Optic disc cupping and prematurity. Large cups as a possible low birth weight sequel

In a previous ophthalmic study of ex-prematures around the age of 10 years it was accidentally found that cupping of the optic disc was significantly more pronounced in children of a low birth weight (less than 2000 g) than in full-term controls (Fledelius 1976). This was true for cup size (cup/disc diameter ratio) as well as depth (as indicated by a visible cribriform plate). The present analyses make up an extension of the above study, with additional calculations based on some of its data. Within the ex-prematures (n = 268) the cup size did not seem to be related to birth weight, sex, or visual acuity. Eyes with myopia of prematurity were not especially 'loaded' with large cups. For the whole sample (including the 187 full-term control there was a weak association between cup size and refraction (and axial eye length). Larger cups occurred relatively more often in myopic eyes. Possible mechanisms behind early changes in disc are discussed (astroglial hypothesis--distension of disc--loss of retinal nerve fibers). It is felt that this new observation--large disc cupping as a possible low birth weight sequel--has to be substantiated by further clinical evidence, as statistical type 1 error (mass significance) cannot be ruled out.

[Anterior ocular segment study with the Scheimpflug rotational camera in refractive surgery candidates]

PURPOSE

To analyze the anterior segment of refractive surgery candidates and establish the variability pattern in this population regarding corneal volume, anterior chamber volume and depth and corneal thickness, using the noncontact three dimensional analyzer Pentacam.

METHODS

A retrospective study of 297 eyes of 149 patients was conducted using Pentacam. According to the spherical equivalent value two groups were created, myopia (n=242 eyes) and hyperopia (n=55 eyes), to analyze the variables of corneal volume, anterior chamber volume and depth and corneal thickness.

RESULTS

The mean values of the myopia group were: corneal total volume 59.37 +/- 3.51 mm(3), corneal volume at 3 mm 3.87 +/- 0.23 mm(3), at 5 mm 11.31 +/- 0.67 mm(3), and at 7 mm 24.30 +/- 1.43 mm(3), anterior chamber volume 198.74 +/- 32.40 mm(3), anterior chamber depth 3.19 +/- 0.28 mm and corneal thickness 533.33 +/- 33.47 mm. In the hyperopia group, the mean total corneal volume was 60.77 +/- 3.31 mm(3), corneal volume at 3 mm from the apex was 4.01 +/- 0.20 mm(3), at 5 mm was 11.73 +/- 0.58 mm(3), and at 7 mm was 25.09 +/- 1.21 mm(3), the anterior chamber volume was 146.61 +/- 32.86 mm(3), the anterior chamber depth was 2.76 +/- 0.38 mm and the corneal thickness was 550.52 +/- 29.49 mm. The difference between the groups was significant for all variables (p<0.05).

CONCLUSION

We observed in this study that patients with myopia had lesser mean corneal volume and pachymetry, and greater anterior chamber depth and volume compared with hyperopic patients.

Effects of refraction and axial length on childhood optic disk parameters measured by optical coherence tomography

PURPOSE

To assess the effects of refraction and axial length on optical coherence tomography (OCT) measures of childhood optic disk parameters.

DESIGN

Population-based cross-sectional study.

METHODS

Of 4,118 children examined in the Sydney Myopia Study (Sydney Childhood Eye Study) from 34 randomly selected primary schools and 21 secondary schools from 2003 through 2005, 3,529 (85.7%) were included in the analysis (1,395 6-year-old children [year 1 students] and 2,134 12-year-old children [year 7 students]). Comprehensive standardized eye examinations included best-corrected visual acuity, cycloplegic autorefraction, biometry measurements, and fast optic disk scans using OCT.

RESULTS

After adjusting for magnification, the mean optic disk area was positively associated with axial length (P(trend) < .0001, both age groups) but was not associated consistently with spherical equivalent refraction (SER).

CONCLUSIONS

Optic disk parameters in childhood are influenced by axial length, but not by refractive error itself.

Prevalence of hyperopia and associations with eye findings in 6- and 12-year-olds

PURPOSE

To describe the prevalence of hyperopia and associated factors in a representative sample of Australian schoolchildren 6 and 12 years old.

DESIGN

Population-based cross-sectional study.

PARTICIPANTS

Schoolchildren ages 6 (n = 1765) and 12 (n = 2353) from 55 randomly selected schools across Sydney.

