Funduscopic systems: magnification in ametropia and aphakia

The magnification of the fundus image with various forms of funduscopy in ametropia and aphakia is poorly understood. This paper investigates these relationships. Direct and indirect ophthalmoscopy and biomicroscopic funduscopy is included. The Gullstrand Simplified Schematic Eye is modified by changing either the axial length, the power of the cornea, or the index of refraction of the lens to produce ametropia. Aphakia is produced by considering these same eyes with the crystalline lens removed. The magnification of these various eye/funduscope systems is presented, along with general principles illustrated by the figures.     

儿童屈光不正与立体视觉

目的探讨儿童屈光不正对立体视觉的影响。方法采用颜少明等《立体视觉检查图》对60例正常儿童及115例矫正视力正常的屈光不正患儿进行立体视阈值检查并进行统计学处理。结果远视眼立体视阈值明显高于正常组及近视眼组（P＜0．005），且随屈光度增高而增高，随发生年龄增高而降低，近视眼组与正常组之间无差异（P＞0．05）。近视眼之间戴眼镜前后立体视阈值无显著性，而远视眼戴镜后立体视阈值明显下降（P＜0．005）。结论屈光不正对立体视功能影响是由于视力下降引起。提示及早发现屈光不正，及时预防、矫正屈光不正性弱视，对保证立体视功能的正常发育具有重要意义     

Magnification characteristic of a +90-diopter double-aspheric fundus examination lens

PURPOSE: To investigate the magnification characteristic of the +90-D double-aspheric fundus examination lens for biomicroscopic measurement of the optic disc. METHODS: A calibrated Gullstrand-type model eye adjusted for axial ametropia between -12.5 and +12.6 D was used to measure the change in magnification of the system with refractive error and variation in fundus lens position. A correction factor p (in degrees per millimeter) at different axial ametropias was also calculated. RESULTS: The total change in magnification of the system from myopia to hyperopia was -15.1% to +13.7%. When the fundus lens position was altered with respect to the model eye by +/-2 mm under myopic conditions, the change in magnification of the system was -4.8% to +8.1%. In the hyperopic condition the change was -4.8% to +6.0%. The fundus lens exhibited a linear relationship between p and the degree of ametropia of the model eye and a constant relationship between p and ametropia of -5 to +5 D. CONCLUSIONS: Axial ametropia has a significant effect on biomicroscopic measurement of the optic disc with the +90-D lens. Therefore, a correction factor (p) was calculated that can be used in calculations for determining true optic disc size. These findings may be important for improving clinical disc biometry.     

The optics of comparative ophthalmoscopy

One factor peculiar to the practice of comparative ophthalmoscopy is the very large variation in ocular size of the animals examined, a factor which is ignored in current textbook treatments of the subject. We have computed values of lateral magnification, axial magnification, angular field of view and linear field of view for 19 species of terrestrial vertebrates. The dimensional value of a 1 diopter change in direct ophthalmoscopic focus was also determined. The anterior focal length of the eye in air and the vitreal refractive index were the intrinsic optical parameters of the animal's eye necessary for these calculations. Where these values were not available from the literature, the vitreal refractive index was assumed to be 1.336 and the anterior focal length was estimated as two-thirds of the axial length using a regression equation we derived from data in the literature. The angular field of view in ophthalmoscopy was shown to be invariant in the emmetropic eye and equal to the angular subtense of the ophthalmoscopic beam. The lateral field of view and retinal depth corresponding to a 1 diopter change in direct ophthalmoscopic focus varied directly with the anterior focal length of the eye. The remaining parameters of lateral and axial magnification varied inversely with the anterior focal length of the animal's eyes. These findings provide a basis for evaluating the relative size and significance of ophthalmoscopically viewed features in terrestrial vertebrate eyes.     

