IMI 2021 Yearly Digest.

Purpose: The International Myopia Institute (IMI) Yearly Digest highlights new research considered to be of importance since the publication of the first series of IMI white papers. Methods: A literature search was conducted for articles on myopia between 2019 and mid-2020 to inform definitions and classifications, experimental models, genetics, interventions, clinical trials, and clinical management. Conference abstracts from key meetings in the same period were also considered. Results: One thousand articles on myopia have been published between 2019 and mid-2020. Key advances include the use of the definition of premyopia in studies currently under way to test interventions in myopia, new definitions in the field of pathologic myopia, the role of new pharmacologic treatments in experimental models such as intraocular pressure-lowering latanoprost, a large meta-analysis of refractive error identifying 336 new genetic loci, new clinical interventions such as the defocus incorporated multisegment spectacles and combination therapy with low-dose atropine and orthokeratology (OK), normative standards in refractive error, the ethical dilemma of a placebo control group when myopia control treatments are established, reporting the physical metric of myopia reduction versus a percentage reduction, comparison of the risk of pediatric OK wear with risk of vision impairment in myopia, the justification of preventing myopic and axial length increase versus quality of life, and future vision loss. Conclusions: Large amounts of research in myopia have been published since the IMI 2019 white papers were released. The yearly digest serves to highlight the latest research and advances in myopia.

Performance of Topological Perception in the Myopic Population.

Purpose: Discriminating objects' topological property (TP) is a primitive function of visual representation, which is reported to be associated with magnocellular (M) visual pathway, temporal lobe (TL), and superior colliculus (SC)-pulvinar subcortical pathway. Previous studies have shown that M pathway and TL were affected in high myopia (HM) subjects. The study was accordingly designed to explore whether topological perception performance was abnormal in HM subjects. Methods: 30 mildly myopic, 25 moderately myopic, 35 highly myopic, and 20 emmetropic subjects were enrolled. All participants underwent a comprehensive ophthalmological assessment including automated refraction, intraocular pressure, Humphrey 10-2 standard automated perimetry, ocular fundus photography and swept-source optical coherence tomography. Defined by differences in hole, TP and non-TP discrimination with letters "E", "S", "P", "d" as stimuli in the central and peripheral regions was performed using the MATLAB 2017 software. d-primes extracted from the software were analyzed within each group. The correlation of peripheral TP/non-TP deficit with spherical equivalent (SE), axial length (AL) and average peripapillary retinal nerve fiber layer (RNFL) thickness was performed. Results: The patterns of topological perception performance were similar among the groups. TP discrimination peripherally was significantly better than that centrally in the mild myopia (P < .001), moderate myopia (P < .001), high myopia (P < .001) and emmetropia groups (P = .001). In the peripheral region, TP d-prime scores were significantly better than non-TP d-prime scores (all P < .001). The main and interaction effects of eccentricity and stimulus type were statistically significant(P < .05). There was no statistically significant correlation between peripheral TP/non-TP deficit and SE, AL or average RNFL thickness (P > .05). Conclusions: The current study first showed that patterns of topological perception among the myopic population were similar and not affected by the severity of myopia.

Quantitative assessment of the retinal microvasculature and choriocapillaris in myopic patients using swept-source optical coherence tomography angiography.

