Refractive Error Components Research Articles

Higher order aberrations according to spherical, and astigmatic refractive errors in children

ABSTRACT Clinical relevance The results of this study present novel insights into the impact of spherical and astigmatic refractive errors on overall, corneal and internal aberrations and may provide a clear understanding of the emmetropisation process and the development of visual function. Background This study aimed to assess the association between overall, corneal and internal higher-order aberrations and the spherical and astigmatic components (magnitude and angle) of refractive error in a large sample of children. Methods A total of 311 children aged 7 – 8 years old were classified based on spherical equivalent refraction (myopic, emmetropic and hyperopic); magnitude of astigmatism (none, low and moderate); and angle of astigmatism (with-the-rule, against-the-rule and oblique). Refractive error and overall, corneal and internal higher-order aberrations were measured using the OPD-Scan III workstation. Results Regarding spherical equivalent refraction, myopic eyes had greater root mean square (RMS) overall higher-order values, total spherical, tetrafoil and secondary astigmatism aberrations, and internal higher-order, total spherical and tetrafoil aberrations in comparison to emmetropic eyes. The magnitude of astigmatism was positively associated with all overall RMS aberrations and with internal higher order, coma, total coma, total spherical and tetrafoil aberrations. Eyes with with-the-rule astigmatism showed higher RMS values of coma and total coma compared to eyes with against-the-rule and oblique astigmatism. Conclusions Higher-order aberrations are dependent on the spherical as well as astigmatic components of refractive error. These findings enhance the current understanding of the emmetropisation process and visual function development.

Non-pathologic components are associated with reduced visual acuity in myopes after spectacle correction.

To find the association between reduced best-corrected visual acuity and non-pathologic components after optical correction in individuals with low to high myopia. Myopic children under 16 years of age were reviewed using electronic medical records and the following data were extracted and recorded: participant's age, gender, uncorrected visual acuity (UCVA), manifest refraction, and best corrected visual acuity (BCVA). Spherical equivalent and cylinder were classified into low, moderate, and high categories based on the magnitude range. Similarly, astigmatism was defined into with-the-rule, against-the-rule, and oblique based on the location of the steepest meridian. Reduced BCVA was defined when the decimal visual acuity was less than 0.66 (equivalent to Snellen's acuity of 6/9 or 20/30). Logistic regression was performed to test the factors associated with reduced visual acuity after optical correction in the absence of myopic pathologic changes. Statistical significance was considered if P < 0.05. Overall 44.9% (N = 242/538) of myopes had reduced best-corrected visual acuity (BCVA) and none of the patients had pathologic myopic lesions. Using logistic regression, we found that high spherical refraction (OR 27.98, 95% CI 14.43-54.25, P < 0.001) and moderate spherical refraction (OR 5.52, 95% CI 2.56-11.91, P < 0.001) were significantly associated with reduced best corrected visual acuity despite any pathological lesions. Additionally, oblique and ATR astigmatism were associated with reduced visual acuity in myopic children with (OR 2.05, 95% CI 0.77-5.42) and (OR 1.59, 95% CI 0.82-3.08). Higher magnitude of refractive error components causes reduced visual acuity in the absence of pathologic changes.

Factors associated with reduced visual acuity in myopes with and without ocular pathologies after optical correction.