New frontiers for the perioperative data method for IOL calculation following corneal refractive surgeries

PURPOSE: To evaluate the efficiency of the perioperative data method for intraocular lens (IOL) calculation after correction of myopia and hyperopia with different techniques, including reoperated cases. METHODS: Thirty-five eyes (26 patients) that developed cataract after corneal refractive procedures were evaluated retrospectively. They were categorized according to initial error of refraction into myopes and hyperopes and according to types of refractive procedures into ablative, incisional, both, or others. Reoperated cases were also considered. Number of refractive procedures was noted. Time interval between the first procedure and cataract extraction was indicated. Perioperative method was used to calculate the K value. SRK/T formula was used to calculate IOL power. Difference between intended and finally achieved manifest refraction was an indicator for efficiency of the calculation. RESULTS: Postoperatively, 77.2% of cases had manifest refraction +/-1.5 D of intended refraction. There was no difference between myopes and hyperopes in terms of final manifest refraction, best-corrected visual acuity, and difference between intended and finally achieved manifest refraction. Similarly were groups of different types of surgeries. Efficiency of the method decreased with high axial lengths and low IOL powers. Neither the number of refractive surgeries nor time interval between surgeries affected efficiency of the method. CONCLUSIONS: The perioperative data method is equally effective for myopes and hyperopes. The types, numbers of refractive procedures, as well as the time interval between refractive surgery and cataract extraction do not alter the credibility of the method. In high degrees of myopia, the method gives less accurate results.     

Magnification-corrected indirect biomicroscopy of the optic nerve head

Background Proper use of the new Super VitreoFundus and SuperPupil XL non-contact slit-lamp lenses for clinical disc biometry requires knowledge of their comparative magnification.Methods The optical performance of each fundus lens is described in terms of axial magnification, lens position, and the correction factor p (in degrees per millimeter) using a calibrated Gullstrand-type model eye adjusted for axial ametropia between –12.5 D and +12.6 D.Results The total change in axial magnification from myopia to hyperopia was –13.3% to +15.6% (Super VitreoFundus lens), and –13.9% to +14.1% (SuperPupil XL lens). When the fundus lens position was altered with respect to the model eye by ±2 mm under myopic conditions the change in axial magnification was –5.1% to +7.7% (Super VitreoFundus lens), and –6.5% to +9.7% (SuperPupil XL lens). In the hyperopic condition the change was –3.8% to +5.8%, and –4.9% to +7.3%. Both fundus lenses exhibited a linear relationship between p and degree of ametropia of the model eye, while only the Super VitreoFundus lens displayed a constant relationship between p and ametropia of –5 D to +5 D.Conclusions Using the fundus lens correction factor (p), the clinician may be able to estimate the dimensions of optic nerve head features with sufficient accuracy to allow clinical decisions to be made in the evaluation of patients with diagnosed or suspected glaucoma.     

Magnification-corrected photodynamic therapy

Background To present a method for performing photodynamic therapy (PDT) with a constant predictable light fluence based on actual laser spot magnification. Methods A calibrated Gullstrand-type model eye with a scale of half circles in the centre of the artificial fundus was used for this study. The axial length of the model eye was set to different values ranging from 20 to 31 mm, and the actual laser spot magnification of four indirect condensing laser lenses were determined using a PDT laser unit. Results Equations for determining the actual laser spot magnification were calculated for each laser lens. The total change in laser spot magnification from hyperopia (axial length 20 mm) to myopia (axial length 31 mm) was −20% to +24.8% for Mainster Standard lens (Ocular Instruments Inc, Bellevue, Washington, USA), −15.7% to +27.7% for Mainster Wide Field lens (Ocular Instruments Inc), −16.3% to +33.1% for Volk Transequator lens (Volk Optical Inc, Mentor, Ohio, USA), and −19.2% to +24.4% for Volk PDT Laser lens (Volk Optical Inc). Conclusions Axial length of the eye has a considerable effect on PDT laser spot magnification when an indirect laser lens is used. By calculating the actual laser spot magnification in conjunction with knowledge of the true greatest linear dimension of the neovascular lesion, the clinician may be able to deliver a constant predictable amount of light fluence to the fundus independent of the axial length of the PDT treating eye. No Grant/Financial Support. The authors have no financial interest in any of the products discussed in this article.     