PURPOSE: To study the retinal capillary microvasculature and the choriocapillaris (CC) in myopic eyes using swept-source optical coherence tomography angiography (SS-OCTA). METHODS: Patients with high myopia (≥ - 6D; axial length ≥ 26.5 mm), moderate myopia (≥ - 3D, < - 6D), and age-matched healthy subjects presenting to the Shanghai General Hospital and Doheny-UCLA Eye Centers were enrolled in this prospective, multicenter study. Any subjects with evidence of macular abnormalities suggestive of pathologic myopia were excluded. SS-OCTA at both sites was performed using a Zeiss PLEX Elite instrument with a 6 × 6 mm scan pattern centered on the fovea. Two repeated volume scans were acquired for image averaging. The instrument pre-defined en face slab of the superficial and deep retinal capillary microvasculature was used to isolate and display the superficial and deep retinal capillaries. A slab spanning from 21 to 31 µm deep to the RPE fit line was used to isolate and display the CC. The OCTA images were exported for averaging using Image J. Littmann's method and the Bennett formula were applied to adjust for the impact of magnification in the high and moderate myopia groups. The resultant images were then binarized. Though projection artifact removal software was used, regions below the large superficial retinal vessels were excluded for quantitative analyses of the deep retinal capillary plexus and the CC. Vessel density (VD) and vessel length density (VLD) of the superficial and deep retinal capillary plexus (SCP, DCP) and CC flow deficit (FD) were analyzed, quantified, and compared between different groups. RESULTS: Twenty-five eyes of 25 patients with high myopia, 25 eyes of 25 patients with moderate myopia, and 25 eyes of 25 normal age-matched controls were included in this study. The VD of the SCP was lower in the high myopia group compared with the emmetropic control groups (p < 0.05), but the VD of the DCP demonstrated no significant difference among the three groups (p > 0.05). The VLDs of the SCP were lower in the high and moderate myopia groups compared with the control group (p < 0.05), while the VLD of the DCP was lower in the high myopia group compared with the moderate myopia and emmetropic control group (p < 0.05). The CC FD% in the high myopia group was significantly greater than both the control and moderate myopia subjects (p < 0.05). Of note, the severity of the CC flow deficit was not correlated with choroidal thickness (p > 0.05). CONCLUSION: The retinal microvasculature may demonstrate alterations in highly myopia eyes. The CC in macular regions shows greater impairment in eyes with high myopia compared with eyes with lesser degrees of myopia, and these deficits are already present in the absence of features of pathologic or degenerative myopia. The threshold of CC FD leading to myopic maculopathy remains to be defined.

Prevalence of macular complications related to myopia - Results of a multicenter evaluation of myopic patients in eye clinics in France.

PURPOSE: Uncorrected refractive errors are the first cause of vision impairment worldwide. High myopia is a frequent cause of sight-threatening chorioretinal complications. The aim of this study was to evaluate the prevalence of macular complications, visual impairment and blindness in patients with myopia. METHODS: A cross-sectional multicenter study carried out in French eye clinics mainly dedicated to refractive errors. Myopia severity was defined as mild (-0.5 to -3 D), moderate (-3 to -6 D), high (-6 to -10 D) and very high (more than -10 D). Macular complications related to myopia included lacquer cracks, myopic choroidal neovascularization, chorioretinal atrophy and retinoschisis. The prevalences of macular complications, blindness and vision impairment were estimated with respect to degree of myopia and age. Eligibility criteria were myopia on the left eye of -0.5 D or more. Exclusion criteria included any missing data related to subjective refractive error, age, gender and any history of cataract or refractive surgery. RESULTS: Data files from 198 641 myopic individuals with a mean age of 34 years (SD: 15 years) were analysed. The prevalence of mild, moderate, high and very high myopia was, respectively, 65.95%, 26.14%, 6.72% and 1.19%. The prevalence of macular complications in the high and very high myopia groups was 0.5% [0.39-0.64] and 4.27% [3.49-5.17]. The prevalence of blindness or vision impairment was observed in 10.10% [8.91-11.39%] of the very high myopic group. At 60 years old or over, the prevalences of blindness or vision impairment were, respectively, 9.75% [7.91-11.85%] and 25.71% [21.00-30.87%] in the high and very high myopia groups. CONCLUSIONS: This multicenter cross-sectional study provides new insights in terms of prevalence of macular complications related to myopia. To our knowledge, this is one of the largest European studies focusing on individuals with myopia, particularly on the macular complications and the functional consequences in relation to myopia.

Association of the ZC3H11B, ZFHX1B and SNTB1 genes with myopia of different severities.

OBJECTIVE: To investigate the associations of single-nucleotide polymorphisms (SNPs) in the ZC3H11B, ZFHX1B, VIPR2, SNTB1 and MIPEP genes with severities of myopia in Chinese populations. METHODS: Based on previous myopia genome-wide association studies, five SNPs (ZC3H11B rs4373767, ZFHX1B rs13382811, VIPR2 rs2730260, SNTB1 rs7839488 and MIPEP rs9318086) were selected for genotyping in a Chinese cohort of 2079 subjects: 252 extreme myopia, 277 high myopia, 393 moderate myopia, 366 mild myopia and 791 non-myopic controls. Genotyping was performed by TaqMan assays. Allelic frequencies of the SNPs were compared with myopia severities and ophthalmic biometric measurements. RESULTS: The risk allele T of ZC3H11B SNP rs4373767 was significantly associated with high myopia (OR=1.39, p=0.007) and extreme myopia (OR=1.34, p=0.013) when compared with controls, whereas ZFHX1B rs13382811 (allele T, OR=1.33, p=0.018) and SNTB1 rs7839488 (allele G, OR=1.71, p=8.44E-05) were significantly associated with extreme myopia only. In contrast, there was no significant association of these SNPs with moderate or mild myopia. When compared with mild myopia, subjects carrying T allele of rs4373767 had a risk of progressing to high myopia (spherical equivalent ≤-6 dioptres) (OR=1.29, p=0.017). Similarly, the T allele of rs13382811 also imposed a significant risk to high myopia (OR=1.36, p=0.007). In quantitative traits analysis, SNPs rs4373767, rs13382811 and rs7839488 were correlated with axial length and refractive errors. CONCLUSIONS: We confirmed ZC3H11B as a susceptibility gene for high and extreme myopia, and ZFHX1B and SNTB for extreme myopia in Chinese populations. Instead of myopia onset, these three genes were more likely to impose risks of progressing to high and extreme myopia.

