Changes of Functional Optical Zone After LASIK for Hyperopia and Hyperopic Astigmatism

PURPOSE

To evaluate which factors may influence the size of the postoperative functional optical zone after hyperopic LASIK.

METHODS

Thirty-three eyes with a mean spherical equivalent of +3.55 ± 1.28 diopters (D) underwent LASIK with a Technolas 217 C-LASIK laser (Bausch & Lomb Surgical, Munich, Germany). After 1 week and 1, 4, and 12 months, the authors examined refraction, corneal refractive power by means of computerized videokeratography (Technomed C-Scan; Baesweiler, Germany), and uncorrected/corrected distance visual acuity (UDVA/CDVA). According to the degree of hyperopia, they were divided into low hyperopia (spherical equivalent ≤ 3.00 D) and high hyperopia (spherical equivalent > 3.00 D) groups.

RESULTS

One year postoperatively, 82% of all eyes had a UDVA of 0.5 or better; in 88%, the spherical equivalent did not deviate more than 1.00 D from the attempted value. Three eyes were slightly undercorrected. After an initial overcorrection (-0.27 D) with subsequent regression, the refraction remained stable at +0.17 D from the fourth postoperative month (low hyperopia group: +0.14 D; high hyperopia group: +0.19 D after 1 year). After 1 year, the functional optical zone diminished by 32%; the reduction was more pronounced in eyes with higher hyperopia: -1.85 ± 1.09 mm (range: +0.5 to -3.4 mm) in the low hyperopia group (P < .0001) and -2.25 ± 1.24 mm (range: +1 to -3.9 mm) in the high hyperopia group (P < .0001). Preoperative spherical equivalent and preoperative corneal refractive power affected the postoperative size of the functional optical zone additively.

CONCLUSIONS

An expected small functional optical zone in high hyperopia may not be regarded as a compelling exclusion criterion, but can induce possible side effects such as glare and halos. [J Refract Surg. 2018;34(7):476-481.].

Retrospective evaluation of the influence of pupil size on visual acuity after KAMRA inlay implantation

PURPOSE

To investigate the influence of pupil size on visual acuity after KAMRA inlay (AcuFocus, Inc., Irvine, CA) implantation.

METHODS

Five hundred eighty-four presbyopic eyes of 584 patients who underwent LASIK were evaluated. Uncorrected near visual acuity (UNVA), uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and corrected near visual acuity (CNVA) were measured. Two groups were classified: small pupil (pupil diameter < 6 mm) and large pupil (pupil diameter ≥ 6 mm) for both mesopic (pupil diameter < 4 mm) and photopic (pupil diameter ≥ 4 mm) pupil size parameters. The follow-up period was 6 months.

RESULTS

There were no significant differences in UNVA (P = .98) and CNVA (P = .16) between the mesopic pupil size groups; however, there were significant differences in UDVA (P = .023) and CDVA (P = .039). There was a weak correlation between pupil size and UDVA of the large mesopic pupil size group (rs = 0.129, P = .04). There were no significant differences in UNVA (P = .78), CNVA (P = .92), UDVA (P = .19), and CDVA (P = .60) for the photopic pupil size groups.

CONCLUSIONS

Pupil size does not have an influence on the resultant visual acuity after KAMRA inlay implantation. No correlation was found between preoperative and postoperative pupil size and visual acuity for the mesopic pupil groups.

Comparison of 3 pupillometers for determining scotopic pupil diameter

PURPOSE

The pupil diameter under low ambient illumination is diagnostically valuable for refractive surgery. The aim of study was to compare the NeurOptics® Pupillometer, Sirius®, and Ocular Wavefront Analyser® in determining scotopic pupil diameter.

MATERIALS AND METHODS

A total of 96 eyes of 48 subjects were included. The scotopic pupil size was measured with 3 instruments and the measurements repeated following instillations of 1% cyclopentolate. Agreement between the instruments was assessed.

RESULTS

The mean measurement obtained by Sirius was significantly larger than Ocular Wavefront Analyser and NeurOptics. The Ocular Wavefront Analyser measured significantly smaller than the others. The mean cycloplegic pupillary diameters (7.73±0.70 mm with NeurOptics, 7.42±0.45 mm with Ocular Wavefront Analyser, and 8.06±0.76 mm with Sirius) were significantly different obtained by 3 instruments (p<0.001, for each; one-way analysis of variance and paired t tests).

CONCLUSIONS

The differences between measured pupil diameters with or without cycloplegia obtained by the NeurOptics, Sirius, and Ocular Wavefront Analyser were significant and have unacceptable levels of disagreement. These results may not be related to illumination and accommodation only, but also to measurement algorithms and technical differences of the devices.

Distribution of photopic pupil diameter in the Tehran eye study

PURPOSE

To determine the photopic pupil diameter and its determinants in a sample derived from a population-based survey in Tehran.

METHODS

In a cross-sectional study with a stratified random cluster sampling approach, 410 people age 14 years and over were selected from those residing in the first four municipality districts of Tehran after applying exclusion criteria, and 800 eyes (399 right eyes and 401 left eyes) were examined with the Orbscan II. The main outcome measure was the mean pupil diameter under photopic conditions, and possible correlations with potential determinants were evaluated through linear regression analyses. The design effect of a cluster sampling approach was observed and adjusted for.

RESULTS

The mean age of the participants was 40.6 +/- 16.8 years and 38.8% were male. The mean photopic pupil diameter (PPD) was 3.70 mm (range 2.30 to 5.10; 95% confidence interval (CI) 3.62 to 3.78). The mean PPD was 3.67 mm (95% CI, 3.54 to 3.81) in men and 3.72 mm (95% CI, 3.63 to 3.81) in women (p = 0.481). There was a significant reduction of 0.021 mm in PPD per year of aging (r = -0.49, p < 0.001). There was also a significant inverse correlation between PPD and spherical equivalent (r = -0.12, p = 0.034), while there was 0.66-mm increase in PPD with every 1.0-mm increase in the anterior chamber depth (ACD) (p < 0.001). Anisocoria, defined as a pupil diameter difference more than 0.4 mm between two eyes, was observed in 12.2% of the study population.

CONCLUSION

While the mean PPD measured with the Orbscan II was 3.70 mm in a sample derived from a population-based survey in Tehran, the scarcity of similar studies and reports concerning the pupil diameter measured with the Orbscan II makes it difficult to draw eligible comparisons. The pupil diameter has reverse correlations with age and spherical equivalent, a direct correlation with ACD, but is not correlated with gender.