Socio-economic differences in accessing NHS spectacles amongst children with differing refractive errors living in Scotland

Background/objectivesAdults living in more deprived areas are less likely to attend an eye examination, resulting in greater visual impairment from undiagnosed eye disease and a widening of health inequalities. It is unknown if the introduction of free NHS eye examinations and help with spectacle costs has benefited children in Scotland. This study aimed to explore factors associated with accessing NHS spectacles including level of deprivation, refractive error, urbanity and age.Subjects/methodsNHS-financed General Ophthalmic Services (GOS) 3 supplement the cost of spectacles for children under 16 years. Administrative data on the spectacle refraction dispensed were obtained from Information Services Division (ISD) for mainland Scotland, 2018, and categorised by: Emmetropes/low hyperopes (reference group), myopes and moderate/high hyperopes. Data were linked to the Scottish Index of Multiple Deprivation (SIMD) quintile.ResultsData included 108, 043 GOS 3 claims. Greater deprivation was associated with greater GOS 3 claims p = 0.041. This was most evident in emmetropic/low hyperopic children and in moderate/high hyperopic children. GOS 3 claims in the myopes group increased with age across all SIMD and decreased with age in the moderate/high hyperope group (all p < 0.001). GOS 3 claims were not associated with urbanity for all Health Boards (p = 0.13).ConclusionsChildren in areas of greater deprivation and in more rural areas are not disadvantaged in accessing NHS spectacles. This did not vary by refractive error group. This suggests that health policy in Scotland is accessible to those from all deprivation levels and refractive errors.Subject terms: Epidemiology, Epidemiology     

Construction of a model eye and its applications

Construction details are given of a model eye, based on the Bennett and Rabbetts schematic eye. It incorporates a cornea, lens, and spherical fundus. Distilled water filled the anterior and vitreous chambers. By means of a micrometer screw, the vitreous chamber depth can be precisely varied to produce axial ametropia from +11 to -17 D. Readings taken over the greater part of this range with a Topcon Autorefractor RM-A6500 were found to be repeatable and reproducible within +/- 0.25 D. The model eye was used to investigate the relationship between the actual size of a fundus feature and its photographic image in two different fundus cameras. With a Zeiss Oberkochen camera of telecentric design the magnification was found to remain constant whatever the degree of axial ametropia, whereas with a Carl Zeiss Jena camera the magnification varied linearly with ametropia. A technique developed by Littmann for determining the actual size of a retinal feature when using a fundus camera of telecentric design is discussed briefly.     

Corneal asphericity and apical curvature in children: a cross-sectional and longitudinal evaluation

PURPOSE: The contour of the human cornea is closely modeled by a conic section, which is fully described by asphericity (Q) and apical radius of curvature (r(o)). The relationship between corneal shape and other ocular dimensions in children, including anterior and vitreous chamber depths, axial length, and spherical equivalent refractive error, was investigated. METHODS: Corneal asphericity and r(o) were calculated by using corneal topography data on 643 children (72 myopes, 370 emmetropes, and 201 hyperopes), ages 6 to 15 years, who participated in the Orinda Longitudinal Study of Myopia (OLSM) during 1991. Measurements from a younger subset of these children, including 8 myopes, 92 emmetropes, and 75 hyperopes, ages 6 to 9 years in 1991, were compared to 1996 data for longitudinal analysis. RESULTS: Mean +/- SD Q of the 1991 study sample was -0.346 +/- 0.101, representing a prolate corneal shape. Almost all (99.7%) of the corneas examined were prolate. Corneal asphericity was less prolate among myopes than in emmetropes and hyperopes (P = 0.010). Less prolate corneas were related to deeper anterior chamber depths among emmetropes (r = 0.324, P < 0.0001) and hyperopes (r = 0.275, P < 0.0001), but not among myopes (r = 0.230, P = 0.0515). Flatter values of r(o) were related to longer vitreous chamber depth (r = 0.607, P < 0.0001) and axial length (r = 0.606, P < 0.0001) in all refractive error groups. Initial corneal shape was unrelated to change in refractive error over a 5-year period. CONCLUSIONS: Most corneas examined in this study were prolate in contour. Deeper anterior chamber depths were related to less prolate corneas among emmetropes and hyperopes, which is probably the result of mechanical influences on the peripheral cornea as the anterior chamber elongates during ocular growth. Longitudinal results suggest initial corneal shape is of little or no value in predicting refractive error progression.     

