Mean Spherical Refractive Error Research Articles

Refractive errors in infants with retinopathy of prematurity treated using laser or anti-vascular endothelial growth factor monotherapy

Background: Infants treated for retinopathy of prematurity (ROP) could develop visually significant refractive errors. In this study, we report pre-treatment refractive errors in premature infants with treatment-requiring ROP treated using laser or anti-VEGF monotherapy and compare the components of post-treatment refractive error values between the two treatment groups at different follow-up timepoints.
 Methods: In this retrospective cohort study, we analyzed 360 eyes of 181 premature infants with treatment-requiring ROP who were referred to Farabi Eye Hospital, Tehran, Iran between March 2020 and April 2021. Of the 360 eyes, 195 received laser monotherapy (laser treatment group) and 165 received an intravitreal anti-VEGF injection (anti-VEGF therapy group). All included eyes underwent pre- and post-treatment cycloplegic refraction. Cycloplegia was induced for each infant by instilling a mixed eye drop containing 1% tropicamide, 2.5% phenylephrine, and 0.5% tetracaine (in equal volumes) in each eye three times at five-minute intervals. Cycloplegic refraction was performed 30 minutes after the third instillation.
 Results: The mean (standard deviation [SD]) gestational age (GA) and birth weight (BW) of the infants were 29.0 (2.0) weeks and 1241.0 (403.0) g, respectively. The male-to-female ratio in the entire study cohort was 107 (59.1%) / 74 (40.9%), whereas the ratios in the anti-VEGF therapy group and laser treatment group were 47 (56.6%) / 36 (43.4%) and 60 (61.2%) / 38 (38.8%), respectively. The pre-treatment assessment revealed that 218 (60.6%) eyes were hyperopic, 112 (31.1%) were myopic, and 30 (8.3%) were emmetropic. In the anti-VEGF therapy group, 87 (52.7%) eyes were hyperopic, 63 (38.2%) were myopic, and 15 (9.1%) were emmetropic. In the laser treatment group, 131 (67.2%) eyes were hyperopic, 49 (25.1%) were myopic, and 15 (7.7%) were emmetropic. The mean (SD) spherical refractive error and spherical equivalent of refractive error (SEQ) at the 1-week, 1-month, and > 6-month post-treatment follow-up timepoints; the mean cylindrical refractive error at the 3-month post-treatment timepoint; and the mean SEQ at the time of ROP regression were significantly different between the treatment groups (all P < 0.05). The rate of anisometropia increased significantly from 3.4% at baseline to 9.2% at the 6-month post-treatment follow-up timepoint (P < 0.05).
 Conclusions: In this study, the most common pre-treatment refractive status of all included eyes with treatment-requiring ROP and eyes in each treatment group was hyperopia, followed by myopia and emmetropia. At the more than 6-month post-treatment follow-up, cycloplegic refraction revealed that the laser-treated eyes were significantly more hyperopic than the anti-VEGF-treated eyes, a finding similar to the pre-treatment refraction results. Further studies of same cohort with a longer follow-up period and a control group are needed to determine the real-world effect of each treatment modality on the refractive statuses of children treated for ROP.

Temporal summation in myopia and its implications for the investigation of glaucoma.

We have previously demonstrated the upper limit of complete spatial summation (Ricco's area) to increase in non-pathological axial myopia compared to non-myopic controls. This study sought to investigate whether temporal summation is also altered in axial myopia to determine if this aspect of visual function, like in glaucoma, is influenced by reductions in retinal ganglion cell (RGC) density. Achromatic contrast thresholds were measured for a GIII-equivalent stimulus (0.43° diameter) of six different stimulus durations (1-24 frames, 1.1-187.8 ms) in 24 participants with axial myopia (mean spherical refractive error: -4.65D, range: -1.00D to -11.25D, mean age: 34.1, range: 21-57 years) and 21 age-similar non-myopic controls (mean spherical refractive error: +0.87D, range: -0.25D to +2.00D, mean age: 31.0, range: 18-55 years). Measurements were performed at 10° eccentricity along the 90°, 180°, 270° and 360° meridians on an achromatic 10 cd/m2 background. The upper limit of complete temporal summation (critical duration, CD) was estimated from the data with iterative two-phase regression analysis. There was no significant difference (p = 0.90, Mann-Whitney U-test) in median CD between myopes (median: 44.3 ms; IQR: 26.5, 51.2) and non-myopes (median: 41.6 ms; IQR: 27.3, 48.5). Despite RGC numbers underlying the stimulus being significantly lower in the myopic group (p < 0.001), no relationship was observed between the CD estimate and co-localised RGC number (Pearson's r = -0.13, p = 0.43) or ocular length (Pearson's r = -0.08, p = 0.61). Unlike spatial summation, temporal summation is unchanged in myopia. This contrasts with glaucoma where both temporal and spatial summation are altered. As such, perimetric methods optimised to test for anomalies of temporal summation may provide a means to differentiate between conditions causing only a reduced RGC density (e.g., myopia), and pathological processes causing both a reduced RGC density and RGC dysfunction (e.g., glaucoma).