[Application of wavefront analysis in clinical and scientific settings. From irregular astigmatism to aberrations of a higher order--Part II: examples]

In recent years, wavefront analysis has ceased to be purely a laboratory application and emerged as a method used in ophthalmological diagnosis. This development has been promoted mainly by the widespread use of wavefront-guided LASIK (laser in situ keratomileusis). However, aberrometry is still not a common diagnostic technique, and for many ophthalmologists interpretation of the results is difficult. The second part of this serial paper reviews findings that are relevant for the ophthalmological community and highlights current scientific applications in this area.

Higher-order aberrations and visual acuity after LASEK

BACKGROUND

To determine ocular higher-order aberrations (HOAs) in eyes with supernormal vision after myopic astigmatic laser subepithelial keratomileusis (LASEK) and to compare the findings with those in eyes with natural supernormal vision.

METHODS

Ocular HOAs were measured after LASEK in 20 eyes of 12 myopic astigmatic patients with postoperative uncorrected visual acuity (UCVA) of >20/16 (group 1). Patients who were included in the study had no visual symptoms like glare, halo or double vision. The measurements were taken 8.3 +/- 3 months after LASEK surgery. In group 2 ocular HOAs were examined in 20 eyes of 10 subjects with natural UCVA of >20/16 as a control. Measurements were taken across a pupil with a diameter of 4.0 mm and 6.0 mm. Root-mean-square (RMS) values of HOAs, Z(3)-1, Z(3)1, Z(4)0, Z(5)-1, Z(5)1 and Z(6)0 were analyzed.

RESULTS

The mean RMS values for each order were higher in group 1 when compared with group 2 at 4.0 mm and 6.0 mm pupil diameters. There was no statistically significant difference between groups in spherical and coma aberrations (P > 0.05). Mean RMS values for total HOAs were 0.187 +/- 0.09 microm at 4.0 mm and 0.438 +/- 0.178 microm at 6.0 mm pupil in group 1 and 0.120 +/- 0.049 microm at 4.0 mm and 0.344 +/- 0.083 microm at 6.0 mm pupil in group 2. The difference between groups in total HOAs was statistically significant at 4.0 mm and 6.0 mm pupil diameters (P < 0.05).

CONCLUSION

Ocular HOAs exist in eyes with supernormal vision. After LASEK, the amount of HOAs of the eye increases under both mesopic and photopic conditions. However the amount of HOA increase does not seem to be consistent with visual symptoms.

[Optical quality after refractive corneal surgery]

Correction of myopia, hyperopia and astigmatism within its indicated margin by means of refractive corneal surgical procedures such as LASIK and surface ablation (e.g. PRK) is one of the standard procedures in ophthalmology. Now that advances in the fields of surgical techniques and the technical devices employed have further progressed in terms of safety and predictability, research also focuses on optical quality. "Optical quality" is not a clearly defined parameter, but can be captured indirectly by means of directly measured data. One has to start with the anatomical properties of the eye, which determine the optical images on the retinal level. The quality of the retinal image influences the eye's function, i.e. acuity and contrast perception. Finally, there is the subjective perception of the image we receive. "Optical quality" as such is reflected by the patient's evaluation of this image perception. Three phenomena are especially responsible for deterioration of the quality of the retinal image: diffraction, aberrations and dispersion. Some of the methods for measuring optical quality are subjective questionnaires, functional testing procedures for measuring visual acuity and contrast sensitivity, optical measuring procedures for the determination of optical quality, as well as biomicroscopy, aberrometry and corneal topography for assessing anatomical changes.

Influence of pupil and optical zone diameter on higher-order aberrations after wavefront-guided myopic LASIK

PURPOSE

To investigate the influence of pupil and optical zone (OZ) diameter on higher-order aberrations (HOAs) after myopic wavefront-guided laser in situ keratomileusis (LASIK).

METHODS

Twenty-seven myopic eyes of 19 patients were included. The mean preoperative spherical equivalent was -6.86 diopters (D) +/- 1.24 (SD) (range -4.25 to -9.5 D); the mean planned OZ diameter was 6.26 +/- 0.45 mm (range 5.7 to 7.1 mm). All patients had uneventful wavefront-guided LASIK (Zyoptix version 3.1, Bausch & Lomb) and an uncomplicated follow-up of 12 months. Wavefront measurements were performed with a Hartmann-Shack sensor in maximum mydriasis preoperatively and 12 months after LASIK. Wavefront errors were computed for pupil diameters (PDs) of 3.0, 3.5, 4.0, 5.0, 6.0, and 7.0 mm for the individual OZ diameter and for the individual mydriatic PD (7.93 +/- 0.46 mm). The impact of the relationship between pupil diameter and OZ diameter (fractional clearance [FC]) on HOA was described and quantified using curvilinear regression with a 4th-order polynomial fit.

RESULTS

There was a reproducible relationship between FC and the amount of induced HOA. The change in HOA root mean square and primary spherical aberration (Z(4)0) was significantly correlated with FC. If the OZ was 16.5% larger than the pupil (FC = 1.17), only half the amount of HOA was expected to be induced than if the OZ equaled the pupil. In contrast, an OZ that was 9% smaller than the pupil (FC = 0.91) resulted in an HOA induction 50% higher than at FC = 1.

CONCLUSION

The OZ zone to pupil ratio (fractional clearance) had a significant impact on HOA induction after wavefront-guided LASIK.

Comparison of Corneal Higher-Order Aberrations Induced by Myopic and Hyperopic LASIK

OBJECTIVE

To compare the change in anterior corneal higher-order (third- to fifth-order) aberrations (HOAs) induced by myopic and hyperopic LASIK.

DESIGN

Retrospective comparative case series.

PARTICIPANTS

One hundred eyes (50 myopes and 50 hyperopes) of 59 patients were included. The mean preoperative spherical equivalent (SE) was -4.22+/-1.78 diopters (D; range, -1.25 to -8.00 D) in the myopic group (group A) and +2.72+/-1.25 D (range, +0.25 to +5.00 D) in the hyperopic group (group B).

INTERVENTION

LASIK was performed using a conventional spherocylindrical laser algorithm (Planoscan V2.9992, Bausch & Lomb/Technolas, Munich, Germany). Optical zone diameter was 6.70+/-0.32 mm (range, 6-7 mm) in group A and 6.59+/-0.19 mm (range, 6.5 to 7 mm) in group B. Third to fifth corneal HOA were computed for a pupil diameter of 6 mm from corneal topographic examinations before and 1 month after surgery.

