Subjective Quality of Vision

LETTERS TO THE EDITOR

Subjective Quality of Vision Colm McAlinden, PhD Jyoti Khadka, PhD To the Editor: Konrad Pesudovs, PhD We read with interest the study by Sia et al,1 which Bedford Park, South Australia appeared in the January 2012 issue of the Journal of Eirini Skiadaresi, MD Refractive Surgery, comparing epi-LASIK and photore- Swansea, United Kingdom fractive keratectomy, particularly with regards to the questionnaire used to assess quality of vision. The The authors have no proprietary interest in the materials presented questionnaire consisted of a 10-point scale ranging herein. from 1 (no symptoms) to 10 (severe, disabling symptoms). The results found the subjective optical quality REFERENCES was the same between the two procedures for vision 1. Sia RK, Coe CD, Edwards JD, Ryan DS, Bower KS. Visual out- fl uctuations, double vision, glare, light sensitivity, comes after epi-LASIK and PRK for low and moderate myopia. J Refract Surg. 2012;28(1):65-71. halos, starbursts, patient satisfaction, postoperative 2. Thomee R, Grimby G, Wright BD, Linacre JM. Rasch analysis of vision quality, and the chance to have the procedure Visual Analog Scale measurements before and after treatment again. of Patellofemoral Pain Syndrome in women. Scand J Rehabil Med. We would like to propose that a potential reason 1995;27(3):145-151. why no difference was found between the two proce- 3. Pesudovs K, Noble BA. Improving subjective scaling of pain dures is the quality of the questionnaire, which has a using Rasch analysis. J Pain. 2005;6(9):630-636. number of fl aws. First, with 10 response options per 4. Pesudovs K, Burr JM, Harley C, Elliott DB. The development, assessment, and selection of questionnaires. Optom Vis Sci. question, it is unlikely that respondents will be able 2007;84(8):663-674. to adequately differentiate 10 levels for each ques- 5. Schallhorn SC, Kaupp SE, Tanzer DJ, Tidwell J, Laurent J, tion, which will introduce error.2 Respondents typi- Bourque LB. Pupil size and quality of vision after LASIK. cally use only 4 or 5 categories.3 Second, with ordinal Ophthalmology. 2003;110(8):1606-1614. response options (1, 2, 3…etc), the differences be- 6. McAlinden C, Pesudovs K, Moore JE. The development of an instrument to measure quality of vision: the Quality of Vision (QoV) tween each response may be unequal. Using a Rasch- questionnaire. Invest Ophthalmol Vis Sci. 2010;51(11):5537-5545. scaled questionnaire would overcome this issue, as 7. McAlinden C, Skiadaresi E, Pesudovs K, Moore JE. Quality of it provides a linear-estimated measure with a known vision after myopic and hyperopic laser-assisted subepithelial step size between each response. Additional benefi ts keratectomy. J Cataract Refract Surg. 2011;37(6):1097-1100. of Rasch analysis in the context of questionnaire development and scoring are described elsewhere.4 Third, the questions asked may not represent the full Reply: extent of potential quality of vision symptoms. Poten- We thank McAlinden and coauthors for their in- tial questions should be derived from existing ques- terest in our article1 and we are eager to discuss their tionnaires, literature reviews, focus groups, and pa- concerns regarding the fi ndings of our study. McAlin- tient interviews. Lastly, the authors cited a study by den et al believe that the reason we did not fi nd a sig- Schallhorn et al5 after the description of their ques- nifi cant difference in postoperative subjective optical tionnaire, presumably to indicate they used the same quality (eg, vision fl uctuations, double vision, glare, questionnaire. However, the description does not ap- light sensitivity, halos, starbursts, patient satisfaction, pear to match the questionnaire used in the Schall- postoperative vision quality, and the chance to have horn et al study. the procedure again) and patient satisfaction was be- We would encourage researchers wishing to in- cause of the inadequate quality of the questionnaire. vestigate subjective quality of vision in future stud- We respectfully disagree with these assertions and ap- ies to apply a validated questionnaire scored using preciate the opportunity to address them sequentially. Rasch analysis, such as the Quality of Vision (QoV) First, McAlinden et al believe the number of points questionnaire.6,7 This questionnaire consists of 10 that comprised our Likert scale (10) was in fact too questions and measures quality of vision with simu- many, patients could not adequately differentiate 10 lation photographs across the three scales: symptom levels for each question, and that ideally we should frequency, severity, and bothersome nature. The QoV have used 4 to 5 categories. We disagree with this as- questionnaire has been shown to be highly sensitive sertion for several reasons. The literature is rich with to changes in quality of vision that occur over time authors who claim that a Likert scale should consist after surface ablation6 and would have ideally suited of various X number of points.2 In the end, it depends the Sia et al study. on the goals of the study, the scientifi c question, and