Comparison of ocular component growth curves among refractive error groups in children

PURPOSE: To compare ocular component growth curves among four refractive error groups in children. methods Cycloplegic refractive error was categorized into four groups: persistent emmetropia between -0.25 and +1.00 D (exclusive) in both the vertical and horizontal meridians on all study visits (n = 194); myopia of at least -0.75 D in both meridians on at least one visit (n = 247); persistent hyperopia of at least +1.00 D in both meridians on all visits (n = 43); and emmetropizing hyperopia of at least +1.00 D in both meridians on at least the first but not at all visits (n = 253). Subjects were seen for three visits or more between the ages of 6 and 14 years. Growth curves were modeled for the persistent emmetropes to describe the relation between age and the ocular components and were applied to the other three refractive error groups to determine significant differences. results At baseline, eyes of myopes and persistent emmetropes differed in vitreous chamber depth, anterior chamber depth, axial length, and corneal power and produced growth curves that showed differences in the same ocular components. Persistent hyperopes were significantly different from persistent emmetropes in most components at baseline, whereas growth curve shapes were not significantly different, with the exception of anterior chamber depth (slower growth in persistent hyperopes compared with emmetropes) and axial length (lesser annual growth per year in persistent hyperopes compared with emmetropes). The growth curve shape for corneal power was different between the emmetropizing hyperopes and persistent emmetropes (increasing corneal power compared with decreasing power in emmetropes). conclusions Comparisons of growth curves between persistent emmetropes and three other refractive error groups showed that there are many similarities in the growth patterns for both the emmetropizing and persistent hyperopes, whereas the differences in growth lie mainly between the emmetropes and myopes.     

Psychometric properties of the National Eye Institute-Refractive Error Quality of Life instrument

OBJECTIVE: To estimate the psychometric properties of a vision-targeted measure of health-related quality of life, the National Eye Institute-Refractive Error Quality of Life survey (NEI-RQL), which includes 13 scales designed to assess the impact of refractive error and its correction on day-to-day life. DESIGN: Cross-sectional survey. PARTICIPANTS: The NEI-RQL was self-administered by 667 myopes, 380 hyperopes, and 114 emmetropes recruited from the practices of 6 medical centers. All participants had near and distance visual acuity of 20/32 or better in the worse eye while benefiting from their current method for correction of refractive error (glasses, contact lens, refractive surgery). METHODS: Mean scores, standard deviations, internal consistency reliability, and test-retest intraclass correlations were estimated for the NEI-RQL scales. Item discrimination was assessed by item-scale correlations. Construct validity was evaluated by assessing the sensitivity of scale scores to type of refractive error, type of refractive error correction, and spherical equivalent. Construct validity of the NEI-RQL was compared to those of the Medical Outcomes Study 36-item short-form health survey (SF-36) and the National Eye Institute Vision Functioning Questionnaire (NEI VFQ-25) in a random subsample of respondents. MAIN OUTCOME MEASURES: The 13 NEI-RQL scales-clarity of vision, expectations, near vision, far vision, diurnal fluctuations, activity limitations, glare, symptoms, dependence on correction, worry, suboptimal correction, appearance, and satisfaction with correction. RESULTS: Emmetropes tended to score significantly better on the NEI-RQL scales than myopes and hyperopes. The method of refractive error correction was also associated with NEI-RQL scores. In addition, the NEI-RQL multi-item scales accounted for 29% of the variance in the NEI-RQL satisfaction with correction item beyond that explained by the SF-36 and the NEI VFQ-25. CONCLUSION: These results support the reliability and construct validity of the NEI-RQL. The instrument appears to be useful for comparisons of people with different types of correction for refractive error.     

