Comparison of topographic indices that correlate with visual acuity in videokeratography

Comparison of Corneal Irregularity After Recurrent and Primary Pterygium Surgery Using Fourier Harmonic Analysis

Purpose

To the best of our knowledge, few detailed investigation of astigmatism with recurrent pterygium currently exists. We aimed to evaluate corneal irregularity after recurrent pterygium surgery.

Methods

This observational study included consecutive patients who underwent recurrent pterygium surgery and were observed for >12 months postoperatively via corneal examination. Patients who underwent primary pterygium surgery during the same period served as controls. Pterygium size and corneal irregularity evaluated with Fourier harmonic analysis (spherical component, regular astigmatism, asymmetry component, and higher-order irregularity) were compared between groups preoperatively and at 1, 3, 6, and 12 months postoperatively.

Results

Overall, 203 eyes of 203 patients (age, 66.5 ± 9.5 years) were included, of which 44 eyes had recurrent pterygium and 159 had primary pterygium. Regular astigmatism in the recurrent pterygium group was higher than that in the primary pterygium group preoperatively and at 1 and 3 months postoperatively. The asymmetry component and higher-order irregularity in the recurrent pterygium group were higher than those in the primary pterygium group at all observation points.

Conclusions

Fourier harmonic analysis showed that larger corneal irregularity that could not be corrected with spectacles persisted for a long time after recurrent pterygium excision than after primary pterygium excision. Thus, recurrence prevention is critical for primary pterygium surgery.

Translational Relevance

We demonstrated that larger corneal irregularity that could not be corrected with spectacles remained long after excision of recurrent pterygium compared with excision of primary pterygium; thus, the prevention of recurrence is clinically important for primary pterygium surgery in terms of corneal irregularity.

Corneal Topography for Intraocular Lens Selection in Refractive Cataract Surgery

The purpose of this review is to evaluate the usefulness of corneal topography to select premium intraocular lenses (IOLs), including aspherical IOLs, toric IOLs, and multifocal IOLs, in refractive cataract surgery. Corneal topography can detect corneal regular astigmatism, corneal irregular astigmatism (higher-order aberrations [HOAs]) including spherical aberration, and corneal shape abnormalities after corneal refractive surgery. Surgeons can explain to the patients with significant corneal HOAs about its effect on postoperative visual function before surgery. Multifocal IOLs should not be selected for such eyes. For eyes with abnormal corneal shape, appropriate IOL power calculation formulae can be applied. In the case of toric IOLs, regular astigmatism and corneal HOAs should be checked. Before implanting an aspheric IOL, it is ideal to confirm spherical aberration of the cornea is not below the normal range. Because corneal HOAs, abnormal corneal shape after corneal refractive surgery, corneal regular astigmatism, and corneal spherical aberration increase postoperative refractive errors and poor vision quality with premium IOLs, corneal topography before cataract surgery is helpful in screening patients who are not appropriate candidates for premium IOLs.

Long-term changes and effect of pterygium size on corneal topographic irregularity after recurrent pterygium surgery

This retrospective observational study compared long-term topographic changes after recurrent- and primary-pterygium surgery depending on pterygium size. Patients who underwent recurrent-pterygium excision between 2002–2013 and age, sex, and pterygium size-matched controls who underwent primary-pterygium surgery were included (33 eyes of 33 patients in each group). Pterygium size was graded per advancing edge position: <1/3 of corneal diameter (grade 1), outside the pupil (grade 2), and within the pupillary area (grade 3). Surface asymmetry index (SAI), surface regularity index (SRI) in corneal topography, and uncorrected and best-spectacle-corrected visual acuity were compared before and 1, 3, 6, and 12 months postoperatively. Three, 17, and 13 eyes had grades 1, 2, and 3, respectively. In grade 2, the SAI and SRI were respectively significantly larger at all observation points (p = 0.01, 0.03, 0.02, 0.02, and 0.004) and before and 6 and 12 months postoperatively (p = 0.02, 0.04, and 0.03) in recurrent pterygium. In grade 3, the SAI was significantly larger before and 1, 3, and 12 months postoperatively (p = 0.04, 0.01, 0.01, and 0.02) and the SRI was significantly larger before and 12 months postoperatively (p < 0.001, 0.02) in recurrent pterygium. Corneal irregularity persisted 12 months after recurrent-pterygium surgery compared with that in same-size primary pterygium.