MAIN OUTCOME MEASURES

Change in corneal HOAs, derived from corneal topography.

RESULTS

Total HOA root mean square (RMS) changed in group A by 0.167+/-0.180 microm (factor 1.53) and in group B by 0.341+/-0.341 microm (factor 1.89). The mean induction of coma RMS was significantly different in both groups (myopes, 0.092+/-0.195 microm; hyperopes, 0.252+/-0.305 microm; P<0.05). For spherical aberration (Z 4,0), the myopic group showed a significant increase (0.130+/-0.120 microm; factor 1.6; P<0.001), whereas the hyperopic group showed a significant decrease (-0.317+/-0.158 microm; factor 0.76; P<0.001). Fifth-order aberrations showed an increase in both groups, which was higher in group B (0.069+/-0.120 microm; factor 2.46) than in group A (0.005+/-0.065 microm; factor 1.49).

CONCLUSIONS

Myopic and hyperopic LASIK had different patterns of HOA induction. Myopic LASIK induced positive spherical aberrations and positive secondary astigmatism, whereas hyperopic LASIK induced negative spherical aberrations and negative secondary astigmatism. Hyperopic LASIK induced more third- and fifth-order comalike aberrations than myopic LASIK.

Comparison of dynamic digital pupillometry and static measurements of pupil size in determining scotopic pupil size before refractive surgery

PURPOSE

To compare 2 digital infrared pupillometers.

SETTING

Anterior Segment Service, Moorfields Eye Hospital, London, England.

METHODS

Eighty-eight eyes of 44 healthy subjects were recruited into the study. The scotopic pupil size was measured with 2 instruments, a digital pupillometer (Procyon) and a Hartman-Shack wavefront aberrometer (Visx WaveScan). Agreement between the instruments was assessed.

RESULTS

There were 21 men and 23 women with a mean age 38.1 years +/- 9.2 (SD) (range 23 to 62 years). The mean scotopic pupil diameter was significantly larger with the WaveScan (6.61 +/- 0.92 mm) than with the Procyon pupillometer (6.40 +/- 0.90 mm), P<.001.

CONCLUSIONS

There was good agreement in measurement of scotopic pupil size between the two instruments. The larger pupil diameter found with the Visx WaveScan than with the Procyon digital pupillometer probably represents the different illumination level used by each instrument, the effects of accommodation, and target fogging.

Use of the artificial iris implant in patients with aniridia

BACKGROUND

Aniridia (or partial aniridia) often occurs as a result of a penetrating ocular trauma. This condition may cause symptoms including glare, light sensitivity, reduced vision, and asymmetric appearance. Options for these patients include specialty contact lenses, corneal tattooing, and artificial iris implants. This article details six patients who experienced penetrating trauma with significant iris tissue loss and who chose to have an artificial iris implant.

CASE REPORTS

Six patients with traumatic aniridia were enrolled in a single-site, single-surgeon study. They were followed for one year postoperatively. All six were complex cases that had multiple eye problems, such as aphakia, corneal scarring, corneal graft rejection, and retinal detachment. All participants were male. All patients experienced decrease in glare and light sensitivity following artificial iris implant surgery. Two experienced improved best-corrected vision (BCVA). All six patients felt the cosmetic appearance of their affected eye improved.

CONCLUSIONS

The artificial iris device provides an effective means of treating traumatic aniridia. Optometrists often work with patients who have experienced a penetrating ocular trauma, with complete or partial aniridia as a complication. In cases in which nonsurgical means are not effective in returning the patient to comfort and productivity, an artificial iris implant should be considered.

Effect of expanding the treatment zone of the Nidek EC-5000 laser on laser in situ keratomileusis outcomes

PURPOSE

To evaluate the effect of expanding the treatment zone of the Nidek EC-5000 laser on postoperative visual acuity as well as night glare and halos after laser in situ keratomileusis (LASIK) using 4 ablation zone diameters.

SETTING

Division of Ophthalmology, Evanston Northwestern Healthcare and Northwestern University Medical School, Glenview, Illinois, USA.

METHODS

This prospective study comprised 301 eyes of 154 consecutive patients who had LASIK in 1 or both eyes using the Nidek EC-5000 laser by 1 surgeon with experience in keratomileusis and excimer laser refractive surgery. A 6.5 mm optical zone was used with a transition zone 1.0 mm larger than the pupil under scotopic conditions (7.5, 8.0, 8.5, or 9.0 mm). Targeted correction was calculated according to a customized clinical nomogram. All patients were queried about glare and halos preoperatively and 3 months postoperatively using a questionnaire assigning numeric values to the degree of perceived visual disturbance (0 = no glare or halos, 1 = minimal, 2 = moderate, 3 = severe).

RESULTS

The baseline uncorrected visual acuity (UCVA) was 20/200 or worse in 293 eyes. The baseline best spectacle-corrected visual acuity was 20/20 or better. The mean preoperative refractive sphere was -6.33 diopters (D) +/- 2.80 (SD) (range -1.00 to -16.25 D) and the mean preoperative refractive cylinder, 0.86 +/- 0.83 D (range 0 to +3.25 D). Three months postoperatively, 78% of eyes had a UCVA of 20/20 and 99%, of 20/40 or better. Preoperatively, 94 eyes (31%) had glare and halos. At 3 months, glare, halos, or both were present in 19 eyes of 11 patients (6.3%) (P<.0001); in 14 eyes, patients reported less severe glare and halos postoperatively than preoperatively.

CONCLUSIONS

The use of a peripheral transition zone 1.0 mm larger than the pupil under scotopic conditions resulted in a low incidence of glare and halos postoperatively and did not adversely affect visual acuity. There was no increase in postoperative complications including corneal ectasia.

Wavefront-guided LASIK with the Zyoptix 3.1 system for the correction of myopia and compound myopic astigmatism with 1-year follow-up

OBJECTIVE

To assess safety, efficacy, predictability, stability, and change in aberrations after wavefront-guided LASIK for myopia and myopic astigmatism.

DESIGN

Prospective, nonrandomized, self-controlled trial.

PARTICIPANTS

Wavefront-guided LASIK was performed in 97 eyes in a 1-year trial. Treated eyes had a mean subjective manifest spherical equivalent (SE) of -5.22+/-2.07 diopters (D), with a range of -0.25 to -9.00 D of myopia and 0 to -3.25 D of astigmatism.

