Stimulus deprivation myopia in human congenital ptosis: a study of 95 patients

The influence of the environment and lifestyle on myopia

BACKGROUND

Myopia, commonly known as near-sightedness, has emerged as a global epidemic, impacting almost one in three individuals across the world. The increasing prevalence of myopia during early childhood has heightened the risk of developing high myopia and related sight-threatening eye conditions in adulthood. This surge in myopia rates, occurring within a relatively stable genetic framework, underscores the profound influence of environmental and lifestyle factors on this condition. In this comprehensive narrative review, we shed light on both established and potential environmental and lifestyle contributors that affect the development and progression of myopia.

MAIN BODY

Epidemiological and interventional research has consistently revealed a compelling connection between increased outdoor time and a decreased risk of myopia in children. This protective effect may primarily be attributed to exposure to the characteristics of natural light (i.e., sunlight) and the release of retinal dopamine. Conversely, irrespective of outdoor time, excessive engagement in near work can further worsen the onset of myopia. While the exact mechanisms behind this exacerbation are not fully comprehended, it appears to involve shifts in relative peripheral refraction, the overstimulation of accommodation, or a complex interplay of these factors, leading to issues like retinal image defocus, blur, and chromatic aberration. Other potential factors like the spatial frequency of the visual environment, circadian rhythm, sleep, nutrition, smoking, socio-economic status, and education have debatable independent influences on myopia development.

CONCLUSION

The environment exerts a significant influence on the development and progression of myopia. Improving the modifiable key environmental predictors like time spent outdoors and engagement in near work can prevent or slow the progression of myopia. The intricate connections between lifestyle and environmental factors often obscure research findings, making it challenging to disentangle their individual effects. This complexity underscores the necessity for prospective studies that employ objective assessments, such as quantifying light exposure and near work, among others. These studies are crucial for gaining a more comprehensive understanding of how various environmental factors can be modified to prevent or slow the progression of myopia.

Refractive error characteristics and influence on ocular parameters in patients with unilateral congenital ptosis

Background

The study aimed to investigate the difference in refractive status and ocular parameters between ptotic and fellow eyes in patients with unilateral congenital ptosis.

Methods

Thirty patients (53% males, age 22.00 ± 11.41 years) with unilateral congenital ptosis diagnosed and treated at the First Affiliated Hospital of Sun-yat Sen University were enrolled and underwent detailed refractive examinations from March 2019 to February 2022. Ocular biometric measurements were performed by an IOL Master 700 biometer. The differences in refractive error characteristics, best-corrected visual acuity (BCVA), and ocular parameters including axial length (AL), central corneal thickness (CCT), aqueous depth (AQD), anterior chamber depth (ACD), lens thickness (LT), and keratometry values between ptotic and fellow eyes were analysed.

Results

A lower BCVA (logMAR, median (IQR), 0.00 (− 0.13,0.00), P = 0.009) and a higher incidence of amblyopia (n (%), 7(23%), P = 0.016) were observed in ptotic eyes. The CCT of ptotic eyes was greater than that of fellow eyes (mean ± SD, 539.83 ± 26.73 μm, P < 0.001). The keratometry values at the flat axis (K1) and mean corneal power (Km) were smaller in ptotic eyes (mean ± SD, 42.11 ± 1.49 D, 42.68 ± 1.52 D, respectively, both P = 0.001). There was no significant difference in AL between ptotic and fellow eyes.

Conclusions

Congenital ptosis influences ocular parameters, mainly causing a thicker and flatter cornea. Patients with unilateral congenital ptosis might have lower BCVA in the ptotic eyes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-022-02511-x.

Hyperopic anisometropia with a shorter axial length ipsilateral to the ptotic eye in children with congenital ptosis

BACKGROUND

To investigate the clinical characteristics of children with congenital ptosis, with particular attention given to the incidence of anisometropia, and the difference in axial length (AL) between the right and left eyes.

METHODS

The medical charts of 55 patients with congenital ptosis at Niigata University Medical and Dental Hospital were retrospectively analyzed. Clinical characteristics, including age, cycloplegic refraction, AL, and the presence of amblyopia and its causes were analyzed.

RESULTS

Age at the initial visit was 16 ± 20 (mean ± standard deviation, the same applies below) months. Of the 49 patients whose cycloplegic refraction was measured, hyperopic anisometropia, defined as ≥ one-diopter difference in spherical equivalent (SE), was observed in 1/11, 9/27 and 5/11 patients with bilateral, right, and left ptosis, respectively. Among 14/38 patients with hyperopic anisometropia involving unilateral ptosis, 13 demonstrated a larger SE in the ptotic eye than in the non-ptotic eye. The inter-eye difference in AL (AL of the ptotic eye minus that of the non-ptotic eye) in six patients with unilateral ptosis and hyperopic anisometropia ipsilateral to the ptotic eye (-0.29 ± 0.40 mm) was significantly smaller than that in three patients with unilateral ptosis and no hyperopic anisometropia (0.38 ± 0.29 mm).

