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Effect of preoperative pupil measurements on glare, halos, and visual function after photoastigmatic refractive keratectomy1
Effect of preoperative pupil measurements on glare, halos, and visual function after photoastigmatic refractive keratectomy Weldon W. Haw, MD, Edward E. Manche, MD ABSTRACT Purpose: To prospectively assess the effect of preoperative variables such as pupil size on glare, halos, and visual function after photoastigmatic refractive keratectomy (PARK). Setting: Department of Ophthalmology, Stanford University School of Medicine, Stanford, California, USA. Methods: Ninety-three eyes had PARK for primary compound myopic astigmatism. Preoperative pupil diameters were measured under scotopic and photopic illuminance conditions. Postoperatively, patients were evaluated at 1, 3, 6, 9, 12, 18, and 24 months. A regression model was performed to evaluate the predictive value of assessing preoperative variables such as pupil diameter on the development of glare and halos, contrast sensitivity, and best spectacle-corrected visual acuity (BSCVA) under scotopic, photopic, and glare conditions. Results: The greater magnitude loss of BSCVA under scotopic conditions in the early postoperative period as well as the slower recovery to preoperative levels in eyes with larger scotopic pupil diameters were not statistically significant (P ⬎ .05). An increase in symptoms of glare was related more to the attempted level of spherical equivalent (SE) correction than to the pupil size during the first 12 postoperative months (P ⬍ .01). The photoablation dimensions as determined by the attempted level of astigmatic correction may result in decreases in the glare BSCVA up to 12 months after PARK (P ⫽ .03). At the 2 year follow-up, pupil diameter under both scotopic and photopic illuminance conditions was not predictive of any of the measured outcomes variables. Conclusions: An assessment of preoperative pupil size and the attempted level of both SE and astigmatic correction may be useful in identifying patients at risk of developing symptoms or declines in visual performance after PARK. However, follow-up studies are indicated to identify variables predictive of poor visual outcomes following excimer laser refractive surgery. J Cataract Refract Surg 2001; 27: 907–916 © 2001 ASCRS and ESCRS
© 2001 ASCRS and ESCRS Published by Elsevier Science Inc.
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PREOPERATIVE PUPIL MEASUREMENTS AND PARK
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ultiple studies have evaluated corneal aberrations following excimer laser refractive keratectomy.1–5 Aberrations resulting from photoablation of the central cornea and the resulting clearance zone (difference between the pupil and ablation zone) with the excimer laser may account for symptoms of glare, halos, disturbances in night vision, and decreases in visual performance with psychophysical measures.6 –17 Pupil dilation (ie, during scotopic conditions) may significantly increase these aberrations following photorefractive keratectomy (PRK).1–2 Corneal modulation transfer function calculations suggest that these aberrations may result in a significant loss of visual performance following PRK, especially in eyes with larger pupil diameters.18 In this study, we prospectively evaluated the effect of preoperative variables such as pupil size on the patient’s perception of glare and halos as well as on the visual performance up to 2 years after photoastigmatic refractive keratectomy (PARK).
Patients and Methods Ninety-three eyes of 56 patients with primary compound myopic astigmatism with between ⫺1.0 and ⫺7.0 diopters (D) of sphere and between ⫺1.0 and ⫺5.0 D of astigmatism had PARK. Preoperatively, the patient had a complete ophthalmic history and examination including refraction, slitlamp examination, Goldmann applanation tonometry, dilated fundus examination, contrast sensitivity function test, and a measurement of best spectacle-corrected visual acuity (BSCVA). Contrast sensitivity was measured with the sinusoidal pattern CSV 1000-E (Vector Vision) under scotopic (21 lux) and photopic (324 lux) conditions. Best spectacle-corrected visual acuity was measured under glare, scotopic, and photopic conditions using the Lighthouse Distance Visual Acuity Test (Lighthouse Low Vision Products). Pupil size was measured with a standard pupil gauge (millimeters) on a Accepted for publication March 5, 2001.
near card under scotopic (21 lux) and photopic (324 lux) conditions. The patient did not wear spectacles during pupil measurement. All references to pupil sizes refer to preoperative measurements made in this fashion. Astigmatic alignment was achieved by marking the horizontal axis (0 to 180 degrees) with a surgical marking pen (Devon Industries) using a horizontal slit beam at the slitlamp with patients seated in the upright position. After topical proparacaine hydrochloride 0.5% (Ophthetic威), ofloxacin 0.3% (Ocuflox威), and diclofenac sodium 0.1% (Voltaren威) were instilled, the corneal epithelium was removed with a blunt PRK spatula. Photoastigmatic refractive keratectomy was performed with the Summit Apex Plus excimer laser with standard laser parameters. A 6.5 ⫻ 5.0 mm elliptical ablation zone was delivered through a poly(methyl methacrylate) erodible astigmatic mask system. A bandage contact lens was placed on the eye until the cornea had completely reepithelialized. Postoperative eye medications included topical Ocuflox 4 times daily for 4 days or until the epithelium was healed and topical fluorometholone 0.1% (FML威) 4 times daily for 1 month and then twice a day for 1 month. Patients were prospectively evaluated at 1, 3, 6, 9, 12, 18, and 24 months. Best spectacle-corrected visual acuity under glare, scotopic, and photopic conditions was measured as described at each postoperative visit. Contrast sensitivity was measured as described at 6, 12, and 24 months. Each patient completed a survey rating adverse symptoms such as glare, halos, and visual blurring. The patient scored each symptom on a scale of 0 (none) to 5 (severe). This survey was conducted at the preoperative examination and 6, 12, and 24 months postoperatively. The SPSS Graduate Pack for Windows V6.1.3 (SPSS Inc.) was used to determine statistical significance. To determine the statistical association between dependent and independent continuous variables, a linear regression model was performed. Differences were considered to be statistically significant when the P value was less than 0.05.
