Accuracy of Goldmann, ocular response analyser, Pascal and TonoPen XL tonometry in keratoconic and normal eyes

Aim: The aim of this study was to evaluate the practicality and accuracy of tonometers used in routine clinical practice for established keratoconus (KC). Methods: This was a prospective study of 118 normal and 76 keratoconic eyes where intraocular pressure (IOP) was measured in random order using the Goldman applanation tonometer (GAT), Pascal dynamic contour tonometer (DCT), Reichert ocular response analyser (ORA) and TonoPen XL tonometer. Corneal hysteresis (CH) and corneal resistance factor (CRF), as calculated by the ORA, were recorded. Central corneal thickness (CCT) was measured using an ultrasound pachymeter. Results: The difference in IOP values between instruments was highly significant in both study groups (p<0.001). All other IOP measures were significantly higher than those for GAT, except for the Goldmann-correlated IOP (average of the two applanation pressure points) (IOPg) as measured by ORA in the control group and the CH-corrected IOP (corneal-compensated IOP value) (IOPcc) measures in the KC group. CCT, CH and CRF were significantly less in the KC group (p<0.001). Apart from the DCT, all techniques tended to measure IOP higher in eyes with thicker corneas. Conclusion: The DCT and the ORA are currently the most appropriate tonometers to use in KC for the measurement of IOPcc. Corneal factors such as CH and CRT may be of more importance than CCT in causing inaccuracies in applanation tonometry techniques.

Clinical outcomes after implantation of a new hydrophobic acrylic toric IOL during routine cataract surgery

PURPOSE: To assess the clinical outcomes after implantation of a new hydrophobic acrylic toric intraocular lens (IOL) to correct preexisting corneal astigmatism in patients having routine cataract surgery. SETTING: Four hospital eye clinics throughout Europe. DESIGN: Cohort study. METHODS: This study included eyes with at least 0.75 diopter (D) of preexisting corneal astigmatism having routine cataract surgery. Phacoemulsification was performed followed by insertion and alignment of a Tecnis toric IOL. Patients were examined 4 to 8 weeks postoperatively; uncorrected distance visual acuity (UDVA), corrected distance visual acuity, manifest refraction, and keratometry were measured. Individual patient satisfaction with uncorrected vision and the surgeon’s assessment of ease of handling and performance of the IOL were also documented. The cylinder axis of the toric IOL was determined by dilated slitlamp examination. RESULTS: The study enrolled 67 eyes of 60 patients. Four to 8 weeks postoperatively, the mean UDVA was 0.15 logMAR G 0.17 (SD) and the UDVA was 20/40 or better in 88% of eyes. The mean refractive cylinder decreased significantly postoperatively, from -1.91 +/- 1.07 D to -0.67 +/- 0.54 D. No significant change in keratometric cylinder was observed. The mean absolute IOL misalignment from the intended axis was 3.4 degrees (range 0 to 12 degrees). The good UDVA resulted in high levels of patient satisfaction. CONCLUSION: Implantation of the new toric IOL was an effective, safe, and predictable method to manage corneal astigmatism in patients having routine cataract surgery.

Tablet App halometer for the assessment of dysphotopsia

Purpose To assess the validity and repeatability of the Aston Halometer. Setting University clinic, United Kingdom. Design Prospective, repeated-measures experimental study. Methods The halometer comprises a bright light-emitting-diode (LED) glare source in the center of an iPad4. Letters subtending 0.21° (∼0.3 logMAR) were moved centrifugally from the LED in 0.05 degree steps in 8 orientations separated by 45 degrees for each of 4 contrast levels (1000, 500, 100, and 25 Weber contrast units [Cw]) in random order. Bangerter occlusion foils were inserted in front of the right eye to simulate monocular glare conditions in 20 subjects (mean age 27.7 ± 3.1 years). Subjects were positioned 2 meters from the screen in a dark room with the iPad controlled from an iPhone via Bluetooth operated by the researcher. The C-Quant straylight meter was also used with each of the foils to measure the level of straylight over the retina. Halometry and straylight repeatability was assessed at a second visit. Results Halo size increased with the different occlusion foils and target contrasts (F = 29.564, P <.001) as expected and in a pattern similar to straylight measures (F = 80.655, P <0.001). Lower contrast letters showed better sensitivity but larger glare-obscured areas, resulting in ceiling effects caused by the screen's field-of-view, with 500 Cw being the best compromise. Intraobserver and interobserver repeatability of the Aston Halometer was good (500Cw: 0.84 to 0.93 and 0.53 to 0.73) and similar to the straylight meter. Conclusion The halometer provides a sensitive, repeatable way of quantifying a patient-recognized form of disability glare in multiple orientations to add objectivity to subjectively reported discomfort glare.

