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PubMed1995

How applicable are animal myopia models to human juvenile onset myopia?

Investigations into the plasticity of eye growth and refractive error development have significantly expanded our knowledge of animal models of myopia in the last 15 yr. The applicability of this information is as yet undetermined, but hopefully this information will be useful in learning more about human myopia. This paper presents a critical review of the animal myopia literature as those data relate to the human condition. Differences between the chicken, tree shrew, and primate animal models of myopia are outlined, and the various experimental paradigms used to investigate refractive error development and ocular growth in the chicken are compared. Specific arguments against the application of animal models of myopia to the etiology of human juvenile onset myopia include the following: (1) there is no deprivation of form vision in the environment of the school-aged child as severe as that required to induce myopia in animals; (2) the sensitive period for deprivation myopia in animals appears to be too early to account for human juvenile onset myopia; and (3) studies in the chicken using spectacle lenses to create dioptric blur involve a choroidal thickness modulation that has no human analog. Ultimately, the results of investigations into the cellular and biochemical modulation of eye growth in animals may be the most relevant to human myopia.

Animals↗
PubMed1991

The use of the 193-nm excimer laser for myopic photorefractive keratectomy in sighted eyes. A multicenter study.

Photorefractive keratectomy was performed at three centers using the 193-nm excimer laser on 31 sighted myopic eyes. Preoperative refractive errors (spherical equivalent) ranged from -12.00 to -4.00 diopters (D) (mean, -6.49 +/- 1.75 D). Peribulbar anesthesia, a 5.2- to 6.0-mm beam diameter, and topical corticosteroids were used for up to 6 months after surgery. The epithelium healed within 3 to 4 days, and all patients returned to their best corrected visual acuity within 1 line of their preoperative acuity. There was minimal subepithelial reticular haze, peaking at 3 weeks and diminishing over the next 3 to 4 months, which was not felt to be visually significant. At 6 months, the average residual refractive error was -1.85 +/- 2.5 D. Sixty-eight percent of eyes were corrected within 2 D and 55% within 1 D of attempted correction. There was no significant change in astigmatism, contrast sensitivity, corneal sensation, or endothelial cell counts. This preliminary work shows that photorefractive keratectomy has promise in the reduction of moderate myopia.

Adult↗
PubMed1995

How predictable are the results of excimer laser photorefractive keratectomy? A review.

At the close of 1994, the AOA News reported that at least 14 companies were preparing to market equipment for excimer laser photorefractive keratectomy (PRK). More than a dozen PRK centers had been formed for the purpose of recruiting optometrists to co-manage PRK patients. Because the surgery is a "no-touch" computer-driven procedure whose duration is measured in seconds, the preoperative and postoperative care of PRK patients will assume major importance. Optometrists who will be asked to take part in the management of PRK patients must be able to counsel patients on matters such as the predictability of the procedure in terms of postoperative refractive error and visual acuity, as well as the possibility of unintended consequences such as difficulty in night driving. Information currently available, mainly as a result of studies conducted in other countries, shows that the results of PRK are highly predictable for preoperative myopia up to about -3.00 D and somewhat less predictable for myopia between -3.00 and -6.00 D, whereas for myopia greater than -6.00 D the probability of achieving a full correction decreases rapidly with increasing amounts of myopia. As compared to radial keratotomy (RK) in which the postoperative refractive error drifts relentlessly in the hyperopic direction, PRK brings about an initial hyperopic shift followed by regression leading to increasing myopia. Researchers disagree on the cause of the postoperative hyperopic shift and regression, and on the value of various methods of controlling regression including the use of wider and deeper ablation profiles and the postoperative use of corticosteroids and nonsteroid anti-inflammatory drugs. It is too early to determine whether the myopic creep in PRK will be as persistent as the hyperopic creep in RK, but it is likely that whereas presbyopic post-RK patients may have adequate distance vision but require corrective lenses for reading, presbyopic post-PRK patients may be sufficiently myopic to require lenses for distance vision but not for reading.

Adult↗
PubMed1999

Timing of retinal redetachment after removal of intraocular silicone oil tamponade.

