Short-term changes in ocular biometry and refraction after discontinuation of long-term orthokeratology

OBJECTIVE: To assess refractive and biometric changes 1 week after discontinuation of lens wear in subjects who had been wearing orthokeratology (OK) contact lenses for 2 years. METHODS: Twenty-nine subjects aged 6 to 12 years and with myopia of -0.75 to -4.00 diopters (D) and astigmatism of ≤1.00 D participated in the study. Measurements of axial length and anterior chamber depth (Zeiss IOLMaster), corneal power and shape, and cycloplegic refraction were taken 1 week after discontinuation and compared with those at baseline and after 24 months of lens wear. RESULTS: A hyperopic shift was found at 24 months relative to baseline in spherical equivalent refractive error (+1.86±1.01 D), followed by a myopic shift at 1 week relative to 24 months (-1.93±0.92 D) (both P<0.001). Longer axial lengths were found at 24 months and 1 week in comparison to baseline (0.47±0.18 and 0.51±0.18 mm, respectively) (both P<0.001). The increase in axial length at 1 week relative to 24 months was statistically significant (0.04±0.06 mm; P=0.006). Anterior chamber depth did not change significantly over time (P=0.31). Significant differences were found between 24 months and 1 week relative to baseline and between 1-week and 24-month visits in mean corneal power (-1.68±0.80, -0.44±0.32, and 1.23±0.70 D, respectively) (all P≤0.001). Refractive change at 1 week in comparison to 24 months strongly correlated with changes in corneal power (r=-0.88; P<0.001) but not with axial length changes (r=-0.09; P=0.66). Corneal shape changed significantly between the baseline and 1-week visits (0.15±0.10 D; P<0.001). Corneal shape changed from a prolate to a more oblate corneal shape at the 24-month and 1-week visits in comparison to baseline (both P≤0.02) but did not change significantly between 24 months and 1 week (P=0.06). CONCLUSIONS: The effects of long-term OK on ocular biometry and refraction are still present after 1-week discontinuation of lens wear. Refractive change after discontinuation of long-term OK is primarily attributed to the recovery of corneal shape and not to an increase in the axial length.

A comparison of the effects of ocular preservatives on mammalian and microbial ATP and glutathione levels

The aim of this study was to investigate the mechanism of action of the preservative sodium chlorite (NaClO2), and the relationship with intracellular glutathione depletion. A detailed comparison of the dose responses of two cultured ocular epithelial cell types and four species of microorganism was carried out, and comparisons were also made with the quaternary ammonium compound benzalkonium chloride (BAK), and the oxidant hydrogen peroxide (H2O2). The viability of mammalian and microbial cells was assessed in the same way, by the measurement of intracellular ATP using a bioluminescence method. Intracellular total glutathione was measured by reaction with 5,5'-dithiobis-2-nitrobenzoic acid in a glutathione reductase-dependent recycling assay. BAK and H2O2 caused complete toxicity to conjunctival and corneal epithelial cells at similar to25 ppm, in contrast to NaClO2 , where >100 ppm was required. The fungi Candida albicans and Alternaria alternata had a higher resistance to NaClO2 than the bacteria Staphyloccus aureus and Pseudomonas aeruginosa , but the bacteria were extremely resistant to H2O2 NaClO2 caused substantial depletion of intracellular glutathione in all cell types, at concentrations ranging from <10 ppm in Pseudomonas , 25-100 ppm in epithelial cells, to >500 ppm in fungal cells. The mechanisms of cytotoxicity of NaClO2 , H2O2 and BAK all appeared to differ. NaClO2 was found to have the best balance of high antibacterial toxicity with low ocular toxicity. The lower toxicity of NaClO2 to the ocular cells, compared with BAK and H2O2 , is in agreement with fewer reported adverse effects of application in the eye.

Adverse events and discontinuations during 18 months of silicone hydrogel contact lens wear