Impact of Dry Eye on Prolonged Reading

SIGNIFICANCE

Patients with dry eye frequently report difficulty with reading. However, the impact of dry eye on reading has not been studied in detail. This study shows the unfavorable effect of dry eye on reading speed and offers mechanisms that may be responsible.

PURPOSE

The purpose of this study was to evaluate the impact of dry eye signs as well as symptoms on both short-duration out-loud and prolonged silent reading.

METHODS

This study included 116 patients with clinically significant dry eye, 39 patients with dry eye symptoms only, and 31 controls, 50 years or older. After the Ocular Surface Disease Index (OSDI) questionnaire, objective testing of dry eye (tear film stability studies, Schirmer's test, and ocular surface staining) was performed. Total OSDI score and two subscores (vision related and discomfort related) were calculated. A short-duration out-loud reading test and a 30-minute sustained silent reading test were performed. Reading speed for each test was calculated as words per minute (wpm) and compared across the three groups.

RESULTS

Patients with clinically significant dry eye read slower than controls measured with sustained silent reading test (240 vs. 272 wpm, P = .04), but not with short-duration out-loud reading test (146 vs. 153 wpm, P = .47). Patients with dry eye symptoms only did not have slower reading speed measured using either reading test as compared with controls. However, vision-related OSDI subscore independently was associated with slower reading speed (P = .02). Multivariable regression models demonstrated that each 1-point (between 0 and 6) increase in corneal staining score led to a 10-wpm decrease in sustained silent reading speed (P = .01).

CONCLUSIONS

This study demonstrates a significant negative impact of dry eye (particularly presence of corneal staining) on prolonged reading. Prolonged reading task may serve as an objective clinically relevant test to measure the impact of dry eye on vision-related quality of life.

Detection of increase in corneal irregularity due to pterygium using Fourier series harmonic analyses with multiple diameters

PURPOSE

To determine steep increase of corneal irregularity induced by advancement of pterygium.

METHODS

A total of 456 eyes from 456 consecutive patients with primary pterygia were examined for corneal topography and advancement of pterygium with respect to the corneal diameter. Corneal irregularity induced by the pterygium advancement was evaluated by Fourier harmonic analyses of the topographic data that were modified for a series of analysis diameters from 1 mm to 6 mm. Incidences of steep increases in the asymmetry or higher-order irregularity components (inflection points) were determined by using segmented regression analysis for each analysis diameter.

RESULTS

The pterygium advancement ranged from 2% to 57%, with a mean of 22.0%. Both components showed steep increases from the inflection points. The inflection points in the higher-order irregularity component altered with the analysis diameter (14.0%-30.6%), while there was no alternation in the asymmetry components (35.5%-36.8%). For the former component, the values at the inflection points were obtained in a range of 0.16 to 0.25 D.

CONCLUSION

The Fourier harmonic analyses for a series of analysis diameters revealed that the higher-order irregularity component increased with the pterygium advancement. The analysis results confirmed the precedence of corneal irregularity due to pterygium advancement.

Proposal for a Novel Severity Grading System for Pterygia Based on Corneal Topographic Data

PURPOSE

To propose a grading system of pterygium severity based on corneal higher-order irregularity (HOI) and to evaluate postoperative changes in corneal irregularity of the graded pterygia.

METHODS

In 268 eyes of 226 patients undergoing excision surgery of primary nasal pterygium, Placido corneal topography images were taken before and until 6 months after surgery. The best-corrected visual acuity (BCVA) and pterygium size with respect to the corneal diameter were also measured. HOI components within 1.0-, 3.0-, and 5.0-mm diameters were obtained using Fourier harmonic analysis of corneal topography data. With threshold levels when the HOIs for 3 diameters steeply increased, 4 levels of grading from 0 (mild) to 3 (severe) were determined. Associations of the grades with the preoperative surface regularity index (SRI), irregular components (IRRs) obtained from the 3.0-mm diameter Fourier analysis, and BCVA were examined. Time-course changes in the indexes after surgery were evaluated for each grade.

