Low Luminance Visual Acuity and Low Luminance Deficit In

Journal of Clinical Medicine

Article Low Luminance Visual Acuity and Low Luminance Deﬁcit in Proliferative Diabetic Retinopathy

Eleni Karatsai 1, Piyali Sen 1,2 , Sarega Gurudas 2 and Sobha Sivaprasad 1,2,*

1 NIHR Moorﬁelds Biomedical Research Centre, London EC1V 2PD, UK; [email protected] (E.K.); [email protected] (P.S.) 2 Institute of Ophthalmology, University College, London EC1V 9EL, UK; [email protected] * Correspondence: [email protected]; Tel.: +44-7817886759

Abstract: This study aimed to determine the relation of best corrected visual acuity (BCVA) and low luminance visual acuity (LLVA) in proliferative diabetic retinopathy (PDR) following treatment with either aflibercept or pan-retinal photocoagulation (PRP). The study was conducted as a post-hoc analysis of the CLARITY trial in which naïve and PRP treated PDR patients were randomised to receive either aflibercept or PRP. BCVA and LLVA were assessed at baseline and at week 52. Our analyses showed that the BCVA and LLVA correlate well in treatment naïve PDR with an average low luminance deficit of 11.79 Early Treatment Diabetic Retinopathy Score (ETDRS) letters. However, LLVA at lower levels of BCVA showed more variance. Post aflibercept therapy, the mean change in BCVA and LLVA at 52 weeks after aflibercept was +2.1 (SD 6.05) letters and +0.39 (SD 5.6) letters, respectively. Similarly, after PRP, it was −2.5 (SD 4.9) letters and −1.9 (SD 8.7) letters, respectively. When comparing treatment arms, BCVA change was found to be statistically significant (p < 0.001) whereas LLVA was not (p = 0.11). These findings show that LLVA does not respond as well as BCVA following any treatment for PDR, even though BCVA and LLVA both test foveal function. Keywords: best corrected visual acuity; low luminance visual acuity; proliferative diabetic retinopa- Citation: Karatsai, E.; Sen, P.; thy; pan-retinal photocoagulation; aflibercept; low luminance deficit Gurudas, S.; Sivaprasad, S. Low Luminance Visual Acuity and Low Luminance Deficit in Proliferative Diabetic Retinopathy. J. Clin. Med. 1. Introduction 2021, 10, 358. https://doi.org/ 10.3390/jcm10020358 Proliferative diabetic retinopathy (PDR) is characterised by the development of retinal or optic nerve neo-vascularisation in people with diabetes. Left untreated, PDR can result Received: 30 December 2020 in severe visual loss [1]. Pan-retinal photocoagulation (PRP) is an established treatment for Accepted: 15 January 2021 this condition but it destroys the peripheral retina causing regression of the retinal and optic Published: 19 January 2021 nerve neovascularization [2]. Repeated PRP sessions may be required to treat recurrence of neo-vascularisation and may be associated with visual function loss such as peripheral Publisher’s Note: MDPI stays neutral field loss, impaired dark adaptation and reduced contrast sensitivity [3]. Recently, repeated with regard to jurisdictional claims in intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) agents have published maps and institutional affil- been shown to be as effective as PRP in a five year follow-up study [4]. These anti-VEGF iations. agents modulate the disease process and cause regression of the neo-vascularisation, but the disease recurs when the therapy is stopped. Both PRP and anti-VEGF agents stabilise visual acuity in PDR [4,5]. The CLARITY study showed that aflibercept, an anti-VEGF agent, resulted in superior visual outcome Copyright: © 2021 by the authors. compared to PRP in eyes with treatment with naïve PDR or active PDR after initial PRP [5]. Licensee MDPI, Basel, Switzerland. Aflibercept was injected every month for three months followed by pro-re-nata dosing to This article is an open access article treat recurrences, reactivation or new onset neo-vascularisation over 52 weeks [6]. distributed under the terms and Visual acuity tests such as the Snellen and Early Treatment Diabetic Retinopathy conditions of the Creative Commons Score (ETDRS) are established in the assessment of visual function [7]. However, these are Attribution (CC BY) license (https:// tested on high contrast charts and are affected by light scatter and wavefront aberrations. creativecommons.org/licenses/by/ Visual acuity is often not affected in PDR unless complications such as diabetic macu- 4.0/).