Clinical performance of a custom-designed soft contact lens in patients with keratoconus and intolerance to rigid contact lenses.

This study evaluated the efficacy and safety of YOUSOFT® soft contact lens (CL) (TOMEY-CL) in patients with keratoconus and intolerance to rigid CLs. Retrospective observational study. Thirty-six eyes of 20 patients (14 men and 6 women) with keratoconus and rigid CL intolerance were included in the study. Four patients were unilateral. The mean age was 33.1 ± 11.7 (± standard deviation) years, the mean spherical refractive error was -4.99 ± 3.97 D, and the mean cylindrical refractive error was -3.39 ± 2.13 D. The following examinations were performed at baseline and were repeated at every visit; refractometry, visual acuity, corneal topography and pachymetry with an anterior OCT system. Corneal endothelial cell density was evaluated at baseline and every 6 months. Slit-lamp examination was also performed to confirm the CL condition and ocular health at every visit. Seventeen patients (85%) were able to continue using the Yousoft. Among 3 patients (15%) who dropped out, 2 were dissatisfied with their visual outcomes and one had trouble with lens handling. Uncorrected visual acuity was 1.08 ± 0.43 (range: 0.22 to 2.00) logMAR at baseline, and best CL-corrected visual acuity was 0.01 ± 0.15 (range: -0.18 to 0.40) logMAR, showing a significant improvement after wearing Yousoft (P < 0.0001). The endothelial cell density did not change significantly, with 2373 ± 482 at baseline and 2402 ± 464 cells/mm2 at the latest visit after lens prescription (P = 0.351). There were no severe complications such as corneal infiltrates or infectious keratitis throughout the study period. This study showed the efficacy and acceptable safety of Yousoft for patients with keratoconus and intolerance to rigid CLs.

Effect of axial length and anterior chamber depth on the peripheral refraction profile.

To evaluate the effect of axial length (AL) and anterior chamber depth (ACD) on peripheral refractive profile in myopic patients compared to emmetropic participants. This cross-sectional study was conducted in right eyes of 58 participants of whom 38 were emmetropic and 20 were myopic. Central and peripheral refraction were measured at 10°, 20°, and 30° eccentricities in nasal and temporal fields using an open-field autorefractor. The Lenstar LS900 was used to measure ACD and AL. The participants were divided into three groups of short (<22.5 mm), normal (22.5-24.5 mm), and long eye (>24.5 mm) according to AL and three groups of low ACD (<3.00 mm), normal ACD (3.00-3.60 mm), and high ACD (>3.60 mm) according to ACD. The mean age of the participants was 22.26±3.09y (range 18-30y). The peripheral mean spherical refractive error showed a hypermetropic shift in myopic and emmetropic groups although this shift was more pronounced in the myopic group. The results showed significant changes in the spherical equivalent, J0, and J45 astigmatism in all gazes with an increase in eccentricity (P<0.001). The pattern of refractive error changes was more noticeable in long and short eyes versus normal AL eyes. Moreover, the pattern of peripheral refractive changes was much more prominent in the high ACD group versus the normal ACD group and in the normal ACD group versus the low ACD group. Peripheral refraction changes are greater in participants with AL values outside the normal range and deeper ACD values compared to participants with normal AL and ACD.

RPGR-Associated Dystrophies: Clinical, Genetic, and Histopathological Features.