RESULTS

There were 62, 65, 41, and 100 eyes in grades 0 to 3, respectively. Preoperatively, the SRI in grade 3 was significantly higher than in the other grades (P < 0.001), and the IRR and BCVA varied with the grade (P < 0.001). Between 1 and 6 months postoperatively, grade 3 pterygia showed significant changes in the SRI and IRR (P = 0.013 and 0.017, respectively), whereas there was no change after 3 months postoperatively in the SRI, IRR, and BCVA for all other grades.

CONCLUSIONS

The proposed grading effectively classified the severity of pterygia and evaluated postoperative restoration of corneal irregularity. Using corneal topographic data allowed for objective evaluation of pterygium severity.

Topographic changes after excision surgery of primary pterygia and the effect of pterygium size on topograpic restoration

OBJECTIVE

To assess the effect of pterygium size on time-course change of corneal topography after excision surgery of primary pterygium.

METHODS

Retrospective case series included eyes that underwent excisions of primary pterygium. Pterygium size was graded according to the advancing edge position: less than one third of corneal diameter (grade 1), outside the pupil (grade 2), and within the pupillary area (grade 3). Time-course changes in corneal refractive power, astigmatism, and irregularity (surface regularity and asymmetry indices) in corneal topographies over 12 months postoperatively were compared between the pterygium size grades.

RESULTS

Pterygium excision was performed on 562 eyes, consisting of 119, 338, and 105 eyes with grades 1 to 3, respectively. Grade 1 did not change in corneal irregularity, and there was no difference between grades 1 and 2, except for corneal astigmatism at 6 months. Grade 3 showed significantly higher corneal refractive power and irregularity than grade 1 until 3 and 6 months, respectively, whereas corneal astigmatism was higher over 12 months.

CONCLUSIONS

Topographic changes after primary pterygium excision were associated with pterygium size. Pterygium advancing over the pupillary area required 6 to 12 months for corneal topography restoration, resulting in slow recovery of visual acuity.

Characterization of corneal structure in keratoconus

The increasing volume of patients interested in refractive surgery and the new treatment options available for keratoconus have generated a higher interest in achieving a better characterization of this pathology. The ophthalmic devices for corneal analysis and diagnosis have experienced a rapid development during the past decade with the implementation of technologies such as the Placido-disk corneal topography and the introduction of others such as scanning-slit topography, Scheimpflug photography, and optical coherence tomography, which are able to accurately describe not only the geometry of the anterior corneal surface but also that of the posterior surface, as well as pachymetry and corneal volume. Specifically, anterior and posterior corneal elevation, corneal power, pachymetry maps, and corneal coma-like aberrometry data provide sufficient information for an accurate characterization of the cornea to avoid misleading diagnoses of patients and provide appropriate counseling of refractive surgery candidates.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Quantitative evaluation of night vision and correlation of refractive and topographical parameters with glare after orthokeratology

PURPOSE

To evaluate night vision disturbance and investigate correlations between pre- and post-treatment parameters and glare scores in orthokeratology patients.

METHODS

Twenty-eight right eyes of 28 patients were enrolled in this study. Corneal topography and a night vision test (NVT) to evaluate the extent of glare were performed after orthokeratology. From the corneal topography, two indices [surface regularity index (SRI) and surface asymmetry index (SAI)] were calculated. Fourier analysis was performed on the topographic data from the central 6 mm, and data were decomposed into asymmetric and higher order components for analysis.

RESULTS

There was no correlation between the glare score and pre-treatment keratometric value, pre-treatment cylinder, post-treatment sphere, and post-treatment cylinder. However, there was a statistically significant correlation between pre-treatment sphere and glare score (Pearson correlation coefficient, r = -0.54, p < 0.01). SRI and SAI significantly correlated with glare score (SRI: r = 0.52, p < 0.01, SAI: r = 0.41, p < 0.05). Higher order and asymmetric components were also significantly correlated with glare score (asymmetry: r = 0.61, p < 0.01, higher order: r = 0.67, p < 0.001).

CONCLUSIONS

The glare score was significantly correlated with corneal irregularity, and appeared to be a beneficial parameter for assessment of night vision performance in patients receiving orthokeratology.