PURPOSE. To report differences in the incidence of adverse events and discontinuations found in a group of neophyte contact wearers using two different silicone hydrogel contact lenses on a daily- and continuous-wear basis during an 18-month period. METHODS. Sixty-one subjects were initially examined, and 53 were eligible to participate in the study. Eligible subjects were randomly assigned to wear one of two silicone hydrogel materials: lotrafilcon A or balafilcon A lenses on a daily- or continuous-wear basis. After an initial screening, subjects were monitored weekly for the first month and then after 3, 6, 12, and 18 months. The incidence of adverse events, including corneal infiltrative events, superior epithelial arcuate lesions, and contact lens-induced papillary conjunctivitis, and discontinuations in each of the four contact lens groups were recorded. RESULTS. Twenty-two adverse events were found. A higher incidence of adverse events was found in subjects wearing lotrafilcon A lenses than in those wearing balafilcon A lenses (χ = 4.40, P=0.04). There were fewer adverse events in subjects wearing lenses on a daily-wear basis than in those wearing lenses on a continuous-wear basis (χ = 5.98, P=0.01). Eight subjects discontinued from the study as a result of recurrent corneal infiltrative events (one), vision problems (two), excessive ocular discomfort (one), relocation (one), noncompliance with the study protocol (one), and being lost to follow-up (two). No significant differences were found in the number of discontinuations between the two lens types (χ = 0.66, P=0.42) and wearing regimens (χ = 0.08, P=0.78). CONCLUSIONS. Lotrafilcon A lenses were associated with a higher incidence of adverse events than balafilcon A lenses were, and this difference is attributed to the difference in the incidence of corneal infiltrative events. Subjects wearing lenses on a daily-wear basis had fewer adverse events than did subjects wearing lenses on a continuous-wear basis. Both lens types and wearing regimens showed a similar incidence of discontinuations. © 2007 Lippincott Williams & Wilkins, Inc.

The relation between physical properties of the anterior eye and ocular surface temperature

PURPOSE. To examine the relation between ocular surface temperature (OST) assessed by dynamic thermal imaging and physical parameters of the anterior eye in normal subjects. METHODS. Dynamic ocular thermography (ThermoTracer 7102MX) was used to record body temperature and continuous ocular surface temperature for 8 s after a blink in the right eyes of 25 subjects. Corneal thickness, corneal curvature, and anterior chamber depth (ACD) were assessed using Orbscan II; noninvasive tear break-up time (NIBUT) was assessed using the tearscope; slit lamp photography was used to record tear meniscus height (TMH) and objective bulbar redness. RESULTS. Initial OST after a blink was significantly correlated only with body temperature (r = 0.80, p < 0.0005), NIBUT (r = -0.68, p < 0.005) and corneal curvature (r = -0.40, p = 0.05). A regression model containing all the variables accounted for 70% (p = 0.002) of the variance in OST, of which NIBUT (29%, p = 0.004), and body temperature (18%, p = 0.005) contributed significantly. CONCLUSIONS. The results support previous theoretical models that OST radiation is principally related to the tear film; and demonstrate that it is less related to other characteristics such as corneal thickness, corneal curvature, and anterior chamber depth. © 2007 American Academy of Optometry.

Anterior ophthalmic imaging

Improvements in imaging chips and computer processing power have brought major advances in imaging of the anterior eye. Digitally captured images can be visualised immediately and can be stored and retrieved easily. Anterior ocular imaging techniques using slitlamp biomicroscopy, corneal topography, confocal microscopy, optical coherence tomography (OCT), ultrasonic biomicroscopy, computerised tomography (CT) and magnetic resonance imaging (MRI) are reviewed. Conventional photographic imaging can be used to quantify corneal topography, corneal thickness and transparency, anterior chamber depth and lateral angle and crystalline lens position, curvature, thickness and transparency. Additionally, the effects of tumours, foreign bodies and trauma can be localised, the corneal layers can be examined and the tear film thickness assessed. © 2006 The Authors.

Changes in ocular physiology, tear film characteristics, and symptomatology with 18 months silicone hydrogel contact lens wear

Purpose. The purpose of this study was to evaluate the longitudinal changes in ocular physiology, tear film characteristics, and symptomatology experienced by neophyte silicone hydrogel (SiH) contact lens wearers in a daily-wear compared with a continuous-wear modality and with the different commercially available lenses over an 18-month period. Methods. Forty-five neophyte subjects were enrolled in the study and randomly assigned to wear one of two SiH materials: lotrafilcon A or balafilcon A lenses on either a daily- (LDW; BDW) or continuous-wear (LCW; BCW) basis. Additionally, a group of noncontact lens-wearing subjects (control group) was also recruited and followed over the same study period. Objective and subjective grading of ocular physiology were carried out together with tear meniscus height (TMH) and noninvasive tear breakup time (NITBUT). Subjects also subjectively rated symptoms and judgments with lens wear. After initial screening, subsequent measurements were taken after 1, 3, 6, 12, and 18 months. Results. Subjective and objective grading of ocular physiology revealed a small increase in bulbar, limbal, and palpebral hyperemia as well as corneal staining over time with both lens materials and regimes of wear (p < 0.05). No significant changes in NITBUT or TMH were found (p > 0.05). Subjective symptoms and judgment were not material- or modality-specific. Conclusions. Daily and continuous wear of SiH contact lenses induced small but statistically significant changes in ocular physiology and symptomatology. Clinical measures of tear film characteristics were unaffected by lens wear. Both materials and regimes of wear showed similar clinical performance. Long-term SiH contact lens wear is shown to be a successful option for patients. Copyright © 2006 American Academy of Optometry.