Influence of fogging lenses and cycloplegia on open-field automatic refraction

PURPOSE: To compare refractive values measured with and without cycloplegia, or with fogging lenses, using an open-field auto-refractor. METHODS: One hundred and forty-two young adults were enrolled from a university population; 96 were female (67.6%) and 46 were male (32.4%), the age range was 18-26 years (mean 22.3 +/- 3.7 years). The refraction measurement was obtained for the right eye of each subject with the Grand Seiko Auto Ref/Keratometer WAM-5500 (GS) under three conditions, always in this sequence: (1) without cycloplegia (GS), (2) without cycloplegia but using a + 2.00 D fogging lens (GS_2D) and (3) with cycloplegia (GS_cycl). RESULTS: When the average values of spherical equivalent were compared, both accommodation control strategies were almost equally successful: GS, M = -0.85 +/- 2.21 D; GC_2D, M = -0.53 +/- 2.10 D and GS_cycl, M = -0.57 +/- 2.24 D (Kruskal-Wallis test, p < 0.001). When the results were analysed separately for different refractive groups, emmetropes and hyperopes show statistically significant differences while myopes did not. When both accommodation strategies were compared there was a trend for more myopic subjects to display more negative values under cycloplegia, while low myopes, emmetropes and hyperopes tend to display more negative values with the +2.00 D fogging lenses, suggesting this was less effective for accommodation control. CONCLUSIONS: Over-refraction through +2.00 D fogging lenses is useful to achieve additional relaxation of the accommodative response in a similar way to cycloplegia when open-field autorefraction is performed in young adults.     

Model of human refractive error development.

PURPOSE: To construct a model of refractive error development that can account for the different interactive mechanisms and time courses of refractive error in the hyperope (HYP), emmetrope (EMM), early-onset myope (EOM), and late-onset myope (LOM) over the first 30 years of life. METHODS: First, a baseline short-term (1 mo.) simulation of a previously developed nearwork-induced transient myopia (NITM) model was performed under both far- and near-viewing paradigms to obtain the critical relationships between AErms and refractive error for the four refractive groups. Then, two control pathways were added to the NITM model. The genetically-controlled pathway was associated with the long-term growth of the cornea, lens, and the eyeball. The environmentally-controlled pathway was associated with retinal-defocus during nearwork, wherein the root mean square (rms) of the accommodative error (AE) above a threshold level resulted in an increase in axial length of the eyeball. The thresholds for defocus-induced axial length change were empirically determined to correspond to the differential susceptibility in the four refractive groups. The combination of effects from the two pathways produced the overall refractive error. The relationship between AErms and refractive error was combined with the two control pathways for the long-term simulations (30 yrs: the initial 15 yrs using a far-viewing paradigm followed by an additional 15 yrs using a near-viewing paradigm) to quantify refractive error development as related to daily nearwork activity in the four refractive groups. RESULTS: All refractive groups began early in life with a genetically-determined hyperopic refractive error. The HYP had the lowest susceptibility or highest threshold to retinal defocus effects, and remained at a hyperopic level. The EMM exhibited a relative myopic shift in the first 2 years to become and remain at emmetropia. In the myopic groups, the EOM exhibited both a genetically-controlled component (starting 2 years of age) and a defocus-induced component (starting at 15 years of age), whereas the LOM manifested only a defocus-induced factor (starting at 15 years of age) in the development of myopia. In addition, simulations indicated that emmetropization occurred only for "induced" refractive error that was less than 0.5 D, which was consistent with the non-monotonic relationship between AErms and refractive error, wherein the minimum AErms occurred at 0.5 D. CONCLUSIONS: The model showed that both genetic and defocus-induced environmental factors play important roles in the development of refractive error in the different refractive groups. The model also provides a framework for further detailed quantitative analysis of the processes of refractive error development and emmetropization.     