From Department of Ophthalmology, Stanford University School of Medicine, Stanford, California, USA. Neither author has a financial interest in any product mentioned. Reprint requests to Edward E. Manche, MD, Stanford University School of Medicine, Department of Ophthalmology, 300 Pasteur Drive, Suite A175, Stanford, California 94305, USA. 908
Results The mean preoperative sphere was –3.88 D ⫾ 1.83 (SD) (range ⫺1.0 to –7.0 D), the mean preoperative astigmatism, –2.19 ⫾ 0.90 D (range ⫺1.0 to –5.0 D),
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Figure 1. (Haw) Distribution of pupil diameter under scotopic and photopic illuminance conditions during the preoperative examination. Measurements were made with a standard pupillary gauge on a near card.
and the mean preoperative spherical equivalent (SE), – 4.98 ⫾ 1.80 D (range ⫺1.75 to – 8.50 D). Forty-nine eyes (52.7%) were in women and 44 eyes (47.3%), in men. The mean patient age was 41.40 ⫾ 8.54 years (range 26 to 58 years). Prior to the 2 year follow-up, 24 eyes (25.8%) required retreatment. These eyes are excluded from the 2 year follow-up results. Fifty-nine (71.1%) of the remaining eyes were available for analysis. The distribution of pupil size under scotopic and photopic conditions is shown in Figure 1. Figures 2 to 15 are topographic maps that demonstrate the effect of scotopic and photopic pupil size on symptoms of glare, halo, visual blurring, and visual performance. Visual performance results are recorded as a change in BSCVA (Snellen lines) and a change in contrast sensitivity (log units) under standard illuminance conditions. Pupil size was measured to the nearest 1.0 mm. A linear extrapolation model was performed between pupil size measurements. For example, Figure 12 plots the effect of photopic pupil size on scotopic BSCVA at each postoperative interval. The horizontal x-axis is the postoperative interval recorded in months following PARK treatment, while the vertical y-axis is the photopic pupil size recorded according to the previously described method. As in a topographic map, the color changes on the graph represent different degrees of loss or gain of BSCVA (Snellen lines) for each corresponding x and y point. The legend for this color change is designated at the lower righthand corner of the graph: white represents a mean gain of 0 to 1 Snellen lines, black represents a mean loss of 0 to 1 Snellen lines, and gray represents a mean loss of 1 to 2 Snellen lines. Thus, Figure 12 demonstrates a mean loss of 0 to 1 Snellen lines (black tone) during the first 6
Figure 2. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on the change in the glare score at each postoperative follow-up.
months after PARK treatment for photopic pupil sizes of approximately 2.0 to 4.0 mm. For photopic pupil sizes of 5.0 mm, the initial loss of BSCVA was between 1 and 2 Snellen lines (light gray tone) during the first month. After 6 months, there was a mean gain of 0 to 1 Snellen lines (white tone) in the photopic BSCVA for most pupil sizes. Symptoms of Glare, Halo, and Visual Blurring As shown in Figure 2, a preoperative photopic pupil size of approximately 4.0 to 5.0 mm showed an increase in glare symptoms from the preoperative level at all postoperative intervals. In contrast, eyes with photopic pupils ⬍ 4.0 to 5.0 mm showed a tendency toward a decrease in glare, especially at 24 months. A larger preoperative scotopic pupil size did not correlate with an increase in glare symptoms (Figure 3). While there was no statistically significant contribution of preoperative photopic or scotopic pupil size to glare
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Figure 3. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in the glare score at each postoperative follow-up.
Figure 4. (Haw) Topographic map illustrates the effect of photopic
Figure 5.
(Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in the halo score at each postoperative follow-up.
Figure 6. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on the change in the visual blurring score at each postoperative follow-up.
symptoms, the attempted level of correction (SE) did play a role in the development of glare symptoms at both 6 (P ⬍ .01; adjusted r2 ⫽ 0.10) and 12 (P ⬍ .01; adjusted r2 ⫽ 0.09) months. By 18 and 24 months, these were not statistically significant. Neither preoperative astigmatic or sphere corrections contributed to the development of glare at any postoperative interval (P ⬎ .05). Symptoms of halos were most pronounced in the first 6 to 12 months in photopic pupil sizes of approximately 4.0 to 5.0 mm (Figure 4). Eyes with small photopic pupils (ⱕ2.0 to 3.0 mm) demonstrated a rapid recovery of halo symptoms between 18 and 24 months,
which was not seen in eyes with larger photopic pupils. Scotopic pupil size did not have a statistically significant effect on halo symptoms at any postoperative interval (Figure 5). Although neither scotopic nor photopic pupil size was correlated with halo symptoms (P ⬎ .05), there was a slight correlation between high astigmatic correction and the development of halos at 12 months (P ⬍ .01, adjusted r2 ⫽ 0.09). Symptoms of visual blurring were higher at every postoperative interval in photopic pupil sizes ⱖ5.0 mm than in photopic pupils ⬍5.0 mm (Figure 6). This was statistically significant at 12 months (P ⬍ .01; adjusted r2 ⫽ 0.10). Scotopic pupil size did not contribute to the
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pupil size (mm) on the change in the halo score at each postoperative follow-up.
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Figure 7. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in the visual blurring score at each postoperative follow-up.
development of visual blurring symptoms (Figure 7) (P ⬎ .05). Best Spectacle-Corrected Visual Acuity Under Glare, Photopic, and Scotopic Conditions There was an initial decrease in BSCVA under glare conditions in all photopic pupil sizes 1 month after
PARK (Figure 8). Glare BSCVA did not recover to the preoperative level until 9 months in eyes with 2.0 mm photopic pupil diameters compared to 3 to 6 months in eyes with photopic pupils ⬎2.0 mm. Glare BSCVA was temporarily decreased for 1 to 6 months in all scotopic pupil sizes (Figure 9). However, neither scotopic nor photopic pupil sizes significantly predicted changes in the glare BSCVA for any measured postoperative interval (P ⬎ .05). Figure 10 shows a return of mean photopic BSCVA to the preoperative level within 3 to 6 months in eyes with photopic pupils ⱖ4.0 mm and between 9 and 24 months in eyes with photopic pupils of 2.0 to 3.0 mm. As shown in Figure 11, photopic BSCVA recovered to the preoperative levels more quckly in eyes with ⬎5.0 mm scotopic pupil sizes (3 to 6 months) than in eyes with ⱕ5.0 scotopic pupil sizes (over 9 months). However, the effect of scotopic pupil sizes did not significantly predict changes in the photopic BSCVA (P ⬎ .05). An initial decrease in the scotopic BSCVA was shown in all photopic pupil sizes during the first 6 months following PARK, with the largest decrease in photopic pupils ⱖ5.0 mm (Figure 12). Recovery oc-
Figure 8. (Haw) Topographic map illustrates the effect of photopic pupil size on the change in BSCVA under glare conditions (Snellen lines) at each postoperative follow-up.
