Differences In Corneal Curvature Research Articles

Lowe Oculocerebrorenal Syndrome Comparison of Anterior Segment Anatomy in Eyes with and without Glaucoma

Ultrasound biomicroscopy comparison of two infants with Lowe oculocerebrorenal syndrome, one with glaucoma and one without, found differences in corneal curvature, iris thickness, trabecular-iris angle, and lens morphology are potential glaucoma-associated features.

Evaluation of central corneal thickness and corneal curvature in patients with rheumatoid arthritis

Background: Rheumatoid arthritis is an autoimmune disease. It is a chronic disease that causes symmetrical deforming type of polyarthritis. Rheumatoid arthritis most commonly involves the anterior segment of the eye. It causes keratoconjunctivitis sicca, episcleritis, scleritis, sclerosing keratitis, stromal keratitis, paracentral keratolysis, and peripheral ulcerative keratitis. Aims and Objectives: The purpose of this study was to evaluate central corneal thickness (CCT) and corneal curvature in patients with rheumatoid arthritis. We also evaluated the association between CCT, corneal curvature, and rheumatoid arthritis severity. Materials and Methods: A total of 49 rheumatoid arthritis patients and 49 control subjects were enrolled in this study. The study was conducted in the ophthalmology department of SRM medical college, Chennai. A detailed ophthalmological examination was performed on each subject. Dry eye evaluation was done using Shirmers test, tear breakup time, and corneal fluorescein staining. The CCT and corneal curvature were measured by ultrasonic pachymetry and auto keratorefractometer, respectively. For statistical analysis, we used chi-square test, Fisher exact test, student t-test, and ANOVA test. Results: Mean CCT in all rheumatoid arthritis patient group eyes was 532.78±14.03 micrometers. Mean CCT in rheumatoid arthritis with dry eye was 522.3±11.10 micrometer, in rheumatoid arthritis without dry eye was 536.90±11.60 micrometer and control patients’ group was 564.80±20 micrometer respectively. The difference of CCT was found to be statistically significant (P<0.05) between rheumatoid arthritis and control eyes. Mean corneal curvature was 42.71D±2.16 in all rheumatoid arthritis patients. Mean corneal curvature was 42.7D±1.6 in rheumatoid arthritis with dry eye, 42.8D±2.5 in rheumatoid arthritis without dry eye, and 42.5D±2.1 in control eye, respectively. Our result did not show statistically significant difference in corneal curvature between the rheumatoid arthritis patients and control patients. CCT and corneal curvature were not associated with rheumatoid arthritis activity and rheumatoid arthritis duration. Conclusion: The CCT was thinner in rheumatoid arthritis patients than control patients. In order to improve the quality of vision of rheumatoid arthritis patients, we suggest including pachymetry as a routine ophthalmic examination in them. Pachymetry will be helpful in diagnosing and guiding clinical treatment in these patients.

Myopia control with soft multifocal contact lenses: 18-month follow-up.

PURPOSE:The study aimed to establish the outcome of multifocal contact lenses (MFCL) (Multistage + 1.50D and Proclear + 3.00D) on myopia progression and axial length elongation over an 18-month period.METHODS:Thirty myopic schoolchildren (5 males and 25 females) aged between 13 and 15 years were randomly assigned to wear either single vision contact lens (SVCL), Multistage MFCL + 1.50D, or Proclear +3.00D MFCL for 1½ years using a double-masked design. Cycloplegic refraction, corneal curvature, and axial length were measured.RESULTS:Myopia progression was controlled by 38.6% and 66.6% in children wearing Multistage + 1.50D and Proclear +3.00D MFCL, respectively, in comparison to children wearing SVCL over an 18-month period. In terms of axial elongation, this study found a 31.1% and 63.2% control in axial elongation over 18 months of treatment in comparison to the SVCL group. No statistical significant difference in corneal curvature was found between initial and last visits for all the three groups (SVCL, P = 0.90; Multistage + 1.50 MFCL, P = 0.78, and Proclear + 3.00 MFCL, P = 0.05).CONCLUSION:Proclear +3.00D MFCL was revealed to cause slow development of myopia and axial elongation among myopic schoolchildren. MFCL with higher add powers could be more effective on myopia progression in comparison with moderate add powers.