CONCLUSIONS

At our institute, children with congenital ptosis had a high incidence of hyperopic anisometropia ipsilateral to the ptotic eye. Furthermore, this condition was associated with a shorter axial length. These results indicate that refractive correction for hyperopic anisometropia is important for proper visual development in children with congenital ptosis.

A genetic risk score and number of myopic parents independently predict myopia

PURPOSE

To investigate whether a genetic risk score (GRS) improved performance of predicting refractive error compared to knowing a child's number of myopic parents (NMP) alone.

METHODS

This was a retrospective analysis of data from the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort study. Refractive error was assessed longitudinally between age 7-15 using non-cycloplegic autorefraction. Genetic variants (n = 149) associated with refractive error from a Consortium for Refractive Error And Myopia (CREAM) genome-wide association study were used to calculate a GRS for each child. Using refractive error at ages 7 and 15 years as the outcome variable, coefficient of determination (R² ) values were calculated via linear regression models for the predictors: NMP, GRS and a combined model.

RESULTS

Number of myopic parents was weakly predictive of refractive error in children aged 7 years, R²  = 3.0% (95% CI 1.8-4.1%, p < 0.0001) and aged 15 years, R²  = 4.8% (3.1-6.5%, p < 0.0001). The GRS was also weakly predictive; age 7 years, R²  = 1.1% (0.4-1.9%, p < 0.0001) and 15 years R²  = 2.6% (1.3-3.9%, p < 0.0001). Combining the 2 variables gave larger R² values at age 7, R²  = 3.7% (2.5-5.0%, p < 0.0001) and 15, R²  = 7.0% (5.0-9.0%, p < 0.0001). The combined model improved performance at both ages (both p < 0.0001).

CONCLUSION

A GRS improved the ability to detect children at risk of myopia independently of knowing the NMP. We speculate this may be because NMP captures information concerning environmental risk factors for myopia. Nevertheless, further gains are required to make such predictive tests worthwhile in the clinical environment.

The relationship between image degradation and myopia in the mammalian eye

BACKGROUND

In all species studied, myopia develops if the eye is deprived of detailed vision during development (form deprivation myopia). However, different degrees of spatial image deprivation produce different effects and have not been described in the mammalian eye. Therefore, the effect of image degradation on guinea pig emmetropisation was investigated.

METHODS

Eighty-one guinea pigs wore a treatment on one eye from 6 to 13 days of age. There were four treatments: a translucent diffuser (no lines or edges were visible through the diffuser); one of five Bangerter foils (BF: 0.8, 0.6, 0.4, 0.2, light perception only), which differed in their cut-off spatial frequencies; a 'ring mount' control with no filter; or one of two neutral density filters that reduced luminance only (ND, optical density grades 0.1 and 0.6). Refractive error and ocular elongation were measured after seven days of treatment.

RESULTS

The extent of induced myopia and ocular growth were related to the amount of image degradation (mean difference between the treated and untreated eyes changed in a graded manner -7.0 D to -0.2 D and from 85 µm to seven µm respectively, for spatial frequency cut-offs between zero and 24 cycles per degree). Corresponding reductions in luminance from ND filters did not increase eye growth and caused significantly less myopia than the BFs that caused a similar luminance decrement. The greatest myopia occurred when no or limited spatial information was available to the eye, but moderate myopia still occurred with spatial frequency cut-offs of six and 12 cycles per degree, well beyond the visual acuity range of guinea pigs.

CONCLUSION

Excessive ocular growth and myopia are most robust when induced by spatial frequency reductions within the visual acuity range but can also be induced beyond this. Either the mechanism of ocular growth can detect supra-threshold spatial frequencies, possibly due to aliasing, or it is sensitive to small amounts of contrast degradation.

Human parallels to experimental myopia? A literature review on visual deprivation

Raviola and Wiesel's monkey eyelid suture studies of the 1970s laid the cornerstone for the experimental myopia science undertaken since then. The aim has been to clarify the basic humoral and neuronal mechanisms behind induced myopization, its eye tissue transmitters in particular. Besides acquiring new and basic knowledge, the practical object of the research is to reduce the burden of human myopia around the world. Acquisition and cost of optical correction is one issue, but associated morbidity counts more, with its global load of myopia-associated visual loss and blindness. The object of the present PubMed literature-based review is to evaluate apparent similarities between experience from disturbed imaging in experimental laboratory science and varieties within the spectrum of childhood human myopia. So far, the main impression is that macroscopical optical deprivation appears absent in the prevalent types of human myopia, nor is myopia a regular sequel where early eye pathology has led to poor imaging and optical deprivation. Optical aberrations of a higher order are a relatively new issue in myopia research, and microstructural deprivation is only marginally dealt within the survey. Links between experimental and human myopia appear mainly occasional, and with only few examples in humans where factual parallels appear credible. Clinical and epidemiological data on refraction remain important, in particular with a view to life style and environmental factors. Such knowledge may further serve as inspiration to the laboratory research, which aims at solving the basic enigmas on a tissue level.