METHODS

Detailed eye examinations included cycloplegic autorefraction, ocular biometry, cover testing, and dilated fundus examination. Information on birth and medical history were obtained from a parent questionnaire.

MAIN OUTCOME MEASURES

Moderate hyperopia defined as spherical equivalent (SE) refraction of > or =+2.00 diopters (D), and eye conditions including amblyopia, strabismus, astigmatism, and anisometropia.

RESULTS

Prevalences of moderate hyperopia among children ages 6 and 12 were 13.2% and 5.0%, respectively; it was more frequent in children of Caucasian ethnicity (15.7% and 6.8%, respectively) than in children of other ethnic groups. Compared with children without significant ametropia (-0.49 < or = SE refraction < or = +1.99 D), the prevalence of eye conditions including amblyopia, strabismus, abnormal convergence, and reduced stereoacuity was significantly greater in children with moderate hyperopia (all Ps < 0.01). Maternal smoking was significantly associated with moderate hyperopia among 6-year-olds (P = 0.03), but this association was borderline among 12-year-olds (P = 0.055). Early gestational age (<37 weeks) and low birth weight (<2500 g) were not statistically significant predictors of moderate hyperopia in childhood.

CONCLUSIONS

Moderate hyperopia was strongly associated with many common eye conditions, particularly amblyopia and strabismus, in older children. Birth parameters did not predict moderate hyperopia.

Laser Epithelial Keratomileusis for the Correction of Hyperopia Using a 7.0-mm Optical Zone With the Schwind ESIRIS Laser

PURPOSE

To investigate the efficacy of laser epithelial keratomileusis (LASEK) for the correction of hyperopia using a 7.0-mm optical zone and a 9.0-mm total ablation zone diameter with the Schwind ESIRIS flying-spot laser.

METHODS

Forty-seven patients (70 eyes) were treated with a mean preoperative spherical equivalent refraction of +2.32 diopters (D) (range: 0 to +5.00 D). All eyes underwent LASEK using 15% alcohol with a 20-second application.

RESULTS

An intact epithelial flap was obtained in 66 (94%) eyes. In 70 eyes at 12 months, the mean spherical equivalent refraction was +0.09 D (range: -0.75 to +1.00 D) with all (100%) eyes within +/- 1.00 D of the intended correction and 60 (86%) eyes within +/- 0.50 D. In 40 eyes with 24-month follow-up, the refractive correction remained stable after 6 months. Hyperopic cylindrical corrections were attempted in 49 eyes (range: +0.25 to +5.00 D) with vector analysis demonstrating a mean 102% correction at 12 to 24 months. In 60 non-amblyopic eyes, uncorrected visual acuity was > or = 20/20 in 47 (78%) eyes. Thirty-three (47%) eyes gained 1 to 2 lines of Snellen decimal equivalent best spectacle-corrected visual acuity, 30 (43%) eyes showed no change, and 7 (10%) eyes lost 1 line. Eight (11%) eyes at 12 to 24 months had grade +/- 1 of paracentral corneal haze and 57 (81%) had no haze. At 12 months (n = 70), the safety index was 1.06 with an efficacy index of 0.95. Analysis of higher order wavefront aberrations showed no significant changes in root-mean-square values post-operatively, except for a significant reduction of fourth order spherical aberration (P < .05).

CONCLUSIONS

Laser epithelial keratomileusis for hyperopia up to +5.00 D using a 7.0-mm optical zone with the Schwind ESIRIS laser provides excellent refractive and visual outcomes with minimal complications. In eyes followed for 24 months, the refractive correction remained stable after 6 months.

Prospective Evaluation of PermaVision Intracorneal Implants Using In Vivo Confocal Microscopy

PURPOSE

To report effects of the PermaVision intracorneal lens at the cellular level using in vivo confocal microscopy.

METHODS

Four eyes implanted with intracorneal lenses beneath an IntraLase flap for correction of hyperopia were evaluated preoperatively and 1 to 6 months postoperatively.

RESULTS

Intracorneal lenses were tolerated in three eyes with little or no haze observed clinically and good visual results. Minimal keratocyte activation was detected by confocal microscopy, and cell density was decreased posterior to the implants. Epithelial thinning was observed 1 month after implantation. Thickness stabilized by 6 months but remained thinner than baseline (33 +/- 2 microm vs 48 +/- 8 microm, P < .01). The fourth eye had a complicated course with early flap displacement followed by diffuse lamellar keratitis. Confocal microscopy revealed activated keratocytes throughout the anterior stroma. The implant was removed, and recovery was promising.