J. Clin. Med. 2021, 10, 358. https://doi.org/10.3390/jcm10020358 https://www.mdpi.com/journal/jcm J. Clin. Med. 2021, 10, 358 2 of 10

lar oedema and/or ischaemia, epiretinal membrane, vitreous haemorrhage or tractional changes involve the fovea. Mesopic visual acuity testing uses reduced contrast and is more translatable to real- world tasks such as driving at night [8]. It has also been shown to correlate better with certain diseases than visual acuity [9,10]. Although mesopic visual acuity is also a foveal function, this pathway is more complex and less well understood. This pathway is influenced by both the photoreceptors and the post-receptoral pathway [11]. Hypoxia is the key driver of PDR. As retinopathy advances, the hypoxic stimulus from capillary drop-off causes the development of new blood vessels on the retina and/or the optic disc. As the rod photoreceptors require a significant amount of oxygen during dark adaptation, this imbalance between oxygen demand and supply may compromise the function of the rod photoreceptors. However, subjective impairment of night vision has been rarely reported by people with untreated PDR [12]. Cone photoreceptors are also affected in diabetic retinopathy [13]. It is unclear whether mesopic visual acuity may be a better test of visual function than photopic visual acuity in eyes with PDR. Mesopic or low luminance visual acuity (LLVA) is measured by adding a neutral density (ND) filter to the refraction for best corrected visual acuity (BCVA) whilst keeping the vision chart and lighting conditions of the room stable so that luminance is reduced by 2.0 log units [14]. Alternatively, the vision chart can be dimmed by a ND to provide the same effect. The difference between BCVA and LLVA is the low luminance deficit (LLD). In clinical trials on geographic atrophy, LLD of 20 letters or worse is a prognostic indicator of disease progression. It is not known whether there is a dissociation between BCVA and LLVA in PDR. It is also unknown whether LLD is uniformly affected in all PDR eyes or whether it is dependent on baseline BCVA. Similarly, a change in LLVA and LLD before and after PRP may reveal the impact of PRP despite unchanged BCVA. In this study, we aimed to study the relation of LLVA and BCVA in PDR and to measure any differences in LLVA outcomes after treatment of PDR with PRP and anti-VEGF therapy. The research questions included: (1) what is the correlation between LLVA and BCVA in treatment of naïve PDR patients? (2) Is the dissociation between BCVA and LLVA (BCVA-LLVA = LLD) constant or does it vary with BCVA or LLVA in treatment naïve PDR? (3) In treatment of naïve PDR patients, does the change in BCVA and LLVA with aflibercept therapy differ from those treated with PRP by 52 weeks? (4) Does LLD differ in each type of treatment? (5) In eyes, previously treated with PRP, does repeat PRP worsen LLVA more than BCVA over 52 weeks?

2. Materials and Methods This study is a post-hoc analysis of fully anonymised data obtained from the CLARITY trial so a separate institutional review board approval was not required. The CLARITY trial compared aﬂibercept versus PRP for patients with either treatment naïve or active PDR post initial PRP. Each participant provided informed consent and the trial was approved by the National Research Ethics Committee Service London, South East (14/LO/0203) [5].

2.1. CLARITY Study Participants Patients with Type 1 or 2 diabetes with treatment naïve PDR or active PDR post initial PRP with BCVA of 54 or more Early Diabetic Retinopathy Study (ETDRS) letters with sufﬁcient media clarity were deemed eligible for the study. Key exclusion criteria included coexistent ocular pathology that can affect visual acuity, macular oedema, dense vitreous haemorrhage, ﬁbrovascular proliferation or tractional retinal detachment.

