Quality of Vision After Refractive Surgery 19 Thomas Kohnen, Jens Bühren, Thomas Kasper, Evdoxia Terzi

$Quality of Vision After Refractive Surgery 19 Thomas Kohnen, Jens Bühren, Thomas Kasper, Evdoxia Terzi$

The authors have no proprietary interest in any of the devices used in this study.

| Core Messages proving with more experience, better technolo- ∑ After inventing, evaluating and perfecting gy and scientific evaluation. Success or failure of refractive surgical procedures in recent refractive procedures, defined by criteria like years, one of the current efforts is to safety, efficacy, stability and predictability [13] is focus on “quality of vision”after various based on Snellen acuity. However, some patients refractive surgical interventions present with anatomically perfect results and ex- ∑ Quality of vision is acceptable if a refractive cellent visual outcome with respect to these cri- surgical procedure results in retinal image teria measured in Snellen acuity,but complain of quality that does not produce a subjective visual disturbances like decreased contrast, dif- or objective decrease in vision ferent colour perception, glare, halos or simply ∑ Quality of vision after refractive surgery “bad vision”. In some cases the problem can be is a complex topic with many variables explained, e.g. by residual astigmatism or a de- ∑ Measuring quality of vision involves centred ablation zone in excimer surgery or the four major parameters: patient’s sensation, optic diameter of a phakic intraocular lens im- functional, optical and anatomical features plant on halo perception, in other cases an im- ∑ For corneal surgery, optical zone, pupil size mediate answer is not found. On the contrary, in and ablation depth, for lens procedures, retrospect there should have been problems (6- centration and optic design play a major mm ablation zone for LASIK with 7-mm sco- role topic pupil size diameter) that fortunately have ∑ The overall improvement of the quality of never occurred. Therefore determining the out- vision after refractive surgical interventions come seems to be more complex. Why do only will be a major step for the success of some patients complain? Are some complaints refractive surgery associated with simple residual refractive error or are there other much more sophisticated reasons for visual disturbances yet unknown to the patients [14]? The present chapter gives an 19.1 overview of how quality of vision could be de- Introduction fined and determined and summarises typical disturbances which are known to date. After inventing, evaluating and perfecting refractive surgical procedures in recent years, one of the current efforts is to focus on “quality of vi- 19.2 sion” after various surgical interventions. The Defining Quality of Vision number of surgical procedures to correct refractive errors is steadily increasing, old procedures Although “quality of vision”seems to be a major are replaced by newer, mostly better ones, the concern in modern refractive surgery there is complication rate is decreasing, and the results no systematic approach to define quality of vi- of each of the established procedures are im- sion as yet. Certainly, quality of vision is not a 304 Chapter 19 Quality of Vision After Refractive Surgery

Fig. 19.1. Overview of the different levels of factors affecting quality of vision