INTERVENTION

After a microkeratome cut, a wavefront-based excimer ablation (Zyoptix 3.1) was performed. The full treatment to achieve emmetropia of an early nomogram provided by the system manufacturer was used in all procedures.

MAIN OUTCOME MEASURES

Safety, efficacy, predictability, and stability were evaluated at 1, 3, and 12 months postoperatively. Wavefront changes of higher order aberrations (HOAs) at 1 year were determined for pupil sizes of 3.5 and 6 mm.

RESULTS

At 1 year postoperatively, uncorrected visual acuity (VA) was 20/20 or better in 83% of the eyes, and 20/40 or better in 98%. The mean subjective manifest SE at 1 year was -0.25+/-0.43 D; it was within 0.50 D in 77% and within 1.0 D in 95%. No eye lost > or =2 lines of best spectacle-corrected VA (BSCVA) at 1 year postoperatively; 40 eyes gained 1 line of BSCVA, and 5 eyes gained 2 lines. The total HOA root mean square (RMS) increased on average by a factor of 1.23+/-0.57 with a 3.5-mm pupil; for the 6 mm pupil, the increase factor was 1.52+/-0.36. No change or reduction in the total HOA RMS was observed in 45.5% of the eyes for a 3.5-mm pupil and in 20.6% for a 6-mm pupil. There was a significant increase of primary spherical aberration (Z 4,0) by a factor of 4.11+/-10.17 for 3.5-mm pupils and 4.31+/-6.76 for 6-mm pupils.

CONCLUSIONS

Wavefront-guided LASIK using Zyoptix 3.1 is an effective and safe procedure for the treatment of myopia and myopic astigmatism. Although in close to half of the eyes HOAs could be reduced, there was still undercorrection and induction of HOAs with the algorithm employed.

Monocular versus binocular pupillometry

PURPOSE

To quantify differences between monocular and binocular pupil size measurement under scotopic and mesopic conditions.

SETTING

Department of Ophthalmology, Johannes Gutenberg-University, and Department of Medical Biometry, Epidemiology and Informatics, University of Mainz, Mainz, Germany.

METHODS

Computerized dynamic pupillometry (P2000 SA, Procyon Instruments Ltd.) was used at 3 illumination levels: scotopic at 0.03 lux, mesopic low at 0.82 lux, and mesopic high at 6.4 lux. One hundred forty eyes of 70 healthy volunteers without ocular pathology were examined. The subjects were divided into 2 groups. In the first group, the pupil diameter was measured binocularly first. In the second group, monocular measurement was performed first. For statistical analysis, data description was based on medians and quartiles of the respective pupil diameter measurements. Intraindividual significance was based on sign tests, and interindividual comparison were based on 2-sample Wilcoxon tests.

RESULTS

In all eyes, statistically significant differences were found in pupil size, with higher values for the monocular measurement under low and high mesopic conditions (P=.000). For scotopic conditions, a trend toward higher values in monocular measurement was observed that approached statistical significance.

CONCLUSIONS

Results indicate that binocular measurement may imitate the patient's life conditions more realistically. Therefore, in eyes with a large pupil diameter with the risk for postoperative scotopic phenomena, binocular measurement should be considered before refractive surgery.

Pupil Size in Refractive Surgery Candidates

PURPOSE

To assess pupil size measurements obtained under scotopic and mesopic conditions with the Procyon pupillometer and under photopic conditions with the Humphrey videokeratographer.

METHODS

The pupil sizes of 96 candidates for refractive surgery (192 eyes) were measured with the Procyon pupillometer PS2000 SA and the Humphrey Atlas 992 corneal topographer. Anisocoria and pupillary unrest were analyzed according to gender (two groups: 51 females and 45 males), age (five groups: 20 to 30 yr, 31 to 40 yr, 41 to 50 yr, 51 to 60 yr, older than 60 yr) and level of refraction (five groups: >-6.00 D SE, -6.00 to -3.00 D SE, -3.00 to 0 D SE, 0 to +2.50 D SE, +2.50 to +5.00 D SE).

RESULTS

The median value of pupil diameter measured with the Procyon pupillometer at the scotopic (0.04 lux), mesopic-low (0.4 lux), and mesopic-high (4 lux) levels of illumination were 6.54+/-0.88 mm; 5.62+/-0.95 mm, and 4.09+/-0.76 mm, respectively. The median pupil size with the Humphrey topographer was 3.65+/-0.62 mm. Pupillary unrest was highest at the mesopic-high level of illumination, with a median value of 0.31+/-0.34 mm. Median pupil size measured with both instruments at all light levels dropped significantly after the fifth decade of life (P<.05, ANOVA).

CONCLUSIONS

The Procyon pupillometer and Humphrey videokeratographer revealed an inverse correlation between the pupil size and the age, but no relationship with gender or level of refraction. The Procyon pupillometer provides an objective method for measuring pupil size at controlled light levels with a permanent printed record.

Comparison of the Colvard Pupillometer and the Zywave for Measuring Scotopic Pupil Diameter

PURPOSE

To evaluate the accuracy and repeatability of two pupillometers.

METHODS

Two pupillometers, the Colvard and Zywave, were used to measure scotopic pupil diameter for 64 consecutive patients. Accuracy and repeatability were assessed by two independent examiners and statistical analysis was performed using the comparison method described by Bland and Altman.

RESULTS

Mean scotopic pupil diameter was 5.96 +/- 0.69 mm with the Colvard pupillometer and 5.77 +/- 0.85 mm with the Zywave. The difference between the Colvard and Zywave measurements was 0.21 +/- 0.56 mm (P < .001). The coefficient of interrater repeatability was smaller for the Colvard (0.59) than for the Zywave (1.17). The mean difference between the pupillometers for each examiner was 0.17 +/- 0.47 mm (P < .01) for examiner 1 and 0.26 +/- 0.64 mm (P < .01) for examiner 2.

CONCLUSIONS

Scotopic pupil diameter measured with the Zywave was statistically but not clinically significantly smaller than that measured with the Colvard pupillometer. The Zywave produced an inter-rater repeatability comparable to other devices although not as good as the Colvard pupillometer.

Pupil size and the ablation zone in laser refractive surgery: Considerations based on geometric optics

PURPOSE

To determine whether the currently accepted method of selecting a minimum ablation zone size for refractive surgery based on dark-adapted pupil diameter is substantiated by geometric optical analysis.

SETTING

Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, Texas, USA.