This study describes the clinical, genetic, and histopathological features in patients with RPGR-associated retinal dystrophies. Nine male patients from eight unrelated families underwent a comprehensive ophthalmic examination. Additionally, the histopathology of the right eye from a patient with an end-stage cone-rod-dystrophy (CRD)/sector retinitis pigmentosa (RP) phenotype was examined. All RPGR mutations causing a CRD phenotype were situated in exon ORF15. The mean best-corrected visual acuity (BCVA, decimals) was 0.58 (standard deviation (SD)): 0.34; range: 0.05–1.13); and the mean spherical refractive error was −4.1 D (SD: 2.11; range: −1.38 to −8.19). Hyperautofluorescent rings were observed in six patients. Full-field electroretinography responses were absent in all patients. The visual field defects ranged from peripheral constriction to central islands. The mean macular sensitivity on microperimetry was 11.6 dB (SD: 7.8; range: 1.6–24.4) and correlated significantly with BCVA (r = 0.907; p = 0.001). A histological examination of the donor eye showed disruption of retinal topology and stratification, with a more severe loss found in the peripheral regions. Reactive gliosis was seen in the inner layers of all regions. Our study demonstrates the highly variable phenotype found in RPGR-associated retinal dystrophies. Therapies should be applied at the earliest signs of photoreceptor degeneration, prior to the remodeling of the inner retina.

Short Interruptions of Imposed Hyperopic Defocus Earlier in Treatment are More Effective at Preventing Myopia Development

The purpose of this study was to evaluate the effect of interrupting negative lens wear for short periods early or late during the development of lens-induced myopia in marmosets. Sixteen marmosets were reared with a −5D contact lens on their right eye (plano on contralateral eye) for 8 weeks. Eight marmosets had lenses removed for 30 mins twice/day during the first four weeks (early interruption) and eight during the last four weeks (late interruption). Data were compared to treated controls that wore lenses continuously (N = 12) and untreated controls (N = 10). Interocular differences (IOD) in vitreous chamber (VC) depth and central and peripheral mean spherical refractive error (MSE) were measured at baseline and after four (T4) and eight (T8) weeks of treatment. Visual experience during the interruptions was monitored by measuring refraction while marmosets were seated at the center of a 1 m radius viewing cylinder. At T4 the eyes that were interrupted early were not different from untreated controls (p = 0.10) and at T8 had grown less and were less myopic than those interrupted later (IOD change from baseline, VC: +0.07 ± 0.04 mm vs +0.20 ± 0.03 mm, p < 0.05; MSE: −1.59 ± 0.26D vs −2.63 ± 0.60D, p = 0.13). Eyes interrupted later were not different from treated controls (MSE, p = 0.99; VC, p = 0.60) and grew at the same rate as during the first four weeks of uninterrupted lens wear (T4 − T0: 3.67 ± 1.1 µm/day, T8 − T4: 3.56 ± 1.3 µm/day p = 0.96). Peripheral refraction was a predictive factor for the amount of myopia developed only when the interruption was not effective. In summary, interrupting hyperopic defocus with short periods of myopic defocus before compensation occurs prevents axial myopia from developing. After myopia develops, interruption is less effective.

The Refractive Error of Professional Baseball Players.

High levels of visual acuity are required to hit a baseball effectively. Research has shown that any decrease in vision is likely caused by low-order optical aberrations. This study is designed to validate the SVOne autorefractor, and describe the amount and type, of low-order optical aberrations present in a large cohort of professional baseball players. A retrospective chart review on the 608 Major League Baseball players evaluated during the 2016 Spring Training Season was performed. Results for a subset of players who had both manifest refraction as well as autorefraction were calculated. Subsequently, after determining the accuracy of the autorefraction system in this population, refractive results for the entire population were determined. There was a borderline statistically significant difference in mean spherical refractive error (M) between the manifest refraction and the SVOne auto refraction (-0.273D in the manifest refraction method vs. -0.503D in the SVOne method, P = .06) in the subset of athletes who underwent both tests. Additionally, there was no difference in the J0 or J45 cylindrical component vectors for each method. For the entire eligible population, the SVOne autorefraction system found a mean spherical refractive error (M) of -0.228D, a J0 value of -0.013D, and a J45 value of -0.040D. These data suggest that the SVOne autorefraction system is generally able to measure the refractive error in the baseball population. The system was slightly biased, often reporting more myopia in myopic subjects. Thus, careful evaluation of the refractive status of these athletes coupled with careful subjective refractive correction for those with less than average vision for baseball is strongly suggested.