metric which can be determined in a straight “quality of vision”, typical features of “good” or line, e.g. like the objective refraction or the axial “bad” vision have to be catalogued. At the next length of the eye. Therefore, operationalisation step, factors of the underlying pathway in is necessary to access the somewhat vague con- Fig. 19.1 and their association with “good” or cept of “quality of vision”. Vision is a complex “bad” vision should be identified. This would process and the perception of a visual stimulus enable one to establish evidenced-based ap- is affected by many factors which are illustrated proaches to improve quality of vision after re- in a simplified way in Fig. 19.1. Primarily, fractive surgery or to forestall bad outcomes anatomic features such as characteristics of the and patient dissatisfaction. corneal surface, corneal curvature, clearness of the optical media and axial length of the eye determine the quality of the retinal image. The 19.2.1 quality of the retinal image influences basic vi- Subjective Symptoms sual tasks like resolution and contrast detection. Finally, the image is processed by the visual sys- It is important to mention that for most patients tem. A variety of subtle mechanisms (e.g. the their visual impression with a particular correc- Stiles-Crawford effect) provide compensation tion (glasses or contact lenses) before undergo- for errors of the optical system of the eye. This ing refractive surgery is their reference for the leads to a specific perception of the initial visu- post-operative situation. Obviously, some un- al stimulus. The final valuation of the overall wanted visual phenomena are familiar to all re- image quality by the viewer depends on many fractive surgical patients, e.g. blurry vision be- intrinsic factors and situations. Given the same cause of residual refractive error. Other retinal image, the letter “E”as shown in Fig. 19.1, symptoms, like haloes, starbursts, ghosting and might appear crisp to one and blurry to the oth- loss of contrast sensitivity may be new to the pa- er observer.Therefore,when defining “quality of tient and cause certain alarm. The patient’s ex- vision”, one should start with the patient’s as- pectations and tolerance to possible side effects sessment of his quality of vision. This is crucial, play a key role for the outcome. Some patients because it is the patient who ultimately decides definitely report starbursts and haloes, but they if his vision is “good” or “bad”. Conversely, the nevertheless are comfortable with the result. changes made by refractive surgery are changes Connecting the same eye to another brain could of anatomy. For an operational definition of possibly result in an extremely unhappy patient. 19.2 Defining Quality of Vision 305

Thus, it is both important to know what side-ef- dure. Correlation of functional results with sub- fects have to be expected performing a certain jective symptoms on the one hand and with ob- treatment and how the patient’s assessment of jective measurements on the other hand will es- his quality of vision would be influenced by tablish connections between the patient’s these symptoms. In a clinical environment, a complaints and the quantitative measurements careful anamnesis would address the patient’s performed in clinical practice and trials. subjective symptoms, whereas in clinical trials standardised questionnaires should be used to quantify symptoms. There is a range of ques- 19.2.3 tionnaires on vision and daily activities, some Optical Image Quality set up for cataract patients, some recently created to assess refractive procedures (see Sect. An ideal optical system would depict an object 19.3). These questionnaires are very important without loss of contrast or resolution,i.e.a point for understanding and defining quality of vi- will be imaged as a point. In fact, the eye is not a sion, because they are the link between the pa- perfect optical system. There are three major tient’s sensations and all other measurements reasons for degradation of the retinal image: [20]. diffraction, aberrations and scatter. Diffraction is only clinically relevant for small pupil sizes (<3 mm),whereas aberrations and scatter (stray 19.2.2 light) are important factors which influence Visual Function quality of vision, particularly at larger pupil sizes. All three conditions affect the retinal im- Most patient complaints regarding refractive age by transforming a point-shaped object into surgery concern some type of decrease in visu- a more or less fuzzy dot. Lower-order aberra- al function. Blurriness or fuzziness of sight can tions, known as prismatic, spherical and cylin- become evident in reduction of the contrast drical error [tilt, defocus and astigmatism in sensitivity function with diminishing maxi- terms of Zernike polynomials, (see Chap. 17)] mum contrast sensitivity on the one hand and are dominant in many eyes and have tremen- decreasing maximum resolution on the other dous impact on image quality. Besides the low- hand. There is a large variety of psychophysical er-order aberrations, other irregularities, tests to determine visual function,ranging from known as higher-order aberrations (HOA) have standard Snellen acuity charts to contrast sensi- been described. Coma and spherical aberration tivity or low-contrast acuity tests up to sophisti- are two aberrations leading to characteristic cated procedures to assess haloes, glare disabil- image degradation and have been well-known ity and stray light (see Sect. 19.3). Up to now, the for quite some time. They have been included in main outcome measure in assessment of refrac- the set of Zernike polynomials, which can be tive-surgical procedures was “Snellen acuity”, used to describe the wavefront error of a certain the angular visual acuity determined by high- optical system in a systematic way [3, 28]. From contrast optotypes. As many activities in daily the wavefront error of an eye, several metrics as life do not take place under optimal lighting the point spread function (PSF; the distribution conditions, Snellen acuity reflects only one ele- of light intensity at the retinal focal plane when ment of visual function and gives only partial a point-shaped light source is imaged) or the insight into the quality of vision. Thus, contrast modulation transfer function (MTF, the degree sensitivity or low-contrast visual acuity testing of contrast transfer of a sinusoidal grating as a will play a major role besides Snellen acuity function of spatial frequency) can be derived testing to determine quality of vision. For the (see Chap. 17). These metrics, which could be definition of quality of vision, the psychophysi- obtained easily by objective measurements cal tests act as a standardised representation of (wavefront sensing or double-pass measure- single visual tasks that may be more or less af- ments) reflect the retinal image quality of the fected in daily life by a refractive surgical proce- eye considering the eye as an optical instrument 306 Chapter 19 Quality of Vision After Refractive Surgery