Figure 9. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in BSCVA under glare conditions (Snellen lines) at each postoperative follow-up.
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Figure 10. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on the change in BSCVA under photopic conditions (Snellen lines) at each postoperative follow-up.
Figure 11. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in BSCVA under photopic conditions (Snellen lines) at each postoperative follow-up.
Figure 12. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on the change in BSCVA under scotopic conditions (Snellen lines) at each postoperative follow-up.
curred by 6 months. Scotopic pupils ⱖ6.0 mm showed a tendency toward a larger initial decrease in the scotopic BSCVA in the first 1 to 3 months (Figure 13). Recovery was also slower in eyes with larger scotopic pupil sizes. Eyes with scotopic pupils larger than approximately 6.0 mm did not recover to the preoperative levels until after 12 months. In contrast, eyes with scotopic pupils ⬍6.0 mm recovered to their preoperative level by 6 months. Despite this tendency, there was no predictive effect of scotopic pupil size on scotopic BSCVA 912
(P ⬎ .05). A slight predictive effect of the attempted level of astigmatic correction was demonstrated in the initial decrease of scotopic BSCVA 1 month after PARK (P ⫽ .03). However, this effect was small (adjusted r2 ⫽ 0.04). Contrast Sensitivity The effect of photopic pupil size on photopic contrast sensitivity was not statistically significant at 2 years (Figure 14). Higher levels of attempted SE correction
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Figure 13. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in BSCVA under scotopic conditions (Snellen lines) at each postoperative follow-up.
Figure 14. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on contrast sensitivity (log units) under photopic conditions 24 months after PARK.
Figure 15. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on contrast sensitivity (log units) under scotopic conditions 24 months after PARK.
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were minimally correlated with a decrease in the 12.0 spatial frequency (P ⫽ .01, adjusted r2 ⫽ 0.09). Figure 15 illustrates the change in contrast sensitivity as a function of scotopic pupil size under scotopic illuminance conditions 2 years after PARK. There was a clinically insignificant decline in contrast at the 3.0 cycles per degree (cpd) spatial frequency in most scotopic pupil sizes. Recovery of scotopic contrast sensitivity in eyes with ⱕ6.0 mm scotopic pupil sizes was more complete at spatial frequencies ⬎12.0 cpd. However, the effect of scotopic pupil size on scotopic contrast sensitivity was statistically insignificant. Higher levels of attempted SE correction were minimally predictive of a decrease in the 12.0 and 18.0 spatial frequencies (P ⫽ .02 and P ⫽ .03, respectively).
Discussion Multiple studies have demonstrated an alteration in the distribution and magnitude of coma and spherical aberrations following pupil dilation after PRK.1,2 In a study by Oshika et al.,2 there was a 25- to 32-fold increase in total wavefront aberrations with simulated pupil dilation after PRK compared to a 5- to 6-fold increase before PRK. In this study, the total wavefront aberrations did not return to normal by the 12 month followup. Thus, it is not surprising that some patients may complain of illuminance-dependent symptoms that may be related to the physiologic pupil dilation during scotopic conditions.19 A study has objectively demonstrated the role of PRK ablation profiles and clearance zones on visual performance tests such as contrast sensitivity.6 The attempted level of correction has also been implicated in an increased magnitude of aberration1 and patient symptoms.11 Our results confirm studies suggesting that the level of attempted correction and therefore the depth of ablation play a role in the increase in symptoms of glare in the early postoperative period. The level of attempted SE correction was related to an increase in symptoms of glare during 6 months (P ⬍ .01) and 12 months (P ⬍ .01) after PARK. Martinez et al.1 found the magnitude of the surgically induced aberration to be strongly correlated with the attempted correction (adjusted r2 ⫽ 0.6 at 1 month in a 7.0 mm pupil). In our study, by 6 and 12 months, the attempted level of SE correction did not account for 914
most of the glare symptoms (adjusted r2 of 0.10 and 0.09, respectively). At each of these intervals, there was a mean increase in the glare score of 0.37 and 0.35 for each diopter of attempted SE correction. This represented a 27% and 26% increase in the glare score from the preoperative level. After 12 months, the level of attempted correction lost its predictive effect for glare symptoms. The level of attempted SE correction was also weakly related to an increase in the halo score at 12 months (P ⬍ .01; adjusted r2 ⫽ 0.09). However, the level of SE did not contribute to changes in the BSCVA under photopic, scotopic, or glare conditions. Preoperative scotopic pupil diameter was not statistically correlated with symptoms of glare and halos. It also was not statistically predictive of decreases in contrast sensitivity or loss of BSCVA under glare, scotopic, or photopic conditions at any of the measured postoperative periods. In addition, the greater magnitude loss of BSCVA under scotopic conditions in the early postoperative period as well as the slower recovery to preoperative levels in eyes with larger scotopic pupil diameters were not statistically significant. A larger sample size may have been useful in establishing statistical significance and confirming previous reports suggesting that visual performance may demonstrate a decline in function related to clearance zones compromised by large pupil diameters.6 Most studies deal with the role of large or scotopic pupil sizes in the development of patient symptoms or decreases in visual performance, since aberrations are heightened following increased clearance zones resulting from smaller ablation profiles or larger pupil sizes. The role of photopic pupil measurements is not well studied. However, photoablation of the central visual axis would be expected to introduce some optical irregularities despite the clearance zones. In fact, Oshika et al.2 demonstrate corneal wavefront aberrations occurring in 3.0 mm pupils after excimer laser photoablation despite a 5.5 mm ablation zone using the Nidek EC5000 excimer laser. In our study, photopic pupil diameter was minimally predictive of increased loss of BSCVA under photopic conditions 6 months after PARK. Although simulated glare tests more closely resemble conditions under photopic conditions than under scotopic conditions,1 neither the glare symptoms nor the loss of glare BSCVA was related to photopic pupil size.