Considering that a certain proportion of high myopes have reduced visual acuity even after full optical correction, this study aimed to investigate the association between various refractive error components (sphere, cylinder and axis orientation) and reduced visual acuity in individuals with low to high myopia with and without pathologic myopia lesions. We analysed data from randomly selected eyes of 11,258 individuals with myopia (mean ± SD spherical equivalent (SE) -3.2± 2.9D; range: -0.5D to -21.5D). In total, 10,528 individuals had no pathologic myopia lesions. Sphere, cylinder and SE refraction were classified into mild, moderate and high categories. Astigmatism was defined as with-the-rule, against-the-rule or oblique based on the axis orientation. Reduced best-corrected visual acuity was defined as ≥0.18 logMAR. Logistic regression was performed to test factors associated with reduced visual acuity with and without pathologic myopia lesions. Overall, 6.4% (N= 720/11,258) of myopes had reduced best-corrected visual acuity. High sphere (≤-6.0D; Odd ratios [OR]: 16.1; 95% CI: 2.1-126.5), high cylinder (<-2.0DC; OR: 2.5; 95% CI: 1.8-3.4), against-the-rule (OR: 1.5; 95% CI: 1.1-2.0) and oblique astigmatism (OR: 1.6; 95% CI: 1.2-2.1) were significantly (p≤ 0.008) associated with reduced visual acuity in the absence of pathologic myopia lesions. Both moderate SE and high myopic SE were also associated with reduced visual acuity. In the presence of pathologic myopia lesions, tessellated fundus (OR: 6.9; 95% CI: 3.5-14.1), chorioretinal atrophy (OR: 7.7; 95% CI: 2.6-19.9) and choroidal neovascularisation (OR: 37.4; 95% CI: 3.3-419.3) were significantly (p≤ 0.003) associated with reduced visual acuity. Even after full optical correction, both refractive components and pathologic myopia lesions can independently cause reduced visual acuity, regardless of the degree of myopia.

Phakic Intraocular Lens Implantation After Deep Anterior Lamellar Keratoplasty: Retrospective Case Series Analysis With Long-Term Follow-Up.

PurposeTo report outcomes of phakic intraocular lens (IOL) implantation after deep anterior lamellar keratoplasty (DALK) to correct high ametropia.SettingCentro Hospitalar Universitário do Porto, Portugal.MethodsRetrospective case series with 11 eyes submitted to phakic IOL implantation after DALK. Main outcomes measured were uncorrected and corrected distance visual acuity (UDVA and CDVA), refractive error components, tomographic parameters and endothelial cell density (ECD). The minimum follow-up was 3 years for all cases.ResultsMean ECD loss was 8.7±6.7% at 1 year, 13.1±8.6% at 3 years (n=11; p=0.016, p=0.007, respectively) and 14.0±20.4% at 5 years (n=5, p=0.212). Mean logMAR UDVA increased from 1.27±0.90logMAR preoperatively to 0.16±0.15logMAR postoperatively (p≤0.001) and no statistically significant differences were registered during follow-up. All patients gained at least 5 lines of UDVA. 54.5% of the eyes gained 1 line in CDVA postoperative and only one eye lost one CDVA line through follow-up. Efficacy and safety indexes at 1 and 3 years were 1.01–0.97 and 1.24–1.21, respectively. Mean spherical equivalent was reduced from −7.84±4.63 D preoperatively to −1.05±1.07 D postoperatively (p=0.001). Mean percentage of reduction in refractive cylinder and spherical error was 83.8±15.8% and 73.1±31.5%, respectively, p≤0.001 for both. In one eye there was a significantly gradual ECD loss over 5 years follow-up and the patient will be submitted to IOL explant.ConclusionPhakic IOLs were effective for correction high ametropia after DALK, showing high efficacy and safety indexes with stability over time. However, it was registered a continuing endothelial cell loss postoperatively, which assumed to be higher than those reported in eyes without DALK.

Fourier Analysis of Corneal Irregular Astigmatism Due to the Anterior Corneal Surface in Dry Eye.