Clinical evaluation of the Oculus Keratograph

AIM: To determine the validity and reliability of the measurement of corneal curvature and non-invasive tear break-up time (NITBUT) measures using the Oculus Keratograph. METHOD: One hundred eyes of 100 patients had their corneal curvature assessed with the Keratograph and the Nidek ARKT TonorefII. NITBUT was then measured objectively with the Keratograph with Tear Film Scan software and subjectively with the Keeler Tearscope. The Keratograph measurements of corneal curvature and NITBUT were repeated to test reliability. The ocular sensitivity disease index questionnaire was completed to quantify ocular comfort. RESULTS: The Keratograph consistently measured significantly flatter corneal curvatures than the ARKT (MSE difference: +1.83±0.44D), but was repeatable (p>0.05). Keratograph NITBUT measurements were significantly lower than observation using the Tearscope (by 12.35±7.45s; pp < 0.001) and decreased on subsequent measurement (by -1.64 ± 6.03s; p < 0.01). The Keratograph measures the first time the tears break up anywhere on the cornea with 63% of subjects having NI-TBUT's <5s and a further 22% having readings between 5 and 10s. The Tearscope results were found to correlate better with the patients symptoms (r = -0.32) compared to the Keratograph (r = -0.19). Conclusions: The Keratograph requires a calibration off-set to be comparable to other keratometry devices. Its current software detects very early tear film changes, recording significantly lower NITBUT values than conventional subjective assessment. Adjustments to instrumentation software have the potential to enhance the value of Keratograph objective measures in clinical practice.

Keratoconus:a review

Keratoconus is the most common primary ectasia. It usually occurs in the second decade of life and affects both genders and all ethnicities. The estimated prevalence in the general population is 54 per 100,000. Ocular signs and symptoms vary depending on disease severity. Early forms normally go unnoticed unless corneal topography is performed. Disease progression is manifested with a loss of visual acuity which cannot be compensated for with spectacles. Corneal thinning frequently precedes ectasia. In moderate and advance cases, a hemosiderin arc or circle line, known as Fleischer's ring, is frequently seen around the cone base. Vogt's striaes, which are fine vertical lines produced by Descemet's membrane compression, is another characteristic sign. Most patients eventually develop corneal scarring. Munson's sign, a V-shape deformation of the lower eyelid in downward position; Rizzuti's sign, a bright reflection from the nasal area of the limbus when light is directed to the limbus temporal area; and breakages in Descemet's membrane causing acute stromal oedema, known as hydrops, are observed in advanced stages. Classifications based on morphology, disease evolution, ocular signs and index-based systems of keratoconus have been proposed. Theories into the genetic, biomechanical and biochemical causes of keratoconus have been suggested. Management varies depending on disease severity. Incipient cases are managed with spectacles, mild to moderate cases with contact lenses and severe cases can be treated with keratoplasty. This article provides a review on the definition, epidemiology, clinical features, classification, histopathology, aetiology and pathogenesis, and management and treatment strategies for keratoconus.

