. These results indicate that Snellen letters are more sensitive than gratings to a patient's refractive errors, emphasize the differences between Snellen and grating acuity, and indicate that the minimum angle of resolution (MAR) concept is not applicable to letters.

Adult↗
PubMed1992

Neonatal eye growth and emmetropisation--a literature review.

The refractive development of the neonatal eye has been the subject of much study and debate. In this paper the hypothetical mechanisms of emmetropisation and their relationship to the development of refractive errors will be reviewed. The evidence supporting visual feedback control of eye growth will be described, and the role of ocular accommodation will be discussed.

Accommodation, Ocular↗