To evaluate corneal irregular astigmatism due to the anterior corneal surface using Fourier harmonic analysis with a Placido ring-based corneal topographer (Placido-based topographer) and three-dimensional anterior segment optical coherence tomography (OCT) in dry eyes. Forty-four eyes of 44 subjects with dry eye and 20 eyes of 20 normal control subjects were enrolled. Corneal topographic data were obtained using a Placido-based topographer and OCT. Dioptric data from the central 3-mm zone of the anterior corneal surface were decomposed using Fourier harmonic analysis. Spherical, regular astigmatism, and irregular astigmatism (asymmetry and higher-order irregularity) refractive error components of the cornea from the two imaging modalities were compared. Both asymmetry and higher-order irregularity values were significantly greater in dry eyes than in control eyes for both the Placido-based topographer and OCT measurements (all P<0.05). In dry eyes, measured values of asymmetry and higher-order irregularities were significantly smaller when obtained with OCT than with the Placido-based topographer (both P<0.001). By contrast, these parameters were not significantly different between the two devices in control eyes. In dry eyes, severity of superficial punctate keratopathy in the central corneal region was correlated with irregular astigmatism. The amount of corneal irregular astigmatism, quantified using Fourier harmonic analysis, was significantly higher in dry eyes than in normal eyes. Measurements obtained with OCT and the Placido-based topographer differed in subjects with dry eyes. Therefore, caution should be practiced when trying to use these measurements interchangeably.

A contralateral eye study comparing characteristics of corneal endothelial cells in bilateral keratoconus patients with unilateral corneal Vogt's striae

PurposeThe aim of this study was to analyze and compare corneal endothelial cell morphology and characteristics in bilateral keratoconus (KCN) patients with unilateral Vogt's striae. MethodsFifty patients aged 20–38 years were recruited in this cross-sectional contralateral eye study. In this study, corneal endothelial cell parameters were evaluated in patients with bilateral KCN and unilateral Vogt's striae using the Topcon SP2000P specular microscope (Topcon, Tokyo, Japan). ResultsIn the current study, there were no significant differences in corneal endothelial cell parameters including endothelial cell density (ECD), hexagonal cell ratio (HEX), and coefficient of variance of cell size (CV) between the KCN groups with and without Vogt's striae, [(2968.34 ± 276.65 vs. 2980.05 ± 253.30, P = 0.618), (51.88 ± 13.57 vs. 53.24 ± 9.31, P = 0.658), and (32.50 ± 5.40 vs. 32.97 ± 4.07, P = 0.467), respectively]. Also, among study groups with and without Vogt's striae, ECD did not correlate with anterior chamber depth (ACD) [(P = 0.564, r = 0.09), (P = 0.219, r = −0.18), respectively], maximum keratometry (Kmax) [(P = 0.215, r = 0.18), (P = 0.898, r = 0.02), respectively], and central corneal thickness (CCT) [(P = 0.989, r = −0.02), (P = 0.643, r = −0.07), respectively].Our results showed significant differences in corrected and uncorrected distance visual acuity (UDVA), cycloplegic refractive error components (calculated by vectorial analysis), CCT, and Kmax between two study groups (all P < 0.05) except for J45 (Jackson cross cylinder, axes at 45 and 135°) (P = 0.131). ConclusionsWe were not able to find the statistically significant differences in ECD, HEX, and CV between KCN eyes with and without Vogt's striae. Despite clinical and tomographic results, it seems that Vogt's striae cannot cause deterioration in the corneal endothelial morphology.

Hybrid contact lenses for visual management of patients after keratoplasty

This study aims to report the outcomes of new-generation hybrid contact lenses for visual rehabilitation of postkeratoplasty patients. Twenty eyes of twenty postkeratoplasty patients were fitted with hybrid lenses. Each patient's keratometric values, ocular surface irregularity indices, central corneal thickness (CCT), uncorrected visual acuity (UCVA), spectacle-corrected visual acuity, contact lens-corrected visual acuity, contact lens fitting data, and contact lens daily wearing time were recorded. Follow-up examinations were performed at 1st week, 1st month, and 3rd month visit after successful fitting of the lenses. The mean age of the patients was 38.42 ± 4.89 years. The mean spherical component of refractive error was -4.46 ± 2.1 D, and the mean astigmatism was -5.31 ± 1.55 D. The median UCVA was 1.00 logarithm of the minimum angle of resolution (logMAR) which improved to 0.40 logMAR after spectacle correction. The median visual acuity with hybrid contact lenses was 0.05 logMAR. The median CCT was 544.4 μm and increased to 549.2 μm at 3 months after contact lens wear. The difference was not statistically significant (P = 0.38). The mean follow-up of patients was 4.32 ± 0.45 months. Eighteen of twenty patients reported a mean of 8.37 ± 1.95 h comfortable wearing time per day during this period. Two patients discontinued contact lens wearing due to conjunctival hyperemia. No graft-related complications such as decompensation, rejection, and infection were documented during the follow-up period. The new-generation hybrid contact lenses can be considered helpful in the visual management of postcorneal graft patients, particularly who are unable to achieve an adequate visual outcome with spectacles.