METHODS

An optical model of the anterior segment was developed to calculate the effective corneal refractive diameter (ECRD), which is the diameter of the area of cornea that refracts all incident light rays arising from objects along the line of sight though the physical pupil (PP). The concept of the entrance pupil (EP) was reexamined and developed, and the ECRD was calculated over a range of corneal curvatures (K), anterior chamber depths (ACDs), and EP sizes. The model was generalized to include oblique light rays. Calculations were performed using MatLab Optimization Toolbox software (The MathWorks).

RESULTS

For a given EP size, the ECRD was significantly influenced by K and slightly influenced by ACD.

CONCLUSIONS

For objects on the line of sight, the ECRD was smaller than the EP in all cases. Regarding rays from objects in the periphery, the ECRD expanded rapidly as the angle of oblique incidence increased. For objects on the line of sight, the ECRD is always smaller than the clinically measured pupil (EP) because the EP is substantially magnified relative to the PP. Ablation zones larger than the EP should, in theory, prevent scattered or defocused light rays from contributing to the foveal image. When considering objects in the periphery, the increase in ECRD is sufficiently rapid that current refractive procedures cannot stop scattered light from these objects from contributing to the retinal image.

Effect of pupil size on visual function under monocular and binocular conditions in LASIK and non-LASIK patients

PURPOSE

To compare binocular and monocular vision in patients treated with laser in situ keratomileusis (LASIK) and in non-LASIK patients.

SETTING

Jules Stein Eye Institute, Los Angeles, California, USA.

METHODS

This comparative cross-sectional study comprised 20 postoperative LASIK patients and 20 non-LASIK ametropic patients. LogMAR visual acuity, contrast sensitivity, and infrared pupillometry were tested. Outcome measures were better-eye monocular acuity, binocular acuity, better-eye contrast sensitivity, binocular contrast sensitivity, and pupil diameter under monocular and binocular conditions.

RESULTS

Binocular visual acuity and contrast sensitivity were statistically significantly better than the visual acuity in the better eye (P =.0047 to <.0001) in both patient groups. Pupil diameter was statistically significantly smaller under the binocular condition than the monocular condition (P <.0001) in both groups.

CONCLUSIONS

Monocular testing induced larger pupil diameters, which was associated with reduced vision compared to binocular measurements in LASIK and non-LASIK patients.

Comparison of a digital and a handheld infrared pupillometer for determining scotopic pupil diameter

To compare a digital infrared pupillometer with a handheld infrared pupillometer for determining scotopic pupil size. Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. In 100 eyes of 50 healthy individuals (mean age 38.8 years +/- 10.7 [SD]), the scotopic pupil size was measured with a digital (Procyon) and a handheld (Colvard) infrared pupillometer. After dark adaptation of 1 minute, measurements were performed with both devices by 2 examiners (E1 and E2). Agreement and repeatability were analyzed using a comparison method described by Bland and Altman. The mean scotopic pupil diameter was 5.90 +/- 0.97 mm (range 3.24 to 7.91 mm) with the Procyon and 5.78 +/- 0.98 mm (range 3.00 to 7.30 mm) with the Colvard pupillometer. The mean difference between the 2 devices was -0.01 mm (E1) and -0.24 mm (E2). The limits of agreement ranged from 2.84 (E1) to 3.24 (E2). The coefficients of repeatability were 0.64 (Procyon) and 1.16 (Colvard). The mean difference between E1 and E2 was -0.10 for the Procyon and 0.13 for the Colvard pupillometer. The limits of agreement ranged from 1.28 (Procyon) to 2.32 (Colvard). The digital infrared pupillometer (Procyon) demonstrated better repeatability and agreement in measuring scotopic pupil size than a handheld device (Colvard).

Night vision disturbances after corneal refractive surgery

A certain percentage of patients complain of "glare" at night after undergoing a refractive surgical procedure. When patients speak of glare they are, technically, describing a decrease in quality of vision secondary to glare disability, decreased contrast sensitivity, and image degradations, or more succinctly, "night vision disturbances." The definitions, differences, and methods of measurement of such vision disturbances after refractive surgery are described in our article. In most cases of corneal refractive surgery, there is a significant increase in vision disturbances immediately following the procedure. The majority of patients improve between 6 months to 1 year post-surgery. The relation between pupil size and the optical clear zone are most important in minimizing these disturbances in RK. In PRK and LASIK, pupil size and the ablation diameter size and location are the major factors involved. Treatment options for disabling glare are also discussed. With the exponential increase of patients having refractive surgery, the increase of patients complaining of scotopic or mesopic vision disturbances may become a major public health issue in the near future. Currently, however, there are no gold-standard clinical tests available to measure glare disability, contrast sensitivity, or image degradations. Standardization is essential for objective measurement and follow-up to further our understanding of the effects of these surgeries on the optical system and thus, hopefully, allow for modification of our techniques to decrease or eliminate post-refractive vision disturbances.

Evaluation of corneal functional optical zone after laser in situ keratomileusis

PURPOSE

To evaluate the corneal functional optical zone (FOZ) after laser in situ keratomileusis (LASIK) using a primary 6.0 mm ablation diameter without a transition zone.

SETTING

University-based practice.

METHODS

In this retrospective study, 76 eyes of 53 patients who had LASIK for myopia were evaluated. The size of the preoperative and postoperative FOZ was compared in each eye. Preoperative refraction, attempted correction, and achieved correction were correlated with the preoperative and postoperative FOZ using regression analysis.

RESULTS

After LASIK, the FOZ decreased a mean 1.2 mm +/- 0.67 (SD) (P < 0.0001). The size of the FOZ was correlated with the preoperative manifest refraction, attempted correction, and achieved correction (P <.0001). The FOZ reduction was significantly correlated with the preoperative manifest refraction, attempted correction, and achieved correction (P <.05). Before LASIK, there was no correlation between the FOZ and the preoperative manifest refraction (P = 0.9427).

CONCLUSIONS

Spherical aberrations exist within the laser ablation zone and are related to the amount of myopic treatment. This has implications for patients with large pupil diameters under mesopic conditions. Future studies are necessary to understand the implications in patients with high refractive errors.

Risk factors for self-reported visual symptoms with Intacs inserts for myopia

OBJECTIVE

Potential risk factors and visual performance measures were evaluated for relationship to self-report of clinical visual symptoms after the refractive procedure for placement of Intacs microthin prescription inserts for myopia.

DESIGN

Retrospective nonrandomized comparative study.