Noninvasive assessment of tear stability with the tear stability analysis system in tear dysfunction patients

PURPOSE

To evaluate tear film stability in patients with tear dysfunction and an asymptomatic control group by using the novel, noninvasive Tear Stability Analysis System (TSAS).

METHODS

In this prospective case-control study, 45 patients with dysfunctional tear syndrome (DTS) were stratified into three groups (1, 2, and 3/4) based on clinical severity, with higher scores indicating more severe symptoms; 25 asymptomatic control subjects were evaluated. TSAS measurements were performed with the RT-7000 Auto Refractor-Keratometer (Tomey Corporation, Nagoya, Japan). Images of ring mires projected onto the cornea every second for 6 seconds were captured and analyzed. Focal changes in brightness were calculated as numerical ring breakup (RBU) values, and the elapsed time when the cumulative values (RBU sum) exceeded a threshold was defined as the ring breakup time (RBUT).

RESULTS

RBUTs in the DTS groups were all significantly lower than those in the control subjects, with the lowest values found in DTS 3/4. RBUT was significantly shorter in DTS 3/4 than in DTS 1 (P<0.001). The change in RBU sum over a 6-second period in the DTS groups combined or between the individual groups was statistically significant (P<0.001), as was the difference between the 1- and 6-second values. For distinguishing between asymptomatic controls and DTS, the sensitivity and specificity of a 5.0-second RBUT cutoff were 82.0% and 60.0%, respectively.

CONCLUSIONS

The TSAS may be a useful, noninvasive instrument for evaluating tear stability and for classifying DTS severity.

Effect of Warm Compress Therapy From Hard-Boiled Eggs on Corneal Shape

PURPOSE

Hard-boiled eggs can be used for warm compresses, but the pressing force may distort the corneal shape. This study investigated the effect of warm compress therapy on the corneal shape by using hard-boiled eggs as the heat source.

METHODS

Twenty-five young adult Chinese were recruited, and 1 eye was randomly selected to undergo the following treatment protocols in a random order: hot hard-boiled egg covered with wet cloth gently touching the eyelid; hot hard-boiled egg covered with wet cloth placed close to, but not touching, the eyelid; and cold egg covered with wet cloth gently touching the eyelid. Each treatment protocol lasted for 5 minutes. Eyelid temperature was measured using an infrared thermometer before and every 1 minute during the treatment. Corneal parameters, including SimK, best-fit sphere (BFS), surface asymmetry index (SAI), and surface regularity index (SRI), were measured by a corneal topographer before and after the treatment.

RESULTS

Treatment 1 gave a 3.5 degrees C skin temperature rise within 3 minutes. The skin temperature rise was around 2.5 degrees C in treatment 2. There was no skin temperature change in treatment 3. Both treatments 1 and 3 affected the SAI and SRI. There was no significant change on other corneal parameters from treatments.

CONCLUSION

Because it is difficult to standardize the pressing force, it is recommended to place the hard-boiled egg close to, but not touching, the eyelid during warm compress therapy. The temperature rise from this treatment protocol should be large enough to melt the meibomian gland secretions without distorting the corneal shape.

[Keratoconus: correlations between clinical aspects and Orbscan evaluations]

PURPOSE

To look for potential correlations between clinical and topographical aspects of keratoconus evaluated by Orbscan (Chauvin-Bausch & Lomb).

METHODS

We analyzed 228 keratoconic eyes in a retrospective study over a period of 16 months. The best corrected visual acuity (BCVA) and the corneal opacities were correlated with 26 topographical parameters evaluated by Orbscan.

RESULTS

The maximal keratometry is the parameter that correlated best with clinical aspects. The other well-correlated keratometric parameters were the SimKmax and the Mean Power in the 3-mm zone. The distance between the central point and the point with maximal keratometry is the best localization parameter. The maximal amplitude of elevation on the anterior elevation map and the value of the minimal pachymetry also correlate well with the BCVA. The results were nevertheless quite scattered, but could be explained by bias, which will be corrected in further prospective studies.

CONCLUSION

Orbscan provides useful information to assess the topography of keratoconus. Some parameters correlate well with clinical aspects, which may lead to a new clinico-topographical classification. More investigations are necessary to reduce the scattering of the results.