Outcomes of Toric Iris-Claw Phakic Intraocular Lens Implantation After Deep Anterior Lamellar Keratoplasty for Keratoconus.

To assess visual and refractive outcomes of toric iris-claw phakic intraocular lens (IOL) implantation in patients who had previously undergone deep anterior lamellar keratoplasty (DALK). Retrospective case series including 24 eyes of 24 patients implanted with toric Artiflex or Artisan (Ophtec BV, Groningen, Holland) phakic IOL following DALK for keratoconus. During a 12-month follow-up, the main outcome measures were uncorrected and corrected distance visual acuities (UDVA and CDVA), refractive error components, topographic parameters, and endothelial cell count. Alpins vectorial analysis was performed. At the last follow-up, the spherical equivalent (SE) was within ±0.50 diopters (D) in 71% of eyes and within ±1.00 D in 92% of eyes. Mean refractive astigmatism was reduced from -4.92 ± 1.55 D (range: -2.50 to -8.00 D) preoperatively to -0.66 ± 0.61 D (range: -2.00 to 0.00 D) after treatment, and 76.5% of cases were within ±1.00 D. No significant differences (P = .123) were detected in spherical equivalent values between 3- and 12-month follow-up visits. No eyes lost lines in CDVA, and 54% of eyes gained one or more lines. Postoperative UDVA was 20/40 or better in 88% of eyes. Efficacy and safety indexes at 12 months were 0.93 and 1.00, respectively. Mean endothelial cell loss was 6.10% at 12 months postoperatively. No intraoperative or postoperative complications were noted over the follow-up period. The implantation of a toric iris-claw phakic IOL has shown high efficacy and safety in this series and may be considered as a reasonable option for the management of refractive errors after DALK. [J Refract Surg. 2017;33(8):538-544.].

An alternative clinical routine for subjective refraction based on power vectors with trial frames.

Subjective refraction determines the final point of refractive error assessment in most clinical environments and its foundations have remained unchanged for decades. The purpose of this paper is to compare the results obtained when monocular subjective refraction is assessed in trial frames by a new clinical procedure based on a pure power vector interpretation with conventional clinical refraction procedures. An alternative clinical routine is described that uses power vector interpretation with implementation in trial frames. Refractive error is determined in terms of: (i) the spherical equivalent (M component), and (ii) a pair of Jackson Crossed Cylinder lenses oriented at 0°/90° (J0 component) and 45°/135° (J45 component) for determination of astigmatism. This vector subjective refraction result (VR) is compared separately for right and left eyes of 25 subjects (mean age, 35±4years) against conventional sphero-cylindrical subjective refraction (RX) using a phoropter. The VR procedure was applied with both conventional tumbling E optotypes (VR1) and modified optotypes with oblique orientation (VR2). Bland-Altman plots and intra-class correlation coefficient showed good agreement between VR, and RX (with coefficient values above 0.82) and anova showed no significant differences in any of the power vector components between RX and VR. VR1 and VR2 procedure results were similar (p≥0.77). The proposed routine determines the three components of refractive error in power vector notation [M, J0 , J45 ], with a refraction time similar to the one used in conventional subjective procedures. The proposed routine could be helpful for inexperienced clinicians and for experienced clinicians in those cases where it is difficult to get a valid starting point for conventional RX (irregular corneas, media opacities, etc.) and for refractive situations/places with inadequate refractive facilities/equipment.