CONCLUSIONS

Implantation of intracorneal lenses can induce side effects of epithelial thinning, keratocyte loss, and keratocyte activation.

Corneal Shape and Optical Performance After One Night of Corneal Refractive Therapy for Hyperopia

PURPOSE

To investigate the corneal shape and optical performance following one night of Corneal Refractive Therapy for hyperopia (CRTH).

METHODS

Twenty subjects (spherical equivalent: -2.14 +/- 2.54 D) were fit with a Paragon CRTH lens (Dk = 100) on one eye randomly. The other eye served as the control. Aberrations, refractive error, and corneal topography at various locations along the horizontal meridian were measured at baseline prior to lens insertion, and immediately after lens removal and at 1, 3, 6, 12, and 28 hours later. Root mean square wavefront errors were measured using a 4.5 mm pupil size.

RESULTS

After one night of CRTH lens wear, the central cornea steepened and paracentral region flattened in the experimental eyes (p < 0.001), whereas no significant location effect was found in the control eyes (p = 0.139). Refractive error (mean +/- SE) changed by 1.23 +/- 0.21 D (p < 0.001). The defocus increased by 0.58 +/- 0.09 microm (p < 0.001). Higher-order aberrations, coma, and spherical aberrations increased by factors of 2.69, 2.58, and 4.07, respectively (all p < 0.001). Spherical aberrations shifted from positive to negative. Astigmatism did not change over time (p = 0.771). All parameters returned to baseline by 28 hours (all p > or = 0.808). Aberrations and refractive error did not change in the control eyes (all p > or = 0.082). CONCLUSIONS.: The CRTH lens steepens the central cornea and flattens the paracentral region, which alters the ametropia by inducing a myopic shift. It appears to be effective for correcting hyperopia and also is reversible.

Intraocular lens power calculation in short eyes

PURPOSE

To compare the accuracy of the Hoffer Q and SRK-T formulae in eyes below 22 mm in axial length, using biometry measured with partial coherence inferometry (PCI), without a customised ACD constant.

METHODS

Data were retrospectively and prospectively collected by identifying eyes of axial length below 22 mm in the records of the intraocular lens (IOL) master and in preoperative notes. Biometry was performed using PCI and IOL power was calculated using both SRK-T and Hoffer Q formulae. Refractive outcome was measured and the accuracy of the two formulae compared.

RESULTS

Forty-one eyes of 41 patients were identified with an axial length <22 mm. Axial lengths ranged from 21.96 to 20.29 with a mean of 21.51 mm, and IOL power ranging from 23 dioptres (D) to 29 D. The Hoffer Q formula showed a mean prediction error of 0.61 D (SD 0.80) compared with the SRK-T, which showed a mean prediction error of 0.87 D (SD 0.829). A paired t-test found that the Hoffer Q was significantly more accurate than the SRK-T formula (P<0.001).

CONCLUSIONS

Hoffer Q was found to be more accurate than the SRK-T formula in this series of eyes <22 mm axial length when customised ACD constants are not used. Royal College of Ophthalmologists guidelines may need to be adjusted in accordance with these findings. This study underlines the importance of monitoring outcomes, and suggests different customisations are needed for different formulae, with a higher correction if the SRK-T formula is used for short eyes.

Centration on the Cornea Vertex Normal During Hyperopic Refractive Photoablation Using Videokeratoscopy

PURPOSE

To evaluate a method for centering the ablation in standard hyperopic LASIK using an excimer laser with a video-based eye tracker system.

METHODS

Results of 52 consecutive hyperopic eyes treated with the ESIRIS excimer laser were retrospectively reviewed. Ablation was shifted from the pupil center to the vertex normal of the cornea using pupillary offset measured with the Keratron Scout videokeratoscope. Outcomes were assessed 3 months postoperatively.

RESULTS

All eyes preoperatively had a nasally oriented vertex normal in relation to the pupil center. Three months postoperatively a refractive outcome of < 0.50 diopters of spherical equivalent was achieved in 94% (49/52) of eyes. No eye lost more than one line of best spectacle-corrected visual acuity.

CONCLUSIONS

Standard hyperopic LASIK with the ESIRIS laser system leads to good predictable efficacy and safety results when the ablation center is shifted to the cornea vertex normal based on videokeratoscopy data.