PURPOSE: To evaluate the interval between removal of intraocular silicone oil tamponade and retinal redetachment after pars plana vitrectomy, and to investigate factors influencing the length of the interval. PATIENTS AND METHODS: The retrospective study included 42 eyes of 42 consecutive patients who experienced a retinal redetachment after silicone oil had been removed 8.0+/-6.2 months after an initial pars plana vitrectomy including intraocular silicone oil (5,000 centistokes) tamponade. Pars plana vitrectomy had been performed for proliferative vitreoretinopathy caused by complicated rhegmatogenous retinal detachment. RESULTS: The retina redetached 2 days to 5.5 months after silicone oil removal (mean +/- SD, 1.3+/-1.4 months; median, 18 days). Thirteen (30%) of all 42 redetachments occurred in the first 9 days, 21 (50%) of all 42 retinal redetachments occurred in the first 18 days, and 32 (75%) of all 42 retinal redetachments occurred in the first 50 days. The interval between silicone oil removal and retinal redetachment was statistically (by analysis of variance) independent of the method of silicone removal (transpupillary drainage vs via pars plana sclerotomies), refractive error of the eye (P = .62), time between initial pars plana vitrectomy and silicone oil removal (P = .99), visual acuity before silicone oil removal (P = .26), type of anesthesia (P = .69), gender (P = .80), and age (P = .48) of the patients. CONCLUSION: The risk of retinal redetachment decreases steeply with increasing time after silicone oil removal. Three to 5 months after oil removal, retinal redetachment becomes unlikely. The time of retinal redetachment is statistically independent of the method of silicone oil removal, refractive error, time between the preceding pars plana vitrectomy and silicone oil removal, visual acuity before silicone oil removal, type of anesthesia, and gender and age of the patents. These data may be important for scheduling reexaminations and for counseling patients in their planned activities after removal of intraocular silicone oil tamponade.

Adolescent↗
PubMed2005

White lesion in the corneal pigmented ring associated with orthokeratology.

The development of the pigmented corneal arc and a white lesion near the inner margin of the arc in a girl wearing overnight orthokeratology (ortho-k) lenses for myopic control is reported. The girl was examined before and followed up every 6 months after the treatment over a 3-year period. The initial spherical equivalent refractive error and keratometric readings (flattest/steepest meridians) were -2.37 D and 45.00 D/46.75 D respectively in the right eye and -3.12 D and 45.25 D/46.00 D respectively in the left eye. She was wearing ortho-k lenses of a four-zone design made of Boston XO material on a nightly basis. The same lens design was used throughout the monitoring period. Corneal topography showed a rather well-centred treatment zone but vision varied between visits because of fluctuations in residual refractive error. The corneal condition of each eye was unremarkable except for the presence of the pigmented corneal arc first observed 6 months after the commencement of the treatment. The intensity of the arc did not change over the years in the right eye but increased in the left eye. A faint white lesion within the inner border of the left pigmented arc was first observed at the end of the second year and it became more obvious at the end of the third year. This lesion appears to be similar to those reported in intense Fleischer's rings associated with keratoconus. Although the presence of the arc may have no clinical ramification, the change in the intensity and the development of the white lesion may reflect an increased stress exerted on the cornea with continued ortho-k lens wear.

Child↗
PubMed2005

Astigmatism in monkeys with experimentally induced myopia or hyperopia.

PURPOSE: Astigmatism is the most common ametropia found in humans and is often associated with large spherical ametropias. However, little is known about the etiology of astigmatism or the reason(s) for the association between spherical and astigmatic refractive errors. This study examines the frequency and characteristics of astigmatism in infant monkeys that developed axial ametropias as a result of altered early visual experience. METHODS: Data were obtained from 112 rhesus monkeys that experienced a variety of lens-rearing regimens that were intended to alter the normal course of emmetropization. These visual manipulations included form deprivation (n = 13); optically imposed defocus (n = 48); and continuous ambient lighting with (n = 6) or without optically imposed defocus (n = 6). In addition, data from 19 control monkeys and 39 infants reared with an optically imposed astigmatism were used for comparison purposes. The lens-rearing period started at approximately 3 weeks of age and ended by 4 to 5 months of age. Refractive development for all monkeys was assessed periodically throughout the treatment and subsequent recovery periods by retinoscopy, keratometry, and A-scan ultrasonography. RESULTS: In contrast to control monkeys, the monkeys that had experimentally induced axial ametropias frequently developed significant amounts of astigmatism (mean refractive astigmatism = 0.37 +/- 0.33 D [control] vs. 1.24 +/- 0.81 D [treated]; two-sample t-test, p < 0.0001), especially when their eyes exhibited relative hyperopic shifts in refractive error. The astigmatism was corneal in origin (Pearson's r; p < 0.001 for total astigmatism and the JO and J45 components), and the axes of the astigmatism were typically oblique and bilaterally mirror symmetric. Interestingly, the astigmatism was not permanent; the majority of the monkeys exhibited substantial reductions in the amount of astigmatism at or near the end of the lens-rearing procedures. CONCLUSIONS: In infant monkeys, visual conditions that alter axial growth can also alter corneal shape. Similarities between the astigmatic errors in our monkeys and some astigmatic errors in humans suggest that vision-dependent changes in eye growth may contribute to astigmatism in humans.