Comparison of the refractive measurements with hand-held autorefractometer, table-mounted autorefractometer and cycloplegic retinoscopy in children.

PurposeTo evaluate the performance of the hand-held and table-top autorefractokeratometer in measuring refractive errors by comparing them with cycloplegic retinoscopy.MethodsIncluded in the study were 112 eyes of 112 pediatric patients whose mean age was 6.78 ± 2.61 years (range, 2 to 12 years). The refractive errors of all the eyes were measured with and without cycloplegia using a hand held autorefractokeratometer (Retinomax K-plus 3), table top autorefractokeratometer (Canon RK-F1) and performing cycloplegic retinoscopy. The spherical equivalent, cylindrical axis and keratometer values were statistically compared.ResultsThe mean spherical equivalent obtained from the Retinomax K-plus 3 was significantly less hyperopic than that of Canon RK-F1 (p = 0.004) before cycloplegia. When the Bland Altman analysis was performed in comparisons of spherical equivalent values measured with the Retinomax K-plus 3, Canon RK-F1 and cycloplegic retinoscopy, it was seen that almost all of the differences between the measurements remained within the range of ±2 standard deviation. Good agreement was found between Retinomax K-plus 3 and Canon RK-F1 for the Jackson cross-cylinder values at axis 0° and 45°; keratometer values respectively.ConclusionsThe refractive error components were highly correlated between the two instruments and cycloplegic retinoscopy.

Short-term stability in refractive status despite large fluctuations in glucose levels in diabetes mellitus type 1 and 2.

PurposeThis work investigates how short-term changes in blood glucose concentration affect the refractive components of the diabetic eye in patients with long-term Type 1 and Type 2 diabetes.MethodsBlood glucose concentration, refractive error components (mean spherical equivalent MSE, J0, J45), central corneal thickness (CCT), anterior chamber depth (ACD), crystalline lens thickness (LT), axial length (AL) and ocular aberrations were monitored at two-hourly intervals over a 12-hour period in: 20 T1DM patients (mean age ± SD) 38±14 years, baseline HbA1c 8.6±1.9%; 21 T2DM patients (mean age ± SD) 56±11 years, HbA1c 7.5±1.8%; and in 20 control subjects (mean age ± SD) 49±23 years, HbA1c 5.5±0.5%. The refractive and biometric results were compared with the corresponding changes in blood glucose concentration.ResultsBlood glucose concentration at different times was found to vary significantly within (p<0.0005) and between groups (p<0.0005). However, the refractive error components and ocular aberrations were not found to alter significantly over the day in either the diabetic patients or the control subjects (p>0.05). Minor changes of marginal statistical or optical significance were observed in some biometric parameters. Similarly there were some marginally significant differences between the baseline biometric parameters of well-controlled and poorly-controlled diabetic subjects.ConclusionThis work suggests that normal, short-term fluctuations (of up to about 6 mM/l on a timescale of a few hours) in the blood glucose levels of diabetics are not usually associated with acute changes in refractive error or ocular wavefront aberrations. It is therefore possible that factors other than refractive error fluctuations are sometimes responsible for the transient visual problems often reported by diabetic patients.