Simulation of Machine-Specific Topographic Indices for Use Across Platforms

PURPOSE

The objective of this project is to simulate the current published topographic indices used for the detection and evaluation of keratoconus to allow their application to maps acquired from multiple topographic machines.

METHODS

A retrospective analysis was performed on 21 eyes of 14 previously diagnosed keratoconus patients from a single practice using a Tomey TMS-1, an Alcon EyeMap, and a Keratron Topographer. Maps that could not be processed or that contained processing errors were excluded from analysis. Topographic indices native to each of the three devices were recorded from each map. Software was written in ANSI standard C to simulate the indices based on the published formulas and/or descriptions to extend the functionality of The Ohio State University Corneal Topography Tool (OSUCTT), a software package designed to accept the input from many corneal topographic devices and provide consistent display and analysis. Twenty indices were simulated. Linear regression analysis was performed between each simulated index and the corresponding native index. A cross-platform comparison using regression analysis was also performed.

RESULTS

All simulated indices were significantly correlated with the corresponding native indices (p < 0.01), with a mean R of 0.84, ranging from 0.42 to 0.99. Cross-platform comparisons were nonsignificant for specific indices and devices.

CONCLUSION

Topographic indices native to three devices were successfully simulated. Cross-platform comparisons may be limited for specific indices.

Comparison of the NEI-VFQ and OSDI questionnaires in patients with Sjögren's syndrome-related dry eye

Background

To examine the associations between vision-targeted health-related quality of life (VT-HRQ) and ocular surface parameters in patients with Sjögren's syndrome, a systemic autoimmune disease characterized by dry eye and dry mouth.

Methods

Forty-two patients fulfilling European / American diagnostic criteria for Sjögren's syndrome underwent Schirmer testing without anesthesia, ocular surface vital dye staining; and measurement of tear film breakup time (TBUT). Subjects were administered the Ocular Surface Disease Index (OSDI) and the 25-item National Eye Institute Vision Functioning Questionnaire (NEI-VFQ). Main outcome measures included ocular surface parameters, OSDI subscales describing ocular discomfort (OSDI-symptoms), vision-related function (OSDI-function), and environmental triggers, and NEI-VFQ subscales.

Results

Participants (aged 31–81 y; 95% female) all had moderate to severe dry eye. Associations of OSDI subscales with the ocular parameters were modest (Spearman r (ρ) < 0.22) and not statistically significant. Associations of NEI-VFQ subscales with the ocular parameters reached borderline significance for the near vision subscale with TBUT (ρ = 0.32, p = .05) and for the distance vision subscale with van Bijsterveld score (ρ = 0.33, p = .04). The strongest associations of the two questionnaires were for: ocular pain and mental function with OSDI-symptoms (ρ = 0.60 and 0.45, respectively); and general vision, ocular pain, mental function, role function, and driving with OSDI-function (ρ = 0.60, 0.50, 0.61, 0.64, 0.57, and 0.67, respectively).

Conclusions

Associations between conventional objective measures of dry eye and VT-HRQ were modest. The generic NEI-VFQ was similar to the disease-specific OSDI in its ability to measure the impact of Sjögren's syndrome-related dry eye on VT-HRQ.

The effect of punctal occlusion on wavefront aberrations in dry eye patients after laser in situ keratomileusis

PURPOSE

To compare the wavefront aberrations in post-laser in situ keratomileusis (LASIK) dry eye patients before and after punctal occlusion.

DESIGN

Prospective, comparative, nonrandomized study.

METHODS

Wavefront aberrometry was performed on 16 eyes of eight patients with dry eyes after LASIK surgery. Wavefront measurements were taken before and 1 month after punctal plug placement and compared with 10 eyes of post-LASIK patients without clinically dry eyes measured twice 1 month apart. Student t tests were used to assess the statistical significance of differences between pre- and post-punctal plug measurements.

RESULTS

Punctal occlusion in the post-LASIK dry eye patients significantly reduced total, lower, and higher order wavefront aberrations by 47% to 63% (P <.01). Among higher-order aberrations, there were significant reductions in coma and spherical aberration but not in trefoil, after punctal occlusion. The reduction of wavefront aberrations by punctal occlusion in post-LASIK dry eye patients resulted in a significant improvement in quantitative visual acuity assessed using an Early Treatment of Diabetic Retinopathy Study chart and in subjective qualitative vision, confirmed by convolutional analysis using image simulation. No statistically significant differences in any of these metrics were found in the post-LASIK control group without clinically dry eyes measured twice at a similar time interval.