IMI - Myopia Control Reports Overview and Introduction.

With the growing prevalence of myopia, already at epidemic levels in some countries, there is an urgent need for new management approaches. However, with the increasing number of research publications on the topic of myopia control, there is also a clear necessity for agreement and guidance on key issues, including on how myopia should be defined and how interventions, validated by well-conducted clinical trials, should be appropriately and ethically applied. The International Myopia Institute (IMI) reports the critical review and synthesis of the research evidence to date, from animal models, genetics, clinical studies, and randomized controlled trials, by more than 85 multidisciplinary experts in the field, as the basis for the recommendations contained therein. As background to the need for myopia control, the risk factors for myopia onset and progression are reviewed. The seven generated reports are summarized: (1) Defining and Classifying Myopia, (2) Experimental Models of Emmetropization and Myopia, (3) Myopia Genetics, (4) Interventions for Myopia Onset and Progression, (5) Clinical Myopia Control Trials and Instrumentation, (6) Industry Guidelines and Ethical Considerations for Myopia Control, and (7) Clinical Myopia Management Guidelines.

IMI - Defining and Classifying Myopia: A Proposed Set of Standards for Clinical and Epidemiologic Studies.

Purpose: We provide a standardized set of terminology, definitions, and thresholds of myopia and its main ocular complications. Methods: Critical review of current terminology and choice of myopia thresholds was done to ensure that the proposed standards are appropriate for clinical research purposes, relevant to the underlying biology of myopia, acceptable to researchers in the field, and useful for developing health policy. Results: We recommend that the many descriptive terms of myopia be consolidated into the following descriptive categories: myopia, secondary myopia, axial myopia, and refractive myopia. To provide a framework for research into myopia prevention, the condition of "pre-myopia" is defined. As a quantitative trait, we recommend that myopia be divided into myopia (i.e., all myopia), low myopia, and high myopia. The current consensus threshold value for myopia is a spherical equivalent refractive error ≤ -0.50 diopters (D), but this carries significant risks of classification bias. The current consensus threshold value for high myopia is a spherical equivalent refractive error ≤ -6.00 D. "Pathologic myopia" is proposed as the categorical term for the adverse, structural complications of myopia. A clinical classification is proposed to encompass the scope of such structural complications. Conclusions: Standardized definitions and consistent choice of thresholds are essential elements of evidence-based medicine. It is hoped that these proposals, or derivations from them, will facilitate rigorous, evidence-based approaches to the study and management of myopia.

A novel classification of high myopia into anterior and posterior pathologic subtypes.

PURPOSE: High myopia and pathologic myopia are common causes of visual morbidity. Myopic pathology can affect all regions of the retina, though there is currently no classification system to distinguish anterior (peripheral) and posterior (macular) pathology. We hypothesize that these classifications are characterized by distinct demographic and refractive features, highlighting the disparity in types of pathologic myopia. METHODS: Institutional retrospective cohort study. The Stanford University Medical Center Clinical Data Warehouse was used to identify patients with high myopia by ICD-9 and ICD-10 codes. Predetermined ICD diagnoses were then used to classify patients with high myopia into isolated high myopia (IHM), anterior pathologic myopia (APM), posterior pathologic myopia (PPM), and combined pathologic myopia (CPM). A cohort of this population was then manually reviewed to gather refractive data and confirm accuracy of ICD coding. RESULTS: Patients (3274) were identified with high myopia. Overall, 22.1% individuals met criteria for APM, 10.7% for PPM, 17.0% for CPM, and 50.2% for IHM. We identified a significantly higher frequency of females with PPM compared to APM (62.3 vs. 48.3%; OR, 1.73; 95% CI, 1.34 to 2.25), Asian patients with PPM as compared to APM (42.9 vs. 33.3%; OR, 1.50; 95% CI, 1.16 to 1.95), and younger patients with APM compared to PPM (median 45.3 vs. 63.4 years). The refractive error was significantly more myopic in the CPM (median - 9.8D; interquartile range, IQR 6.7) and PPM (median - 10.5D; IQR 9.8) subgroups as compared to the APM (median - 8.1D; IQR 3.5), and IHM (median - 8.2D; IQR 4.1) subgroups (p = 0.003). CONCLUSIONS: High myopia may be divided into four distinct subgroups based on presence and location of pathology, which is associated with differences in age, gender, race, and refractive error.