The Effects of High Lighting on the Development of Form-Deprivation Myopia in Guinea Pigs.

To investigate the effects of high ambient lighting on refraction and ocular biometry in guinea pig models of form-deprivation myopia (FDM). Forty 3-week-old guinea pigs were randomly assigned to groups exposed to either high light (HL, 10,000 lux) or normal light (NL, 500 lux) with normal vision or form deprivation. Throughout the 10-week rearing period, animals were exposed to high light or normal light for 12 hours with a 12-hour light/dark cycle. Refraction, axial length (AL), and radius of corneal curvature (CCR) were measured by cycloplegic retinoscopy, A-scan ultrasonography, and keratometer, respectively. At the end of treatment, form-deprived eyes under high ambient lighting exhibited more hyperopic refraction and shorter AL than those under normal ambient lighting (2.06 ± 1.68 diopters [D; mean ± SD] vs. -0.59 ± 1.56 D, P < 0.001; 8.36 ± 0.13 mm vs. 8.56 ± 0.16 mm, P < 0.001). Deprived eyes under high ambient lighting were relatively more myopic than their contralateral control eyes at the end of treatment (2.06 ± 1.68 D vs. 5.44 ± 0.66 D, P < 0.001). High lighting induced a significant hyperopic shift in normal eyes after 4 weeks of exposure. There were no significant differences in CCR between eyes exposed to high and normal light, nor between deprived eyes and contralateral eyes. High ambient lighting could retard, but not fully inhibit, the development of FDM. High light levels contributed to a greater hyperopic shift in normal eyes during the first 4 weeks of treatment. Corneal curvature was unaffected by either high ambient lighting or form deprivation.

A Prospective Study of Anterior Segment Ocular Parameters in Anisometropia.

PurposeThe aim of this study was to investigate the differences in anterior segment ocular parameters in anisometropia >1 D.MethodsThis study included 202 eyes of 101 subjects ranging from 10 to 40 years of age with anisometropia of 1 D or more. The subjects were divided into groups according to anisomyopia, anisoastigmatism, and anisohypermetropia. After providing informed consent, each patient underwent a detailed ophthalmological examination including cycloplegic refraction, best-corrected visual acuity, cover test, axial length (AL) measurement using A-scan ultrasound biometer, keratometry, anterior chamber depth, and central corneal thickness measurement. For each participant, the eye with greater refractive error was compared to the fellow eye via paired t-tests. Correlations between parameters were studied using the Pearson correlation coefficient.ResultsThe average age of subjects was 21.7 ± 9.3 years. Of 101 subjects, 31 had anisomyopia; 42 had anisohypermetropia; and 28 had anisoastigmatism. A predisposition toward greater myopia in right eyes was noted in anisomyopia (24 of 31 subjects, 77%). The inter-ocular acuity difference was significant in all three groups (p < 0.01). As the degree of anisometropia increased, there was significant positive correlation in the difference in AL in myopes (r = 0.863, p < 0.01) and hypermetropes (r = 0.669, p < 0.01) and the difference in corneal curvature in anisoastigmatism (r = 0.564, p = 0.002) and hypermetropes (r = 0.376, p = 0.014). A significant positive correlation was also present between the anterior chamber depth difference and refractive difference in hypermetropes (r = 0.359, p = 0.020).ConclusionsThis study showed that anisomyopia is correlated only with anterior chamber differences. Anisohypermetropia is correlated with AL differences as well as corneal curvature difference and anterior chamber depth difference. The amount of anisoastigmatism correlates only with corneal curvature difference.