Randomised masked clinical trial of the MGDRx eyebag for the treatment of meibomian gland dysfunction-related evaporative dry eye

Background/aims To investigate the efficacy and safety of the MGDRx EyeBag (The Eyebag Company, Halifax, UK) eyelid warming device. Methods Twenty-five patients with confirmed meibomian gland dysfunction (MGD)-related evaporative dry eye were enrolled into a randomised, single masked, contralateral clinical trial. Test eyes received a heated device; control eyes a non-heated device for 5 min twice a day for 2 weeks. Efficacy (ocular symptomology, noninvasive break-up time, lipid layer thickness, osmolarity, meibomian gland dropout and function) and safety (visual acuity, corneal topography, conjunctival hyperaemia and staining) measurements were taken at baseline and follow-up. Subsequent patient device usage and ocular comfort was ascertained at 6 months. Results Differences between test and control eyes at baseline were not statistically signi ficant for all measurements ( p>0.05). After 2 weeks, statistically significant improvements occurred in all efficacy measurements in test eyes ( p<0.05). Visual acuity and corneal topography were unaffected (p>0.05). All patients maintained higher ocular comfort after 6 months ( p<0.05), although the bene fit was greater in those who continued usage 1-8 times a month (p<0.001). Conclusions The MGDRx EyeBag is a safe and effective device for the treatment of MGD-related evaporative dry eye. Subjective benefit lasts at least 6 months, aided by occasional retreatment. Trial registration number NCT01870180.

Ocular surface temperature:a review

Purpose. To review the evolution in ocular temperature measurement during the last century and examine the advantages and applications of the latest noncontact techniques. The characteristics and source of ocular surface temperature are also discussed. Methods. The literature was reviewed with regard to progress in human thermometry techniques, the parallel development in ocular temperature measurement, the current use of infrared imaging, and the applications of ocular thermography. Results. It is widely acknowledged that the ability to measure ocular temperature accurately will increase the understanding of ocular physiology. There is a characteristic thermal profile across the anterior eye, in which the central area appears coolest. Ocular surface temperature is affected by many factors, including inflammation. In thermometry of the human eye, contact techniques have largely been superseded by infrared imaging, providing a noninvasive and potentially more accurate method of temperature measurement. Ocular thermography requires high resolution and frame rate: features found in the latest generation of cameras. Applications have included dry eye, contact lens wear, corneal sensitivity, and refractive surgery. Conclusions. Interest in the temperature of the eye spans almost 130 years. It has been an area of research largely driven by prevailing technology. Current instrumentation offers the potential to measure ocular surface temperature with more accuracy, resolution, and speed than previously possible. The use of dynamic ocular thermography offers great opportunities for monitoring the temperature of the anterior eye. © 2005 Contact Lens Association of Ophthalmologists, Inc.

Refractive and biometric changes with silicone hydrogel contact lenses

Purpose. This study reports data from an 18-month longitudinal study of neophyte contact lens wearers and compares changes in ocular refraction and biometry induced by daily wear and continuous wear of two different silicone hydrogel (SiH) materials. Methods. Forty-five subjects were enrolled in the study and randomly assigned to wear one of the two silicone hydrogel materials: Lotrafilcon A or Balafilcon A lenses on either a daily or continuous wear basis. Measurements of objective refraction, axial length, anterior chamber depth, corneal curvature, and the rate of peripheral corneal flattening were performed before and 1, 3, 6, 12, and 18 months after initial fitting. Results. Mean spherical equivalent refractive error increased in the myopic direction in all contact lens groups across time (p < 0.001). Axial length was the main biometric contributor to the development of myopia. After 18 months of lens wear, subjects in the Lotrafilcon A group showed the greater mean increase in myopia (i.e., -0.50 D). Conclusions. The results of this study show that increases in myopia, similar if not higher than those found to occur normally in young adult noncontact lens wearers, still occur with silicone hydrogel contact lens wear. The main biometric contributor to the progression of myopia was an increase in axial length. Differences between our results and those of previous studies with silicone hydrogel contact lenses could be attributed to the differing populations used in which both age and occupation may have played a role. Copyright © 2005 American Academy of Optometry.