Variation of Lenticule Thickness for SMILE in Low Myopia.

PURPOSE: To report the impact of increasing minimum lenticule thickness on the safety and efficacy of small incision lenticule extraction (SMILE) in low myopia up to -3.50 diopters (D). METHODS: SMILE was performed in 76 eyes of 76 patients. Thirty-eight eyes of 38 patients with low myopia were prospectively operated on with a programmed minimum lenticule thickness of 15 to 30 µm (thicker lenticule group). Thirty-five eyes suitable for analysis were then retrospectively matched by spherical equivalent to 35 eyes operated on with a minimum standard setting of 10 µm (standard thickness group), as provided in the database of the SMILE Eyes Clinic Linz, Linz, Austria. Comparison of outcomes was performed with the Standard Graphs for Reporting Refractive Surgery and by analysis of higher order aberrations as provided by Scheimpflug imaging. RESULTS: Apart from lenticule thickness, there was no significant difference in preoperative baseline or treatment parameters between both groups. Mean minimum lenticule thickness differed significantly (standard thickness = 10 ± 0 µm; thicker lenticule = 20 ± 5 µm; P < .0001). This also translated into a significant difference in maximum lenticule thickness (standard thickness: 54 ± 11 µm; thicker lenticule: 62 ± 8 µm; P = .0002). Mean SEQ preoperatively was -2.25 ± 0.51 (standard thickness) and -2.24 ± 0.46 (thicker lenticule) D, respectively, and changed to -0.11 ± 0.50 (standard thickness) and +0.01 ± 0.36 (thicker lenticule) D postoperatively (P < .0001 for both comparisons). Uncorrected postoperative visual acuity was -0.08 ± 0.35 (standard thickness) versus -0.10 ± 0.09 (thicker lenticule) logMAR (P = .706). After SMILE, the thicker lenticule group showed better safety (1.20 vs 1.08; P = .025) and efficacy (1.14 vs 0.96; P = .011) indices, translating into more eyes within ±0.50 D from target (91% vs 77%) and with at least 0.0 logMAR visual acuity (97% vs 86%), and fewer eyes losing one (3% vs 17%) and two (0% vs 3%) lines. CONCLUSIONS: Increasing minimum lenticule border thickness seems to improve the safety and efficacy of SMILE in low myopia. [J Refract Surg. 2018;34(7):453-459.].

Myopia: its historical contexts.

Worldwide, and especially in Asia, myopia is a major vision-threatening disorder. From AD 1600 on, to prevent myopia, authors warned against near work without sufficient pauses. There was an abundance of theories about the causes of myopia, the most common one being the necessity of extra convergence on nearby work with thickened extraocular muscles and elevated intraocular pressure. Ocular tenotomies against myopia were in vogue for a while. Axial lengthening of the eye in myopia was mentioned around 1700, but it took 150 years to become accepted as the most prevalent sign of high myopia. In 1864, a lucid concept of myopia and other ametropias arose through a clear separation between accommodation and refraction. Posterior staphyloma was known around 1800 and its association with myopia became evident some 30 years later. There still seems to be no generally accepted classification of myopia and particularly not of degenerative or pathologic myopia. This review focuses on myopia from 350 BC until the 21st century and on the earliest writings on the histology of eyes with posterior staphyloma. A proposal for myopia classification is given.

[Overview of Congenital Stationary Night Blindness with Predominantly Normal Fundus Appearance]. / Überblick über die kongenitale stationäre Nachtblindheit mit überwiegend normalem Fundus.