Aberrometric Outcomes of Intrastromal Corneal Ring Segment (KeraRing 355) Implantation Using PocketMaker Microkeratome in Patients with Keratoconus

Objective: To evaluate aberrometric changes in corneas with keratoconus implanted with intrastromal corneal ring segment (Keraring 355) during a 3-months follow-up. Design: Prospective, consecutive case series Methods: In this interventional study, 22 eyes of 21 keratoconic patients with mean age of 29 ± 6 years who underwent KeraRing 355 intrastromal corneal ring insertion using a Pocket Maker Microkeratome for channel creation and completed at least three months of follow-up were included. Uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA), refractive outcome, Orbscan finding and corneal aberrations were assessed. Results: Three months postoperately, Low order aberration (defocus and astigmatism) decreased significantly (P<0.001). No statistically significant changes were detected in total RMS, trefoil, secondary trefoil and coma. Moreover, a statistically significant increase in quatrefoil, secondary coma, spherical aberration and secondary spherical was found. In term of visual outcomes, the mean UCVA (in LogMAR value) improved significantly from 0.75 ± 0.33 to 0.31 ± 0.23 and the mean BSCVA improved (from 0.31 ± 0.16 to 0.19 ± 0.15) (P<0.05). The mean spherical refractive error improved (from -1.37 ± 1.36 to 0.01 ± 2.47) and the mean cylindrical refractive error decreased significantly (from -3.8 ± 1.03 to -2.1 ± 1.27 (P<0.001)). Also, the mean keratometry value decreased from 47.61 ± 2.03 to 42.50 ± 2.76. Conclusion: KeraRing 355 implantation provided significant improvement in low order aberrations but was not effective in high order aberrations (HOA) in low/moderate keratoconus patients. However, UCVA, BCVA, spherical and cylindrical refractive error and keratometry results improved significantly.

Late clinical characteristics of infants with retinopathy of prematurity and treated with cryotherapy.

To describe the clinical characteristics and late results of patients with retinopathy of prematurity (ROP) treated with "6h cryotherapy". Out of 1252 infants screened for ROP, 52 patients were treated with temporal 6h cryotherapy from 1997 to 2005 were recalled to our clinic. Among these 23 patients were available and 46 eyes of 23 infants were included to evaluate for visual acuity, refractive error, ocular alignment, nystagmus, retinal examination (abnormal branching of retinal vessels, retinal thinning, latis degenerations, tortuosity of vessels, straightening of temporal vessels, narrowing of the angle of vessel in the juxtapapillary entrance, pigment changes, macular heterotopia), optic atrophy and optic disc cupping, axial length at birth and axial length at 1y. The median age at examination was 7 (5-18)y. In 32.6% of patients, the visual acuity was ≤20/200 and the mean best corrected visual acuity was 20/35 as measured with a Snellen chart. Mean spherical refractive error was -1.76±2.69 D. The degree of myopia at the last examination was found to be correlated with the elongation of the eye in the first year of life. Exotropia was present in 17.4% (n=8) of infants and esotropia in 13% (n=6). The most common retinal abnormality was abnormal branching of retinal vessels (82.6%) followed by retinal thinning (52.2%). The late clinical outcomes of infants with ROP treated in our clinic with cryotherapy seems to comparable with results of laser treatment.

Analysis of physical activity in emmetropic and myopic university students during semester and holiday periods: a pilot study

BackgroundPrevious studies (mostly questionnaire‐based in children) suggest that outdoor activity is protective against myopia. There are few studies on young adults investigating both the impact of simply being outdoors versus performing physical activity. The aim was to study the relationship between the refractive error of young adults and their physical activity patterns.MethodsTwenty‐seven university students, aged 18 to 25 years, wore a pedometer (Omron HJ720ITE) for seven days both during the semester and holiday periods. They simultaneously recorded the type of activity performed, its duration, the number of steps taken (from the pedometer) and their location (indoors/outdoors) in a logbook. Mean spherical refractive error was used to divide participants into three groups (emmetropes: +1.00 to ‐0.50 D, low myopes: ‐0.62 to ‐3.00 D, higher myopes: ‐3.12 D or greater myopia).ResultsThere were no significant differences between the refractive groups during the semester or holiday periods; the average daily times spent outdoors, the duration of physical activity, the ratio of physical activity performed outdoors to indoors and amount of near work performed were similar. The peak exercise intensity was similar across all groups: approximately 100 steps per minute, a brisk walk. Up to one‐third of all physical activity was performed outdoors. There were some significant differences in activities performed during semester and holiday times. For example, low myopes spent significantly less time outside (49 ± 47 versus 74 ± 41 minutes, p = 0.005) and performed less physical activity (6,388 ± 1,747 versus 6,779 ± 2,746 steps per day; p = 0.03) during the holidays compared to during semester.ConclusionsThe fact that all groups had similar low exercise intensity but many were not myopic suggests that physical activity levels are not critical. There were differences in the activity patterns of low myopes during semester and holiday periods. This study highlights the need for a larger longitudinal‐based study with particular emphasis on how discretionary time is spent.