Visual outcomes and subjective experience after bilateral implantation of a new diffractive trifocal intraocular lens

Purpose - To assess clinical outcomes and subjective experience after bilateral implantation of a diffractive trifocal intraocular lens (IOL). Setting - Midland Eye Institute, Solihull, United Kingdom. Design - Cohort study. Methods - Patients had bilateral implantation of Finevision trifocal IOLs. Uncorrected distance visual acuity, corrected distance visual acuity (CDVA), and manifest refraction were measured 2 months postoperatively. Defocus curves were assessed under photopic and mesopic conditions over a range of +1.50 to -4.00 diopters (D) in 0.50 D steps. Contrast sensitivity function was assessed under photopic conditions. Halometry was used to measure the angular size of monocular and binocular photopic scotomas arising from a glare source. Patient satisfaction with uncorrected near vision was assessed using the Near Activity Visual Questionnaire (NAVQ). Results - The mean monocular CDVA was 0.08 logMAR ± 0.08 (SD) and the mean binocular CDVA, 0.06 ± 0.08 logMAR. Defocus curve testing showed an extended range of clear vision from +1.00 to -2.50 D defocus, with a significant difference in acuity between photopic conditions and mesopic conditions at -1.50 D defocus only. Photopic contrast sensitivity was significantly better binocularly than monocularly at all spatial frequencies. Halometry showed a glare scotoma of a mean size similar to that in previous studies of multifocal and accommodating IOLs; there were no subjective complaints of dysphotopsia. The mean NAVQ Rasch score for satisfaction with near vision was 15.9 ± 10.7 logits. Conclusions - The trifocal IOL implanted binocularly produced good distance visual acuity and near and intermediate visual function. Patients were very satisfied with their uncorrected near vision.

Design and validity of a miniaturized open-field aberrometer

PURPOSE: To validate a new miniaturised, open-field wavefront device which has been developed with the capacity to be attached to an ophthalmic surgical microscope or slit-lamp. SETTING: Solihull Hospital and Aston University, Birmingham, UK DESIGN: Comparative non-interventional study. METHODS: The dynamic range of the Aston Aberrometer was assessed using a calibrated model eye. The validity of the Aston Aberrometer was compared to a conventional desk mounted Shack-Hartmann aberrometer (Topcon KR1W) by measuring the refractive error and higher order aberrations of 75 dilated eyes with both instruments in random order. The Aston Aberrometer measurements were repeated five times to assess intra-session repeatability. Data was converted to vector form for analysis. RESULTS: The Aston Aberrometer had a large dynamic range of at least +21.0 D to -25.0 D. It gave similar measurements to a conventional aberrometer for mean spherical equivalent (mean difference ± 95% confidence interval: 0.02 ± 0.49D; correlation: r=0.995, p<0.001), astigmatic components (J0: 0.02 ± 0.15D; r=0.977, p<0.001; J45: 0.03 ± 0.28; r=0.666, p<0.001) and higher order aberrations RMS (0.02 ± 0.20D; r=0.620, p<0.001). Intraclass correlation coefficient assessments of intra-sessional repeatability for the Aston Aberrometer were excellent (spherical equivalent =1.000, p<0.001; astigmatic components J0 =0.998, p<0.001, J45=0.980, p<0.01; higher order aberrations RMS =0.961, p<0.001). CONCLUSIONS: The Aston Aberrometer gives valid and repeatable measures of refractive error and higher order aberrations over a large range. As it is able to measure continuously, it can provide direct feedback to surgeons during intraocular lens implantations and corneal surgery as to the optical status of the visual system.

Optical imaging of retina in response to grating stimuli in cats

We examined the intrinsic signals in response to grating stimuli in order to determine whether the light-evoked intrinsic signals of the retina are due to changes in the photoreceptor activities induced by the image projected on to the retina or are due to neural activities of the inner retina. The retinas of the left eye of 12 cats under general anesthesia were examined by a functional imaging fundus camera. Near infrared light was used to monitor the reflectance changes (RCs) of the retina. Vertical grating were used to stimulate the retina at 4 Hz. The spatial frequencies of the gratings were 0.05, 0.11, 0.22, 0.43, 0.86, 1.73, and 3.46 cycles/degree (cpd). Ten images were averaged and used to analyze the RCs to obtain the peak value (PV) of a two dimensional fast Fourier transfer of the RCs. The wavefront aberrations (WA) were measured with a compact wavefront aberrometer and the spatial modulation transfer function (MTF) of the eye was calculated. The retinal reflectance image had a grating pattern. The PV of the spatial sensitivity curve was highest at low spatial frequencies (0.05 and 0.11 cpd), and the sensitivity decreased steeply with an increase in the spatial frequency. RCs were not detectable at 3.46 cpd. The MTF decreased gradually with increases in the spatial frequencies and was 0.68 at 3.46 cpd. The reflectance pattern of the retinal intrinsic signal elicited by grating stimuli of different spatial frequencies was different from that of the MTF. This suggests that the intrinsic signal represents not only the response of the photoreceptors but also other neuronal or vascular changes in the retina.