Anisometropic amblyopia: Axial length versus corneal curvature in children with severe refractive imbalance

To define the ocular parameters associated with anisometropic ambylopia in children with severe hyperopia, myopia, or astigmatism in 1 eye. Anisometropic and fellow eyes of 13 children, ages 7-8, with anisometropia >3.0 D and amblyopia without strabismus or other visually significant ocular pathology were studied. Axial length, corneal curvature, anterior chamber depth, and corneal diameter measurements of amblyopic and fellow eyes were obtained using the IOL Master (Carl Zeiss Meditec, Dublin, CA). Comparing amblyopic eyes with unaffected fellow eyes as reference, patients with anisohyperopia had shorter axial lengths by an average of 1.49 mm (p = 0.001), and patients with anisomyopia had longer axial lengths by an average of 2.26 mm. Corneal astigmatism was the source of amblyogenic refractive error in 1 child. In children with anisometropic amblyopia, interocular differences in spherical refractive error was attributed to axial length with no differences in corneal curvature, whereas theanisoastigmatism observed in 1 case was attributed to asymmetric corneal curvature.

Objective Screening Methods for Prior Refractive Surgery in Donor Tissue

Laser refractive surgery presents a growing contamination of the available corneal donor pool. There currently is no objective method for screening donor tissue for previous refractive surgery. We evaluated the usefulness of pachymetry and curvature maps in the screening of donor corneas. Pachymetry and curvature maps were generated from the Orbscan for 40 normal donor eyes. The average central pachymetry measurement was subtracted from the thinnest average midperipheral pachymetry measurement for each map to generate a normal range of pachymetry measurements. For curvature, the average curvature at the 3-mm zone was subtracted from the average curvature at the 7-mm zone to generate a normal range of corneal curvature. The pachymetry and curvature results from 10 donor eyes that had undergone refractive surgery were then compared with the normal range for each technique. The average difference in pachymetry measurements between the midperipheral and central cornea for normal eyes was 0.040 +/- 0.026 mm. Four of 10 corneas that had undergone refractive surgery were outside two standard deviations of this normal range. The average difference in corneal curvature between the 7-mm zone and the 3-mm zone for the healthy eyes was -0.2 +/- 1.0 diopters. Four (40%) of 10 corneas that had undergone refractive surgery were identified with this method. When combined, the pachymetry and curvature methods detected seven (70%) of 10 corneas that had undergone refractive surgery. Regional differences in thickness and curvature in donor eyes may provide methods for screening for refractive surgery for myopia. Refinement in mathematical manipulations may further improve the sensitivity of these techniques.

Experimental implantation of posterior chamber prototype intraocular lenses for the feline eye

Abstract Objective To measure postoperative anterior chamber depth (ACD), corneal curvature, and refractive state of feline eyes after lens removal and implantation of a prosthetic intraocular lens (IOL) and determine appropriate IOL use in cats. Animals 8 clinically normal adult cats. Procedure A-scan ultrasonic biometry, keratometry, and streak retinoscopy were performed on both eyes of each cat before and after lens removal and implantation of a prosthetic IOL. Three diopter (D) IOL strengths were used: 48, 51, and 60 D. Measurements were recorded for 12 weeks after surgery. Results IOL were well tolerated by cats, with no serious complications attributable to implantation or presence of the IOL. The ACD was significantly greater after (8.30 mm) than before (4.97 mm) surgery; however, it became slightly more shallow during the 4 weeks after surgery, suggesting that the IOL shifted anteriorly in the eye. Significant difference in corneal curvature was not detected before or after surgery among eyes with various IOL. Twelve weeks after surgery, eyes with 48-, 51-, and 60-D IOL had mean ± SD refractive state of +2.1 ± 0.49, +0.42 ± 0.20, and -2.6 ± 0.78 D, respectively. Linear regression analysis of refractive state on IOL power for all eyes at 12 weeks after surgery predicted that +52.8-D IOL was necessary to best approximate emmetropia in these cats. Conclusion and Clinical Relevance IOL of substantially higher diopter strength than that needed in dogs was required to achieve emmetropia after lens extraction in cats. A 52- to 53-D IOL is required to correct feline eyes to near emmetropia after lens removal. (Am J Vet Res 1998;59:1339–1343)

The susceptible period for deprivation-induced myopia in tree shrew.