THE EFFECT OF LOW POWER GLASSES AT CLOSE DISTANCES ON VISUAL PERFORMANCE.

The purpose of this study was to reveal if the use of low power ophthalmic glasses (diopter values within the ± 1.00D range) in ophthalmic care may be beneficial for the treatment of low refractive vision disorders. 40 university students (10 men, 30 women), who used low power glasses at close distances (for reading on paper or on a computer screen: 40-60 centimeters approximately), voluntarily took part in this study. Ages of the participants ranged from 20 to 43 years (M = 24.9, SD = 4.4). Mean spherical refractive error was -0.38 diopters (SD = 0.49; range= -1.00-0.88). A yes/no Signal Detection procedure was used to assess whether the participants' visual sensitivity (d') or criterion of response (c) changed when they used the optical correction. There were no changes in visual sensitivity index, but significant changes in criterion of response were observed when the students used their optical correction. Changes in the criterion of response suggested the presence of a placebo effect.

Prevalence of cataract after collagen copolymer phakic intraocular lens implantation for myopia, hyperopia, and astigmatism

To evaluate the prevalence of cataract after Implantable Collamer Lens phakic intraocular lens (pIOL) implantation with different models at different ages and for different refractive powers. Fernández-Vega Ophthalmological Institute, Oviedo, Spain. Retrospective nonrandomized clinical study. The pIOL (models V4, V4b, or V4c) was implanted in all cases. The study included 3420 eyes (1898 patients). The mean patient age at surgery was 31.2 years ± 6.4 (SD) (range 18 to 50 years) and the mean spherical refractive error, -7.27 ± 5.24 diopters (D) (range -26.5 to 12.5 D). Twenty-one eyes (0.61%) of 15 patients had pIOL explantation (all model V4) because cataract developed. The mean age of the patients who had explantation was 39.43 ± 4.57 years; 7 were younger than 40 years, and 8 were 40 years or older. The mean spherical equivalent was -10.1 ± 5.41 D; 3 eyes had a pIOL power less than -10.50 D, 4 eyes between -10.50 D and -13.50 D, and 14 higher than -13.50 D. The mean time between pIOL implantation and cataract surgery was 4.2 ± 1.8 years. No eye with implantation of the latest models (V4b and V4c) developed cataract. The mean vault distance in eyes that developed cataracts was 103 ± 69 μm. The incidence of cataract was low after pIOL implantation at the 6-year follow-up. The rate of cataract was higher in older patients and in those with high refractive errors. No author has a financial or proprietary interest in any material or method mentioned.

One Year Outcomes of Photorefractive Keratectomy with the Application of Mitomycin-C in the Treatment of Mild to Moderate Hyperopia.

Purpose:To evaluate refractive and visual outcomes of photorefractive keratectomy with mitomycin-C. (PRK-MMC) for the treatment of mild to moderate hyperopia.Materials and Methods:This case series enrolled 21 patients with up to +5.50 diopters (D) of hyperopia. All 42 eyes were treated with the Concerto (Wavelight) or the Technolas 217-Z (Bausch and Lomb) excimer laser. Outcome measures included best corrected distance vision acuity (BCVA) and uncorrected distance vision correction and refraction at 1, 3, 6, and 12 months postoperatively.Results:Mean patient age was 44.8 ± 11.3 years. Preoperatively, mean manifest refractive spherical equivalent (MRSE) was + 2.00 D ± 0.76 D and mean spherical refractive error was + 2.57 D ± 0.87 D (range, +1.25 D to + 5.50 D). At 12 months postoperatively, mean MRSE was + 0.1 D ± 0.61 D. MRSE was within ± 0.50 D of emmetropia in 29 eyes (69%), and 18 eyes (43%) had 20/20 uncorrected distant visual acuity. BCVA increased by two lines or more in three eyes (7.1%) and one line in two eyes (4.7%); 31 eyes showed no change, three eyes (7.1%) lost one line, and three other eyes (7.1%) lost two lines of BCVA. No eyes lost more than two lines of BCVA. Complications included Grade 2 peripheral haze in two eyes which cleared by 12 months postoperatively.Conclusion:PRK-MMC was a safe and predictable method for the correction of mild to moderate hyperopia.