Anterior cervical hypertrichosis and mental retardation

Anterior cervical hypertrichosis or hairy throat is a rare dysmorphic sign described in a total of 19 patients so far. The association with a number of additional features has been reported, including mental retardation. We report on another patient with this condition who also had moderate mental retardation, mildly dysmorphic facial features, obesity, hypermetropia and additional hair anomalies (low dorsal hair line on the neck, lumbosacral hypertrichosis). Karyotype and array comparative genomic hybridization analysis at 1 Mb resolution were normal.

Optic disc size in a population based study in northern China: the Beijing Eye Study

AIM

To determine the optic disc size in the adult Chinese population in an urban and a rural region of Beijing.

METHODS

The population based, cross sectional cohort study included 4439 subjects out of 5324 subjects invited to participate (response rate 83.4%). It was divided into a rural part (1973 (44.4%) subjects) and an urban part (2466 (55.6%) subjects). Mean age was 56.2 (SD 10.6) years (range 40-101 years). Colour optic disc photographs were morphometrically examined. Main outcome measure was optic disc area.

RESULTS

Optic disc photographs were available for 4027 (90.7%) subjects. Mean optic disc area measured 2.65 (0.57) mm2 (range 1.03 mm2-7.75 mm2). Optic disc area was significantly (p<0.001) correlated with myopic refractive error, with a steep decrease in optic disc area from high myopia to the mid-range of refractive error, a slightly horizontal course in the refractive error range between -8 dioptres and +4 dioptres, and a further decrease in optic disc area towards higher hyperopia. Optic disc area was not related to age (p = 0.14) or sex (p = 0.93) (optic disc area, males: 2.65 (0.56) mm2 versus females: 2.65 (0.57) mm2). "Microdiscs" may be defined as smaller than 1.51 mm2, and "macrodiscs" as larger than 3.79 mm2.

CONCLUSIONS

Compared with data of preceding studies, mean optic disc size is larger in Chinese people than in white people. In Chinese people highly hyperopic eyes have significantly smaller optic discs, and highly myopic eyes have significantly larger optic discs than emmetropic eyes.

[Laser thermokeratoplasty in the treatment of hyperopia in children]

The effectiveness, safety, and stability of multimodality treatment for hyperopia, hyperopic and mixed astigmatism complicated by amblyopia and anisometropia were studied in 117 patients (117 eyes) aged 9 to 16 years, by using the new laser units "Lik-100" and "Glasser" at 1.54 microm. The patients were divided into 3 groups: 1) 43 patients (43 eyes) with hyperopia, spheric anisometropia and amblyopia; 2) 38 patients (38 eyes) with hyperopia, simple and complicated hyperopic astigmatism, astigmatic anisometropia, and amblyopia; 3) 36 patients (36 eyes) with hyperopia, simple and complicated hyperopic astigmatism, mixed anisometropia, and amblyopia. All the groups underwent multimodality treatment involving laser thermokeratoplasty and drug therapy for amblyopia. In children and adolescents, the refraction effect was 2.99 and 3.61 (mean 3.37 +/- 0.60) diopters, respectively. Astigmatism diminished by 2.01 diopters (63%) in children and by 2.62 diopters (79%) in adolescents (mean 2/35 diopters). The predictability of a refraction effect in the range of +/- 0.5 diopters averaged 77% in all the groups. Anisometropia diminished by an average of 2.88 +/- 0.8 diopters, which was 85% of the baseline data (the upper range of residual refraction was not more than 1.5 diopters. In all the groups, uncorrectable visual acuity increased by an average of 0.36 diopters (0.43 and 0.4 diopters in children and adolescents, respectively); correctable visual acuity increased by an average of 0.22 diopters (0.36 and 0.31 diopters in children and adolescents, respectively). Loss of correctable visual acuity lines did not greater than 2.7% (5 eyes). That of endothelial cells was not more than 6-8%. The angle of squint strabismus could be decreased or corrected in 79% after treatment. Binocular vision restored in 57%.

Treatment-induced shifts of ocular reference axes used for measurement centration

PURPOSE

To determine the shifts of the main corneal reference points in dependence of the chosen centration axis for the treatment.

SETTING

Federal Institute of Technology Zurich, Institute of Biomedical Engineering, Zurich, Switzerland.