Journal of Refractive Surgery • Vol. 28, No. 5, 2012 313 Letters to the Editor

Rose K. Sia, MD the sample subjects. Our main concern entering the Charles D. Coe, PhD study was distinguishing between two similar sur- Denise S. Ryan, MS gical procedures. By confi ning the possible alterna- Washington, DC tives to 4 or 5 categories, a signifi cant loss of statis- Jayson D. Edwards, MD tical power may occur, and an inability to show a Jacksonville, Florida signifi cant difference when one exists would result. Kraig S. Bower, MD With the large number of patients in our study, we Baltimore, Maryland believed variability would be benefi cial, providing a more accurate refl ection of our patients’ subjec- The authors have no financial interest in the materials presented herein. tive assessments. The large (N) in our study would The views expressed in this letter are those of the authors and do not then result in much smaller standard deviations (SD), reflect the official policy of the Department of Army/Navy/Air Force, critical when determining statistical signifi cance. Department of Defense, or U.S. Government. Finally, we believed the large number of points of our Likert scales without an associated description REFERENCES for each point approximated a continuous variable 1. Sia RK, Coe CD, Edwards JD, Ryan DS, Bower KS. Visual out- and negating one of the hallmark criticisms of ordinal comes after epi-LASIK and PRK for low and moderate myopia. J Refract Surg. 2012;28(1):65-71. data. We would like to point out that McAlinden et 2. Cox EP. The optimal number of response alternatives for a al, using the instrument that they developed in their scale: a review. J Marketing Res. 1980;17(4):407-422. 3 previous study, a comparison between hyperopic 3. McAlinden C, Pesudovs K, Moore JE. The development of an in- and myopic laser-assisted subepithelial keratectomy strument to measure quality of vision: the Quality of Vision (QoV) utilizing their Rasch-scaled Quality of Vision (QoV) questionnaire. Invest Ophthalmol Vis Sci. 2010;51(11):5537-5545. questionnaire, did not fi nd a signifi cant difference 4. McAlinden C, Skiadaresi E, Pesudovs K, Moore JE. Quality of either.4 There is a much greater difference in surgical vision after myopic and hyperopic laser-assisted subepithelial keratectomy. J Cataract Refract Surg. 2011;37(6):1097-1100. technique, ablation profi le, and refractive correction 5. Schallhorn SC, Kaupp SE, Tanzer DJ, Tidwell J, Laurent J, between these two surgical procedures (hyperopic Bourque LB. Pupil size and quality of vision after LASIK. and myopic LASEK) than in myopic epi-LASIK and Ophthalmology. 2003;110(8):1606-1614. photorefractive keratectomy. 6. Bourque LB, Kaupp SE, Riopelle D, Pangelinan C Schallhorn Second, the instrument we used was derived from SC. Characteristics of PRK patients pre- and post-surgery: the 5 U.S. Navy Aviation Retention Study [ARVO abstract, poster the questionnaire used by Schallhorn et al. At the 2646]. Invest Ophthalmol Vis Sci. 2001. time our study was done, the questionnaire scale 7. Hays RD, Morales LS, Reise SP. Item response theory and structure had been examined and refi ned to include health outcomes measurement in the 21st century. Med Care. questions that were considered most relevant and to 2000;38(9 Suppl):II28-II42. which statistical analysis of responses had the greatest 6 correlation to associated clinical fi ndings. Although IOL Scaffold Technique for Posterior respondents typically use only 4 or 5 categories, the change from the 5-point ordinal rating scale to a Capsule Rupture VIDEO Video available on 10-point scale more closely approximates an interval To the Editor: www.Healio.com/JRS scale. Also, the scale was assumed to be a multidimen- We present a new technique called “IOL scaffold” sional scale. The Rasch model works only with ordi- to prevent nucleus drop without extending the origi- nal variables and is restricted by defi nition to a single nal corneal incision. We used a three-piece foldable dimension.7 The instrument we used was also shown intraocular lens (IOL) as a “scaffold” for preventing the to be reliable by a high level of internal consistency, nucleus drop in soft to moderate nucleus after poste- and Cronbach’s ␣-coeffi cients were approximately rior capsular rupture (PCR). 0.8 (PRK: μ=0.78, SD=0.05, range=0.74 to 0.83; epi- When PCR occurs, anterior vitrectomy is performed LASIK: μ=0.80, SD=0.04, range=0.76 to 0.86). Rasch- through the main port with the vitrectomy cutter. A scaled questionnaire, such as the QoV, may be highly viscoelastic substance is injected into the anterior sensitive to changes in quality of vision over time in a chamber and the nuclear fragments are brought into within-group comparison; however, it might not offer the anterior chamber. An anterior chamber maintainer any advantage over other validated questionnaires or transconjunctival 23-gauge trocar cannula is used when seeking to compare subjective quality of vision for infusion during the procedure. A three-piece fold- changes between two or more refractive procedures. able IOL is then injected via the injector through the existing corneal wound and maneuvered below the nucleus (Fig). The leading haptic of the IOL is posi-