CONCLUSIONS

Wavefront aberrometry provides a useful, objective assessment of post-LASIK dry eye patients before and after punctal plug placement. Aggressive treatment of dry eyes may be important before obtaining wavefront measurements that serve as the basis for planning refractive corneal laser treatments and retreatments.

Assessing the severity of keratitis sicca with videokeratoscopic indices

PURPOSE

To determine the correlation between the regularity indices of the Tomey TMS-2N computerized videokeratoscopy (CVK) instrument (Tomey, Waltham, MA) with conventional measures of dry eye symptoms and disease.

DESIGN

A retrospective, clinic-based, case-control study.

PARTICIPANTS

A total of 16 eyes of 16 asymptomatic normal subjects and 74 eyes of 74 patients with reports of ocular irritation.

METHODS

Corneal surface regularity and potential visual acuity indices of the Tomey TMS-2N CVK instrument were evaluated in patients with ocular irritation symptoms and in normal subjects.

MAIN OUTCOME MEASURES

The surface regularity index (SRI), surface asymmetry index (SAI), potential visual acuity index (PVA), and irregular astigmatism index (IAI) of the Tomey TMS-2N were compared between normal and dry-eye patients. Severity of dry-eye symptoms was assessed with a validated questionnaire. Schirmer 1 test (without anesthesia), biomicroscopic meibomian gland evaluation with a composite severity score (MGD score), fluorescein tear break-up time (TBUT), and corneal fluorescein staining were performed. The correlations between CVK indices of the Tomey TMS-2N and the symptom severity score, Schirmer 1 test, MGD score, TBUT, and corneal fluorescein staining score were studied.

RESULTS

Dry-eye patients had greater mean symptom severity scores, lower Schirmer 1 test scores, greater MGD scores, more rapid TBUT, and greater total corneal fluorescein staining scores (P < 0.001 for all parameters). The SRI, SAI, and IAI were all significantly greater in dry-eye patients than normal subjects. These were 0.46 +/- 0.36 (normal) versus 1.09 +/- 0.76 (dry) for the SRI (P = 0.0017), 0.30 +/- 0.15 (normal) versus 0.90 +/- 1.09 (dry) for the SAI (P = 0.0321), and 0.42 +/- 0.28 (normal) versus 0.56 +/- 0.24 (dry) for the IAI (P = 0.0321). The PVA index was significantly lower in the dry-eye patients (0.89 +/- 0.13) than normal eyes (0.68 +/- 0.23; P = 0.0008). The SRI, SAI, and IAI were positively correlated with total and central corneal fluorescein staining scores (P < 0.00001 for all indices). An SRI (> or =0.80), SAI (> or =0.50), and IAI (> or =0.50) had sensitivities in predicting total corneal fluorescein staining (score > or = 3) of 89%, 69%, and 82%, respectively. The specificity of these indices was 80%, 78%, and 82%, respectively. In all 90 eyes, the mean SRI was greater in subjects older than 50 years (P = 0.012) compared with younger patients, whereas no age effect was noted in the dry-eye patients. The SRI and PVA index showed better correlation with symptoms of blurred vision than the best-corrected visual acuity.

CONCLUSIONS

Patients with ocular irritation have an irregular corneal surface that may contribute to their irritation and visual symptoms. Because of their high sensitivity and specificity, the regularity indices of the Tomey TMS-2N have the potential to be used as objective diagnostic indices for dry eye, as well as a means to evaluate the severity of this disease.

Predicted corneal visual acuity in keratoconus as determined by ray tracing

PURPOSE

To evaluate the optical quality of the central anterior corneal surface in normal eyes and in eyes with keratoconus, and to investigate the accuracy of the predicted corneal visual acuity (PCVA) index as determined by ray tracing analysis.