Magnifying prismatic lenses for vitrectomy

PURPOSE: Viewing the fundus at higher magnification during vitrectomy makes surgical procedures much safer; however, the scope of magnification of the peripheral fundus has been limited. For better visualization of the periphery of the fundus, we have developed two new contact lenses called magnifying prismatic lenses. METHODS: The magnifying 15 degrees and 30 degrees prismatic lenses are made of a glass with a high index of refraction (n = 1.883). The lenses have a convex upper surface to provide a magnified view of the peripheral fundus. RESULTS: These magnifying 15 degrees and 30 degrees prismatic lenses provide an approximately 2x magnified view of the peripheral fundus. They also provide a more extensive view of the peripheral fundus than a regular (plano-concave) prismatic lens when the eye is tilted. CONCLUSION: The magnifying prismatic lenses are useful for viewing into the peripheral fundus with higher magnification.     

Visual function and change in quality of life after bilateral refractive lens exchange with the ReSTOR multifocal intraocular lens

PURPOSE: To evaluate vision and quality of life and explore the correlation between vision and change of quality of life after bilateral refractive lens exchange of the Acrysof SA60D3 ReSTOR multifocal intraocular lens (IOL) for correction of ametropia in presbyopic populations. METHODS: Pre- and postoperatively, the National Eye Institute Refractive Error Quality of Life Instrument (NEI-RQL) was self-administered by 30 consecutive refractive lens exchange patients, including 19 myopes and 11 hyperopes. The change of NEI-RQL scores was determined for each subscale covering a specific aspect of quality of life. Refraction, visual acuity, and contrast sensitivity function were evaluated 3 and 6 months postoperatively. RESULTS: Postoperatively, all patients achieved binocular uncorrected distance and near visual acuity of 20/30 or better. Photopic contrast sensitivity function decreased significantly at high spatial frequencies (P < .05). Overall scores of expectations, activity limitations, dependence on correction, appearance, and satisfaction were significantly higher postoperatively (P < .05). Greater improvement in near vision and dependence on correction was achieved in hyperopes. However, glare scores were significantly lower postoperatively (P < .001). Lower preoperative uncorrected near visual acuity was associated with higher scores for dependence on correction in myopes (r = 0.51, P = .027), and overall patient satisfaction correlated significantly with postoperative uncorrected distance visual acuity (r = -0.44, P = .015). CONCLUSIONS: Refractive lens exchange with the ReSTOR IOL in presbyopic patients provided good visual function and better patient satisfaction compared with preoperative corrections. Improvement in vision-related quality of life was most evident in hyperopes. A slight reduction in contrast sensitivity function appears to have no influence on quality of life.     

Nonoptical determinants of aniseikonia

Interocular differences in apparent size (aniseikonia) are typically associated with interocular differences in refractive error (anisometropia). Aniseikonia is generally thought to reflect disparities in retinal image size that often accompany anisometropia. This assumption was examined with seven highly anisometropic subjects who were tested under conditions in which no substantial retinal image size differences were present. Using a dichoptic size matching task, consistent and large (mean = 22%) aniseikonias were found. Myopic anisometropes exhibit perceptual minification, while hyperopes demonstrate perceptual magnification when using their more ametropic eye. Both ultrasonic and fundus examinations of these subjects indicate that differential retinal growth or stretching is responsible for these findings.     

Normative data for axial elongation in Asian children

Aim

To determine the influence of refractive error (RE), age, gender and parental myopia on axial elongation in Chinese children and to develop normative data for this population.