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It is interesting that the level of astigmatic correction did not affect our outcome variables more dramatically. Since the dimensions of the elliptical photoablation are dependent on the level of attempted astigmatic correction, this would be expected to affect the clearance zone (difference between the treatment zone and pupil diameter). The clearance zone has been shown to correlate with changes in contrast sensitivity at spatial frequencies of 6 and 12 cpd.6 In our study, we found that astigmatic correction adversely predicted a poor performance of BSCVA under glare conditions 1, 9, and 12 months after PARK and the contrast sensitivity under photopic conditions at 12 months. However, the contribution was minimal. There are several limitations to our study. Confounding factors such as corneal haze may also contribute to increased symptoms and poor visual performance scores. In addition, we introduced a selection bias by excluding retreatment eyes after the 6 month analysis. (All retreatments were performed after 6 months.) The eyes having retreatment have a higher SE and are therefore at risk of corneal aberrations and developing postoperative symptoms.1,11 Establishing statistical significance may be more difficult with our distribution of pupil diameters, which demonstrate a small number of eyes in the extreme ranges of the photopic (ⱕ2.0 mm and ⱖ5.0 mm) and scotopic (⬍4.0 mm and ⱖ8.0 mm) illuminance conditions. Also, measuring pupil diameter with a near card is a subjective measurement that introduces observer variation. A standard pupillary gauge may also inadequately determine the true pupil size in dim illumination. In some patients, infrared pupillometers may be more accurate in determining pupil diameter and account for patients experiencing illumination-dependent symptoms despite a “normal” pupil measurement.20 Thus, a prospective study of symptoms of glare and halos using more objective research pupillometers to measure pupil diameters would contribute to our understanding of these issues. Other difficulties in estimating pupil sizes stem from the optical properties of the anterior segment. It has been demonstrated that because the location of the virtual entrance pupil differs from the true pupil by approximately 0.5 mm, this may result in an observerbased overestimation of the true pupil diameter by
14%.21 However, while this source of error in determining the pupil diameter would be expected to be larger for larger pupil sizes, it would also be expected to result in systematic overestimation of true pupil size. In summary, although we did not find a statistical correlation between preoperative pupil sizes and the development of symptoms of glare and halos, we did identify potential relationships that may support the measurement of pupil diameters preoperatively. An assessment of preoperative pupil sizes and the attempted level of both the SE and astigmatic correction may be useful in identifying patients who may be at risk of developing symptoms or declines in visual performance following PARK. However, the predictive effect of preoperative pupil measurements may not be clinically significant by the 2 year follow-up.
References 1. Martinez CE, Applegate RA, Klyce SD, et al. Effect of pupillary dilation on corneal optical aberrations after photorefractive keratectomy. Arch Ophthalmol 1998; 116:1053–1062 2. Oshika T, Klyce SD, Applegate RA, et al. Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis. Am J Ophthalmol 1999; 127:1–7 3. Oliver KM, Hemenger RP, Corbett MC, et al. Corneal optical aberrations induced by photorefractive keratectomy. J Refract Surg 1997; 13:246 –254 4. Seiler T, Reckmann W, Maloney RK. Effective spherical aberration of the cornea as a quantitative descriptor in corneal topography. J Cataract Refract Surg 1993; 19: 155–165 5. Hersh PS, Shah SI, Geiger D, et al. Corneal optical irregularity after excimer laser photorefractive keratectomy. J Cataract Refract Surg 1996; 22:197–204 6. Wachler BSB, Durrie DS, Assil KK, Krueger RR. Role of clearance and treatment zones in contrast sensitivity: significance in refractive surgery. J Cataract Refract Surg 1999; 25:16 –23 7. Ghaith AA, Daniel J, Stulting RD, et al. Contrast sensitivity and glare disability after radial keratotomy and photorefractive keratectomy. Arch Ophthalmol 1998; 116: 12–18 8. Niesen U, Businger U, Hartmann P, et al. Glare sensitivity and visual acuity after excimer laser photorefractive keratectomy for myopia. Br J Ophthalmol 1997; 81: 136 –140 9. Wang Z, Chen J, Yang B. Comparison of laser in situ keratomileusis and photorefractive keratectomy to cor-
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10.
11.
12.
13.
14.
15.
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rect myopia from –1.25 to – 6.00 diopters. J Refract Surg 1997; 13:528 –534 Ficker LA, Bates AK, Steele ADMcG, et al. Excimer laser photorefractive keratectomy for myopia: 12 month follow-up. Eye 1993; 7:617– 624 Halliday BL. Refractive and visual results and patient satisfaction after excimer laser photorefractive keratectomy for myopia. Br J Ophthalmol 1995; 79:881– 887 Butuner Z, Elliot DB, Gimbel HV, Slimmon S. Visual function one year after excmier laser photorefractive keratectomy. J Refract Corneal Surg 1994; 10:625– 630 Niesen UM, Businger U, Schipper I. Disability glare after excimer laser photorefractive keratectomy for myopia. J Refract Surg 1996; 12:S267–S2688 Verdon W, Bullimore M, Maloney RK. Visual performance after photorefractive keratectomy; a prospective study. Arch Ophthalmol 1996; 114:1465–1472 O’Brart DPS, Lohmann CP, Fitzke FW, et al. Nightvision after excimer laser photorefractive keratectomy: haze and halos. Eur J Ophthalmol 1994; 4:43–51
16. Baron WS, Munnerlyn C. Predicting visual performance following excimer photorefractive keratectomy. Refract Corneal Surg 1992; 8:355–362 17. Hamberg-Nystro¨m H, Tengroth B, Fagerholm P, et al. Patient satisfaction following photorefractive keratectomy for myopia. J Refract Surg 1995; 11(suppl):S335– S336 18. Oliver KM, Hemenger RP, Corbett MC, et al. Corneal optical aberrations induced by photorefractive keratectomy. J Refract Surg 1997; 13:246 –254 19. O’Brart DPS, Gartry DS, Lohmann CP, et al. Excimer laser photorefractive keratectomy for myopia: comparison of 4.00- and 5.00-millimeter ablation zones. J Refract Corneal Surg 1994; 10:87–94 20. Salz J. Screening for pupil size in prospective refractive surgery patients (letter). J Cataract Refract Surg 1998; 24:292–293 21. Uozato H, Guyton DL. Centering corneal surgical procedures. Am J Ophthalmol 1987; 103:264 –275; correction, 852
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© 2001 ASCRS and ESCRS Published by Elsevier Science Inc.