METHODS

Computer simulations were performed on several variants of the Gullstrand-Emsley schematic eye, which was modified by an off-axis fovea. Refractive corrections were simulated by centering Munnerlyn's formula on each of the 4 corneal reference points determined in the preoperative eye: the optical axis, the line of sight, the visual axis, and the first corneal reflex. Subsequently, the postoperative locations of these axes were determined and compared with the preoperative values.

RESULTS

The postoperative line of sight was found to depend least on the choice of the preoperative centration axis for both myopic and hyperopic treatments. It undergoes a maximum movement of 0.040 mm when centering a +5 diopter correction on the preoperative line of sight, whereas the corneal reflex, which is used for centering most topography systems, can move by more than 0.10 mm.

CONCLUSIONS

Centration of the correction on the preoperative line of sight enabled good comparability between preoperative and postoperative measurements that use the line of sight as a reference axis. Yet, centration of the treatment on the preoperative line of sight does not ensure comparability between preoperative and postoperative measurements that use the corneal reflex as a reference axis such as most corneal topography systems. Axis shifts might lead to misinterpretation of data such as a wrong diagnosis of a decentered ablation or changes in the Zernike representation.

Analysis of refractive state ratios and the onset of myopia

PURPOSE

To develop formulae for the refractive state ratios, axial length growth and the age of onset (A*) of myopia. Calculated results are compared with measurements.

METHODS

Using an image equation, the axial length in the ametropic state (L) is related to the length in the emmetropic state (L*) and refractive error (D) by a rate of change M (D mm(-1)). Three refractive state ratios are defined: C1 = L/r1, C2 = L/L* and C3 = L/H, where r1 and H are the anterior surface radius of the cornea and the transverse dimension of the eye, respectively. The age of onset A* is calculated by the rate of change of refractive error (M) and the axial growth rates N and N* in the ametropic and emmetropic states, respectively.

RESULTS

The three ratios C1, C2 and C3 are increasing function of the myopia power, for example, C1 = 3.4, 3.1, 2.9 for D = -8, 0, +4 dioptres, respectively. The calculated C1* (for the emmetropic state) varies between 3.08 and 3.14, depending on corneal shape, and C3 = 0.985, 1.0, 1.04 for D = +3, 0, -3 dioptres: these values are consistent with measured data. For a typical system with effective focal length F = 22.25 mm, L* = 24.2 mm and L = 23.4, 24.9, 25.9 mm for D = +2, -2, -5 dioptres, respectively. The calculated rates of change of refractive error M = 2.3-2.9 D mm(-1) for F = 22-23 mm are also consistent with measured values 2.4-2.7 D mm(-1). The age of onset A* is calculated to be proportional to 1/(M dN), where dN = N-N* is the axial growth rate difference between the ametropic and emmetropic states and may be used as a better predictor for myopia onset than the conventional ratio L/r1. The A* is given by the crossing of L and L* curves, in which myopia onset occurs earlier for larger M dN.

CONCLUSION

The theory provides formulae to calculate various refractive state ratios, which are consistent with measurements. By defining two rate functions, M and N, the onset of myopia can be predicted.

Automated Visual Axis Alignment for Refractive Excimer Laser Ablation

PURPOSE

To describe the use of new laser alignment and delivery software in the NIDEK Advanced Vision Excimer laser platform (NAVEX) that allows centration based on surgeon specification.

METHODS

Descriptive article with a case report.

RESULTS

The software allows specification via numeric entry of the exact placement of the laser tapered to the position of the visual axis or the line of sight.

CONCLUSIONS

The ability to specify the exact location of the laser ablation based on pupil position is fundamental in patients undergoing custom ablation and those with eccentric fixation. A conservative treatment strategy is recommended for initial experience with this alignment software.

Measurement of Combined Corneal, Internal, and Total Ocular Optical Quality Analysis in Anterior Segment Pathology With the OPD-Scan and OPD-Station

PURPOSE

To show the clinical use of the NIDEK OPD-Scan wavefront aberrometer and OPD-Station software in anterior segment surgery and pathology.

METHODS

Case examples are presented along with discussion about the relevant clinical data obtained from the OPD-Scan and OPD-Station software.

RESULTS

Six case examples including cataract surgery, secondary IOL implantation, phakic intraocular lens surgery, pterygium surgery, contact lens fitting, and multifocal ablations are discussed.

CONCLUSIONS

A complete understanding of the optics of the eye facilitates a better clinical comprehension of a variety of conditions in anterior segment surgery and pathology.