Congenital stationary night blindness (CSNB) is a clinically and genetically heterogeneous group of non-progressive retinal disorder with largely normal fundus appearance. The mode of inheritance can be autosomal dominant (adCSNB), autosomal recessive (arCSNB) or X-chromosomal (XLCSNB). Additional ocular signs can be myopia, hyperopia, strabismus, nystagmus and reduced visual acuity. The Riggs and Schubert-Bornschein form of CSNB can be discriminated by electroretinography. While the Riggs form represents a dysfunction of the rods, a signal transmission defect from photoreceptors to bipolar cell is described in patients with the more frequently occurring Schubert-Bornschein form. The Schubert-Bornschein form can be further divided into incomplete (icCSNB) and complete (cCSNB) showing different electroretinograms (ERGs). While patients with cCSNB show a dysfunction of the ON-signaling pathway, patients with icCSNB show a dysfunction of the ON- and OFF-signaling pathways, affecting visual acuity as well. Using classical linkage, candidate gene analyses and more recent next-generation sequencing approaches, to date, mutations in 13 different genes have been associated with this disease. In vitro and in vivo models showed a correlation of the phenotype of patients with the expression, protein localization and function of the respective molecules: genes, mutated in patients with the Riggs form of CSNB have an important role in the rod phototransduction cascade. Genes mutated in patients with icCSNB, code for proteins important for glutamate neurotransmitter release at the synaptic cleft of the photoreceptors. Genes mutated in patients with cCSNB, code for proteins important for glutamate uptake and further signal transmission to the ON-bipolar cells. Preliminary in vivo studies showed that CSNB may be cured by gene therapy. These studies concerning CSNB are important for the precise diagnosis of patients with this disease, but are also helpful in deciphering key molecules essential for signal transmission from photoreceptors to bipolar cells. So far, it is a poorly understood field.

The effect of transient glare on shape discrimination threshold in myopic adults.

BACKGROUND: The aim was to evaluate the effect of transient glare on shape discrimination threshold (SDT) in myopic adults. METHODS: A total of 162 myopic subjects were enrolled. Of these, 121 had low to mid myopia (-1.00 D to -6.00 D) and 41 had high myopia (-6.13 D to -10.25 D). All subjects had corrected visual acuity of 6/6 or better, and only data for the right eye were included in the study. SDTs were measured with circular D4 (fourth derivative of Gaussian) radial frequency patterns with a radial frequency of four, peak spatial frequency of three cpds, and mean radius of 1.5 degrees. SDTs were measured under two conditions, with and without the presence of transient glare while the stimulus was displayed (duration = 500 ms). RESULTS: Without transient glare, SDTs were not different between the low-mid (23.84 ± 6.02 arcsec) and high myopia groups (25.17 ± 5.98 arcsec, p = 0.16, Mann-Whitney test). With transient glare, SDTs in all subjects became significantly higher (p < 0.001, Wilcoxon signed-rank test). SDTs in the high myopia group (55.53 ± 18.59 arcsec) became significantly higher than those in the low to mid myopia group (47.55 ± 15.06 arcsec, p = 0.014, Mann-Whitney test). The increments were significantly higher in the high myopia group (28.94 arcsec versus 20.88 arcsec, p = 0.031, Mann-Whitney test). Multiple regression showed that SDTs with glare were significantly associated with SDTs without glare (p < 0.001) and the presence of high myopia (p = 0.015). CONCLUSIONS: Transient glare significantly increased SDTs in all myopic subjects, with the increment in subjects with high myopia being significantly larger than those in subjects with low to mid myopia.

Postoperative Corneal Asphericity in Low, Moderate, and High Myopic Eyes After Transepithelial PRK Using a New Pulse Allocation.