0886-3350/01/$–see front matter PII S0886-3350(01)00871-9
PREOPERATIVE PUPIL MEASUREMENTS AND PARK
M
ultiple studies have evaluated corneal aberrations following excimer laser refractive keratectomy.1–5 Aberrations resulting from photoablation of the central cornea and the resulting clearance zone (difference between the pupil and ablation zone) with the excimer laser may account for symptoms of glare, halos, disturbances in night vision, and decreases in visual performance with psychophysical measures.6 –17 Pupil dilation (ie, during scotopic conditions) may significantly increase these aberrations following photorefractive keratectomy (PRK).1–2 Corneal modulation transfer function calculations suggest that these aberrations may result in a significant loss of visual performance following PRK, especially in eyes with larger pupil diameters.18 In this study, we prospectively evaluated the effect of preoperative variables such as pupil size on the patient’s perception of glare and halos as well as on the visual performance up to 2 years after photoastigmatic refractive keratectomy (PARK).
Patients and Methods Ninety-three eyes of 56 patients with primary compound myopic astigmatism with between ⫺1.0 and ⫺7.0 diopters (D) of sphere and between ⫺1.0 and ⫺5.0 D of astigmatism had PARK. Preoperatively, the patient had a complete ophthalmic history and examination including refraction, slitlamp examination, Goldmann applanation tonometry, dilated fundus examination, contrast sensitivity function test, and a measurement of best spectacle-corrected visual acuity (BSCVA). Contrast sensitivity was measured with the sinusoidal pattern CSV 1000-E (Vector Vision) under scotopic (21 lux) and photopic (324 lux) conditions. Best spectacle-corrected visual acuity was measured under glare, scotopic, and photopic conditions using the Lighthouse Distance Visual Acuity Test (Lighthouse Low Vision Products). Pupil size was measured with a standard pupil gauge (millimeters) on a Accepted for publication March 5, 2001.
near card under scotopic (21 lux) and photopic (324 lux) conditions. The patient did not wear spectacles during pupil measurement. All references to pupil sizes refer to preoperative measurements made in this fashion. Astigmatic alignment was achieved by marking the horizontal axis (0 to 180 degrees) with a surgical marking pen (Devon Industries) using a horizontal slit beam at the slitlamp with patients seated in the upright position. After topical proparacaine hydrochloride 0.5% (Ophthetic威), ofloxacin 0.3% (Ocuflox威), and diclofenac sodium 0.1% (Voltaren威) were instilled, the corneal epithelium was removed with a blunt PRK spatula. Photoastigmatic refractive keratectomy was performed with the Summit Apex Plus excimer laser with standard laser parameters. A 6.5 ⫻ 5.0 mm elliptical ablation zone was delivered through a poly(methyl methacrylate) erodible astigmatic mask system. A bandage contact lens was placed on the eye until the cornea had completely reepithelialized. Postoperative eye medications included topical Ocuflox 4 times daily for 4 days or until the epithelium was healed and topical fluorometholone 0.1% (FML威) 4 times daily for 1 month and then twice a day for 1 month. Patients were prospectively evaluated at 1, 3, 6, 9, 12, 18, and 24 months. Best spectacle-corrected visual acuity under glare, scotopic, and photopic conditions was measured as described at each postoperative visit. Contrast sensitivity was measured as described at 6, 12, and 24 months. Each patient completed a survey rating adverse symptoms such as glare, halos, and visual blurring. The patient scored each symptom on a scale of 0 (none) to 5 (severe). This survey was conducted at the preoperative examination and 6, 12, and 24 months postoperatively. The SPSS Graduate Pack for Windows V6.1.3 (SPSS Inc.) was used to determine statistical significance. To determine the statistical association between dependent and independent continuous variables, a linear regression model was performed. Differences were considered to be statistically significant when the P value was less than 0.05.
From Department of Ophthalmology, Stanford University School of Medicine, Stanford, California, USA. Neither author has a financial interest in any product mentioned. Reprint requests to Edward E. Manche, MD, Stanford University School of Medicine, Department of Ophthalmology, 300 Pasteur Drive, Suite A175, Stanford, California 94305, USA. 908
Results The mean preoperative sphere was –3.88 D ⫾ 1.83 (SD) (range ⫺1.0 to –7.0 D), the mean preoperative astigmatism, –2.19 ⫾ 0.90 D (range ⫺1.0 to –5.0 D),
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Figure 1. (Haw) Distribution of pupil diameter under scotopic and photopic illuminance conditions during the preoperative examination. Measurements were made with a standard pupillary gauge on a near card.