and ignoring the role of neural image transfer both patient and examiner. Some of the tests and processing. This is of high value when as- could be added easily to a clinical setting,others sessing the plain optical effect of a certain re- will be reserved for investigational purposes. fractive procedure or comparing different tech- Before describing the tests in detail, some niques, because these metrics are objective. initial comments on desirable testing conditions should be made: First, visual testing, particularly in myopes, needs to be performed un- 19.2.4 der the same conditions pre- and post- The Role of Anatomy operatively. Only the best pre-operative measurement (often better with contact lenses than The anatomy of the eye plays a major role for with spectacles) should be compared to the quality of vision,because the effects achieved by post-operative outcome, because the patient refractive surgery, side effects included, are ex- will always compare the result to the optimal clusively anatomical. Therefore, anatomy is the pre-operative situation. Second, at least in the “input” level of the pathway in Fig. 19.1, in con- clinical setting, there should be internal stan- trast to the subjective symptoms, which repre- dards on how to test. Up to now there have only sent the “output” level. This is very important been few standards for a common procedure because all other changes are consequences of like testing visual acuity, mostly applied in the anatomical change induced by surgery. Ex- cases of medico-legal issues. Interestingly, no amining anatomy does not provide direct con- guidelines for determining Snellen acuity or clusions on quality of vision, but it gives per- contrast sensitivity in refractive surgery have as haps the most objective feedback on the precise yet been established. In different studies, or in effect of the treatment. Establishing correla- daily practice, different investigators and de- tions between anatomy, function and subjective vices may be involved and produce biased re- symptoms enables further improvements in the sults, making these results less comparable. It is field of refractive surgery and safer treatments important to point out that testing visual acuity to provide good quality of vision. or contrast sensitivity means determining psychophysical thresholds. It is desirable that all Summary for the Clinician these thresholds are tested pre- and post-opera- ∑ Quality of vision after refractive surgery tively under comparable and reproducible is a complex topic with many variables conditions which means, to name only some, which are influenced by many factors, similar optotypes and lightening conditions, both extrinsic and intrinsic forced-choice testing, no feedback by the inves- ∑ Thus, for a working definition it could be tigator and low probability of guessing [14]. stated that a good quality of vision is given When the threshold is defined as the steepest if a refractive surgical procedure does not point of the psychometric function and rigor- affect the retinal image quality in the way ous forced-choice is applied, acuity values can that vision is experienced worse than be around 20/10 even without “super normal before surgery correction” [32]. The following sections give an overview of common tests which test parameters that are 19.3 relevant for quality of vision. In a clinical envi- Measuring Quality of Vision ronment not all of the test types could be used, but it is helpful to have a range of routine exam- From the operational definition for quality of inations such as standardised anamnesis, visual vision given above, it can be concluded that sev- acuity (VA), contrast sensitivity (CS), corneal eral parameters could be assessed to determine topography and aberrometry to assess the out- optical quality before and after refractive sur- come of the procedures carried out in the clini- gery. However, many of the tests are not part of cal setting. clinical routine and therefore uncommon to 19.3 Measuring Quality of Vision 307