PARTICIPANTS/INTERVENTION

Patients were participants in the U.S. Food and Drug Administration phase III KeraVision prospective clinical trials.

MAIN OUTCOME MEASURES

Study participants (n = 263) were retrospectively classified into one of three outcome groups on the basis of postoperative self-reported visual symptoms and/or request for Intacs inserts removal through month 24. Differences between outcome groups in visual acuity, refractive error, corneal geometry, corneal topography, type of preoperative corrective lens wear, and demographic variables were evaluated with multivariate logistic regression.

RESULTS

Clinical trial participants who had preoperative mean keratometry >45 diopters (D) (adjusted odds ratio [OR], 0.43; 95% confidence interval [CI], 0.21, 0.85, P = 0.02), manifest refractive astigmatism of 0.75 D or 1.00 D (adjusted OR, 0.52; 95% CI, 0.25, 1.08, P = 0.08), measured uncorrected visual acuity > or =2 lines better than that predicted by their respective cycloplegic refractive error (adjusted OR, 0.39; 95% CI, 0.14, 1.12, P = 0.08) and/or had worn soft contact lenses (adjusted OR, 0.58; 95% CI, 0.32, 1.04, P = 0.07) tended to be less likely to report postoperative clinical visual symptoms with Intacs inserts. Risk of clinical visual symptoms and request for Intacs inserts removal approximately doubled for each 0.50 D of additional postoperative defocus equivalent (crude OR, 1.86; 95% CI, 1.39, 2.48, P = 0.00). Controlling for postoperative defocus and important preoperative risk factors, subjects who reported significant clinical visual symptoms were more likely to have had preoperative uncorrected visual acuity that was worse than that predicted by their respective cycloplegic refractive error (adjusted OR, 1.84; 95% CI, 0.98, 3.42, P = 0.06). Risk of reporting clinical visual symptoms was increased with mesopic pupil diameter > or =6.5 mm (adjusted OR, 1.76; 95% CI, 0.96, 3.24, P = 0.07). Within the group of patients who reported postoperative clinical visual symptoms, 71 of 122 (58%) had ceased reporting them by month 24.

CONCLUSIONS

Adjusting for important risk factors simultaneously, this study suggested that certain preoperative characteristics may increase or decrease the likelihood, depending on the characteristic, of refractive surgery candidates to report significant clinical visual symptoms with Intacs inserts.

Anterior Corneal Optical Aberrations Induced by Photorefractive Keratectomy for Hyperopia

PURPOSE

Photorefractive keratectomy (PRK) for hyperopia requires both a steepening of the central cornea and a flattening of the mid-periphery to achieve its effect and is likely to affect the optical aberrations of the eye.

METHODS

Nine patients underwent PRK to correct between +2.00 and +4.00 D of hyperopia (first eye treated for each patient) using the Summit Technology Apex Plus excimer laser. Anterior corneal aberrations for pupil diameters of 3, 5.5 and 7 mm were estimated from corneal topography data (TMS-1), assuming a uni-index, single surface cornea. Refractive error was assessed using retinoscopy and standard subjective tests.

RESULTS

Apart from the intended change in refraction (mean spherical equivalent manifest refraction, +4.60 +/- 1.60 D before surgery and +0.70 +/- 1.60 D at 1 year after surgery), the most significant change was in spherical aberration. Anterior corneal spherical aberration was positive (+1.60 +/- 0.60 D for a 5.5-mm pupil) before surgery and became negative after surgery (-1.80 +/- 1.20 D at 1 year). The change in spherical aberration was related to the achieved change in refractive error.

CONCLUSIONS

The large change (approximately 3.00 D) in spherical aberration (from positive to negative aberration) has implications for the optical performance of the whole eye, where the effects of lenticular aberration must also be considered.

Scotopic measurement of normal pupils: Colvard versus Video Vision Analyzer infrared pupillometer

PURPOSE

To prospectively measure the scotopic pupil diameter in a normal population and to compare 2 infrared pupillometers for these measurements.

SETTING

Johann Wolfgang Goethe-University, Department of Ophthalmology, Frankfurt am Main, Germany.

METHODS

The Colvard infrared pupillometer was compared to the Video Vision Analyzer (VIVA) infrared pupillometer under scotopic light conditions in 33 participants (aged 19 to 55 years). Reliability was assessed by 2 independent examiners (E1, E2). Statistical analysis was performed using a comparison method by Bland and Altman.

RESULTS

Mean pupil diameter was 6.16 mm +/- 1.20 (SD) (range 3.20 to 9.00 mm) with all measurements taken under scotopic illumination. The mean scotopic pupil diameter was 6.08 +/- 1.16 mm (range 3.2 to 8.4 mm) with the Colvard pupillometer and 6.24 +/- 1.28 mm (3.5 to 9.0 mm) with the VIVA pupillometer. The mean differences between the Colvard and VIVA were -0.27 mm (E1) and -0.05 mm (E2). Limits of agreement ranged from 1.4 (Colvard) to 2.4 (VIVA). The coefficients of repeatability ranged from 0.7 (Colvard) to 1.1 (VIVA).

CONCLUSIONS

A mean scotopic pupil diameter of 6.15 mm with a maximal pupil size of 9.00 mm can be expected in a normal population; this should be considered in refractive corneal and refractive lens surgery. Measurements with the Colvard pupillometer were more reliable and precise than those with the VIVA pupillometer.

Improvement of visual function with glare testing after photorefractive keratectomy and radial keratotomy

PURPOSE

To evaluate the effect of a glare source on visual function in patients after photorefractive keratectomy and radial keratotomy.

METHODS

Thirteen patients (22 eyes) who underwent photorefractive keratectomy and 20 patients (40 eyes) who underwent radial keratotomy were evaluated in this cross-sectional study. LogMAR visual acuity and contrast sensitivity were measured. Pupils were measured with the Rosenbaum card. A halogen/tungsten glare source approximated the luminance of headlights of an oncoming car at 100 feet.

RESULTS

In the photorefractive keratectomy and radial keratotomy groups, pupils were significantly smaller (P<.01) and the pupillary clearance of the ablation zone in photorefractive keratectomy and the clear zone in radial keratotomy were significantly larger under the glare condition (P<.01). In the photorefractive keratectomy group, visual acuity and contrast sensitivity under the glare condition were significantly higher than in the no-glare condition (P = .02). In the radial keratotomy group, contrast sensitivity under the glare condition was significantly higher than under the no-glare condition (P = .001 to .003).