and the mean preoperative spherical equivalent (SE), – 4.98 ⫾ 1.80 D (range ⫺1.75 to – 8.50 D). Forty-nine eyes (52.7%) were in women and 44 eyes (47.3%), in men. The mean patient age was 41.40 ⫾ 8.54 years (range 26 to 58 years). Prior to the 2 year follow-up, 24 eyes (25.8%) required retreatment. These eyes are excluded from the 2 year follow-up results. Fifty-nine (71.1%) of the remaining eyes were available for analysis. The distribution of pupil size under scotopic and photopic conditions is shown in Figure 1. Figures 2 to 15 are topographic maps that demonstrate the effect of scotopic and photopic pupil size on symptoms of glare, halo, visual blurring, and visual performance. Visual performance results are recorded as a change in BSCVA (Snellen lines) and a change in contrast sensitivity (log units) under standard illuminance conditions. Pupil size was measured to the nearest 1.0 mm. A linear extrapolation model was performed between pupil size measurements. For example, Figure 12 plots the effect of photopic pupil size on scotopic BSCVA at each postoperative interval. The horizontal x-axis is the postoperative interval recorded in months following PARK treatment, while the vertical y-axis is the photopic pupil size recorded according to the previously described method. As in a topographic map, the color changes on the graph represent different degrees of loss or gain of BSCVA (Snellen lines) for each corresponding x and y point. The legend for this color change is designated at the lower righthand corner of the graph: white represents a mean gain of 0 to 1 Snellen lines, black represents a mean loss of 0 to 1 Snellen lines, and gray represents a mean loss of 1 to 2 Snellen lines. Thus, Figure 12 demonstrates a mean loss of 0 to 1 Snellen lines (black tone) during the first 6
Figure 2. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on the change in the glare score at each postoperative follow-up.
months after PARK treatment for photopic pupil sizes of approximately 2.0 to 4.0 mm. For photopic pupil sizes of 5.0 mm, the initial loss of BSCVA was between 1 and 2 Snellen lines (light gray tone) during the first month. After 6 months, there was a mean gain of 0 to 1 Snellen lines (white tone) in the photopic BSCVA for most pupil sizes. Symptoms of Glare, Halo, and Visual Blurring As shown in Figure 2, a preoperative photopic pupil size of approximately 4.0 to 5.0 mm showed an increase in glare symptoms from the preoperative level at all postoperative intervals. In contrast, eyes with photopic pupils ⬍ 4.0 to 5.0 mm showed a tendency toward a decrease in glare, especially at 24 months. A larger preoperative scotopic pupil size did not correlate with an increase in glare symptoms (Figure 3). While there was no statistically significant contribution of preoperative photopic or scotopic pupil size to glare
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Figure 3. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in the glare score at each postoperative follow-up.
Figure 4. (Haw) Topographic map illustrates the effect of photopic
Figure 5.
(Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in the halo score at each postoperative follow-up.
Figure 6. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on the change in the visual blurring score at each postoperative follow-up.
symptoms, the attempted level of correction (SE) did play a role in the development of glare symptoms at both 6 (P ⬍ .01; adjusted r2 ⫽ 0.10) and 12 (P ⬍ .01; adjusted r2 ⫽ 0.09) months. By 18 and 24 months, these were not statistically significant. Neither preoperative astigmatic or sphere corrections contributed to the development of glare at any postoperative interval (P ⬎ .05). Symptoms of halos were most pronounced in the first 6 to 12 months in photopic pupil sizes of approximately 4.0 to 5.0 mm (Figure 4). Eyes with small photopic pupils (ⱕ2.0 to 3.0 mm) demonstrated a rapid recovery of halo symptoms between 18 and 24 months,
which was not seen in eyes with larger photopic pupils. Scotopic pupil size did not have a statistically significant effect on halo symptoms at any postoperative interval (Figure 5). Although neither scotopic nor photopic pupil size was correlated with halo symptoms (P ⬎ .05), there was a slight correlation between high astigmatic correction and the development of halos at 12 months (P ⬍ .01, adjusted r2 ⫽ 0.09). Symptoms of visual blurring were higher at every postoperative interval in photopic pupil sizes ⱖ5.0 mm than in photopic pupils ⬍5.0 mm (Figure 6). This was statistically significant at 12 months (P ⬍ .01; adjusted r2 ⫽ 0.10). Scotopic pupil size did not contribute to the
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pupil size (mm) on the change in the halo score at each postoperative follow-up.
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Figure 7. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in the visual blurring score at each postoperative follow-up.
development of visual blurring symptoms (Figure 7) (P ⬎ .05). Best Spectacle-Corrected Visual Acuity Under Glare, Photopic, and Scotopic Conditions There was an initial decrease in BSCVA under glare conditions in all photopic pupil sizes 1 month after
PARK (Figure 8). Glare BSCVA did not recover to the preoperative level until 9 months in eyes with 2.0 mm photopic pupil diameters compared to 3 to 6 months in eyes with photopic pupils ⬎2.0 mm. Glare BSCVA was temporarily decreased for 1 to 6 months in all scotopic pupil sizes (Figure 9). However, neither scotopic nor photopic pupil sizes significantly predicted changes in the glare BSCVA for any measured postoperative interval (P ⬎ .05). Figure 10 shows a return of mean photopic BSCVA to the preoperative level within 3 to 6 months in eyes with photopic pupils ⱖ4.0 mm and between 9 and 24 months in eyes with photopic pupils of 2.0 to 3.0 mm. As shown in Figure 11, photopic BSCVA recovered to the preoperative levels more quckly in eyes with ⬎5.0 mm scotopic pupil sizes (3 to 6 months) than in eyes with ⱕ5.0 scotopic pupil sizes (over 9 months). However, the effect of scotopic pupil sizes did not significantly predict changes in the photopic BSCVA (P ⬎ .05). An initial decrease in the scotopic BSCVA was shown in all photopic pupil sizes during the first 6 months following PARK, with the largest decrease in photopic pupils ⱖ5.0 mm (Figure 12). Recovery oc-
Figure 8. (Haw) Topographic map illustrates the effect of photopic pupil size on the change in BSCVA under glare conditions (Snellen lines) at each postoperative follow-up.
Figure 9. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in BSCVA under glare conditions (Snellen lines) at each postoperative follow-up.
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Figure 10. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on the change in BSCVA under photopic conditions (Snellen lines) at each postoperative follow-up.
Figure 11. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in BSCVA under photopic conditions (Snellen lines) at each postoperative follow-up.