Animals↗
PubMedDate not supplied

Wavefront aberration outcomes of LASIK for high myopia and high hyperopia.

PURPOSE: To determine the higher order aberrations at the corneal first surface after conventional LASIK for high myopia and high hyperopia. METHODS: This was a retrospective study using a convenience sample with subjects divided into five groups by level of refractive correction. Group 1 were normals, having no eye disease or previous surgery, but may have had refractive error. Group 2 had low myopia (-1.00 to -5.87 D), group 3 high myopia (> 6.00 D), group 4 low hyperopia (+1.00 to +3.87 D), and group 5 high hyperopia (> 4.00 D). LASIK was performed using a Technolas 217 laser. Corneal topography was taken with Orbscan II, and Placido data exported to VOLPro software v6.71. Wavefront aberrations were determined for a 6.0-mm pupil. RESULTS: The study included 264 subjects-group 1 (normal), n=204; group 2 (low myopia), n=20; group 3 (high myopia), n=20; group 4 (low hyperopia), n=10; and group 5 (high hyperopia), n=10. The spherical equivalent refractive error corrected (mean +/-SD) was 0.00 +/- 0.00 D in group 1, -3.92 +/- 1.47 D in group 2, -9.53 +/- 2.06 D in group 3, +2.49 +/- 0.51 D in group 4, and +5.54 +/- 1.22 D in group 5. The total higher order root-mean-square (RMS) wavefront aberration was 0.38 +/- 0.07 microm in group 1, 0.69 +/- 0.22 microm in group 2, 1.36 +/- 1.79 microm in group 3, 0.64 +/- 0.34 microm in group 4, and 1.76 +/- 0.54 microm in group 5. Spherical aberration was 0.25 +/- 0.06 mcirom in group 1, 0.45 +/- 0.11 microm in group 2, 0.64 +/- 0.29 microm in group 3, -0.11 +/- 0.15 microm in group 4, and -0.56 +/- 0.22 microm in group 5. The refractive correction (Rx) was highly correlated to total higher order RMS for myopic correction higher order RMS = 0.38 - 0.07 Rx, R2=0.52, and for hyperopic correction higher order RMS = 0.18 + 0.28 Rx, R2 = 0.75. CONCLUSIONS: Conventional LASIK increases all corneal higher order aberrations with induced aberrations increasing with the magnitude of refractive correction. High refractive corrections, both myopic (>6.00 D) and hyperopic (>5.00 D), can lead to very high levels of corneal higher order aberrations.

Astigmatism↗
PubMedDate not supplied

The safety and efficacy of photorefractive keratectomy after laser in situ keratomileusis.