A retrospective study: form-deprivation myopia in unilateral congenital ptosis

BACKGROUND

The aim of this retrospective study was to investigate the relationship between unilateral congenital ptosis in patients older than eight years and their refractive state and spherical equivalent refraction (SER).

METHODS

The study involved a review of the clinical records of 85 patients admitted to the First Affiliated Hospital, Sun Yat-sen University between 1998 and 2010 with unilateral congenital ptosis. The average age was 16.83 years (nine to 27 years). The patients were classified into mild (27 cases), moderate (37 cases) or severe (21 cases) ptosis according to the degree of the droopy eyelid covering the cornea. The fellow eyes served as controls.

RESULTS

In 85 eyes with unilateral ptosis, the frequency of myopia (SER of -0.50 D or more myopia) was significantly higher than in the fellow eye (47 versus 32, p = 0.031). The frequency of myopia in eyes with severe unilateral ptosis was significantly higher than in the fellow eyes (16 versus 7, p = 0.012), whereas there were no significant differences in patients with mild (15/27 versus 13/27, p = 0.79) or moderate (16/37 versus 12/37, p = 0.47) unilateral ptosis. Similarly, the SER was significantly more myopic in eyes with severe ptosis compared with the fellow eye (-1.37 D versus -0.85 D, p = 0.01), whereas no significant differences were found in patients with mild or moderate unilateral ptosis.

CONCLUSIONS

The results showed a higher frequency of myopia and more myopic SER in eyes with severe unilateral ptosis compared with the fellow eye. The myopia found in eyes with unilateral ptosis might be caused by a mechanism similar to that resulting in myopia among animals subjected to form deprivation. It is important to pay attention to possible refractive error in patients with unilateral ptosis. Surgical correction of unilateral ptosis at an early age is recommended.

Postnatal refractive development in the Brown Norway rat: Limitations of standard refractive and ocular component dimension measurement techniques

PURPOSE

The genetic tractability of the rat and its larger eye size as compared to the mouse make it an attractive model for studies of ocular development and emmetropisation. This study aimed to provide normative data in the strain of rat being used for the rat genome sequencing project whilst also evaluating standard measurement techniques.

METHODS

Ocular refraction (retinoscopy, Hartinger coincidence optometry) and ocular component dimensions (keratometry, A-scan ultrasonography, calliper measures, eye weight) were measured at intervals from eye-opening to adulthood.

RESULTS

There was no convincing evidence of visually guided emmetropisation during normal development. Key measurement techniques such as high-resolution A-scan ultrasonography, which work effectively in several other animal species, were unusable or inaccurate in the rat.

CONCLUSIONS

This study found no evidence of emmetropisation during normal development in rat. As in mice, technical difficulties prevent accurate measurement of ocular refraction and vitreous chamber depth and may complicate tests of emmetropisation to imposed blur.

Monocular deprivation in an identical twin

PURPOSE

The scientific literature contains minimal human studies of the effect of monocular deprivation on a single eye of twins. This report examines the effects of early visual deprivation on axial length measurements by comparing the refractive findings and axial length measurements of identical twins' 4 eyes, 1 visually deprived and 3 nondeprived.

METHODS

A retrospective record review was performed on the medical records of identical 6-year-old Hispanic female twins. Both patients had received eye care at the University Optometric Center, State University of New York, for a period of at least 5 years. Subsequently, an Internal Review Board-approved prospective study was undertaken. Each twin received a comprehensive eye examination and an A-scan.

RESULTS

The findings of the 3 nondeprived eyes were compared with those of the 1 deprived eye. The 3 nondeprived eyes had at least 20/20 visual acuity, low hyperopia or astigmatism, low with the rule keratometric findings, 12-mm corneal diameters, and A-scan results ranging from 21.0 to 21.55 mm. The remaining eye, which was visually deprived secondary to congenital cataract from birth to 6 months of age, had an aphakic refractive condition, decreased visual acuity, glaucoma, esotropia, and borderline microcornea. Keratometric findings were comparable with those of the other 3 eyes, whereas the A-scan finding was 25.16 mm.

CONCLUSION

This case presented a unique opportunity to directly examine the effect of visual deprivation on axial elongation. Although other factors, such as glaucoma and borderline microcornea, may influence axial elongation, the findings in this patient indicate that a substantial portion, if not all, of the axial elongation can be attributed to early monocular deprivation.