A B C Figure. Intraocular lens (IOL) scaffold technique in a case of A) posterior capsular rupture in a patient with a moderately soft nucleus. B) A 23-gauge trocar infusion cannula is fixed and a foldable IOL injected through the clear corneal wound. C) When the nuclear fragment is brought in the anterior chamber, it is emulsified with the phaco probe above the IOL optic. D) Cortical aspiration is performed and E, F) the IOL is positioned into the ciliary sulcus. D E F

tioned on the iris and the trailing haptic is placed in chance of induced astigmatism. The foldable IOL acts the incision site. The IOL is positioned to block the pu- as a barrier to nucleus pieces dropping into the vitreous pillary zone. The nucleus fragment is emulsifi ed with and works like an artifi cial posterior capsule. In addi- the phaco probe by traditional longitudinal phaco- tion, the possibility of the IOL falling into the vitreous emulsifi cation (see Fig). Once the anterior chamber is is unlikely because one haptic remains outside the eye. cleared of nucleus/epinucleus fragments, the cortex is Although techniques are available to prevent nucleus removed with a phaco probe (low vacuum 150 mmHg) fragment from descending into the vitreous after intra- in aspiration mode. The IOL is positioned on the cap- operative PCR,2-4,6 this method of using the foldable IOL sule in the ciliary sulcus. The corneal wound is closed as a scaffold has not been reported previously. with a suture (10-0 monofi lament). Dhivya Ashok Kumar, MD We have performed this method in 12 eyes, including Amar Agarwal, MS, FRCS, FRCOphth 6 eyes with 50% nucleus, 4 eyes with 30% nucleus, and Gaurav Prakash, MD 2 eyes with 80% epinucleus remaining for phacoemul- Soosan Jacob, MS, FRCS sifi cation when PCR occurred. Signifi cant improvement Athiya Agarwal, MD, DO was noted in uncorrected visual acuity (P=.002, Wilcoxon Soundari Sivagnanam, DNB, FRCS test). Postoperative corrected visual acuity of 20/20 was Chennai, India obtained in 9 eyes. No signifi cant change occurred in the intraocular pressure (P=.136). Mean endothelial cell Prof Amar Agarwal is a paid consultant for AMO, Bausch & Lomb, Ϯ and Staar Surgical. The remaining authors have no financial or pro- loss was 4 1.2%. Immediate postoperative complica- prietary interest in the materials presented herein. tions included grade 2 anterior chamber reaction (2 eyes) and minimal corneal edema (3 eyes). Although this technique may be controversial, we REFERENCES 1. Vejarano LF, Tello A. Posterior capsular rupture. In: Agarwal believe it has some advantages over the usual methods A, ed. Phaco Nightmares: Conquering Cataract Catastrophes. to manage such conditions, including the conversion Thorofare, NJ; SLACK Inc; 2006:253-264. of phacoemulsifi cation to extracapsular cataract extrac- 2. Prasad S, Kamath GG. Converting from phacoemulsifi cation to tion,1,2 or the use of Sheet’s glide to deliver the nucleus.3 ECCE. J Cataract Refract Surg. 1999;25(4):462-463. In eyes with nucleus displaced in the anterior vitreous, 3. Michelson MA. Use of a Sheets’ glide as a pseudo-posterior Viscoat (Alcon Laboratories Inc, Ft Worth, Texas) poste- capsule in phacoemulsifi cation complicated by posterior capsule rupture. European Journal of Implantation and Refractive 4 rior assisted levitation is performed followed by nucleus Surgery. 1993;5:70-72. emulsifi cation with the phacoprobe above a trimmed 4. Chang DF, Packard RB. Posterior assisted levitation for nucleus sheet’s glide. In the above conditions, corneal wound retrieval using Viscoat after posterior capsule rupture. J Cataract extension is required, which can increase the risk of Refract Surg. 2003;29(10):1860-1865. postoperative suture-induced astigmatism. When a 5. Mehta K, Mehta C, Bovet J. HEMA Lifeboat. Video. J Cataract HEMA contact lens life boat is used after PCR,5 it must Refract Surg. 2009;25(2). be removed after nucleus emulsifi cation. However, in 6. Boyd B. Complications of phacoemulsifi cation. Intraoperative- postoperative. In: The Art and Science of Cataract Surgery (Eng- the IOL scaffold technique, there is no need for IOL re- lish ed). Panama: Highlights of Ophthalmology; 2001:249-291. moval or corneal wound extension, which reduces the doi:10.3928/1081597X-20120413-01

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