The effect of digital image resolution and compression on anterior eye imaging

Aim: To determine the theoretical and clinical minimum image pixel resolution and maximum compression appropriate for anterior eye image storage. Methods: Clinical images of the bulbar conjunctiva, palpebral conjunctiva, and corneal staining were taken at the maximum resolution of Nikon:CoolPix990 (2048 × 1360 pixels), DVC:1312C (1280 × 811), and JAI:CV-S3200 (767 × 569) single chip cameras and the JVC:KYF58 (767 × 569) three chip camera. The images were stored in TIFF format and further copies created with reduced resolution or compressed. The images were then ranked for clarity on a 15 inch monitor (resolution 1280 × 1024) by 20 optometrists and analysed by objective image analysis grading. Theoretical calculation of the resolution necessary to detect the smallest objects of clinical interest was also conducted. Results: Theoretical calculation suggested that the minimum resolution should be ≥579 horizontal pixels at 25 × magnification. Image quality was perceived subjectively as being reduced when the pixel resolution was lower than 767 × 569 (p<0.005) or the image was compressed as a BMP or <50% quality JPEG (p<0.005). Objective image analysis techniques were less susceptible to changes in image quality, particularly when using colour extraction techniques. Conclusion: It is appropriate to store anterior eye images at between 1280 × 811 and 767 × 569 pixel resolution and at up to 1:70 JPEG compression.

Incremental nature of anterior eye grading scales determined by objective image analysis

Aim: To use previously validated image analysis techniques to determine the incremental nature of printed subjective anterior eye grading scales. Methods: A purpose designed computer program was written to detect edges using a 3 × 3 kernal and to extract colour planes in the selected area of an image. Annunziato and Efron pictorial, and CCLRU and Vistakon-Synoptik photographic grades of bulbar hyperaemia, palpebral hyperaemia roughness, and corneal staining were analysed. Results: The increments of the grading scales were best described by a quadratic rather than a linear function. Edge detection and colour extraction image analysis for bulbar hyperaemia (r2 = 0.35-0.99), palpebral hyperaemia (r2 = 0.71-0.99), palpebral roughness (r2 = 0.30-0.94), and corneal staining (r2 = 0.57-0.99) correlated well with scale grades, although the increments varied in magnitude and direction between different scales. Repeated image analysis measures had a 95% confidence interval of between 0.02 (colour extraction) and 0.10 (edge detection) scale units (on a 0-4 scale). Conclusion: The printed grading scales were more sensitive for grading features of low severity, but grades were not comparable between grading scales. Palpebral hyperaemia and staining grading is complicated by the variable presentations possible. Image analysis techniques are 6-35 times more repeatable than subjective grading, with a sensitivity of 1.2-2.8% of the scale.

Use of imaging technology to better understand soft contact lens fit dynamics

The principal theme of this thesis is the identification of additional factors affecting, and consequently to better allow, the prediction of soft contact lens fit. Various models have been put forward in an attempt to predict the parameters that influence soft contact lens fit dynamics; however, the factors that influence variation in soft lens fit are still not fully understood. The investigations in this body of work involved the use of a variety of different imaging techniques to both quantify the anterior ocular topography and assess lens fit. The use of Anterior-Segment Optical Coherence Tomography (AS-OCT) allowed for a more complete characterisation of the cornea and corneoscleral profile (CSP) than either conventional keratometry or videokeratoscopy alone, and for the collection of normative data relating to the CSP for a substantial sample size. The scleral face was identified as being rotationally asymmetric, the mean corneoscleral junction (CSJ) angle being sharpest nasally and becoming progressively flatter at the temporal, inferior and superior limbal junctions. Additionally, 77% of all CSJ angles were within ±50 of 1800, demonstrating an almost tangential extension of the cornea to form the paralimbal sclera. Use of AS-OCT allowed for a more robust determination of corneal diameter than that of white-to-white (WTW) measurement, which is highly variable and dependent on changes in peripheral corneal transparency. Significant differences in ocular topography were found between different ethnicities and sexes, most notably for corneal diameter and corneal sagittal height variables. Lens tightness was found to be significantly correlated with the difference between horizontal CSJ angles (r =+0.40, P =0.0086). Modelling of the CSP data gained allowed for prediction of up to 24% of the variance in contact lens fit; however, it was likely that stronger associations and an increase in the modelled prediction of variance in fit may have occurred had an objective method of lens fit assessment have been made. A subsequent investigation to determine the validity and repeatability of objective contact lens fit assessment using digital video capture showed no significant benefit over subjective evaluation. The technique, however, was employed in the ensuing investigation to show significant changes in lens fit between 8 hours (the longest duration of wear previously examined) and 16 hours, demonstrating that wearing time is an additional factor driving lens fit dynamics. The modelling of data from enhanced videokeratoscopy composite maps alone allowed for up to 77% of the variance in soft contact lens fit, and up to almost 90% to be predicted when used in conjunction with OCT. The investigations provided further insight into the ocular topography and factors affecting soft contact lens fit.