Intraocular pressure and associations in children. The Gobi Desert Children Eye Study.

PurposeTo assess the intraocular pressure (IOP) and its association in children in a population living in an oasis in the Gobi Desert.MethodsThe cross-sectional school-based study included all schools in the Ejina region. The children underwent an ophthalmic examination, non-contact tonometry and measurement of blood pressure and body height and weight.ResultsOut of eligible 1911 children, 1565 (81.9%) children with a mean age of 11.9±3.5 years (range: 6–21 years) participated. Mean spherical refractive error was −1.58±2.00 diopters. In multivariate analysis, higher IOP (right eye) was associated with younger age (P<0.001; standardized coefficient beta: −0.13; regression coefficient B: −0.13; 95% Confidence interval (CI):−0.18, −0.07), higher diastolic blood pressure (P<0.001;beta:0.13;B:0.05;95%CI:0.03,0.07), higher corneal refractive power (P<0.001;beta:0.11;B:0.23;95%CI:0.12,0.34), more myopic refractive error (P = 0.035;beta: −0.06;B: −0.10;95%CI: −0.19, −0.001), and Han Chinese ethnicity of the father (P = 0.03;beta:0.06;B:0.42;95%CI:0.04,0.89). If age and diastolic blood pressure were dropped, higher IOP was associated with higher estimated cerebrospinal fluid pressure (CSFP) (P<0.001;beta:0.09; B:0.13;95%CI:0.06,0.21) after adjusting for higher corneal refractive power (P<0.001) and Han Chinese ethnicity of the father (P = 0.04). Correspondingly, higher IOP of the left eye was associated with younger age (P<0.001;beta: −0.15;B: −0.16;95%CI: −0.21, −0.10), female gender (P<0.001;beta:0.09;B:0.65;95%CI:0.30,1.01), higher corneal refractive power (P<0.001;beta:0.08;B:0.19;95%CI:0.06,0.32), more myopic refractive error (P = 0.03;beta: −0.06;B: −0.12;95%CI: −0.22, −0.01), and higher estimated CSFP (P<0.001;beta:0.11;B:0.17;95%CI:0.09,0.24).ConclusionsIn school children, higher IOP was associated with steeper corneal curvature and with younger age and higher blood pressure, or alternatively, with higher estimated CSFP. Corneal curvature radius should be included in the correction of IOP measurements. The potential association between IOP and CSFP as also assumed in adults may warrant further research.

Intrastromal corneal ring segment implantation to correct astigmatism after penetrating keratoplasty

To evaluate the clinical outcomes of implantation of Ferrara intrastromal corneal ring segments (ICRS) in patients with astigmatism after penetrating keratoplasty (PKP). Private clinic, Belo Horizonte, Brazil. Retrospective consecutive case series. Chart records of post-PKP patients who had ICRS implantation from May 2005 to September 2009 were retrospectively reviewed. The following parameters were studied: corrected distance visual acuity (CDVA), keratometry (K) values, spherical equivalent (SE), spherical refractive error, corneal topographic astigmatism, minimum K, and maximum K. The study evaluated 59 eyes (54 patients). The mean CDVA (logMAR) improved from 0.45 ± 0.17 (SD) (range 0.18 to 1.00) to 0.30 ± 0.17 (range 0.00 to 1.00). The mean SE was -6.34 ± 3.40 diopters (D) (range 0.37 to -16.50 D) preoperatively and -2.66 ± 2.52 D (range 0.87 to -10.50 D) postoperatively. The mean spherical refractive error decreased from -7.10 ± 3.07 D (range 2.15 to 16.68 D) preoperatively to -3.46 ± 2.05 D (range 0.88 to 10.79 D) postoperatively. No patient lost visual acuity. The mean corneal topographic astigmatism decreased from 3.37 ± 1.51 D preoperatively to 1.69 ± 1.04 D postoperatively. The mean maximum K value decreased from 48.09 ± 2.56 D to 44.17 ± 2.67 D and the mean minimum K value, from 44.90 ± 2.54 D to 42.46 ± 2.63 D. All changes were statistically significant (P<.0001). Intrastromal corneal ring segments effectively reduced corneal cylinder in patients with astigmatism after PKP.