Biometry of phakic intraocular lens using Scheimpflug photography

PURPOSE

To examine lateral and axial positioning of phakic intraocular lenses (IOLs) with iris fixation in the anterior chamber and to examine short-term stability of the IOL position.

SETTING

The Netherlands Opthalmic Research Institute, Amsterdam, the Netherlands.

METHODS

Thirty patients participated in the study. Thirty-one eyes were implanted with the 204 type myopia IOL, 14 eyes with the 206 myopia IOL, and 8 eyes with the 203 hyperopia IOL. Scheimpflug slitlamp photographs were made through the optical axis along 4 meridians of the eyes. Ray tracing was used to obtain the lateral and axial position of the IOLs.

RESULTS

Centration of the IOL with respect to the pupil's center and the tilt angle of the IOL with respect to the optical axis of the eye were measured. Standard deviation of decentration was 0.21 mm vertically and 0.16 mm horizontally. Standard deviation of tilt was 1.30 degrees vertically and 0.90 degrees horizontally. Tilt and decentration are proportional to each other. Vaulting, the distance between the crystalline lens and the IOL, was constant over a period of 24 months, ranging from 0.2 to 0.8 mm, depending primarily on the radius of curvature of the crystalline lens. A geometric model for this dependence was formulated.

CONCLUSION

Phakic IOLs with iris fixation can be positioned in the eye with submillimeter precision. Axial position of iris-fixated phakic IOLs over time is excellent. Axial position and vaulting can be predicted when the radius of curvature of the crystalline lens is known. The IOL behaves as if mounted slightly above a sphere-the anterior surface of the crystalline lens.

Corneal endothelial cell density decreases with age in emmetropic eyes

PURPOSE

To analyze the corneal endothelial cell density in healthy adult emmetropic subjects.

METHODS

We analyzed the corneal endothelial cell density of a group made up of 225 emmetropic subjects (n=225). As age-matched control groups we analyzed two other groups, one made up of myopic subjects (n=209) and the other made up of hyperopic subjects (n=203). We recorded the mean of three consecutive measurements of the corneal endothelial cell density using the Topcon SP-2000P non-contact specular microscope (Topcon Corp., Tokyo, Japan).

RESULTS

The mean age was 38.6+/-11.8 years, 40.7+/-12.2 years, and 39.2+/-10.5 years for emmetropic, myopic and hyperopic subjects respectively (p=0.994). No significant differences (p=0.920) in endothelial cell density values were found between emmetropic (2985+/-245 cells/mm2), myopic (2936+/-258 cells/mm2) and hyperopic eyes (2946+/-253 cells/mm2). Lower corneal endothelial cell density values were found in older emmetropic (p<0.001), myopic (p<0.001), and hyperopic subjects (p<0.001). A significant correlation between endothelial cell density and age was found in emmetropic (r=-0.958; p<0.001), myopic (r= -0.954; p<0.001) and hyperopic subjects (r= -0.948; p<0.001).

CONCLUSIONS

In healthy emmetropic subjects there is a reduction in corneal endothelial cell density with age although there are no differences in corneal endothelial cell density values between emmetropic, myopic and hyperopic subjects.

Extreme hyperopia is the result of null mutations in MFRP, which encodes a Frizzled-related protein

Nanophthalmos is a rare disorder of eye development characterized by extreme hyperopia (farsightedness), with refractive error in the range of +8.00 to +25.00 diopters. Because the cornea and lens are normal in size and shape, hyperopia occurs because insufficient growth along the visual axis places these lensing components too close to the retina. Nanophthalmic eyes show considerable thickening of both the choroidal vascular bed and scleral coat, which provide nutritive and structural support for the retina. Thickening of these tissues is a general feature of axial hyperopia, whereas the opposite occurs in myopia. We have mapped recessive nanophthalmos to a unique locus at 11q23.3 and identified four independent mutations in MFRP, a gene that is selectively expressed in the eye and encodes a protein with homology to Tolloid proteases and the Wnt-binding domain of the Frizzled transmembrane receptors. This gene is not critical for retinal function, as patients entirely lacking MFRP can still have good refraction-corrected vision, produce clinically normal electro-retinograms, and show only modest anomalies in the dark adaptation of photoreceptors. MFRP appears primarily devoted to regulating axial length of the eye. It remains to be determined whether natural variation in its activity plays a role in common refractive errors.