Clinical monitoring of ocular physiology using digital image analysis

Aim: To examine the use of image analysis to quantify changes in ocular physiology. Method: A purpose designed computer program was written to objectively quantify bulbar hyperaemia, tarsal redness, corneal staining and tarsal staining. Thresholding, colour extraction and edge detection paradigms were investigated. The repeatability (stability) of each technique to changes in image luminance was assessed. A clinical pictorial grading scale was analysed to examine the repeatability and validity of the chosen image analysis technique. Results: Edge detection using a 3 × 3 kernel was found to be the most stable to changes in image luminance (2.6% over a +60 to -90% luminance range) and correlated well with the CCLRU scale images of bulbar hyperaemia (r = 0.96), corneal staining (r = 0.85) and the staining of palpebral roughness (r = 0.96). Extraction of the red colour plane demonstrated the best correlation-sensitivity combination for palpebral hyperaemia (r = 0.96). Repeatability variability was <0.5%. Conclusions: Digital imaging, in conjunction with computerised image analysis, allows objective, clinically valid and repeatable quantification of ocular features. It offers the possibility of improved diagnosis and monitoring of changes in ocular physiology in clinical practice. © 2003 British Contact Lens Association. Published by Elsevier Science Ltd. All rights reserved.

Refractive errors associated with tilted optic discs:a prospective study

Purpose: Tilted disc syndrome has been described to be associated with obliquely directed long axis of the disc, oblique direction of vessels, retinal pigment epithelial conus, hypoplasia of retina, visual field defects and myopic astigmatism. This prospective study looks at corneal astigmatism in eyes with a tilted optic disc. Refractive errors in these eyes were also analyzed. Methods: Patients with tilted optic discs were identified prospectively by clinical evaluation (BI, VK). All the patients with obliquely directed long axis of the disc, oblique direction of vessels and retinal pigment epithelial conus were included in the study. Best corrected visual acuity, slit-lamp examination, optic disc measurements, keratometry and refraction were recorded. Results: Twenty four patients (41 eyes) were recruited for the study. Eighteen (75%) patients had bilateral tilted optic discs. Eighteen patients (75%) were females and six (25%) were males. The mean age was 62 years(range 9 – 86 years). 76% of the patients were myopic and 24% hypermetropic. The mean spherical equivalent was –7.49 dioptres (SD 1.7D, range +6D to -17D). The mean corneal astigmatism was 1.09D (SD 0.9D, range 0.25D to 3.80D). The 6 patients who had unilateral, untilted discs were used as a control group to compare their mean corneal astigmatism (1.32 D) with the rest. Student "t" test was performed. ("p" = 0.49). Conclusions: In our study, tilted disc syndrome was found to be largely bilateral and more commonly seen in females. Myopia was the commonest refractive error associated with this clinical condition. However, 24% of patients in this series were hypermetropic. No correlation between the tilting of the optic disc and significant corneal astigmatism was noted as previously reported.

A new non-contact optical device for ocular biometry

Background: A new commercially available device (IOLMaster, Zeiss Instruments) provides high resolution non-contact measurements of axial length (using partial coherent interferometry), anterior chamber depth, and corneal radius (using image analysis). The study evaluates the validity and repeatability of these measurements and compares the findings with those obtained from instrumentation currently used in clinical practice. Method: Measurements were taken on 52 subjects (104 eyes) aged 18-40 years with a range of mean spherical refractive error from +7.0 D to -9.50 D. IOLMaster measurements of anterior chamber depth and axial length were compared with A-scan applanation ultrasonography (Storz Omega) and those for corneal radius with a Javal-Schiötz keratometer (Topcon) and an EyeSys corneal videokeratoscope. Results: Axial length: the difference between IOLMaster and ultrasound measures was insignificant (0.02 (SD 0.32) mm, p = 0.47) with no bias across the range sampled (22.40-27.99 mm). Anterior chamber depth: significantly shorter depths than ultrasound were found with the IOLMaster (-0.06 (0.25) mm, p <0.02) with no bias across the range sampled (2.85-4.40 mm). Corneal radius: IOLMaster measurements matched more closely those of the keratometer than those of the videokeratoscope (mean difference -0.03 v -0.06 mm respectively), but were more variable (95% confidence 0.13 v 0.07 mm). The repeatability of all the above IOLMaster biometric measures was found to be of a high order with no significant bias across the measurement ranges sampled. Conclusions: The validity and repeatability of measurements provided by the IOLMaster will augment future studies in ocular biometry.