PURPOSE: To evaluate the postoperative asphericity in low, moderate, and high myopic eyes after combined transepithelial photorefractive keratectomy and SmartSurfACE treatment (SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany). METHODS: In this retrospective case series, the outcomes of myopic SmartSurfACE were evaluated at 3 months postoperatively in 106 eyes and divided into low (less than -4.125 diopters [D]), moderate (-4.125 to -6.25 D), and high (more than -6.25 D) myopia groups. In all cases, standard examinations and preoperative and postoperative corneal topography (SCHWIND Sirius) were performed. The analysis comprised evaluating the change in asphericity versus planned correction, comparing expected and achieved postoperative asphericity for all eyes, and comparison of the three groups in terms of the preoperative and postoperatively expected and achieved asphericity. RESULTS At 3 months postoperatively, the low myopia group (n = 33) improved average negative asphericity (Q = -0.04 ± 0.17 preoperative vs -0.19 ± 0.20 postoperative, P < .05). The moderate myopia group (n = 35) maintained or slightly improved average negative asphericity (Q = -0.07 ± 0.14 preoperative vs -0.05 ± 0.24 postoperative, P = .35). For the high myopia group (n = 38), the eyes became more oblate compared to the preoperative status (Q = -0.09 ± 0.15 preoperative vs 0.62 ± 0.70 postoperative, P < .05). In terms of asphericity, the difference between the three groups was not statistically significant preoperatively (P > .10), but showed significant differences postoperatively (P < .007). The cohort's average preoperative corrected distance visual acuity was 0.01 ± 0.04 logMAR (range: 0.0 to 0.18 logMAR) and uncorrected distance visual acuity was 0.03 ± 0.08 logMAR (range: -0.12 to 0.40 logMAR) 3 months postoperatively. CONCLUSIONS: SmartSurfACE maintained or slightly improved preoperative corneal asphericity for low to moderate myopic corrections (up to -6.00 D). This may provide advantages in the quality of vision and the onset of presbyopic symptoms after laser refractive surgery in myopic patients. [J Refract Surg. 2017;33(12):820-826.].

Corneal Breakthrough Haze After Photorefractive Keratectomy With Mitomycin C: Incidence and Risk Factors.

PURPOSE: To identify preoperative and intraoperative factors affecting breakthrough corneal haze incidence after photorefractive keratectomy (PRK) with mitomycin C (MMC). METHODS: In this retrospective study of PRK performed at the Care Vision Refractive Laser Center, Tel Aviv, Israel, a total of 7535 eyes (n = 3854 patients; mean age ± SD, 26 ± 6 years; 55% men) underwent PRK with intraoperative MMC application. Patients with histories of corneal pathology or surgery were excluded. Incidence, time of onset, and corneal haze severity were documented on follow-up of 118 ± 110 days. Eyes were grouped by preoperative refraction [low (≤-3D), moderate (-3D to -6D), or high (>-6D) myopia; low (≤3D) or high (>3D) astigmatism; low or high hyperopia]; by intraoperative time (above or below 40 seconds); and by MMC application time (above or below 40 seconds). The main outcome measures were incidence, onset time, and severity of corneal haze. RESULTS: The haze incidence was 2.1% in eyes with high myopia versus 1.1% in those with low to moderate myopia (P = 0.002), and 3.5 times higher in eyes with high than with low astigmatism (P < 0.05). The overall incidence was higher in eyes treated for hyperopia (10.8%) than for myopia (1.3%) (P = 0.0001). In eyes with moderate myopia, the haze incidence was lower in MMC application time ≥40 seconds (0%) than in <40 seconds (1.3%) (P = 0.03). After surgery, a mild early haze incidence peaked at 68.8 ± 6 days and severe late haze at 115 ± 17 days (P = 0.02). CONCLUSIONS: Hyperopic and large myopic or astigmatic corrections carry higher risk of haze. Longer MMC application might have beneficial haze prevention.

Relationship between functional and structural retinal changes in myopic eyes.

BACKGROUND: The aim of this study was to investigate the retinal structure in different grades of myopia and correlate it with the functional changes detected with multifocal electroretinogram (mf-ERG) and try to show the most important determining factors. METHODS: The study included 80 participants divided into four groups according to their spherical equivalent refractive error, namely, emmetropia (within ± 0.50 D), mild myopia group (greater than -0.50 to -3.00 D), moderate myopia group (more than -3.00 to -6.00 D) and high myopia group (greater than -6.00 D). Full ophthalmologic examination was performed for all participants, including visual acuity (VA), slitlamp examination, Goldmann applanation tonometry, indirect ophthalmoscopy, axial length (AL) measurement, retinal nerve fibre layer thickness assessment and mf-ERG stimulation. RESULTS: Axial length was significantly higher in myopes than emmetropes; also it was higher the greater the degree of myopia. There was a reduction in the amplitude and prolongation of implicit times of mf-ERG in myopia. Also P1 implicit time of the mf-ERG response was prolonged the greater the degree of myopia. The retinal nerve fibre layer was significantly thinner in myopic groups than the emmetropic group. The thinning of the retinal nerve fibre layer increased the more the degree of myopia. Multiple regression analysis of myopic patients showed that AL is the most important determinant of most of the mf-ERG five-rings retinal response density (RRD), mf-ERG four-quadrant (Q) RRD, most of the five-rings P1 amplitude and all five-rings latencies. The most important determinant factors of mean Q RRD were VA, AL and retinal nerve fibre layer thickness. CONCLUSION: The retina of the myope is subject to both structural and functional alterations compared to that of the emmetrope. Significant correlations exist between the functional and structural changes and can be explained on bases of longer AL and increasing myopic refraction.

