REVIEW CURRENT OPINION Introduction to microperimetry and its use in analysis of geographic atrophy in age-related macular degeneration Mostafa Hanout, Nicholas Horan, and Diana V. Do Purpose of review This article discusses recent advances in the fundus-guided perimetry (microperimetry) and its utilization in evaluation and monitoring of patients with geographic atrophy. Recent findings Although best-corrected visual acuity has been gold standard in clinical practice for decades, it does not provide an entire assessment of visual function that determines daily activity and quality of life of a patient. Furthermore, psychophysical tests, including low-luminance visual acuity, reading speed, and contrast sensitivity, cannot be used to quantify retinal sensitivity or detect pattern of retinal dysfunction. Microperimetry provides a true evaluation of visual function by offering fundus-controlled testing through eye-tracking technology that allows for structural and functional correlation and test–retest reliability for the same test point. Furthermore, it enables precise assessment of location and stability of fixation. Recent research has shown microperimetry to be more representative of the macular function in macular diseases. Summary Microperimetry is currently the clinical investigation of choice to assess residual visual functions and functional vision in macular degenerative diseases, especially geographic atrophy. There is an increasing popularity to employ microperimetry in clinical trials investigating new treatments for geographic atrophy, as well as other macular degenerative diseases, as a reliable functional outcome measure. Keywords fixation, geographic atrophy, microperimetry, preferred retinal locus, retinal sensitivity INTRODUCTION low-luminance visual acuity among others. How- The advances in retinal imaging technologies ever, none of these testing parameters has proved have revolutionized contemporary diagnostic in ability to quantify retinal sensitivity or detect ophthalmology and enabled early detection along pattern of retinal dysfunction [2–4]. For many years, with documentation of treatment results of retinal conventional static perimetry has been established diseases. Precise clinical evaluation of retinal, as an essential clinical tool for quantification of especially macular involving, diseases necessitates visual field and retinal threshold especially in glau- correlating both the morphological and the func- coma and neuro-ophthalmological disorders. None- tional aspects. The latter is more self-appreciated by theless, it is often inadequate for accurate evaluation patients, as major visual tasks determining the qual- of macular function, especially with troublesome ity of life of patient grossly depend on it [1]. For eccentric or unsteady fixation, or both [1,5,6]. decades, best-corrected visual acuity has been the gold standard in clinical practice; however, it does not represent an entire assessment of macular func- Stanley M. Truhlsen Eye Institute, University of Nebraska Medical Center, tion. There are several puzzling presentations by Omaha, Nebraska, USA patients whose visual function is inconsistent with Correspondence to Diana V. Do, MD, Stanley M. Truhlsen Eye Institute, visual acuity such as patients with paracentral mac- University of Nebraska Medical Center, 985540 Nebraska Medical ular lesions sparing the foveal center. Several psy- Center, Omaha, NE 68198-5540, USA. Tel: +1 402 559 4276; chophysical tests have been utilized, in addition to fax: +1 402 559 5514; e-mail: [email protected] visual acuity, to evaluate macular function such as Curr Opin Ophthalmol 2015, 26:149–156 Amsler grid, contrast sensitivity, reading speed, and DOI:10.1097/ICU.0000000000000153 1040-8738 Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved. www.co-ophthalmology.com Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. Retinal, vitreous and macular disorders fundus observation during examination [9]. The KEY POINTS main challenge was that the bright light necessary Best-corrected visual acuity, psychophysical tests, and for adequate retinal illumination will interfere with conventional perimetry, albeit useful, do not fulfill the functional testing. With the advent of scanning desired comprehensive assessment of macular function laser ophthalmoscope (SLO), the infrared light in macular degenerative diseases. source permitted simultaneous observation of the fundus during examination and led to introduction Residual visual function has more impact on the patient daily activity and quality of life. of the first microperimeter (SLO 101, Rodenstock, Ottobrunn, Germany) in the year 1982 [9,10]. Microperimetry is currently the clinical investigation of Shortcomings of this device