Figure 12. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on the change in BSCVA under scotopic conditions (Snellen lines) at each postoperative follow-up.
curred by 6 months. Scotopic pupils ⱖ6.0 mm showed a tendency toward a larger initial decrease in the scotopic BSCVA in the first 1 to 3 months (Figure 13). Recovery was also slower in eyes with larger scotopic pupil sizes. Eyes with scotopic pupils larger than approximately 6.0 mm did not recover to the preoperative levels until after 12 months. In contrast, eyes with scotopic pupils ⬍6.0 mm recovered to their preoperative level by 6 months. Despite this tendency, there was no predictive effect of scotopic pupil size on scotopic BSCVA 912
(P ⬎ .05). A slight predictive effect of the attempted level of astigmatic correction was demonstrated in the initial decrease of scotopic BSCVA 1 month after PARK (P ⫽ .03). However, this effect was small (adjusted r2 ⫽ 0.04). Contrast Sensitivity The effect of photopic pupil size on photopic contrast sensitivity was not statistically significant at 2 years (Figure 14). Higher levels of attempted SE correction
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Figure 13. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on the change in BSCVA under scotopic conditions (Snellen lines) at each postoperative follow-up.
Figure 14. (Haw) Topographic map illustrates the effect of photopic pupil size (mm) on contrast sensitivity (log units) under photopic conditions 24 months after PARK.
Figure 15. (Haw) Topographic map illustrates the effect of scotopic pupil size (mm) on contrast sensitivity (log units) under scotopic conditions 24 months after PARK.
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were minimally correlated with a decrease in the 12.0 spatial frequency (P ⫽ .01, adjusted r2 ⫽ 0.09). Figure 15 illustrates the change in contrast sensitivity as a function of scotopic pupil size under scotopic illuminance conditions 2 years after PARK. There was a clinically insignificant decline in contrast at the 3.0 cycles per degree (cpd) spatial frequency in most scotopic pupil sizes. Recovery of scotopic contrast sensitivity in eyes with ⱕ6.0 mm scotopic pupil sizes was more complete at spatial frequencies ⬎12.0 cpd. However, the effect of scotopic pupil size on scotopic contrast sensitivity was statistically insignificant. Higher levels of attempted SE correction were minimally predictive of a decrease in the 12.0 and 18.0 spatial frequencies (P ⫽ .02 and P ⫽ .03, respectively).
Discussion Multiple studies have demonstrated an alteration in the distribution and magnitude of coma and spherical aberrations following pupil dilation after PRK.1,2 In a study by Oshika et al.,2 there was a 25- to 32-fold increase in total wavefront aberrations with simulated pupil dilation after PRK compared to a 5- to 6-fold increase before PRK. In this study, the total wavefront aberrations did not return to normal by the 12 month followup. Thus, it is not surprising that some patients may complain of illuminance-dependent symptoms that may be related to the physiologic pupil dilation during scotopic conditions.19 A study has objectively demonstrated the role of PRK ablation profiles and clearance zones on visual performance tests such as contrast sensitivity.6 The attempted level of correction has also been implicated in an increased magnitude of aberration1 and patient symptoms.11 Our results confirm studies suggesting that the level of attempted correction and therefore the depth of ablation play a role in the increase in symptoms of glare in the early postoperative period. The level of attempted SE correction was related to an increase in symptoms of glare during 6 months (P ⬍ .01) and 12 months (P ⬍ .01) after PARK. Martinez et al.1 found the magnitude of the surgically induced aberration to be strongly correlated with the attempted correction (adjusted r2 ⫽ 0.6 at 1 month in a 7.0 mm pupil). In our study, by 6 and 12 months, the attempted level of SE correction did not account for 914
most of the glare symptoms (adjusted r2 of 0.10 and 0.09, respectively). At each of these intervals, there was a mean increase in the glare score of 0.37 and 0.35 for each diopter of attempted SE correction. This represented a 27% and 26% increase in the glare score from the preoperative level. After 12 months, the level of attempted correction lost its predictive effect for glare symptoms. The level of attempted SE correction was also weakly related to an increase in the halo score at 12 months (P ⬍ .01; adjusted r2 ⫽ 0.09). However, the level of SE did not contribute to changes in the BSCVA under photopic, scotopic, or glare conditions. Preoperative scotopic pupil diameter was not statistically correlated with symptoms of glare and halos. It also was not statistically predictive of decreases in contrast sensitivity or loss of BSCVA under glare, scotopic, or photopic conditions at any of the measured postoperative periods. In addition, the greater magnitude loss of BSCVA under scotopic conditions in the early postoperative period as well as the slower recovery to preoperative levels in eyes with larger scotopic pupil diameters were not statistically significant. A larger sample size may have been useful in establishing statistical significance and confirming previous reports suggesting that visual performance may demonstrate a decline in function related to clearance zones compromised by large pupil diameters.6 Most studies deal with the role of large or scotopic pupil sizes in the development of patient symptoms or decreases in visual performance, since aberrations are heightened following increased clearance zones resulting from smaller ablation profiles or larger pupil sizes. The role of photopic pupil measurements is not well studied. However, photoablation of the central visual axis would be expected to introduce some optical irregularities despite the clearance zones. In fact, Oshika et al.2 demonstrate corneal wavefront aberrations occurring in 3.0 mm pupils after excimer laser photoablation despite a 5.5 mm ablation zone using the Nidek EC5000 excimer laser. In our study, photopic pupil diameter was minimally predictive of increased loss of BSCVA under photopic conditions 6 months after PARK. Although simulated glare tests more closely resemble conditions under photopic conditions than under scotopic conditions,1 neither the glare symptoms nor the loss of glare BSCVA was related to photopic pupil size.