Consensus on recording of gas permeable contact lens fit

Purpose: To develop a new schematic scheme for efficiently recording the key parameters of gas permeable contact lens (GP) fits based on current consensus. Methods: Over 100 established GP fitters and educators met to discuss the parameters proposed in educational material for evaluating GP fit and concluded on the key parameters that should be recorded. The accuracy and variability of evaluating the fluorescein pattern of GP fit was determined by having 35 experienced contact lens practitioners from across the world, grading 5 images of a range of fits and the topographer simulation of the same fits, in random, order using the proposed scheme. The accuracy of the grading was compared to objective image analysis of the fluorescein intensity of the same images. Results: The key information to record to adequately describe the fit of an GP was agreed as: the manufacturer, brand and lens parameters; settling time; comfort on a 5 point scale; centration; movement on blink on a ±2 scale; and the Primary Fluorescein Pattern in the central, mid-peripheral and edge regions of the lens averaged along the horizontal and vertical lens axes, on a ±2 scale. On average 50-60% of practitioners selected the median grade when subjectively rating fluorescein intensity and this was correlated to objective quantification (r= 0.602, p< 0.001). Objective grading suggesting horizontal median fluorescein intensity was generally symmetrical, as was the vertical meridian, but this was not the case for subjective grading. Simulated fluorescein patterns were subjectively and objectively graded as being less intense than real photographs (p< 0.01). Conclusion: GP fit recording can be standardised and simplified to enhance GP practice. © 2013 British Contact Lens Association.

Predicting success with silicone-hydrogel contact lenses in new wearers

Purpose: to evaluate changes in tear metrics and ocular signs induced by six months of silicone-hydrogel contact lens wear and the difference in baseline characteristics between those who successfully continued in contact lens wear compared to those that did not. Methods: Non-invasive Keratograph, Tearscope and fluorescein tear break-up times (TBUTs), tear meniscus height, bulbar and limbal hyperaemia, lid-parallel conjunctival folds (LIPCOF), phenol red thread, fluorescein and lissamine-green staining, and lid wiper epitheliopathy were measured on 60 new contact lens wearers fitted with monthly silicone-hydrogels (average age 36 ± 14 years, 40 females). Symptoms were evaluated by the Ocular Surface Disease Index (OSDI). After six months full time contact lens wear the above metrics were re-measured on those patients still in contact lens wear (n= 33). The initial measurements were also compared between the group still wearing lenses after six months and those who had ceased lens wear (n= 27). Results: There were significant changes in tear meniscus height (p= 0.031), bulbar hyperaemia (p= 0.011), fluorescein TBUT (p= 0.027), corneal (p= 0.007) and conjunctival (p= 0.009) staining, LIPCOF (p= 0.011) and lid wiper epitheliopathy (p= 0.002) after six months of silicone-hydrogel wear. Successful wearers had a higher non-invasive (17.0 ± 8.2. s vs 12.0 ± 5.6. s; p= 0.001) and fluorescein (10.7 ± 6.4. s vs 7.5 ± 4.7. s; p= 0.001) TBUT than drop-outs, although OSDI (cut-off 4.2) was also a strong predictor of success. Conclusion: Silicone-hydrogel lenses induced significant changes in the tear film and ocular surface as well as lid margin staining. Wettability of the ocular surface is the main factor affecting contact lens drop-out. © 2013 British Contact Lens Association.