included semiauto- choice to assess residual visual functions and functional mated stimulus presentation and lack of eye tracker vision in macular degenerative diseases, especially to compensate for ocular movements; the device is geographic atrophy. no longer available in the market. These limitations Microperimetry offers fundus-controlled testing of retinal have been overcome by Nidek MP-1 (Nidek Tech- sensitivity through eye-tracking technology that allows nologies, Padova, Italy) that was introduced to the for structural and functional correlation and test–retest market in 2003 as the first fundus perimeter with eye reliability for the same test point. Furthermore, it tracker that compensates for eye movements based enables precise assessment of location and stability of fixation. on an initial frame. With these new features in Nidek MP-1, exact correlation between retinal dis- Recent trends may call for incorporating microperimetry order and functional defects was rendered possible as a standard functional outcome measure in clinical even in eyes with poor or unstable fixation trials of geographic atrophy. [11,12&,13,14]. Thereafter, in 2006, a more recent Spectral OCT/SLO microperimeter was introduced to the market by OPKO/OTI (OPKO Instrumenta- More recently, microperimetry has effectively tion, Miami, Florida, USA) that incorporated spec- provided fundus-correlated functional testing, tral optical coherence tomography (OCT) with test–retest reliability for the same test point, precise microperimetry, offering an additional advantage assessment of the location and stability of fixation, of correlating retinal dysfunction with the corre- and compensation for ocular movements. By incor- sponding ultrastructural finding as shown by porating these features, microperimetry has become OCT. The technology was later transferred to Optos the clinical investigation of choice to assess residual Inc., and the device was named Optos OCT/SLO visual functions and functional vision in macular (Optos, Dunfermline, Scotland, UK). Optos OCT/ diseases [7,8]. SLO is the only US Food and Drug Adminis- This article covers basic concepts and recent tration-approved microperimeter; it received advances in microperimetry, common market- 510(k) clearance in 2013 [3,15–18]. Macular Integ- available microperimeters, and the steadily growing rity Assessment (MAIA; CenterVue, Padova, Italy) role of microperimetry in clinical evaluation and was the latest instrument to reach the market in monitoring of macular diseases, particularly, geo- 2009, garnished with high-frequency eye tracker graphic atrophy. Latest research observations repor- and a line confocal SLO [6,7]. Table 1 summarizes ted during the review period are also summarized. key differences between the three commercially available microperimeters. EVOLUTION OF MICROPERIMETRY According to many experts in the field, ‘micro- CLINICAL APPLICATIONS OF perimetry’ is not the most accurate naming for this MICROPERIMETRY ocular imaging technology, given the currently used Indeed, microperimetry surpasses conventional peri- examination parameters of stimulus size ranging metry in several aspects in evaluation of retinal sen- from Goldman I to V, and examination field sitivity in macular diseases [19]. One fundamental of up to 158–208 from the foveal center. Rather, advantage of microperimetry is the real-time tracking ‘fundus-correlated perimetry’ or ‘fundus-guided of the fundus throughout perimetric testing. This perimetry’ are considered more accurate names. allows perimetric examination of patients with For sake of simplicity, we used the term ‘micro- eccentric or unstable fixation. The ability of regis- perimetry’ throughout the article [5,6]. The need tration of macular sensitivity results on digital fundus to achieve correlation between clinically apparent photograph allows for functional and structural retinal disorder and functional testing urged the correlation [6]. Furthermore, in conventional peri- demand to design a perimetry device that enables metry, the stimulus is projected on a screen in front 150 www.co-ophthalmology.com Volume 26 Number 3 May 2015 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. Introduction to microperimetry and its role in analysis of geographic atrophy Hanout et al. Table 1. Summary of commercially available microperimeters Nidek MP-1 Optos OCT/SLO MAIA Manufacturer Nidek Technologies, Optos, Dunfermline, CenterVue, Padova, Italy Padova, Italy Scotland, UK Year of arrival to the market 2003 2006 2009 Features of incorporated fundus imaging Infrared and digital color SLO black and white SLO black and white Microperimetric examination parameters Size of the of the microperimetry testing field 458 29.78 368 Fixation assessment