2.2. Treatment Regimen Patients were randomised to have either PRP or repeated intravitreal aﬂibercept 2 mg/0.05 mL. Patients randomised to the aﬂibercept arm received mandated the loading injections and were then re-treated as and when necessary based on the regression patterns J. Clin. Med. 2021, 10, 358 3 of 10

of new vessels [6]. Participants in the PRP arm had PRP at baseline and were re-assessed every eight weeks and re-treated with PRP, if necessary.

2.3. Data Collection In this post-hoc analysis, data on BCVA and LLVA collected in the trial were analysed to answer the research questions. In the trial, refraction was performed by certified op- tometrists and BCVA was recorded using an ETDRS chart tested at four metres. If a patient could not read 20 or more letters at four metres, the test was repeated at one metre. The LLVA was measured at baseline and at week 52 following the same steps as above, but a neutral density filter was held in front of the tested eye to decrease the luminance by 2.0 log units. LLD was defined as the difference in letters read under the two testing conditions (BCVA minus LLVA) letters.

2.4. Outcomes We evaluated the relation between BCVA and LLVA in treatment naïve eyes at baseline. We then analysed whether there was a difference between BCVA and LLVA outcome following anti-VEGF or PRP at 52 weeks. We also examined whether LLVA and LLD worsened with repeated PRP.

2.5. Statistical Analysis All study parameters are reported as a percentage for categorical, mean and standard deviation for continuous variables. Independent t–test or nonparametric Mann Whitney U test was used to compare between groups based on the normality of data. p values of <0.05 were considered statistically signiﬁcant. Spearman Correlation coefﬁcients were reported to show the rank association between BCVA and LLVA in various treatment subgroups reported with 95% CIs. Statistical analysis was performed using Microsoft Excel version 14.0 (2010 Microsoft Corporation) and Stata version 15.1 (Stata Corp 2017, Stata Statistical Software: Release 15, College Station, TX, USA: StataCorp LLC.).

3. Results The flow diagram (Figure1) shows the CLARITY study groups that were evaluated in this post-hoc analysis. Treatment naïve groups with complete data (n = 110) were included to evaluate the correlation of BCVA and LLVA. This group was then assessed for the change in BCVA, LLVA and LLD following treatment with either aflibercept monotherapy (n = 54) or PRP (n = 56). The previously treated PRP group was assessed to understand the change in BCVA, LLVA and LLD and their correlations following repeat PRP (n = 48). The flow chart shows the patients included in this study. J.J. Clin. Clin. Med. Med. 20212021,, 1010,, x 358 FOR PEER REVIEW 44 of of 10 10