Short-term outcomes of small-incision lenticule extraction (SMILE) for low, medium, and high myopia.

PURPOSE: To determine the safety, efficacy, and predictability of small-incision lenticule extraction at 6-month follow-up, depending on the level of the myopic refractive error. The surgeries were performed by a surgeon new to this technique. METHODS: Seventy-one subjects with a mean age of 31.86 ± 5.57 years were included in this retrospective observational study. Subjects were divided into 3 groups depending on the preoperative spherical equivalent (SE): low group from -1.00 D to -3.00 D, medium from -3.25 D to -5.00 D, and high from -5.25 D to -7.00 D. Manifest refraction, corrected distance visual acuity (CDVA), and uncorrected distance visual acuity (UDVA) were measured before surgery and at 6 months after the treatment. RESULTS: In total, 1.4% of the eyes lost 1 line of CDVA after the procedure, whereas 95.8% remained unchanged and 2.8% gained 1 line. A significant undercorrection (p = 0.031) was found in the high myopia group (median -0.50 D), whereas the low and medium groups remained near to emmetropia. In terms of efficacy, no statistically significant intergroup differences for postoperative UDVA (p = 0.282) were found. The vector analysis also showed undercorrection of the preoperative cylinder, even though the standard deviations decreased from 0.9 D in the x axis and 0.7 D in the y axis to 0.24 D and 0.27 D, respectively. CONCLUSIONS: Small-incision lenticule extraction might be a safe, effective, and predictable procedure even for inexperienced surgeons. No differences in efficacy were found among myopia levels even though undercorrections were found for SE and cylinder in high myopia.

Correlation of Sex and Myopia With Corneal Epithelial and Stromal Thicknesses.

PURPOSE: To measure the corneal epithelial thickness (CET) and stromal thickness (ST) in normal subjects, and to also evaluate their correlation with gender, age, and myopia severity. METHODS: A total of 162 normal subjects were enrolled; they were divided into 3 groups based on their refractive status: "low myopia" (-0.25 to -3.0 D), "moderate myopia" (-3.0 to -6.0 D), and "high myopia" (more than -6.0 D). The CET and total corneal thickness were obtained using optical coherence tomography, and the regional thicknesses and topographic variability were compared among the 3 myopia groups and between men and women. Furthermore, the correlation between the thickness measurements and gender, age, and refractive status was analyzed. RESULTS: The CET and ST of the central segment (2 mm in diameter) did not significantly differ between the 3 groups. In the paracentral and midperipheral zones (annuli 2-5 mm and 5-6 mm from the center), the CET in some areas, and the ST in most areas, differed significantly among the 3 groups. The CET values of men and women in the central segment were 54.6 ± 3.5 µm and 52.8 ± 3.5 µm, respectively (P = 0.003). Similar differences were observed in the paracentral and midperipheral zones. Multiple regression analysis suggested that the CET is related to gender, whereas the ST is associated with myopia severity. Age was not correlated with either the CET or ST. CONCLUSIONS: The CET is significantly greater in men than in women, and is not correlated with myopia severity, whereas the ST is inversely correlated with myopia severity, without significant gender difference.

Is the peripapillary retinal perfusion related to myopia in healthy eyes? A prospective comparative study.