19.3.2.2 19.3.1 Low-Contrast VA Subjective: Questionnaires Low-contrast visual acuity can be measured, as Quality of vision can be measured objectively high-contrast visual acuity, by optotypes of a (high- or low-contrast visual acuity, contrast constant low contrast and of varying, decreas- sensitivity, glare disability, wavefront aberra- ing size.Letter charts applying this principle are tions,corneal topographical changes) or subjec- the Reagan charts, the Bailey-Lovie charts and tively by questionnaires. Functional measure- the low-contrast ETDRS charts, that are provid- ments of contrast sensitivity or glare disability, ed at different low contrast levels. Landolt-C measurements of optical parameters like wave- rings are used by the FrACT. front error, and anatomical observations by corneal topography or biomicroscopy can be 19.3.2.3 correlated to the patients’ subjective judgement Contrast Sensitivity on the surgical outcome with questionnaires. Thus, quality of vision can be approached sys- Contrast sensitivity (CS, the reciprocal value of tematically. the minimal contrast which is recognised by the There are questionnaires described in the lit- patient) can be measured with optotypes (let- erature that have been especially developed for ters or Landolt-C rings) or sine-wave gratings post-operative evaluation of refractive patients [9]. [5, 11, 16, 26]. However, until now, none of them Common optotype tests are the Pelli-Robson has been established for general use. For use in charts (Fig. 19.2a) and the Small Letter Contrast a daily clinical environment, a careful anamne- Test [24]. These charts use letters of constant sis with standardised questions (Do you see size but progressively decreasing contrast lev- haloes? How is your night vision?) or a small se- els. Landolt-Cs are used for CS measurements lection of questions is a helpful tool to evaluate by the computer-based FrACT. Based on the the outcome of subsequent procedures. concept of different channels for detection of different spatial frequencies, sine-wave gratings have been used for contrast sensitivity testing 19.3.2 for a long time. Gratings of different spatial fre- Functional quencies with decreasing contrast are provided on each chart. Commonly used sine-wave tests 19.3.2.1 are the Vistech charts, the F.A.C.T. chart High-Contrast VA (Snellen Acuity) (Fig. 19.2b), the Contrast Sensitivity Tester 1800 (Vision Sciences Research Corporation, San High-contrast testing is the first way to assess Ramon, CA) (Fig. 19.2c) and the CSV 1000E. visual acuity in clinical praxis.The common test The Vistech charts and their modification, the principle is to present optotypes of decreasing F.A.C.T. chart, are wall charts. Five spatial fre- size, at a constant contrast level of approximate- quencies, each with nine different contrast lev- ly 100%. High-contrast visual acuity is meas- els are present. The Contrast Sensitivity Tester ured either with letters (e.g. Snellen chart, 1800 integrates a F.A.C.T. chart and provides Bailey-Lovie chart or the ETDRS chart) or Lan- testing under controllable illuminance levels. dolt-C rings. Optotypes can be presented as The CSV 1000E provides gratings at four spatial charts or on a computer screen. Computer tests frequencies, each with eight different contrast such as the Freiburg Visual Acuity and Contrast levels, at 85 cd·m–2. Test (FrACT) [4] use sophisticated algorithms to determine psychophysical thresholds. 308 Chapter 19 Quality of Vision After Refractive Surgery