To examine the susceptible period for deprivation-induced myopia, six groups of tree shrew pups (Tupaia glis belangeri) were monocularly deprived for 12 days with an opaque occluder starting 7, 15, 21, 33, 48, or 63 days after natural eyelid opening. Compared to the untreated fellow control eye, significant myopia and vitreous chamber elongation were produced by the deprivation in all six groups. The effect was greater in the middle three groups in comparison with the youngest and the two oldest groups and the amount of induced myopia and axial elongation was not proportional to the normal rate of axial growth. The peak period of susceptibility was between approximately 15 and 45 days after eye opening during the juvenile, slow-elongation phase of ocular development when the eye is within 7% of its adult axial length. Significant myopia and axial elongation were also induced in adult animals by 70 days of monocular deprivation. To examine recovery from deprivation-induced myopia, the occluder was removed at the end of the 12 day deprivation period. After an additional 48 days of binocular visual experience, no significant myopia was present in the previously deprived eyes in any experimental group. During the recovery period, the elongation rate of the previously deprived eyes was reduced in comparison with the control eyes while normal corneal flattening and lens development continued, thus reducing the myopia. No difference in corneal curvature, relative to the untreated control eyes, was found after deprivation or after the recovery period. Data are presented which suggests that changes in the thickness of the choroid may occur in this mammal during deprivation and recovery that are in the same direction, but of smaller magnitude, than those reported in the chicken. The results of this study provide evidence that visually guided emmetropization occurs in this mammalian species during a period of ocular development analogous to the juvenile period in humans.

Measurements of axial length and radius of corneal curvature in the rabbit eye.

The axial length of the eye, the radius of the anterior corneal surface, and the diameter of the cornea were measured on 40 eyes of 20 New Zealand White rabbits. The ultrasonographic measurements of the axial length of the eye showed a mean value of 15.12 +/- 0.51 mm (15.33 +/- 0.50 mm in males, 14.96 +/- 0.46 mm in females). The mean corneal radius was 7.26 +/- 0.26 mm (7.18 +/- 0.9 mm in males, 7.32 +/- 0.33 mm in females); the mean value of the difference in corneal curvature between two principle meridians was 0.21 +/- 0.12 mm; and the mean horizontal and vertical diameters of the cornea were 13.41 +/- 0.34 mm and 13.02 +/- 0.30 mm, respectively. Although the diameter of the cornea of rabbits was bigger than that of humans (average, horizontal 11.75 mm, vertical 10.55 mm), the axial length of the eye was 0.7 times that of humans (23-24 mm), and the radius of corneal curvature was relatively smaller than that in humans (7.7-7.8 mm).

Steady-state accommodation and ocular biometry in late-onset myopia

The steady-state accommodative responses of emmetropes and late-onset myopes was measured for an array of numbers located at -1, -3 and -5 dioptres using an objective infra-red optometer. Responses were compared for passive (reading numbers) and active (adding numbers) conditions. For the passive condition, the late-onset myopes showed a significantly lower accommodative response than the emmetropic group. No significant differences were found between the two groups for the active condition. Ocular biometric characteristics were also measured in emmetropes, late-onset myopes and early-onset myopes using keratometry and ultrasonography. No significant differences in corneal curvature, anterior chamber depth and crystalline lens thickness were found between the groups. Late-onset myopes exhibited significantly deeper vitreous chambers than emmetropes, which more than accounted for the difference in refractive error between the two refractive groups. We conclude that, while significant differences exist in the accommodative responses of late-onset myopes and emmetropes, late-onset myopia is due predominantly to elongation of the vitreous chamber.

The coefficient of scleral rigidity in normal and glaucomatous eyes.

Within recent years the early diagnosis of glaucoma has made considerable strides even though the management and social consequences of this disease remain as always a challenge to ophthalmology. The tonometer remains one of the most important tools in the early diagnosis of glaucoma, both as a means of measuring the intraocular pressure, as well as a means of carrying out tonography. In conjunction with scotometry, it gives the best indication of the success of medical control of conservative therapy. It has been realized for some considerable time1that all forms of impression tonometry with the Schiotz, McLean, or Gradle tonometers are far from reliable guides of the intraocular pressure, even when accurately standardized, because the indentation is influenced by variations in the scleral rigidity of normal human eyes and to a lesser degree by differences in corneal curvature. It has also been appreciated that tonography is influenced by