PURPOSE: To determine the safety and efficacy of performing photorefractive keratectomy (PRK) in corneas previously treated with laser in situ keratomileusis (LASIK) surgery. METHODS: Fifteen eyes of 14 patients who had initially received LASIK for the treatment of myopia and compound myopic astigmatism were evaluated. Variables included existence of and/or type of flap complication associated with the original LASIK procedure, refractions before and after (3 and 6 months) PRK, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and the development of complications after PRK such as haze, scarring, double vision, or ghosting. RESULTS: All 15 eyes were available for analysis at 6 months. Eleven eyes had experienced flap complications during the initial LASIK procedure and 4 eyes had experienced complications in the LASIK postoperative period. Characteristics prior to performing PRK included 11 myopic and 4 hyperopic eyes. By 6 months after PRK treatment, 87% of eyes had UCVA > or = 20/40, 53% had > or = 20/25, and 40% had > or = 20/20. All eyes had BSCVA of > or = 20/30, with 73% being > or = 20/20. No eye had lost 2 lines of BSCVA and only 1 eye lost 1 line of BSCVA. Sixty percent of eyes were within 1.0 diopters (D) of emmetropia, and 40% were within 0.5 D of emmetropia. A trend towards undercorrection and surgical induction of astigmatism as confirmed by vector analysis was noted. No eye developed significant haze or scarring. CONCLUSIONS: Photorefractive keratectomy may be a safe procedure to perform in corneas previously treated with LASIK surgery. Results show good reduction of refractive error and improvement of UCVA and BSCVA. A significant undercorrection of astigmatism was attributed to surgically induced astigmatism. Further studies are necessary to determine the long-term safety and stability of outcomes.

Astigmatism↗
PubMedDate not supplied

Telemedicine-friendly, portable tonometers: an evaluation for intraocular pressure screening.

PURPOSE: To evaluate the intraocular pressure (IOP) readings from two portable, telemedicine-friendly tonometers for suitability in glaucoma screening. METHODS: 213 eyes of 107 consenting patients attending an eye clinic were tested with an I-care tonometer and a Pulsair-Easy Eye puff-air tonometer. Gold standard IOP was measured with a Goldmann applanation tonometer (GAT). Effect of central corneal thickness, anterior chamber depth and refractive errors on IOP measurements were also analysed. RESULTS: The mean difference of IOP by GAT and both the portable tonometers was +/- 2.2 mmHg. The analysis indicates minimal difference between IOP readings of both the portable tonometers. The mean difference between two consecutive readings by I-care was 0.01 mmHg. Using 21 mmHg as a threshold for suspected glaucoma, both the portable digital tonometers reported a sensitivity of 38% and specificity of >95%. In the subjects studied, central corneal thickness had statistically significant influence on IOP measurements while refractive errors and anterior chamber depth had no significant influence on IOP measurements with any tonometry. CONCLUSION: The IOP readings by both portable tonometers are comparable and were within clinically acceptable range from GAT. These portable tonometers are useful tools for IOP screening.

Adult↗
PubMed2004

A randomized trial of the effects of rigid contact lenses on myopia progression.

OBJECTIVE: To compare the effects of rigid gas-permeable contact lenses (RGPs) and soft contact lenses (SCLs) on myopia progression in children. METHODS: We randomly assigned 116 subjects to wear RGPs or SCLs. Subjects underwent cycloplegic autorefraction, keratometry, and A-scan ultrasonographic axial length measurements at each annual visit. All analyses were conducted according to the original randomization assignment. The primary outcome measure was the 3-year change in spherical equivalent cycloplegic autorefraction. RESULTS: The mean +/- SD spherical equivalent cycloplegic refractive error progressed -1.56 +/- 0.95 diopters (D) for RGP wearers and -2.19 +/- 0.89 D for the SCL wearers during the 3 years of the study (analysis of covariance [ANCOVA], P<.001). The axial growth of the eyes was not significantly different between treatment groups (ANCOVA, P = .57). The steep corneal meridian of the RGP wearers steepened 0.62 +/- 0.60 D, and that of the SCL wearers steepened 0.88 +/- 0.57 D during the 3 years (ANCOVA, P = .01). CONCLUSIONS: The RGP wearers' myopia progressed less than that of the SCL wearers. The corneal curvature of the SCL wearers steepened more than that of the RGP wearers, but the axial growth was not significantly different between the groups. Most refractive error treatment effect was limited to the first year of the trial. The results of the study provide information for eye care practitioners to share with their patients, but they do not indicate that RGPs should be prescribed primarily for myopia control.

Child↗
PubMedDate not supplied

Refraction problems after refractive surgery.

While refractive surgery such as radial keratotomy, epikeratophakia, and corneal relaxing incisions offer many potential benefits to patients, they can also generate optical problems such as overcorrection or undercorrection of the prior refractive error and variable vision. The authors offer suggestions for avoiding problems through proper patient selection; candid preoperative communication with the patient about possible difficulties and limitations; understanding of the physiological changes that may occur; and optical techniques for alleviating postoperative vision problems.