19.3.2.4 Glare, Scatter and Halo Testing

Glare disability can be measured when a glare source is added to a contrast sensitivity test. For testing with letter (Pelli-Robson charts) or gratings (Vistech charts,F.A.C.T.charts) wall charts, a hand-held device,the Brightness Acuity Tester (BAT) can be used to induce a glare effect.In the Contrast Sensitivity Tester 1800, a glare source of varying luminance is integrated in the test system. Landolt-C based glare tests are the Miller-Nadler Glare Tester and the Frankfurt- Freiburg Contrast and Acuity Test System (FF- CATS). The first one uses Landolt-Cs of different contrast levels at a constant spatial frequency, which are surrounded by a glare source of unchanged luminance. The latter is based on the FrACT computer program that displays a Landolt-C rings on a monitor which is surrounded by a glare source of constant luminance created by a circle of eight white light- emitting diodes (LED) in 3° to the centre of the Landolt ring. Devices for testing scotopic vision like the Rodenstock Nyktometer (Rodenstock) or the Mesoptometer (Oculus) test CS at a very low luminance level of 0.032 cd·m–2 and are equipped with an integrated glare source for glare testing. For scientific use, devices to objectively determine forward scatter (van den Berg stray b light meter [30]) and haloes (Tomey Glare and Halo software [17]) have been designed.

19.3.3 Optical:Wavefront Sensing, MTF,PSF

Changes in the optical properties of the eye lead to changes in the quality of the retinal image and thus to changes in quality of vision. Wave- front deformation describes changes in the optical system, and it can be quantified by metrics as the modulation transfer function (MTF) or c the point spread function (PSF) (see Fig. 19.3 and Chap. 17). Fig. 19.2 a–c. Contrast sensitivity tests. a Pelli-Rob- son chart.b F.A.C.T.c Contrast Sensitivity Tester 1800 19.3 Measuring Quality of Vision 309

a c

b d

Fig. 19.3 a–f. Demonstration of the different factors influencing quality of vision with an example of a decentred ablation zone after hyperopic LASIK. a Opacification of hinge region; b decentred ablation in corneal topography; c the increased higher-order aberrations are coma-dominated; d HOA point spread function (PSF); e image simulation of a Snellen chart; f image simulation of a contrast sensitivity function test chart. The final visual perception of the visual stimulus is influenced e by many factors and compensation mechanisms and therefore the images constructed from wavefront data may not represent the patient’s actual perception

f 310 Chapter 19 Quality of Vision After Refractive Surgery

∑ For reporting refractive surgery data, 19.3.4 standardised tests under standardised Anatomical: Biomicroscopy, conditions need to be established Corneal Topography

Slit-lamp biomicroscopy, corneal topography 19.4 and confocal microscopy reveal anatomical Specific Changes in Quality changes resulting from refractive procedures. of Vision After Refractive Surgery Wanted (corneal flattening or steepening) or unwanted (haze, snowflakes, folds, decentra- 19.4.1 tion, surface irregularities; Fig. 19.3) effects on Incisional Surgery the ocular anatomy directly affect quality of vision. Therefore, anatomical observations in The complaints frequently described after radi- post-operative patient care are essential in de- al keratotomy (RK) are glare disability, describing quality of vision as morphological cor- creased contrast sensitivity and image degrada- relates of functional, optical and subjective pa- tions [1, 8]. The incidence of glare disability and rameters. changes in contrast sensitivity is highest imme- In Fig. 19.3 an example case of hyperopic diately after surgery and decreases in most cas- LASIK with a decentred ablation zone and the es after 6 and 12 months. impact of the decentration on different dimen- It has been shown that this negative effect on sions of quality of vision is shown. At the slit- visual performance arises with increasing pupil lamp (Fig. 19.3a) an opacification at the hinge diameter because of increased higher order region could be seen. Corneal topography aberrations [2]. Regarding this, the diameter of (Fig. 19.3b) reveals a decentred ablation with ec- the optical clear zone plays the most important centric steepening. Wavefront analysis of high- role in creating such higher order aberrations er-order aberrations (HOA) (Fig. 19.3c) shows and the appearance of night vision disturbances the coma-dominated wavefront deformation. after radial incisional surgery. Grimmett et al. From the HOA, an HOA point spread function showed that an optical clear zone smaller than (PSF) (Fig. 19.3d) could be derived which repre- 3 mm can provoke such severe glare disability sents the theoretical retinal image which could that patients become unable to drive a car at be obtained after total correction of defocus night or even lose employment [10]. Because of and astigmatism. From the PSF, images that, it is necessary to create an optical clear (Fig. 19.3e,f) could been constructed by convo- zone which is greater than the scotopic or lution to simulate image distortion. For the par- mesopic pupil diameter to reach glare-free vi- ticular case, the typical coma-induced ghosting sion at night [29]. However, this limits the cor- could be visualised. It has to be said, that the fi- rective range of RK because the correction of nal visual perception is influenced by many fac- higher refractive errors causes a smaller optical tors and compensation mechanisms and there- clear zone. fore the images constructed from wavefront Another problem after RK is the variation of data may not represent the patient’s actual per- the refraction from morning to evening (diur- ception. nal shift) which also leads to subjective image degradations. This phenomenon could be per- Summary for the Clinician sistent over years. A possible reason for this is ∑ Measuring quality of vision involves four the corneal instability due to the radial incisions major parameters: patient’s sensation, func- which causes variable corneal steepening tional, optical and anatomical features or/and irregular astigmatism. ∑ Correlation of all four parameters may lead Because of these severe disadvantages, today, to a complete understanding of the visual RK has been abandoned and is not a standard function and quality of vision after refrac- method to correct high myopia. tive surgery 19.4 Specific Changes in Quality of Vision After Refractive Surgery 311