Ametropia and ocular biometry in a U.K. university student population

PURPOSE

The prevalence of myopia is known to vary with age, ethnicity, level of education, and socioeconomic status, with a high prevalence reported in university students and in people from East Asian countries. This study determines the prevalence of ametropia in a mixed ethnicity U.K. university student population and compares associated ocular biometric measures.

METHODS

Refractive error and related ocular component data were collected on 373 first-year U.K. undergraduate students (mean age = 19.55 years +/- 2.99, range = 17-30 years) at the start of the academic year at Aston University, Birmingham, and the University of Bradford, West Yorkshire. The ethnic variation of the students was as follows: white 38.9%, British Asian 58.2%, Chinese 2.1%, and black 0.8%. Noncycloplegic refractive error was measured with an infrared open-field autorefractor, the Shin-Nippon NVision-K 5001 (Shin Nippon, Ryusyo Industrial Co. Ltd, Osaka, Japan). Myopia was defined as a mean spherical equivalent (MSE) less than or equal to -0.50 D. Hyperopia was defined as an MSE greater than or equal to +0.50 D. Axial length, corneal curvature, and anterior chamber depth were measured using the Zeiss IOLMaster (Carl Zeiss, Jena, GmBH).

RESULTS

The analysis was carried out only for white and British Asian groups. The overall distribution of refractive error exhibited leptokurtosis, and prevalence levels were similar for white and British Asian (the predominant ethnic group) students across each ametropic group: myopia (50% vs. 53.4%), hyperopia (18.8% vs. 17.3%), and emmetropia (31.2% vs. 29.3%). There were no significant differences in the distribution of ametropia and biometric components between white and British Asian samples.

CONCLUSION

The absence of a significant difference in refractive error and ocular components between white and British Asian students exposed to the same educational system is of interest. However, it is clear that a further study incorporating formal epidemiologic methods of analysis is required to address adequately the recent proposal that juvenile myopia develops principally from "myopiagenic" environments and is relatively independent of ethnicity.

The study of corneal topography in myopic and hyperopic children

PURPOSE

To compare the differences of corneal topographies in myopic and hyperopic children and study the effect of Atropin on their changes.

METHODS

The refractive components of 136 eyes with different refractive conditions were measured with A-Scan and their corneal topographies with and without cycloplegia were obtained respectively.

RESULTS

The mean corneal power of zones 3mm (MD3, P=0.031) and minor keratometer K2 (P=0.003) of myopia are greater than those of hyperopia without cycloplegia. MD3 (P=0.009) and Keratometer K1 (P = 0.025) increased in hyperopic eyes, while MD3 (P=0.033), K1 (P = 0.035) and K2 (P = 0.002) decreased in myopic eyes significantly after cycloplegia. Similarly, the mean corneal power of zones 5mm (MD5) and 7mm (MD7) in myopic eyes decreased dramatically (P < or = 0.001).

CONCLUSIONS

The corneal power was found to be greater in myopia than that in hyperopia. The effect of Atropin on corneal shape of myopia and hyperopia was in the opposite direction.

[Changes of axial dimensions of the eye during growth in emmetropia, myopia and hyperopia]

PURPOSE

The aim ot this study was to evaluate changes ot axial dimensions ot the eye during growth in emmetropia, myopia and hyperopia.

MATERIAL AND METHODS

We examined 183 children (363 eyes) aged 4 to 19 with emmetropia, myopia and hyperopia. All measurements were performed after cycloplegia with 1% tropicamidum (Polfa Warszawa). Total and corneal refraction was examined with autokeratorefractometer (Nikon NRK-8000). Then we used ultrasound biometer Ocuscan (Alcon, USA), to measure axial length of the eye, axial length of the vitreous cavity, axial dimension of the lens and axial depth of the anterior chamber.

RESULTS AND CONCLUSIONS

1. Growth of the axial length of the emmetropic eyes is finished at the age of 12, in hyperopic eyes in the age of 11 and in myopic eyes growth is proportional until the age of 14 and then significantly accelerates. 2. Growth of the axial length is mainly caused by increasing axial length of vitreous cavity. A little role in human eye growth is also played by increasing depth of the anterior chamber. 3. Between 4 and 19 years old, mean cycloplegic axial dimension of the lens is slightly decreasing in emmetropic and hyperopic eyes, whereas in myopic eyes is constant.