Methods

This is a retrospective analysis of eight longitudinal studies conducted in China between 2007 and 2017. Data of 4701 participants aged 6–16 years with spherical equivalent from +6 to −6D contributed to one, two or three annualised progression data resulting in a dataset of 11,262 eyes of 26.6%, 14.8% and 58.6% myopes, emmetropes and hyperopes, respectively. Longitudinal data included axial length and cycloplegic spherical equivalent RE. Axial elongation was log-transformed to develop an exponential model with generalised estimating equations including main effects and interactions. Model-based estimates and their confidence intervals (CIs) are reported.

Results

Annual axial elongation decreased significantly with increasing age, with the rate of decrease specific to the RE group. Axial elongation in myopes was higher than in emmetropes and hyperopes but these differences reduced with age (0.58, 0.45 and 0.27 mm/year at 6 years and 0.13, 0.06 and 0.05 mm/year at 15 years for myopes, emmetropes and hyperopes, respectively). The rate of elongation in incident myopes was similar to that in myopes at baseline (0.33 vs. 0.34 mm/year at 10.5 years; p = 0.32), while it was significantly lower in non-myopes (0.20 mm/year at 10.5 years, p < 0.001). Axial elongation was greater in females than in males and in those with both parents myopic compared with one or no myopic parent, with larger differences in non-myopes than in myopes (p < 0.01).

Conclusions

Axial elongation varied with age, RE, gender and parental myopia. Estimated normative data with CIs could serve as a virtual control group.     

Biomicroscopy of the fundus in retinal detachment surgery (author's transl)]

Biomicroscopy of the fundus during retinal detachment surgery has the same advantages as indirect ophthalmoscopy. In addition to this, it offers three main advantages over indirect ophthalmoscopy: the observation of the fundus, in an optical cross section of the tissues, the high variation of magnification available, and the observation of the fundus without switching off the light of the operating room. Since 1976--biomicroscopy of the fundus during retinal detachment surgery has been easily performed with the surgical mobile slit lamp manufactured by the firm Zeiss. The angle of the surgical slit lamp can be reduced to 5 degrees. The slit lamp can be used either with the Zeiss OPMI 1 operating microscope or with the Zeiss OPMI 6 operating microscope. The microscope, the contact lens and the surgical instrumentation specialy fitted for biomicroscopy of the fundus during retinal detachment surgery are described. The surgical technique is dealt with, pointing out the practical details which allow for overcoming the own difficulties of biomicroscopy of the fundus during surgery.     

Changes in Lens Power in Singapore Chinese Children during Refractive Development

Purpose. To examine changes in lens power during refractive development in Singapore Chinese children. Methods. Children aged six to nine years from three Singapore schools were invited to participate in the Singapore Cohort study Of the Risk factors for Myopia (SCORM) study. Cycloplegic refractions and biometry were measured annually in the schools over a five year period from 1999. Children were classified into five refractive error groups: persistent hyperopia, emmetropizing hyperopia, persistent emmetropia, newly developed myopia, or persistent myopia. Crystalline lens power was calculated using Bennett's formula. The rate of change per year across the refractive groups was adjusted for age and sex using General Linear Models. Results. There were 1747 children with at least three sets of measurements for lens power calculations. The mean age at baseline was 7.94 ± 0.84 years and the mean spherical equivalent refraction was -0.41 ± 1.71 diopters (D). Lower lens power and lower lens thickness were associated with persistent myopia. As expected, the newly developed myopes and the persistent myopes showed the largest changes in axial length (AL). Changes in lens power and thickness at follow-up were similar in all refractive groups, except for the newly developed myopes, who showed significantly greater decreases in lens power (0.36 vs. 0.29 D/year; P < 0.001) and lens thickness (0.015 vs. 0.0003 mm/year; P < 0.001) than the persistently emmetropic group. Conclusions. Newly developed myopes showed a significantly greater decrease in lens power than other refractive groups, which may be linked to rapid changes in AL and refraction that occur around the onset of myopia.