problems after PRK. This is attributed to larger 19.4.2 refractive differentials between the ablated and Excimer Surgery untouched cornea as well as more haze due to wound healing [21]. 19.4.2.1 Surface Ablation 19.4.2.2 Laser In Situ Keratomileusis (LASIK) After photorefractive keratectomy (PRK), patients often report decreased contrast sensitivi- Just as for surface ablation also after LASIK, ty [8, 31]. Mostly, these complaints change with pupil size, ablation diameter, centration of the time: immediately after surgery, contrast sensi- ablation and the amount of ablation depth play tivity is worse than after 6 months or 1 year. Al- important factors in visual outcome and in the though most patients’ complaints decrease with appearance of visual complaints like monocular time, there are some who still have severe con- diplopia, glare, halos, starbursts and decreased trast sensitivity loss after 12 months or more. contrast sensitivity. These optical phenomena These patients often received treatment of my- appear especially at mesopic or scotopic light- opia higher than 6 dioptres (D) [31]. Also ing conditions. LASIK specific problems may monocular diplopia (ghosting), glare and halos occur due to striae in the flap, epithelial in- may occur after PRK [11]. growth and misalignment of the flap. Fortu- An important factor for the end result of PRK nately,similar to PRK,most complaints improve treatment is the pupil diameter, especially at or resolve with time. night. Seiler et al. showed that spherical aberra- Hersh et al. found that compared to the pre- tions after PRK treatment rose markedly with operative situation with glasses or contact lens- increasing pupil diameter [27]. Because spheri- es, more patients report decreasing rather than cal aberrations lead to blur of the retinal image, worsening of glare symptoms 6 months after patients with large pupils at night could develop LASIK [11]. In the same study, the patients de- night vision disturbances like glare,haloes,star- scribed a mild increase in halo symptoms and bursts and loss of contrast sensitivity. monocular diplopia. Lee et al. found a correla- Of equal importance to pupil size is the diam- tion between halo symptoms and the amount of eter of the ablation zone. It has been shown that attempted correction of the spherical equiva- larger diameters of ablation reduce night halos, lent (SE) [16].They also found a decrease in con- initial hyperopic shift, wound haze and higher trast sensitivity under mesopic and partially order aberrations [6, 22]. With optical computer under photopic lighting conditions, although analysis, Roberts et al. simulated that ablation without any correlation to pupil size (patients’ zones had to be at least as large as pupil aperture pupil diameter was not larger than 7 mm) or at night to preclude glare at the fovea [25]. amount of ablation. Schallhorn et al. and Pop et Also important for a good visual outcome is al.did not find a significant correlation between a well-centred ablation (Fig. 19.3). As a result of pupil size and night vision complaints in pa- decentred ablation patients complain about ha- tients with moderate myopia [23, 26]. Schall- los, glare, monocular diplopia and ghost images horn et al. found increase of glare reports in pa- (Fig. 19.3) [18]. Even subclinical decentrations tients with larger pupil diameters only within may lead to increasing higher-order aberrations the first 3 months. Also, haze and halo reports with image degradation.In this context,it seems were more frequent, but this for all pupil diam- important to centre the ablation to the line of eters and only in the first 3 months.After a peri- sight because it is possible that the geometric od of 6 months, they could not find significant- centre of the pupil moves as the pupil diameter ly increased glare, haze and halo reports changes [7]. compared to pre-operative reports with contact Apart from sufficient ablation diameter and lenses.Like Lee et al.,they suspect the amount of well-centred ablation, the amount of ablation treated spherical equivalent and residual cylin- correlates with a higher incidence of vision der to be the cause of patients’ complaints. They 312 Chapter 19 Quality of Vision After Refractive Surgery