Contact Lenses↗
PubMed2003

Postoperative LASIK visual aberrations and treatment with InterWave-guided multipass, multistage correction.

Visual aberrations such as glare and halo have been well documented after laser in-situ keratomileusis (LASIK). These are more likely in patients with higher refractive errors and large pupil diameters. We present a patient with good Snellen acuity but functional impairment by visual aberrations after LASIK. These symptoms resolved after an InterWave-guided LASIK multipass, multistage enhancement treatment to correct spherical aberrations.

Adult↗
PubMed1993

Pseudophakia for traumatic cataracts in children.

PURPOSE: The purpose of this prospective study is to evaluate the postoperative visual acuity, refractive error, intraocular pressure, and status of the posterior capsule in children with traumatic cataracts who undergo extracapsular cataract extraction and insertion of a posterior chamber lens. METHODS: Extracapsular cataract extraction and primary endocapsular fixation of a posterior chamber lens implant were performed in eight children (age range, 4-17 years) with unilateral traumatic cataracts. RESULTS: There were no intraoperative complications, and seven of eight eyes achieved 20/40 or greater spectacle visual acuity during an average follow-up interval of 10 months (range, 5-20 months). The average postoperative spherical equivalent refractive error was +0.33 diopter (D) (range, -2.25 to +2.12 D); the average postoperative anisometropia was approximately 1 D (range, 0-2.25 D). In one patient, a coagulase-negative staphylococcal endophthalmitis developed 10 days after surgery. In three eyes that had opacified posterior capsules, YAG laser capsulotomy was performed. CONCLUSIONS: These preliminary results suggest that intraocular lens (IOL) implantation may be a safe and effective method of optical correction for children with traumatic cataracts.

Adolescent↗
PubMed1985

Surgical results of second-attempt radial keratotomy.

The safety, efficacy, and stability of second-attempt radial keratotomy were evaluated in 20 eyes of 12 patients from September 1, 1982, to August 31, 1983. The average amount of refractive error change was 1.89 diopters with 1.38 diopters of corneal curvature flattening. The effect of the second-attempt operation was about 60% that of the first-attempt operation. No significant surgical complications were observed in this study.

Adult↗
PubMed2006

Laser in situ keratomileusis flap thickness using the Hansatome microkeratome with zero compression heads.

PURPOSE: To evaluate predictability and possible factors affecting flap thickness in laser in situ keratomileusis (LASIK) using the Hansatome microkeratome (Bausch & Lomb Surgical) with zero compression heads. SETTING: Zentrum für Refraktive Chirurgie Münster, Münster, Germany. METHODS: A prospective nonrandomized comparative (self-controlled) trial analyzing flap thickness in 153 consecutive patients having LASIK using the Hansatome microkeratome with zero compression was conducted. Two hundred thirty-eight eyes that had uncomplicated primary LASIK (n = 237) or secondary LASIK (n = 1) by the same surgeon and same technique using 4 different microkeratomes of the same model were evaluated. Each keratome cut was performed with a new Accuglide (Bausch & Lomb) blade in a 160 microm (n = 89), 180 microm (n = 128), or 200 microm (n = 21) Hansatome zero compression head coupled to a 8.5 mm (n = 106) or 9.5 mm (n = 131) suction ring. Only Hansatome elements with the same serial numbers were combined. Ultrasound subtraction pachymetry was routinely used to determine intraoperative flap thickness. Flap thickness was correlated with microkeratome head dimension, suction ring size, preoperative keratometry obtained by Orbscan IIz (Bausch & Lomb), preoperative corneal thickness as obtained by ultrasound pachymetry, refractive error, and age. RESULTS: Measured intraoperative flap thickness was significantly different (P<.01) from predicted flap thickness. The mean flap thickness was 97 microm +/- 18 (SD) (range 65 to 163 microm), 111 +/- 20 microm (range 61 to 177 microm), and 131 +/- 20 microm (range 89 to 162 microm) for the 160 microm, the 180 microm, and 200 microm heads, respectively. There was a good correlation between microkeratome head and corneal flap thickness. However, there was a variability between devices. There was a low correlation between baseline ultrasound pachymetry at the time of surgery and corneal flap thickness (r = .26) and a small effect of ring size. There was no correlation with keratometry, refractive error, or age. CONCLUSIONS: There was a remarkable difference in the flap thickness of microkeratomes of the same make and model. This emphasizes the need to measure intraoperative flap thickness and to evaluate every microkeratome separately. Factors affecting flap thickness seem to be more device dependent than patient related; obtaining flap thickness in the first eye did not enable predictions of the flap thickness in the fellow eye.