FigureFigure 1.1. FlowFlow chartchart ofof participantsparticipants inin thisthis study.study. PRP:PRP: pan-retinalpan-retinal photocoagulation.photocoagulation. LLVA:LLVA: low low luminance luminance visual visual acuity. acuity. The baseline characteristics of all treatment naïve (n = 110) eyes with active PDR are describedThe baseline in Table characteristics1. The average of LLDall treatment was 11.79 naïve (SD ( 6.08)n = 110) letters, eyes butwith eyes active with PDR better are describedbaseline BCVA in Table had 1. lower The LLDaverage than LLD eyes was with 11 poorer.79 (SD baseline 6.08) letters, BCVA. but This eyes LLD with pattern better is baselinerelated more BCVA to had the variationslower LLD in than LLVA eyes rather with than poorer BCVA. baseline Participants BCVA. withThis BCVALLD pattern less than is related84 letters more (median to the or variations lower 50%) in had LLVA SD LLVAratherof than 8.78 BCVA. compared Participants to participants with BCVA with BCVA less thangreater 84 letters than or (median equal to or 84 lower letters 50%) where hadLLVA SD LLVA SD was of 8.78 5.58 compared (p < 0.001; to test participants for equality with of BCVAvariances). greater Similarly, than or equal in the to upper 84 letters 75% where of BCVA LLVA (greater SD was than 5.58 88 (p ETDRS< 0.001; letters)test for equal- SD for ityLLVA of variances). was 4.19 compared Similarly, toin LLVAthe upper SD in75% the of lower BCVA 75% (greater which than was 88 9.32 ETDRS (p < 0.001).letters) TheSD forsame LLVA applied was for4.19 the compared lower 25% to (LLVALLVA SDSD10.4 in the vs. lower 7.19; p 75%-value which = 0.01). was 9.32 (p < 0.001). The sameThe LLDapplied was for not the inﬂuenced lower 25% by any(LLVA other SD parameters. 10.4 vs. 7.19; There p-value was = no 0.01). difference in LLD betweenThe eyesLLD withwas onlynot influenced NVE (mean by LLD any 11.8 other (SD parameters. 6.1) and eyes There with was NVD no (mean difference 11.7 (SD in LLD6.2) letters).between Mean eyes LLDwith wasonly also NVE similar (mean in LLD pseudo-phakic 11.8 (SD 6.1) versus and phakiceyes with eyes NVD (mean (mean 11.3 11.7(SD 4.7)(SD and6.2) 11.8letters). (SD Mean 6.2)). ThereLLD was was also nosimilar age-related in pseudo-phakic change in LLD. versus The phakic mean eyes LLD (meancategorised 11.3 (SD by age4.7) groupsand 11.8 <60 (SD years, 6.2)). 60–69 There years, was 70–79also no years age-related and 80years change or olderin LLD. was The 16 mean(SD 6.1), LLD 14 categorised (SD 7.7), 12.6 by (SDage 8.1)groups and <60 10.3 year (SDs, 3.1), 60–69 respectively. years, 70–79 years and 80 years or older Thewas correlations16 (SD 6.1), 14 between (SD 7.7), BCVA 12.6 (SD and 8.1) LLVA and in 10.3 treatment (SD 3.1), naïve respectively. eyes are shown in Figure2 . These visual functions are highly correlated although more variations were Tableobserved 1. Demographic with LLVA characteristics in lower levels of treatment of BCVA. naïve eyes at baseline.

Baseline Treatment Naïve (n = 110) Repeated PRP Group (n = 48) Age Mean ± SD 54.37 (14.56) 57.71 (12.04) Age categories N (%) 30–50 years 50 (45.45%) 11 (22.92) 51–70 years 45 (40.91%) 30 (62.5) 71–80 years 15 (13.64%) 7 (14.58)

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J. Clin. Med. 2021, 10, x FOR PEER REVIEW 5 of 10 Table 1. Demographic characteristics of treatment naïve eyes at baseline.