CONCLUSIONS

After photorefractive keratectomy or radial keratotomy, the traditional glare source constricted the pupil and partially masked the optical aberrations, which resulted in an improvement in visual function. A "pupil-sparing" aberration test is needed for evaluation of visual function after refractive surgery.

Agreement and repeatability of infrared pupillometry and the comparison method

OBJECTIVE

To evaluate the accuracy and repeatability of the widely used comparison method of measuring pupil size.

DESIGN

Cross-sectional study.

PARTICIPANTS

Fourteen eyes of seven healthy myopic subjects were examined.

INTERVENTION

Two examiners made two repeated measures of pupil diameters of 14 eyes using Rosenbaum card comparison pupillometry and infrared pupillometry. Subjects fixated on a distant visual acuity chart, and pupils were measured under three luminance conditions. The agreement and inter-rater repeatability of both methods were determined.

MAIN OUTCOME MEASURES

Outcomes were pupil diameters, limits of agreement, and coefficient of repeatability of two examiners.

RESULTS

The mean difference between the two techniques ranged from 0.3 to 0.5 mm. The limits of agreement within two standard deviations ranged from 2.4 to 2.8 mm. Coefficient of repeatability ranged from 0.6 to 1.4 mm for infrared pupillometry and 1.0 to 1.2 mm for Rosenbaum pupillometry. Inter-rater repeatability of Rosenbaum pupillometry was consistently pupil diameter biased. Pupil diameters measured with the Rosenbaum method were consistently larger than diameters measured with the infrared technique for both examiners under all luminance conditions.

CONCLUSIONS

Results indicate that although the mean difference in techniques was small, the range of the agreement between the Rosenbaum and the infrared techniques was large. The Rosenbaum method consistently overestimated pupil diameters and was subject to inter-rater repeatability bias. Rosenbaum pupillometry may not be appropriate when accurate pupil measurements are required. The results have implications for many clinical trials in ophthalmology, including those evaluating refractive surgery that use Rosenbaum comparison pupillometry.

Role of clearance and treatment zones in contrast sensitivity: significance in refractive surgery

PURPOSE

To evaluate the relationship between contrast sensitivity, surgical treatment zone, and clearance (ablation or clear zone-pupil diameter) in photorefractive keratectomy (PRK) and radial keratotomy (RK).

SETTING

Saint Louis University Eye Institute, St. Louis, Missouri, and Hunkeler Eye Center, Kansas City, Missouri, USA.

METHODS

Thirteen patients had PRK and 20, RK. Contrast sensitivity was measured with the Stereo Optical F.A.C.T. (F.A.C.T.) and VectorVision CSV-1000 (VV) charts. Pupils were measured with the Rosenbaum card.

RESULTS

In the PRK group, VV contrast sensitivity at 6 and 12 cycles per degree (cpd) correlated with the ablation zone (r2 = 0.18 and 0.22, respectively), while visual acuity and F.A.C.T. contrast sensitivity did not correlate. In the RK group, both VV and F.A.C.T. contrast sensitivity at 6 cpd correlated with clearance (r2 = 0.29 and 0.12, respectively). Pupils were larger with the VV test than with the F.A.C.T. chart because ambient chart luminance was less in the former.

CONCLUSION

Contrast sensitivity is likely a more sensitive indicator of visual function than acuity in refractive surgery. The VV system unmasks aberrations from the transition zone of ablated and unablated cornea in PRK. Larger samples are needed to determine the critical ablation clearance of the pupil to avoid loss of visual function.

Optimal corneal ablation for eyes with arbitrary Hartmann-Shack aberrations

New technologies for accurately measuring corneal shape and full eye aberrations are now available. An algorithm that uses these technologies to predict the amount of ablation needed to produce a corneal surface that optimally focuses light is developed. It is found that knowledge of the aberrations is far more important than knowledge of corneal shape. Neglect of corneal shape information introduces an error of less than approximately 0.05 micron in the optimal ablation depth. Neglect of the aberrations is a different story. Small changes in the aberration structure, such as going from the optimal ablation to a spherical ablation, introduce ablation changes of greater than 10 microns. It is argued that there are many occasions when less ablation can lead to improved image quality.

Aberrations and retinal image quality of the normal human eye

We have constructed a wave-front sensor to measure the irregular as well as the classical aberrations of the eye, providing a more complete description of the eye's aberrations than has previously been possible. We show that the wave-front sensor provides repeatable and accurate measurements of the eye's wave aberration. The modulation transfer function of the eye computed from the wave-front sensor is in fair, though not complete, agreement with that obtained under similar conditions on the same observers by use of the double-pass and the interferometric techniques. Irregular aberrations, i.e., those beyond defocus, astigmatism, coma, and spherical aberration, do not have a large effect on retinal image quality in normal eyes when the pupil is small (3 mm). However, they play a substantial role when the pupil is large (7.3-mm), reducing visual performance and the resolution of images of the living retina. Although the pattern of aberrations varies from subject to subject, aberrations, including irregular ones, are correlated in left and right eyes of the same subject, indicating that they are not random defects.

Corneal Optical Aberrations Induced by Photorefractive Keratectomy

BACKGROUND

Photorefractive keratectomy causes marked alteration to anterior corneal topography, and is likely to induce major changes to the optical aberrations of the eye.

METHODS

Six diopters (D) of myopia correction was attempted on one eye of 50 patients, randomly allocated to one of three different treatments: 5-mm or 6-mm single ablation zone, or a double ablation (multizone; -5.00 D correction over 4.6 mm and -1.00 D over 6 mm). Topographic data was used to estimate corneal aberration coefficients. These were compared for effect of ablation zone, before and 1 year after photorefractive keratectomy. The coefficients were used to derive modulation transfer functions for the anterior corneal surface.

RESULTS

Corneal spherical aberrations and coma-like aberrations both increased significantly following photorefractive keratectomy (p < 0.001). The mean spherical aberration coefficient increased from 0.36 +/- 0.11 before, to 0.91 +/- 0.37 after treatment, while the mean coma-like aberration coefficient changed from 0.28 +/- 0.16 before, to 0.60 +/- 0.31 after treatment. Ablation zone form had a significant effect on spherical aberration (p = 0.030), but not for coma (p = 0.96). The spherical aberration coefficient increased least for the 6-mm ablation (by 0.38 +/- 0.17), compared with the 5-mm ablation (0.69 +/- 0.45) and the multizone (0.62 +/- 0.38). Corneal modulation transfer functions were reduced significantly following the photorefractive procedure. The effect was greatest for large pupil diameters and for spatial frequencies between 2 and 15 cycles per degree.