The relationship between measurement method and corneal structure on apparent intraocular pressure in glaucoma and ocular hypertension

Purpose: To analyse the relationship between measured intraocular pressure (IOP) and central corneal thickness (CCT), corneal hysteresis (CH) and corneal resistance factor (CRF) in ocular hypertension (OHT), primary open-angle (POAG) and normal tension glaucoma (NTG) eyes using multiple tonometry devices. Methods: Right eyes of patients diagnosed with OHT (n=47), normal tension glaucoma (n=17) and POAG (n=50) were assessed, IOP was measured in random order with four devices: Goldmann applanation tonometry (GAT); Pascal(R) dynamic contour tonometer (DCT); Reichert(R) ocular response analyser (ORA); and Tono-Pen(R) XL. CCT was then measured using a hand-held ultrasonic pachymeter. CH and CRF were derived from the air pressure to corneal reflectance relationship of the ORA data. Results: Compared to the GAT, the Tonopen and ORA Goldmann equivalent (IOPg) and corneal compensated (IOPcc) measured higher IOP readings (F=19.351, p<0.001), particularly in NTG (F=12.604, p<0.001). DCT was closest to Goldmann IOP and had the lowest variance. CCT was significantly different (F=8.305, p<0.001) between the 3 conditions as was CH (F=6.854, p=0.002) and CRF (F=19.653, p<0.001). IOPcc measures were not affected by CCT. The DCT was generally not affected by corneal biomechanical factors. Conclusion: This study suggests that as the true pressure of the eye cannot be determined non-invasively, measurements from any tonometer should be interpreted with care, particularly when alterations in the corneal tissue are suspected.

Functional and perceived benefits of wearing coloured filters by patients with age-related macular degeneration

Background: The aim was to investigate the visual effect of coloured filters compared to transmission-matched neutral density filters, in patients with dry age-related macular degeneration. Methods: Visual acuity (VA, logMAR), contrast sensitivity (Pelli-Robson) and colour vision (D15) were recorded for 39 patients (average age 79.1 ± 7.2 years) with age-related macular degeneration, both in the presence and absence of glare from a fluorescent source. Patients then chose their preferred coloured and matched neutral density transmission filters (NoIR). Visual function tests were repeated with the chosen filters, both in the presence and absence of glare from the fluorescent source. Patients trialled the two filters for two weeks each, in random order. Following the trial of each filter, a telephone questionnaire was completed. Results: VA and contrast sensitivity were unaffected by the coloured filters but reduced through the neutral density filters (p < 0.01). VA and contrast sensitivity were reduced by similar amounts, following the introduction of the glare source, both in the presence and absence of filters (p < 0.001). Colour vision error scores were increased following the introduction of a neutral density filter (from 177.6 ± 60.2 to 251.9 ± 115.2) and still further through coloured filters (275.1 ± 50.8; p < 0.001). In the absence of any filter, colour vision error scores increased by 29.1 ± 55.60 units in the presence of glare (F2,107 = 3.9, p = 0.02); however, there was little change in colour vision error scores, in the presence of glare, with either the neutral density or coloured filters. Questionnaires indicated that patients tended to gain more benefit from the coloured filters. Conclusions: Coloured filters had minimal impact on VA and contrast sensitivity in patients with age-related macular degeneration; however, they caused a small reduction in objective colour vision, although this was not registered subjectively by patients. Patients indicated that they received more benefit from the coloured filters compared with neutral density filters. © 2013 The Authors © 2013 Optometrists Association Australia.