Baseline Treatment Naïve (n = 110) Repeated PRP Group (n = 48) ± AgeMale Mean SD 67 54.37 (60.91%) (14.56) 34 57.71 (70.83) (12.04) AgeFemale categories 43 (39.09%) N (%) 14 (29.17) 30–50T1DM years 55 50 (50.00%) (45.45%) 21 11(43.75) (22.92) 51–70T2DM years 55 45 (50.00%) (40.91%) 27 30(56.25) (62.5) Eyes with71–80 NVD+/ years−NVE 36 15 (32.73%) (13.64%) 19 (39.58%) 7 (14.58) Eyes withMale NVE only 72 67 (65.45%) (60.91%) 28 (58.33%) 34 (70.83) Pseudo-phakicFemale 12 43 (10.91%) (39.09%) 6 14(12.5) (29.17) PhakicT1DM 98 55 (89.09%) (50.00%) 42 21 (87.5) (43.75) Mean best correctedT2DM visual 55 (50.00%) 27 (56.25) 82.94 (SD 7.59) 81.48 (7.65) acuityEyes with (BCVA) NVD+/ −(SD)NVE 36 (32.73%) 19 (39.58%) MedianEyes with BCVA NVE (IQR) only 84 72 (80–88) (65.45%) 82 (77–86.75) 28 (58.33%) Mean lowPseudo-phakic luminance visual 12 (10.91%) 6 (12.5) 71.15 (SD 9.94) 67.88 (7.52) acuity (LLVA)Phakic (SD) 98 (89.09%) 42 (87.5) Mean best corrected visual acuity Median LLVA (IQR) 82.94 73 (66–78) (SD 7.59) 68 (64.25–73) 81.48 (7.65) Mean low(BCVA) luminance (SD) deficit 11.79 (SD 6.08) 13.60(5.51) Median(LLD) BCVA (SD) (IQR) 84 (80–88) 82 (77–86.75) Mean low luminance visual acuity Median LLD (IQR) 71.15 11 (7–15) (SD 9.94) 14 (10–16.75) 67.88 (7.52) (LLVA) (SD) LLD 1–5 letters 13 (11.81) 3(6.25%) Median LLVA (IQR) 73 (66–78) 68 (64.25–73) LLD 6–10 letters 38 (34.55%) 11(22.92%) Mean low luminance deﬁcit (LLD) 11.79 (SD 6.08) 13.60(5.51) LLD 11–14(SD) letters 30 (27.27%) 12(25.00%) LLDMedian 15–19 LLD letters (IQR) 21 11(19.09%) (7–15) 17(35.42%) 14 (10–16.75) LLD 20LLD or 1–5 more letters letters 8 13(7.27%) (11.81) 5(10.42%) 3(6.25%) ProportionLLD 6–10 > mean letters + 2SD 2 38 (1.82%) (34.55%) 2(4.17%) 11(22.92%) SD: standardLLD deviation; 11–14 letters DM: Diabetes Mellitus; 30 NVD: (27.27%) neovascularization elsewhere; 12(25.00%) NVE: neovascularization elsewhere; IQR: interquartile range; LLVA: low luminance visual acuity; LLD: low lu- LLD 15–19 letters 21 (19.09%) 17(35.42%) minance deficit. LLD 20 or more letters 8 (7.27%) 5(10.42%) TheProportion correlations > mean between + 2SD BCVA and LLVA 2 (1.82%) in treatment naïve eyes are 2(4.17%) shown in Fig- ureSD: 2. standard These deviation; visual functions DM: diabetes are mellitus; highly NVD: correlated neovascularization although of themore disc; variations NVE: neovascularization were ob- servedelsewhere; with IQR: LLVA interquartile in lower range; levels LLVA: of low BCVA. luminance visual acuity; LLD: low luminance deﬁcit.

Figure 2. The relation between best corrected visual acuity (BCVA) and low luminance deﬁcit (LLVA) Figurein treatment 2. The relation naïve proliferative between best diabetic corrected retinopathy visual acuity (PDR) (BCVA) eyes. Spearman’s and low luminance Correlation deficit was 0.756 (LLVA) in treatment naïve proliferative diabetic retinopathy (PDR) eyes. Spearman’s Correlation (95% CI: 0.662 to 0.826). was 0.756 (95% CI: 0.662 to 0.826).