Comparing homatropine and atropine in pediatric cycloplegic refractions

To compare cycloplegic efficacy of homatropine and atropine in pediatric refractions and derive a regression formula to calculate refraction findings for both agents. Children between the ages of 4 to 10 years with refractive error underwent cycloplegic refraction with 2% homatropine and 1% atropine by retinoscopy and automated refraction. Refractive data were compared by the use of power vector analysis. Primary outcome measures were spherical equivalent (SE), astigmatic components of refractive error (J(0) and J(45)), overall blur strength of refractive error, and residual accommodation. A total of 63 children with refractive error were enrolled (mean age, 6.7 ± 1.6 years). Compared with homatropine, atropine uncovered significantly greater hyperopic SE in patients with hypermetropia (4.2 ± 2.5 D [atropine] vs 3.5 ± 2.3 D [homatropine]; P < 0.001) as well as myopia (-1.8 ± 1.4 D [atropine] vs -2.1 ± 1.4 D [homatropine]; P < 0.001). Overall blur strength was significantly greater with atropine (3.1 ± 2.1 [atropine] vs 2.9 ± 1.9 [homatropine]; P = 0.003). Homatropine had a significantly greater residual accommodation (1.8 ± 0.4 D [atropine] vs 3.1 ± 0.5 D [homatropine]; P < 0.001). A regression formula was derived. Of the 2 cycloplegic agents, atropine yielded more consistent results than homatropine; however atropine had a relatively slow onset and prolonged effect. Our regression formula may make it possible to derive atropine-like results while using the clinically more versatile homatropine.

Diurnal rhythms of refractive error components in normal chick

Diurnal rhythms of refractive error components in normal chick

The Correlation Between Migraine Headache and Refractive Errors

A literature review reveals historical references to an association between migraine headache and refractive errors, but a lack of scientific evidence relating to these claims. In a masked case-controlled study, we investigated the four aspects of refractive errors that have been implicated in the literature as correlated with migraine: spherical refractive error, astigmatic refractive error, anisometropia, and uncorrected ametropia. We also compared the calculated scalar value of refractive error, aided and unaided visual acuity, and spectacle use in migraine and control groups. We then investigated the relationship between refractive components and key migraine headache variables. Compared with the control group, the migraine group had higher degrees of astigmatic components of refractive error assessed both objectively (C, p = 0.01; C(0), p = 0.01; C(45), p = 0.05) and subjectively (C, p = 0.03; C(0), p = 0.03; C(45), p = 0.05), uncorrected astigmatic components of refractive error (C(0), p = 0.02; C(45), p = 0.04), and anisometropia (p = 0.06). Perhaps the historical literature is indeed correct that low degrees of astigmatism and anisometropia are relevant in migraine. Our most significant finding was of higher degrees of astigmatism in the migraine group. This study does indicate that people who experience migraine headaches should attend their optometrist regularly to ensure that their refractive errors are appropriately corrected.

Angle-supported phakic intraocular lenses followed by laser-assisted in situ keratomileusis for the correction of high myopia

Purpose To evaluate the safety, effectiveness, predictability, and stability of the combination of angle-supported phakic intraocular lens (PIOL) implantation and laser-assisted in situ keratomileusis (LASIK) for the correction of high myopia. Design Noncomparative interventional case series. Methods At the Instituto Oftalmológico de Alicante, Spain, 24 consecutive eyes of 12 patients with a preoperative spherical equivalent between −9 and −26 diopters were studied. Implantation of an angle-supported PIOL was done as the first surgery. Laser-assisted in situ keratomileusis was performed at least 6 months after PIOL surgery, once stability of topography and refraction were proved. Main outcome measures were uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), refraction, applanation tonometry, and corneal endothelial study (cell density, hexagonality, and coefficient of variation), with a minimum follow-up of 12 months after LASIK. Results The mean spherical equivalent refraction decreased from −15.17 ± 5.15 diopters before PIOL implantation to −1.33 ± 1.18 diopters after PIOL surgery and to 0.01 ± 0.53 12 months after LASIK. Uncorrected visual acuity was 0.39 ± 0.12 after PIOL surgery, increasing to 0.65 ± 0.23 12 months after LASIK. There was an increase in 20/40 or better UCVA from 16.6% after PIOL surgery alone to 83.3% after addition of LASIK. At final follow-up, spherical equivalent was within ± 1 diopter of emmetropia in 22 eyes (91.7%) and in 18 eyes (75%) within ± 0.50 diopters. Vector analysis demonstrated that astigmatic components of refractive error after PIOL surgery were well corrected by LASIK. At final follow-up the mean endothelial cell loss was 4.88% ( P < .001). There were no statistically significant differences between mean endothelial cell count, percentage of hexagonality, or coefficient of variation before LASIK and 12 months after LASIK, suggesting that no corneal endothelial damage was produced by LASIK itself. No sight-threatening complications occurred through the follow-up period. Conclusion The combination of angle-supported PIOL implantation and LASIK appears to be a safe, effective, predictable, and stable procedure for the correction of high myopia. This paper emphasizes the benefits of adding LASIK to the use of PIOL alone.