The management of ocular allergy in community pharmacies in the United Kingdom

Background Ocular allergies frequently present in pharmacy practices. However, research into the actual management of ocular allergy in pharmacies is lacking. Objective To determine and quantify history and symptom questioning of a patient with presumed allergic conjunctivitis and management strategies employed by pharmacy staff in the UK. Method A mystery shopper technique was used to simulate an episode of allergic conjunctivitis in 100 community pharmacies across the UK. Results The mean number of questions asked by pharmacy staff to the patient was 3.5 ± 2.6, with a range of 0-10. The most common question was whether the patient had a history of allergies (45 %).Ninety-one percent advised on treatment, with the remaining 9 % directly referring to the patient's general practitioner (n = 4) or pharmacist(n = 4), but only two to their optometrist. The most common treatment suggested was sodium cromoglycate 2 % (50 %). However, many pharmacies advising treatment did not ask the patient's age (37 %), if they wore contact lenses (43 %), or gave dosage advice (43 %). Only 5 % of pharmacies advised follow up and 14 % suggested visiting a general practitioner and 1 % an optometrist if symptoms did not resolve with treatment. Conclusion There is a need for improved ophthalmological training for pharmacy staff with respect to the management of allergic conjunctivitis. © Springer Science+Business Media Dordrecht 2012.

Factors affecting corneoscleral topography

PURPOSE: To evaluate factors affecting corneoscleral profile (CSP) using Anterior Segment Optical Coherence Tomography (AS-OCT) in combination with conventional videokeratoscopy. METHODS: OCT data were collected from 204 subjects of mean age 34.9 years (SD: ±15.2 yrs, range 18 to 65) using the Zeiss Visante AS-OCT and Medmont M300 corneal topographer. Measurements of corneal diameter (CD), corneal sagittal height (CS), iris diameter (ID), corneoscleral junction angle (CSJ) and scleral radius (SR) were extracted from multiple OCT images. Horizontal visible iris diameter (HVID) and vertical palpebral aperture (PA) were measured using a slit lamp graticule. Subject body height was also measured. Associations were then sought between CSP variables and age, height, ethnicity, sex and refractive error data collected. Results: Significant correlations were found between age and ocular topography variables of HVID, PA, CSJ, SR and ID (P<0.0001), while height correlated with HVID, CD and ID, and power vector terms only with vertical plane keratometry, CD and CS. Significant differences were noted between ethnicities with respect to CD (P=0.0046), horizontal and vertical CS (P=0.0068 and P=0.0095), and also horizontal ID (P=0.0010), while the same variables, with the exception of vertical CS, also varied with sex; horizontal CD (P=0.0018), horizontal CS (P=0.0018) and ID (P=0.0012). Age accounted for up to 36% of the variance in CSP variables. Conclusion: Age is the main factor influencing corneoscleral topography; consequently, this should be taken into consideration in contact lens design, in the optimization of surgical procedures involving the cornea and sclera and in IOL selection.

Impact of soft contact lens edge design and mid-peripheral lens shape on the epithelium and its indentation with lens mobility

Purpose. To evaluate the influence of soft contact lens midperipheral shape profile and edge design on the apparent epithelial thickness and indentation of the ocular surface with lens movement. Methods. Four soft contact lens designs comprising of two different plano midperipheral shape profiles and two edge designs (chiseled and knife edge) of silicone-hydrogel material were examined in 26 subjects aged 24.7 ± 4.6 years, each worn bilaterally in randomized order. Lens movement was imaged enface on insertion, at 2 and 4 hours with a high-speed, high-resolution camera simultaneous to the cross-section of the edge of the contact lens interaction with the ocular surface captured using optical coherence tomography (OCT) nasally, temporally, and inferiorly. Optical imaging distortions were individually corrected for by imaging the apparent distortion of a glass slide surface by the removed lens. Results. Apparent epithelial thickness varied with edge position (P < 0.001). When distortion was corrected for, epithelial indentation decreased with time after insertion (P = 0.010), changed after a blink (P < 0.001), and varied with position on the lens edge (P < 0.001), with the latter being affected by midperipheral lens shape profile and edge design. Horizontal and vertical lens movement did not change with time postinsertion. Vertical motion was affected by midperipheral lens shape profile (P < 0.001) and edge design (P < 0.001). Lens movement was associated with physiologic epithelium thickness for lens midperipheral shape profile and edge designs. Conclusions. Dynamic OCT coupled with high-resolution video demonstrated that soft contact lens movement and image-corrected ocular surface indentation were influenced by both lens edge design and midperipheral lens shape profiles. © 2013 The Association for Research in Vision and Ophthalmology, Inc.