Adult↗
PubMed2002

Phenotypic expression of the complete type of X-linked congenital stationary night blindness in patients with different mutations in the NYX gene.

PURPOSE: To describe the clinical phenotype of the complete type of X-linked congenital stationary night blindness (CSNB1) with different types of mutations in the NYX gene. METHODS: The clinical and genetic data from 18 male patients with eight different mutations from two ophthalmological institutes were reviewed. The variability in refractive error, reduced visual acuity and full-field electroretinogram (ERG) recordings was examined. RESULTS: Parameters were quantitatively analyzed based on the classification of mutations according to their predicted effect on protein structure and function. CSNB1 patients with mutations changing structurally conserved residues ( n=12) tended to have a lower degree of myopia than patients with mutations of non-conserved residues ( n=6). Visual acuity loss and the 30 Hz flicker ERG recordings were similar in the two groups. Values for the b/a amplitude ratio tended to be clustered in patients carrying the same mutation. Refractive error and the b/a amplitude ratio were highly correlated between the two eyes of an individual. CONCLUSIONS: These data suggest correlations between phenotypic expression in CSNB1 and individual genotypes as well as class types of mutations based on the extent of structural amino acid conservation. A high inter-eye correlation suggests that other genetic or environmental factors, rather than chance, play a part in determining the phenotypic diversity in CSNB1.

Adolescent↗
PubMed2006

Visual impairments in people with severe and profound multiple disabilities: an inventory of visual functioning.

BACKGROUND: The prevalence of visual impairments in people with severe and profound multiple disabilities (SPMD) is the subject of considerable debate and is difficult to assess. METHODS: In a typical Dutch care organization, all clients with SPMD (n = 76) participated in the study and specific instruments adapted to these clients (requiring a minimum of cooperation) were used to measure visual acuity, the visual field, binocular vision, contrast sensitivity, refractive errors and visual functioning behaviour. RESULTS: We found an unexpected 92% of clients with SPMD to have visual impairments. Previously, only 30% were known to have visual problems. None of the persons observed had normal visual acuity. Subnormal visual acuity was the best result. The severity of the visual impairment was related to the severity of the intellectual disability. In addition to the problem of acuity, impairments in the visual field, impaired contrast sensibility and impaired binocular functioning were found, as well as impaired visual attention, fixation and following. In 22% of the clients observed, refractive errors were found and glasses were advised. CONCLUSIONS: Consequences for caregiving and for modifications of the environment were discussed.

Adolescent↗
PubMed2004

The epidemiology of myopia in Hong Kong.

INTRODUCTION: The prevalence of myopia amongst the Chinese has escalated in recent decades. While this refractive error was previously a little more than an inconvenience and a source of unwanted expense to the affected individuals, it is now sufficiently prevalent to warrant national concern. Myopia is also a major cause of low vision. This review aims to provide information on the prevalence of myopia in the Chinese community in Hong Kong. MATERIALS AND METHODS: Based on a number of studies carried out mainly at the Centre for Myopia Research in The Hong Kong Polytechnic University, myopia in the Chinese community in Hong Kong is described. RESULTS: Infants in Hong Kong appear to have refractive errors similar to infants of European descent; however, by the age of 7 years myopia is already prevalent. The annual incidence of myopia thereafter averages 11% to 12%; by the age of 17 years more than 70% are myopic, and this prevalence is greater than in people of European descent. In Hong Kong, myopia is much less prevalent in the older generation. CONCLUSION: The increase in prevalence of myopia over a short period of time is postulated to be due to environmental factors. Children of Chinese descent have a susceptibility to environmental factors which cause myopia.

Astigmatism↗