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It is interesting that the level of astigmatic correction did not affect our outcome variables more dramatically. Since the dimensions of the elliptical photoablation are dependent on the level of attempted astigmatic correction, this would be expected to affect the clearance zone (difference between the treatment zone and pupil diameter). The clearance zone has been shown to correlate with changes in contrast sensitivity at spatial frequencies of 6 and 12 cpd.6 In our study, we found that astigmatic correction adversely predicted a poor performance of BSCVA under glare conditions 1, 9, and 12 months after PARK and the contrast sensitivity under photopic conditions at 12 months. However, the contribution was minimal. There are several limitations to our study. Confounding factors such as corneal haze may also contribute to increased symptoms and poor visual performance scores. In addition, we introduced a selection bias by excluding retreatment eyes after the 6 month analysis. (All retreatments were performed after 6 months.) The eyes having retreatment have a higher SE and are therefore at risk of corneal aberrations and developing postoperative symptoms.1,11 Establishing statistical significance may be more difficult with our distribution of pupil diameters, which demonstrate a small number of eyes in the extreme ranges of the photopic (ⱕ2.0 mm and ⱖ5.0 mm) and scotopic (⬍4.0 mm and ⱖ8.0 mm) illuminance conditions. Also, measuring pupil diameter with a near card is a subjective measurement that introduces observer variation. A standard pupillary gauge may also inadequately determine the true pupil size in dim illumination. In some patients, infrared pupillometers may be more accurate in determining pupil diameter and account for patients experiencing illumination-dependent symptoms despite a “normal” pupil measurement.20 Thus, a prospective study of symptoms of glare and halos using more objective research pupillometers to measure pupil diameters would contribute to our understanding of these issues. Other difficulties in estimating pupil sizes stem from the optical properties of the anterior segment. It has been demonstrated that because the location of the virtual entrance pupil differs from the true pupil by approximately 0.5 mm, this may result in an observerbased overestimation of the true pupil diameter by
14%.21 However, while this source of error in determining the pupil diameter would be expected to be larger for larger pupil sizes, it would also be expected to result in systematic overestimation of true pupil size. In summary, although we did not find a statistical correlation between preoperative pupil sizes and the development of symptoms of glare and halos, we did identify potential relationships that may support the measurement of pupil diameters preoperatively. An assessment of preoperative pupil sizes and the attempted level of both the SE and astigmatic correction may be useful in identifying patients who may be at risk of developing symptoms or declines in visual performance following PARK. However, the predictive effect of preoperative pupil measurements may not be clinically significant by the 2 year follow-up.
References 1. Martinez CE, Applegate RA, Klyce SD, et al. Effect of pupillary dilation on corneal optical aberrations after photorefractive keratectomy. Arch Ophthalmol 1998; 116:1053–1062 2. Oshika T, Klyce SD, Applegate RA, et al. Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis. Am J Ophthalmol 1999; 127:1–7 3. Oliver KM, Hemenger RP, Corbett MC, et al. Corneal optical aberrations induced by photorefractive keratectomy. J Refract Surg 1997; 13:246 –254 4. Seiler T, Reckmann W, Maloney RK. Effective spherical aberration of the cornea as a quantitative descriptor in corneal topography. J Cataract Refract Surg 1993; 19: 155–165 5. Hersh PS, Shah SI, Geiger D, et al. Corneal optical irregularity after excimer laser photorefractive keratectomy. J Cataract Refract Surg 1996; 22:197–204 6. Wachler BSB, Durrie DS, Assil KK, Krueger RR. Role of clearance and treatment zones in contrast sensitivity: significance in refractive surgery. J Cataract Refract Surg 1999; 25:16 –23 7. Ghaith AA, Daniel J, Stulting RD, et al. Contrast sensitivity and glare disability after radial keratotomy and photorefractive keratectomy. Arch Ophthalmol 1998; 116: 12–18 8. Niesen U, Businger U, Hartmann P, et al. Glare sensitivity and visual acuity after excimer laser photorefractive keratectomy for myopia. Br J Ophthalmol 1997; 81: 136 –140 9. Wang Z, Chen J, Yang B. Comparison of laser in situ keratomileusis and photorefractive keratectomy to cor-
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rect myopia from –1.25 to – 6.00 diopters. J Refract Surg 1997; 13:528 –534 Ficker LA, Bates AK, Steele ADMcG, et al. Excimer laser photorefractive keratectomy for myopia: 12 month follow-up. Eye 1993; 7:617– 624 Halliday BL. Refractive and visual results and patient satisfaction after excimer laser photorefractive keratectomy for myopia. Br J Ophthalmol 1995; 79:881– 887 Butuner Z, Elliot DB, Gimbel HV, Slimmon S. Visual function one year after excmier laser photorefractive keratectomy. J Refract Corneal Surg 1994; 10:625– 630 Niesen UM, Businger U, Schipper I. Disability glare after excimer laser photorefractive keratectomy for myopia. J Refract Surg 1996; 12:S267–S2688 Verdon W, Bullimore M, Maloney RK. Visual performance after photorefractive keratectomy; a prospective study. Arch Ophthalmol 1996; 114:1465–1472 O’Brart DPS, Lohmann CP, Fitzke FW, et al. Nightvision after excimer laser photorefractive keratectomy: haze and halos. Eur J Ophthalmol 1994; 4:43–51
16. Baron WS, Munnerlyn C. Predicting visual performance following excimer photorefractive keratectomy. Refract Corneal Surg 1992; 8:355–362 17. Hamberg-Nystro¨m H, Tengroth B, Fagerholm P, et al. Patient satisfaction following photorefractive keratectomy for myopia. J Refract Surg 1995; 11(suppl):S335– S336 18. Oliver KM, Hemenger RP, Corbett MC, et al. Corneal optical aberrations induced by photorefractive keratectomy. J Refract Surg 1997; 13:246 –254 19. O’Brart DPS, Gartry DS, Lohmann CP, et al. Excimer laser photorefractive keratectomy for myopia: comparison of 4.00- and 5.00-millimeter ablation zones. J Refract Corneal Surg 1994; 10:87–94 20. Salz J. Screening for pupil size in prospective refractive surgery patients (letter). J Cataract Refract Surg 1998; 24:292–293 21. Uozato H, Guyton DL. Centering corneal surgical procedures. Am J Ophthalmol 1987; 103:264 –275; correction, 852
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