CONCLUSIONS

Corneal modulation transfer function calculations suggest that a significant loss of visual performance should be anticipated following photorefractive keratectomy, the effect being greatest for large pupil diameters. Results for three ablation zones show that induced aberrations are least for the largest (6 mm) ablation zone.

Refractive Surgery, Optical Aberrations, and Visual Performance

Visual optics is taking on new clinical significance. Given that current refractive procedures can and do induce large amounts of higher order ocular aberration that often affects the patient's daily visual function and quality of life, we can no longer relegate the considerations of ocular aberrations to academic discussions. Instead, we need to move toward minimizing (not increasing) the eye's aberrations at the same time we are correcting the eye's spherical and cylindrical refractive error. These are exciting times in refractive surgery, which need to be tempered by the fact that after all the research, clinical, and marketing dust settles, the level to which we improve the quality of the retinal image will be guided by the trade-off between cost and the improvement in the quality of life that refractive surgery offers.

Effect of ablation profile on wound healing and visual performance 1 year after excimer laser photorefractive keratectomy

BACKGROUND

Early photorefractive keratectomy ablations were of limited diameter and depth to maintain the integrity of the globe and to minimise postoperative haze. This study evaluated the effects of deeper, larger diameter wounds on refractive stability and corneal haze, and investigated the effects of ablation profile on wound healing and visual performance.

METHODS

One hundred patients undergoing -3.00D and -6.00D corrections were randomised to receive 5 mm, 6 mm, or multizone treatments. The multizone treatment was 6 mm in diameter, but only the depth of the 5 mm treatment. Outcome was measured by Snellen visual acuity, residual refractive error, objective techniques for haze and halos, pupil diameter, subjective night vision, and requirement for retreatment.

RESULTS

Overall, the results of 6 mm treatments were superior to those of 5 mm and multizone treatments: they had a smaller hyperopic shift (p < 0.01), a more predictable (p < 0.001) and stable refractive outcome, less haze (p < 0.05), smaller halos (p < 0.05), fewer subjective night vision problems, and fewer patients required retreatment.

CONCLUSIONS

Analysis of these data and a literature review of corneal wound healing demonstrated that the improved outcome associated with the 6 mm beam did not relate to the depth of ablation. The factor with greatest apparent influence on the development of haze and regression was the slope of the wound surface over the entire area of the ablation. Tapering the wound edge provided no additional benefit, and contributed to night vision problems. It is, therefore, recommended that small diameter or multizone treatments should not be used in low and moderate myopia.

Forward Light Scatter at One Month After Photorefractive Keratectomy

BACKGROUND

Although it is known that backward light scatter increases transiently following most excimer laser photorefractive keratectomies (PRKs), it is not clear that there is a significant increase in forward light scatter, which is of primary concern for the patient. The object of this study was to determine if there is a significant change of forward light scatter at 1 month after (PRK) with an ablation zone diameter of 6 mm.

METHODS

Overlapping subsets of 24 normal myopic eyes were tested before (on the day of surgery) and 1 month after PRK, using three instruments: a Stray Light Meter (16 eyes); a Computerized Stray Light Meter (14 eyes); and a mesopic Increment Threshold-Glare Paradigm (six eyes). Differences between the two eyes before PRK were compared with the differences between the same eye before and after PRK, using repeated measured analysis of variance. In addition, increment threshold data obtained from 22 eyes after PRK were compared with those of 60 controls of the same age range and distribution by a t test.

RESULTS

None of the statistical comparisons approached significance at the alpha = 0.05 level. Changes in light scatter as small as a factor of 1.95 (Stray Light Meter) and 1.55 (Increment Threshold-Glare Paradigm) could be detected as significant with a high power (0.8). Changes larger than a factor of 21 could be detected with a power of 0.8 for the Computerized Stray Light Meter.

CONCLUSIONS

In these data, there is no support for the hypothesis that forward light scatter increases significantly 1 month after PRK with an ablation zone of 6 mm. Any increases in forward light scatter are unlikely to be greater than a factor of 1.5 to 2 under daytime or nighttime illumination conditions.

Corneal topography of excimer laser photorefractive keratectomy

The application of the 193 nm excimer laser for keratorefractive surgery promises to deliver a higher degree of precision and predictability than traditional procedures such as radial keratotomy. The development and evaluation of keratorefractive surgery have benefited from the parallel advances made in the field of corneal topography analysis. We used the Computed Anatomy Topography Modeling System (TMS-1) to analyze a Louisiana State University (LSU) Eye Center series of patients who had photorefractive keratectomy for the treatment of myopia with the VISX Twenty/Twenty excimer laser system. The excimer ablations were characterized by a relatively uniform distribution of surface powers within the treated zone. In the few cases that exhibited marked refractive regression, corneal topography analysis showed correlative changes. With topographical analysis, centration of the ablations relative to the center of the pupil could be evaluated. Marked improvement in centration occurred in the patients of LSU Series IIB in which the procedure to locate the point on the cornea directly over the pupil's center during surgery was refined. Corneal topographical analysis provides objective measures of keratorefractive surgical results and is able to measure the precise tissue removal effect of excimer laser ablation without the uncertainties caused by measuring visual acuity alone. Our observations forecast the need for improved aids to center the laser ablations and for the development of a course of treatment to prevent post-ablation stromal remodeling.

Stray light in radial keratotomy and the influence of pupil size and straylight angle

Glare is a major sequela of the radial keratotomy procedure. We used the straylight meter to measure intraocular light scatter, which is the cause of glare, in eyes after radial keratotomy. This apparatus uses a direct compensation method to assess the amount of intraocular light scatter. Nineteen patients were tested. Nine individuals served as controls. The mean postsurgery time was 60 months. The influence of the number of radial incisions, the pupil size, and the angle of light entering the eye were evaluated with the straylight meter. The results showed straylight values for normal pupil size (mean, 4 mm) to be statistically significantly higher (P = .0044) only for the smallest angle of light deflection studied (3.5 degrees). For dilated pupils (mean, 8 mm), straylight values were statistically significantly higher (P = .00005) for all three angles of light deflection studied. The number of incisions showed no statistically significant relationship to straylight values. Average stray light values were increased by a factor of 1.4 for 4-mm sized pupils and 2.0 for 8-mm sized pupils. There was an overlap in straylight values between the patient population and the control population.