KeraRing Intrastromal Corneal Ring Segments for Correction of Keratoconus

Intrastromal corneal ring segments (ICRSs) are small arc-like implants that are being used increasingly as a minimally invasive treatment for patients with keratoconus. This study assessed the effectiveness of KeraRing implants, a type of ICRS, to treat keratoconus. Retrospective case series descriptive study of 43 patients (55 eyes) with keratoconus who underwent KeraRing implantation from February 2008 to June 2009. Patients who had intraoperative or postoperative complications and/or did not complete at least 6 months of follow-up were excluded. All patients underwent complete ophthalmologic examinations that included measurement of the uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and keratometry before and 2 days, 2 weeks, 1 month, and 3 and 6 months after surgery. The ring segments were chosen based on a nomogram from the manufacturer. Six months postoperatively, the mean UCVA increased significantly (P < 0.05) from 0.10 ± 0.11 to 0.32 ± 0.25 and the mean BSCVA increased from 0.36 ± 0.23 to 0.57 ± 0.24 (P < 0.05). The mean spherical refractive error significantly (P < 0.05) improved from -4.85 ± 2.90 diopters (D) to -1.89 ± 2.68 D, and the mean cylindrical refractive error significantly (P < 0.05) improved from -3.65 ± 1.70 D to -2.60 ± 1.62 D. The mean spherical equivalent significantly (P < 0.05) decreased from -6.68 ± 2.93 D to -3.19 ± 2.75 D, and the mean keratometry value decreased from 51.83 ± 4.14 D to 47.27 ± 3.68 D. The improvement in the UCVA and BSCVA continued over the 6-month postoperative period, but significant changes occurred only during the first 3 months. These changes occurred in patients with all grades of keratoconus. KeraRing implantation provided significant improvement in visual acuity, spherical equivalent, and keratometry results. This ICRS is an effective treatment for managing keratoconus and might delay or even avoid the need for penetrating keratoplasty.

Laser in-situ keratomileusis for refractive error following radial keratotomy

Aim:To evaluate the safety and efficacy of laser in-situ keratomileusis (LASIK) in eyes with residual/induced refractive error following radial keratotomy (RK).Design:Retrospective study.Materials and Methods:A retrospective analysis of data of 18 eyes of 10 patients, who had undergone LASIK for refractive error following RK, was performed. All the patients had undergone RK in both eyes at least one year before LASIK. Parameters like uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), contrast sensitivity, glare acuity and corneal parameters were evaluated both preoperatively and postoperatively.Statistical Software:STATA-9.0.Results:The mean UCVA before LASIK was 0.16±0.16 which improved to 0.64 ± 0.22 (P < 0.001) after one year following LASIK. Fourteen eyes (out of 18) had UCVA of ≥ 20/30 on Snellen's acuity chart at one year following LASIK. The mean BCVA before LASIK was 0.75 ± 0.18. This improved to 0.87 ± 0.16 at one year following LASIK. The mean spherical refractive error at the time of LASIK and at one year after the procedure was –5.37 ± 4.83 diopters (D) and –0.22 ± 1.45D, respectively. Only three eyes had a residual spherical refractive error of ≥ 1.0D at one year follow-up. In two eyes, we noted opening up of the RK incisions. No eye developed epithelial in-growth till 1 year after LASIK.Conclusion:LASIK is effective in treating refractive error following RK. However, it carries the risk of flap-related complications like opening up of the previously placed RK incisions and splitting of the corneal flap.

Flap Buttonhole in Thin-Flap Laser In Situ Keratomileusis: Case Series and Review

To analyze the clinical features and the risk factors leading to formation of flap buttonhole during laser in situ keratomileusis (LASIK) and the postablation visual outcome. Medical records of all eyes that developed flap buttonhole during LASIK were retrospectively reviewed. Pre-LASIK measurements and intraoperative parameters were analyzed to predict the risk factors. A total of 944 eyes underwent LASIK during the study duration. Four eyes (0.42%) developed partial thickness flap buttonhole. Thin-flap LASIK (flap thickness < or =90 microm) was performed in 230 eyes. The incidence of buttonholes in thin-flap LASIK cases was 1.7% (4 of 230). LASIK procedures were performed at a tertiary eye institute between October 2006 and December 2008. The mean age was 31 +/- 8.7 years. Preablation mean spherical refractive error in the affected left eye was -7.8 +/- 1.2 diopters (D), mean steeper axis keratometry was 44.0 +/- 1.56 D, and the mean pachymetry was 520 +/- 16 microm. Buttonholing in the flap occurred in the second (left) eye of all 4 cases. All cases had undergone thin-flap LASIK with 90-microm blade using the Moria M2 microkeratome. Flap diameter was +2/7.5 and 0/8.0 for 2 eyes each. Twelve weeks after the initial procedure, transepithelial phototherapeutic keratectomy/photorefractive keratectomy was performed in all 4 eyes. Postablation visual outcome was 20/20 and 20/25 in 2 eyes each. One patient had a faint subepithelial scar at the last 1-year follow-up. Formation of flap buttonhole is significantly more common in the second eye and with the usage of Moria M2 microkeratome and 90-microm blade. In thin-flap LASIK, the practice of using the same microkeratome blade for the fellow eye, as is commonly followed at many refractive surgery centres, should be abandoned. Intraoperative subtraction pachymetry may be helpful in predicting the risk of buttonhole in the second eye. These precautions are especially mandatory in thin-flap LASIK irrespective of the other associated risk factors.