Development of refractive errors into old age.

To evaluate refractive errors in older adults. The distribution of refractive error components was evaluated in a sample of 569 older adults including 171 participants over the age of 80 years. The mean age was 75.2 years with a range from 59 to 106 years. Emphasis was placed on modern methods of analyzing astigmatic refractive errors, which convert cylindrical refractive errors into primary and oblique components. The known increase in hyperopia after maturity continues into old age. The primary negative astigmatic component increases dramatically in prevalence and amount after age 70 years, whereas the oblique component remains unchanged. Significant anisometropia is common in the oldest old, suggesting failure of emmetropization mechanisms with age. Substantial gender differences exist in refractive changes with age. The continuing changes in all components of refractive error into old age and the surprisingly high prevalence of large amounts of astigmatism and anisometropia emphasize the importance of regular refractive evaluations among the oldest old.

Photorefractive keratectomy for compound myopic astigmatism with an eye cup erodible mask delivery system.

The erodible mask is a new energy delivery system for the 193-nm argon fluoride excimer laser. It consists of a polymethyl-methacrylate button, whose profile is transferred by photoablation onto the corneal surface. We present the 6- and 12-month results of this technique in the correction of compound myopic astigmatism. We performed the mask procedure on 21 eyes of 16 subjects (mean age, 30.7 years; range, 24 to 46) to correct combined myopia and astigmatism. Attempted myopic correction ranged between -1.50 diopters (D) and -10.00 D (mean, -7.07 D). Attempted astigmatic correction ranged between -1.50 D and -4.00 D (mean, -2.46 D). Mean procedure error was: sphere +0.74 D (range, -3.00/+5.00), cylinder -1.41 D (range, -3.50/0.00) at 1 month after surgery; sphere +0.18 D (range, -2.50/+ 3.50), cylinder -1.56 D (range, -4.00/0.00) at 6 months; and sphere -1.30 D (range, -3.00/0.00), cylinder was -1.25 D (range, -2.00/-0.50) at 12 months (10 eyes). During follow up, haze values were never higher than 1, except for one case of haze 2 that regressed to 0 during follow up. Postoperative uncorrected visual acuity improved in all eyes where emmetropia was envisaged; none of the eyes lost spectacle-corrected visual acuity lines 6 or 12 months after surgery. The erodible mask proved effective and fairly predictable mainly in the correction of the spherical component of refractive error, while the correction of astigmatism revealed greater unpredictability, with a constant trend to undercorrection.

Myopia Associated with Retionopathy of Prematurity

A complete analysis of the components of refractive error was performed on ten eyes of five patients with myopia and retinopathy of prematurity (ROP). In comparison to an age-matched control group, these eyes exhibited both lenticular and axial myopia. Only the high crystalline lens powers, which ranged from 22.20 to 44.13 diopters (D) (mean value, 31.27 D), were found to be statistically significant. In two patients, only one eye had high myopia. The lens power in these eyes was approximately 11 D more powerful than the lens of the fellow eye. Further investigation into the ocular changes induced by prematurity and abnormal oxygen metabolism is needed to determine the reason for the high degree of lenticular myopia.

Effects of Non-Contact Tonometry on Refraction

The spherical component of refractive error was measured subjectively before and after noncontact tonometry in 19 eyes and also on the fellow (control) eyes without tonometry. No significant change in this measure of refractive error was found after tonometry. The tested group could not be distinguished from the control group.