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3.1. Treatment Treatment Effect on BCVAandBCVA and LLVALLVA In the afliberceptaflibercept treated treated group group (n ( =n 54),= 54), the the mean mean BCVA BCVA at baseline at baseline was was 82.4 (SD82.4 8.03)(SD 8.03)letters letters and mean and mean LLVA LLVA was 71.7 was (SD 71.7 10.20) (SD letters. 10.20) Theletters. mean The LLD mean at baselineLLD at baseline was 10.8 was (SD 10.84.95) (SD letters. 4.95) letters. In the 56 56 treatment treatment naïve naïve eyes eyes that that underwent underwent PRP, PRP, the the mean mean BCVA BCVA and and LLVA LLVA at baseline were 83.4 (SD 7.17) and 70.6 (SD 9.76) letters, respectively. Mean LLD at baseline was 12.8 (SD 6.89) letters. In the the aflibercept aflibercept treated group, the mean BCVA atat 52 weeks was 84.6 (SD 11.1) letters and meanmean LLVALLVA was was 72.1 72.1 (SD (SD 11.9) 11.9) letters. letters. The The mean mean LLD LLD was was 12.5 (SD12.5 5)(SD letters. 5) letters. The mean The meanchange change in BCVA in BCVA at 52 weeks at 52 weeks after treatment after treatment with aflibercept with aflibercept was +2.1 was (SD +2.1 6.05) (SD letters 6.05) lettersand the and mean the changemean change in LLVA in LLVA was +0.39 was (SD+0.39 5.6) (SD letters. 5.6) letters. The mean The mean change change in LLD in afterLLD afteraflibercept aflibercept was 1.72(SDwas 1.72(SD 5.83). 5.83). 56 treatment naïve eyes underwent PRP PRP and and were also followed up up for for 52 52 weeks. Mean BCVA andand LLVA LLVA at at 52 52 weeks weeks were were 80.9 80.9 (SD (SD 8.6) 8.6) and and 68.8 68.8 (SD (SD 11.7) 11.7) letters letters respectively. respectively.Mean LLDMean at LLD 52 weeks at 52 wasweeks 12.1 was (SD 12.1 6.7) (SD letters. 6.7) Theletters. mean The change mean inchange BCVA in from BCVA baseline from baselineat 52 weeks at 52 after weeks PRP after was PRP−2.5 was (SD −2.5 4.9) (SD letters 4.9) letters and the and mean the mean change change in LLVA in LLVA was − was1.9 −(SD1.9 8.7)(SD letters.8.7) letters. The meanThe mean change change in LLD in LLD following following PRP PRP was −was0.64 −0.64 (SD (SD 7.39). 7.39). The individual patient-levelpatient-level response response to to treatment treatment with with aflibercept aflibercept and and PRP PRP in treatment-in treatment-naïvenaïve eyes is eyes shown is shown in Figure in3 Figure. When 3. we When compared we compared the response the betweenresponse treatment between arms,treat- mentBCVA arms, change BCVA was found change to bewas statistically found to significantbe statistically (p < 0.001)significant but LLVA (p < was0.001) not but (p =LLVA 0.11). wasThe meannot (p change= 0.11). inThe LLD mean between change treatment in LLD betw armseen in treatmenttreatment naïvearms eyesin treatment did not reachnaïve eyesstatistical did not significance reach statistical (p = 0.06; significance independent (p = t-test).0.06; independent t-test).

Figure 3. Shows the participants’ level level of of change change in in best best corrected corrected visual visual acuity acuity (BCVA) (BCVA) and and low low luminance luminance visual visual (LLVA) (LLVA) in treatment naïve patients at 52 weeks. in treatment naïve patients at 52 weeks.

Table 22 showsshows the categorical categorical distribution distribution of of LLD LLD in inboth both treatment treatment arms. arms. Most Most participantsparticipants in both in both arms arms were werewithin within ±5 letters±5 of letters the mean of the difference mean difference of 12 letters of 12observed letters beforeobserved treatment. before treatment. The proportion The proportion of participan of participantsts with LLD > with mean LLD + 2SD > mean in the + aflibercept 2SD in the armaﬂibercept was 4 (7.41%) arm was and 4 (7.41%) PRP was and 3 (5.36%). PRP was 3 (5.36%).

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Table 2. LLD difference between treatment naive arms at 52 weeks. Table 2. LLD difference between treatment naive arms at 52 weeks. Aﬂibercept (n = 54) PRP (n = 56) p-Value Aflibercept (n = 54) PRP (n = 56) p-Value Mean LLD (SD) 12.48 (4.96) 12.14 (6.69) 0.76 a Mean LLD (SD) 12.48 (4.96) 12.14 (6.69) 0.76 a LLD 1–5 letters 1 (1.9%) 9 (16.1%) LLD 1–5 letters 1 (1.9%) 9 (16.1%) LLD 6–10 lettersLLD 6–10 letters 22 (40.7%) 22 14 (40.7%) (25%) 14 (25%) b LLD 11–14 lettersLLD 11–14 18letters (33.3%) 19 18 (33.9%)(33.3%) 0.07 19 (33.9%) 0.07 b LLD 15–19 lettersLLD 15–19 letters 8 (14.8%) 7 8 (12.5%)(14.8%) 7 (12.5%) LLD 20 or more lettersLLD 20 or more 5 (9.3%)letters 7 5 (12.5%) (9.3%) 7 (12.5%) a b a independent sampleindependentt-test; b Fisher’s sample exact t-test; test. Fisher’s exact test.