Alternative Methods of Refraction: A Comparison of Three Techniques

In the developing world, refractive error is a common untreated cause of visual impairment. Lay people may use portable tools to overcome this issue. This study compares three methods of measuring spherical refractive error (SE) performed by a lay technician to a subjective refraction (SR) in a controlled clinical setting and a field trial. Fifty subjects from Boston, MA (mean age, 24.3 y ± 1.5) and 50 from Nicaragua (mean age, 40 y ± 13.7) were recruited. Measures (performed on right eye only) included (1) AdSpecs, adjustable spectacles; (2) Focometer, focusable telescope; (3) Predetermined Lens Refraction (PLR), prescripted lens choices; (4) SR. Examiners were masked and techniques randomized. Student t-test compared mean SE determined by each method (95% confidence intervals). AdSpecs repeatability was evaluated by repeating measures of SE and visual acuity (VA). Mean (SD) SE for Boston subjects determined by SR was -2.46 D (3.2). Mean (SD) SE for AdSpecs, Focometer -2.41 D (2.69), -2.80 D (2.82). Among the 30 Boston subjects considered in analyses of PLR data (see Methods), PLR and SR obtained mean (SD) values of -0.65 D (1.36) and -0.41 D (1.67), respectively, a statistically significant difference of -0.24 D (p = 0.046, t = 2.09). Mean PLR SE had greatest deviation from SR, 0.67 D. 20/20 VA was achieved by SR, AdSpecs, Focometer, and PLR in 98, 88, 84, 96% of subjects. Mean (SD) SE for Nicaragua subjects determined by SR was +0.51 D (0.71). Mean (SD) SE for AdSpecs, Focometer, and PLR was +0.68 D (0.83), +0.42 D (1.13), +0.27 D (0.79). Mean PLR SE had the greatest deviation from the SR by 0.24 D, which was a statistically significant difference. 20/20 VA was achieved by SR, AdSpecs, Focometer, and PLR in 78, 66, 66, 88% of subjects. Repeated measures by AdSpecs were highly correlated. Although the mean value obtained by each technique may be similar to that obtained by SR, substantial and clinically meaningful differences may exist in some individuals; however, where SR is unavailable they could be a feasible alternative.

Short-Term Visual Outcomes of Boston Type 1 Keratoprosthesis Implantation

To report the short-term visual outcomes after keratoprosthesis implantation. Retrospective multi center case series (Wilmer Eye Institute and University of Rochester Eye Institute). One hundred twenty-two patients (126 eyes) with corneal diseases that were deemed ineligible to receive donor corneal transplants. Patients underwent a Boston type I keratoprosthesis procedure for visual rehabilitation. The medical records of the patients were reviewed to assess intraoperative and postoperative complications, uncorrected and best-corrected visual acuity, as well as the degree of refractive error at various time points. One hundred four patients (82.5%) achieved improved vision within 6 months after surgery. An overwhelming majority of those patients who had improved vision had a manifest refraction of plano. The mean spherical refractive error was -0.57 diopters (D) and mean astigmatism was 0.10 D. Cumulatively, 7.1% patients achieved their best-corrected vision at 1 day, 24.6% at 1 week, and 70.6% at 3 months. The patients who achieved their best-corrected visual acuity after the first 3-month period most often were the ones who required multiple surgeries owing to preexisting or postoperative complications. Boston keratoprosthesis seems to provide rapid visual recovery with excellent uncorrected acuity in the early postoperative period. The authors have no proprietary or commercial interest in any of the materials discussed in this article.