METHODS

Twenty keratoconus eyes with contact lens-corrected visual acuity (VA) of 20/20 or better (11 patients, group A) and 20 eyes of 15 normal subjects (group B) were evaluated. After a detailed eye examination including measurement of pupil diameter, keratometry, topography and pachymetry, each subject eye was evaluated using ray tracing analysis with the Technomed C-scan colour ellipsoid topometer, using basic software (Technomed GmbH, Baesweiler, Germany). The PCVA was determined for each patient, and the results were analysed comparatively using two-sample t-test, regression analysis and Pearson correlation analysis.

RESULTS

The average best spectacle-corrected VA was measured as 0.2 +/- 0.2 logMAR (20/32) in group A and -0.1 +/- 0.1 logMAR (20/16) in group B. The average PCVA measurements derived from ray tracing analysis for 3.0 mm, 3.5 mm and 4.0 mm pupil diameters were 0.06 +/- 0.12 logMAR, 0.14 +/- 0.13 logMAR and 0.21 +/- 0.17 logMAR, respectively, in group A, and -0.14 +/- 0.08 logMAR,-0.11 +/- 0.09 logMAR and -0.09 +/- 0.11 logMAR, respectively, in group B. There was good correlation between best corrected VA and PCVA in both groups for all pupil diameters measured (p < 0.007).

CONCLUSION

Predicted corneal visual acuity as determined by ray tracing analysis is useful for estimating best spectacle-corrected VA in normal corneas and the effect of irregular corneal astigmatism on VA in eyes with mild to moderate keratoconus. Further studies are required to evaluate the efficacy of ray tracing in evaluation of aberrations of the optical system of the eye.

Comparison of Subjective Visual Acuity With Visual Acuity Predicted From C-scan Topography

PURPOSE

To compare the capability of objective measures of visual acuity (potential visual acuity from C-scan) to predict subjective visual acuity (best spectacle-corrected visual acuity [BSCVA]).

METHODS

Patients with BSCVA > or = 20/20 were enrolled in four groups (Group 1: normal [33 eyes]; Group 2: < -7.00 D myopia [43 eyes]; Group 3: > or = -7.00 D myopia [28 eyes]; Group 4: At least 1 month after LASIK [93 eyes]). Videokeratography was performed with the ray tracing Technomed C-scan. The potential visual acuity from C-scan was obtained with pupils undilated and intact precorneal tear films. All visual acuity was recorded in logMAR, and the significance of differences between acuities was assessed with a one-way ANOVA test.

RESULTS

The potential visual acuity from C-scan ray tracing of normal and myopic eyes in response to both photopic and mesopic stimuli did not differ. In a given eye, the potential visual acuity from C-scan ray tracing was better than BSCVA, and the difference was statistically significant. Although the potential visual acuity from C-scan of postoperative LASIK eyes in response to photopic stimuli was the same, it decreased under mesopic conditions.

CONCLUSIONS

Potential visual acuity from C-scan overestimates subjective visual acuity due to the inadequate assumptions in ray tracing or individual retinal resolution ability. In addition, the potential visual acuity from C-scan ray tracing varies with pupil diameter in different illumination.

Topographic analysis of corneal regularity after penetrating keratoplasty

PURPOSE

To evaluate the accuracy of the Holladay Diagnostic Summary of the EyeSys Corneal Analysis System in predicting the corneal visual acuity potential in patients who have undergone penetrating keratoplasty (PKP).

METHODS

Astigmatism patterns, refractive and topographic astigmatism, best spectacle-corrected visual acuity (BSCVA), and hard contact lens (HCL) visual acuity of 54 patients were analyzed 3 months after PKP and compared with the Potential Corneal Acuity (PCA) value predicted by the Holladay Diagnostic Summary.

RESULTS

Qualitative patterns of astigmatism (p = 0.01) and refractive (p = 0.002) and topographic (p = 0.0002) astigmatism were significantly correlated with PCA values. Using HCL visual acuities to correct the BSCVA (HCL-corrected BSCVA) for noncorneal causes of reduced vision, we found that the PCA values of 48.1% of the patients were within one line of the HCL-corrected BSCVA; 81.5% were within two lines; and 93.0% were within three lines.

CONCLUSION

The Holladay PCA measurement may be useful in the postoperative evaluation of the optical quality of the central corneal surface in patients who have undergone PKP.