OBJECTIVES: The aim of this study was to evaluate the peripapillary and parafoveal perfusion of young, healthy myopic subjects with spectral domain optical coherence tomography (OCT) angiography. DESIGN: A prospective comparative study was conducted from December 2014 to January 2015. SETTING: Participants recruited from a population-based study performed by the Eye, Ear, Nose and Throat Hospital of Fudan University in Shanghai. PARTICIPANTS: A total of 78 Chinese normal subjects (78 eyes) with different refraction were included. Myopia was divided into 4 groups on the basis of the refractive status: 20 eyes with emmetropia (mean spherical equivalent (MSE) 0.50D to -0.50D), 20 eyes with mild myopia (MSE -0.75D to -2.75D), 20 eyes with moderate myopia (MSE -3.00D to -5.75D), and 18 eyes with high myopia (MSE≤-6.00D). MAIN OUTCOME MEASURES: Peripapillary and parafoveal retinal and choroidal perfusion parameters and their relationships with axial length (AL) and retinal nerve fibre layer (RNFL) thickness were analysed. RESULTS: Significant differences were found for the retinal flow index and vessel density in the peripapillary area among the 4 groups, but not in the parafoveal area. The high myopia group had the lowest peripapillary retinal flow index and vessel density. In addition, there was a negative correlation (ß=-0.002, p=0.047) between the AL and peripapillary retinal flow index and a positive correlation between RNFL thickness and the peripapillary retinal perfusion parameters (flow index: ß=0.001, p=0.006; vessel density: ß=0.350, p=0.002) even after adjustment for other variables. CONCLUSIONS: Highly myopic eyes have a decreased peripapillary retinal perfusion compared with emmetropic eyes. Such vascular features might increase the susceptibility to vascular-related eye diseases.

Four-year visual outcomes after photorefractive keratectomy in pilots with low-moderate myopia.

BACKGROUND: The photorefractive keratectomy (PRK) is approved for Air Force pilots in several nations. The occupational environments of pilots in the Air Force are unique, including extremely high altitude, low oxygen tension, high ultraviolet light exposure and high G-force load. The short-term efficacy and safety of PRK for pilots are documented. However, the study for long-term visual and refractive outcomes of PRK in pilots is limited. OBJECTIVE: To investigate the long-term visual and refractive outcomes in a 4-year follow-up period after PRK in pilots with low to moderate myopia. METHODS: Thirty-eight eyes of 20 subjects that underwent PRK and recruited to Air Force pilot were evaluated preoperatively and at 3, 6, 12, 24, and 48 months postoperatively. RESULTS: The mean patient age was 21.42±0.75 years. The mean preoperative manifest refraction spherical equivalent (SE) was -1.51±1.15 diopters (D). At 4 years postoperatively, the mean SE was -0.29±0.51, 89.5% of eyes achieved 20/20 or better Snellen uncorrected visual acuity, 71.1% of eyes were within ±0.50 D of emmetropia. The refraction stabilised by 6 months and was maintained up to the 4-year follow-up stage. CONCLUSIONS: PRK for pilots with low to moderate myopia is safe and effective in the long term. High-altitude environmental stress exposure has no effect on the refractive stability after PRK. TRIAL REGISTRATION NUMBER: ROKAF-ASMC-2015-IRB-002.

Comparison of Visual Quality After SMILE and LASEK for Mild to Moderate Myopia.

PURPOSE: To compare the objective and subjective quality of vision after femtosecond laser-assisted small incision lenticule extraction (SMILE) and laser-assisted subepithelial keratomileusis (LASEK) for mild to moderate myopia. METHODS: This prospective, comparative study included 65 eyes of 33 patients in the SMILE group, with a mean spherical equivalent (SE) of -4.16 ± 0.82 diopters, and 50 eyes of 25 patients in the LASEK group, with a mean SE of -3.81 ± 0.97 diopters. Visual acuity, corneal topography, contrast sensitivity, and wavefront aberrations were recorded preoperatively and compared with postoperative measurements. A quality of vision questionnaire was scored and analyzed 3 months postoperatively. RESULTS: Three months postoperatively, the SMILE group had fewer (P < .05) higher-order aberrations (HOAs) (0.390 ± 0.175 µm), including spherical aberration (SA) (0.262 ± 0.242 µm), than the LASEK group (HOAs = 0.479 ± 0.148 µm, SA = 0.576 ± 0.287 µm, trefoil = 0.465 ± 0.248 µm). There was no significant difference in the amount of coma and trefoil between the two groups after surgery. Analysis of the scores of glare and halos in the quality of vision questionnaire revealed that SMILE (night glare = 1.25 ± 1.22, halos = 0.97 ± 1.12) provided a better quality of vision (P < .05) than LASEK (night glare = 2.32 ± 1.99, halos = 1.96 ± 1.77). The two groups demonstrated no significant difference in contrast sensitivity 3 months postoperatively. No vision-threatening complications were noted at any stage in either group. CONCLUSIONS: Both SMILE and LASEK are safe and effective surgical procedures in the correction of myopia. SMILE has a lower induction rate of HOAs and a higher degree of patient satisfaction than LASEK at 3 months postoperatively.