hold remodelling effects of the cornea and due to decentration. Modified rounded or non- adaptation mechanisms of the patient responsi- reflective edges reduce this potential for edge ble for this recovery. glare phenomena [15]. Another problem currently discussed is decreased mesopic contrast sensitivity. Holladay et al. named high spherical 19.4.3 aberrations as a possible reason [12]. They pro- Intraocular Lens Procedures pose increasing contrast sensitivity via implan- tation of aspherical IOLs, which reduce spheri- 19.4.3.1 cal aberration to the level found in young Phakic Intraocular Lenses (pIOL) people’s eyes. However, full-scale comparative clinical studies have not yet convincingly The most frequently described visual com- proved these theoretical beginnings. plaints after phakic IOL implantations are glare and halos in mesopic and scotopic lighting con- Summary for the Clinician ditions. Maroccos et al. showed that patients re- ∑ A large diameter of the optical clear zone port glare regardless of whether anterior or for RK plays the most important role in posterior chamber phakic IOLs were implanted avoiding night vision disturbances and [19]. However, they showed that patients with glare 6.0 mm optical diameter irisclaw lenses are sig- ∑ For surface ablation and LASIK, a well- nificantly better than posterior chamber IOLs centred ablation zone is important with smaller optical diameter. Moreover, they for myopic and particularly for hyperopic showed an increase in the halo area, for posteri- treatments or chamber IOLs more than for anterior cham- ∑ Larger ablation zones seem to reduce ber iris-claw lenses. This main reason for this is unwanted visual symptoms stray light due to the IOL edges.At daylight con- ∑ Higher corrections with deep ablation ditions, this stray light causes no complaints, zones seem to correlate with halo reports but with increasing pupil diameter at night, it ∑ In eyes with larger pupils, small optical enters the pupil’s aperture and leads to the de- diameter or decentred phakic IOLs may scribed complaints, and even more so in eyes lead to glare and halos symptoms with large pupil diameter. ∑ Stray light due to decentration of the IOL or opacification of the posterior capsule 19.4.3.2 can provoke light phenomena and glare Refractive Lens Exchange (RLE) disability ∑ Modern posterior chamber lenses with After refractive lens exchange (RLE) with im- squared, truncated optic edges to prevent plantation of an IOL, patient complaints such as PCO may also lead to glare glare disability, halos, light streaks, arcs or circles and loss of contrast sensitivity by night may occur. This can be the result of corneal irregu- 19.5 larities and astigmatism,as well as IOL-depend- Future Approaches to Improve Quality ent. For IOL-dependent problems several possi- of Vision After Refractive Surgery ble reasons exist such as decentration, tilt, anterior or posterior capsule opacifications After quality of vision has been recognised as (PCO), stretch-folds in the posterior capsule or an important factor for refractive surgical inter- the lens design itself.Many of the currently used ventions,the evaluation of current procedures is IOLs have squared, sharp-edged design to pre- necessary. vent PCO. The edges of the IOL may cause pho- The advent of wavefront technology enables topic phenomena, like light arcs or circles and the quantification of higher-order ocular aber- glare, particularly if the pupil diameter is rations (HOA). Experience with adaptive optics greater than the optical diameter of the IOL or from astronomy led to the concept of correcting References 313 ocular HOA by excimer laser surgery (wavefront-guided ablation), which should improve References the image quality of the eye and therefore improve visual outcome. Recent studies demon- 1. Applegate RA, Gansel KA (1990) The importance strate that, on average, wavefront-guided cor- of pupil size in optical quality measurements fol- rections can provide objectively and subjective- lowing radial keratotomy. Refract Corneal Surg 6:47–54 ly better quality of vision than standard 2. Applegate RA, Howland HC, Sharp RP et al (1998) ablation profiles. Corneal aberrations and visual performance af- The concept of customised corneal treat- ter radial keratotomy. J Refract Surg 14:397–407 ments was proposed to improve eyes with poor 3. 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Endl MJ, Martinez CE, Klyce SD et al (2001) Effect means that after lens removal, customised IOLs of larger ablation zone and transition zone on corneal optical aberrations after photorefractive could compensate for residual ocular aberra- keratectomy. Arch Ophthalmol 119:1159–1164 tions. The average cornea has a positive spheri- 7. Fay AM, Trokel SL, Myers JA (1992) Pupil diame- cal aberration, which could be reduced or elim- ter and the principal ray. J Cataract Refract Surg inated by implanting an IOL with negative 18:348–351 spherical aberration (aspheric IOL). All current 8. Ghaith AA, Daniel J, Stulting RD et al (1998) Con- studies have shown that ocular aberrations trast sensitivity and glare disability after radial could be reduced with aspheric IOLs compared keratotomy and photorefractive keratectomy. Arch Ophthalmol 116:12–18 to standard IOLs, but the improvement of visu- 9. Ginsburg AP (1996) Next generation contrast al quality is still under investigation. sensitivity testing. In: Rosenthal B, Cole R (eds) The optic edge design of the IOL after refrac- Functional assessment of low vision. Mosby-Year tive lens exchange can affect optical and me- Book, St. Louis, pp 77–88 chanical performance. The reported optical ef- 10. Grimmett MR, Holland EJ (1996) Complications fects are glare,halos,peripheral arcs of light and of small clear-zone radial keratotomy. Ophthal- other unwanted optical images. Modified IOL mology 103:1348–1356 11. Hersh PS, Steinert RF, Brint SF (2000) Photore- designs are necessary to improve the optical fractive keratectomy versus laser in situ ker- quality of the eye. atomileusis: comparison of optical side effects. Studies to prove all these concepts are neces- Summit PRK-LASIK Study Group. Ophthalmolo- sary. The overall improvement in quality of vi- gy 107:925–933 sion after refractive surgical interventions will 12. Holladay JT, Piers PA, Koranyi G et al (2002) A be a major step for the success of refractive sur- new intraocular lens design to reduce spherical gery. aberration of pseudophakic eyes. J Refract Surg 18:683–691 13. Koch DD, Kohnen T, Obstbaum SA et al (1998) Format for reporting refractive surgical data (editorial). J Cataract Refract Surg 24:285–287 14. Kohnen T (2001) Measuring vision in refractive surgery (editorial). J Cataract Refract Surg 27: 1897–1898 15. Kohnen T (2001) The squared, sharp-edged optic intraocular lens design (editorial). J Catataract Refract Surg 27:485 314 Chapter 19 Quality of Vision After Refractive Surgery

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