3.2. Impact of Repeat3.2. Impact PRP on of BCVA,LLVAandrepeat PRP on BCVA, LLD LLVA and LLD The mean baselineThe BCVAmean baseline of the 48 BCVA participants of the 48 who participants had repeat who PRP had in the repeat study PRP was in the study was 80.8 (SD 7.5) letters80.8 (SD and 7.5) mean letters LLVA and was mean 67.3 LLVA (SD 8.3) was letters. 67.3 (SD Mean 8.3) BCVA letters. at Mean week BCVA 52 was at week 52 was 77.9 (SD 10.2) letters77.9 (SD and 10.2) mean letters LLVA and was mean 63.1 LLVA (SD 13.7) was letters, 63.1 (SD whilst 13.7) mean letters, LLD whilst was mean 14.8 LLD was 14.8 (SD 6.9) letters.(SD The 6.9) mean letters. change The in mean BCVA change from baselinein BCVA at from 52 weeks baseline after at repeat52 weeks PRP after was repeat PRP was −3.6 (SD 8.8) letters−3.6 (SD and 8.8) the letters mean changeand the in mean LLVA change was − in4.77 LLVA (SD 11.99)was −4.77 letters. (SD There 11.99) was letters. There was no signiﬁcant differenceno significant in LLD difference in this in group LLD betweenin this group baseline between and baseline after repeat and PRPafter atrepeat PRP at 52 52 weeks. weeks.

3.3. Correlation3.3. between Correlation Mean Change between in mean BCVAand change LLVAin in BCVA the and Three LLVA Treatment in the three Groups treatment groups Figure4 showsFigure the correlation 4 shows of the mean correlation change inof BCVAmean change and mean in BCVA change and in LLVA mean at change in LLVA 52 weeks in theat treatment 52 weeks naïve in the aflibercept treatment arm, naïve in aflibercept the treatment arm, naïve in the PRP treatment arm and naïve in the PRP arm and in repeat PRP arm.the There repeat was PRP a statistically arm. There significant was a statistically correlation significant between changecorrelation in BCVA between change in and change in LLVABCVA in and treatment change naïvein LLVA eyes in receiving treatment PRP naïve and eyes eyes receiving that had PRP repeat and PRP eyes that had re- (p = 0.001, p < 0.001peat PRP for treatment (p = 0.001, naïve p < 0.001 and repeat for treatment PRP eyes). naïve The and Spearman repeat PRP correlation eyes). The Spearman coefficient for afliberceptcorrelation eyes coefficient was not for statistically aflibercept significant eyes was not (p = statistically 0.073). significant (p = 0.073).

A. Aflibercept B. PRP C. Repeat PRP 20 20 20 0 0 0 -20 -20 -20 LLVA change, ETDRS letters LLVA change, ETDRS letters LLVA change, ETDRS letters LLVA

ρ=0.242(95% CI:-0.027 to 0.479) ρ=0.423(95% CI:0.180 to 0.617) ρ=0.780(95% CI:0.637 to 0.871) -40 -40 -40

-30 -20 -10 0 10 -15 -10 -5 0 5 -40 -20 0 20 BCVA change, ETDRS letters BCVA change, ETDRS letters BCVA change, ETDRS letters

Figure 4. TheFigure correlation 4. The correlationbetween change between in best change corrected in best visual corrected acuity visual (BCVA) acuity and (BCVA) low lumina and lownce luminancevisual acuity (LLVA) was not significantvisual acuity in the (LLVA) (A) aflibercept was not signiﬁcantarm; (B) Panretinal in the (A) photocoagulation aﬂibercept arm; ( B(PRP) Panretinal) in treatment photocoagulation naïve eyes and (C) Re- peat PRP. (PRP) in treatment naïve eyes and (C) Repeat PRP.

Spearman’s correlationSpearman’s coefficients correlation (ρ) coefficients presented with (ρ) presented 95% CIs. Removingwith 95% CIs. the singleRemoving the single observation withobservation high drop with in BCVA high anddrop LLVA in BCVA in A) and Aflibercept, LLVA in A) Spearman’s Aflibercept, correlation Spearman’s correlation coefficient reducescoefficient to 0.198 reduces (95% CI: to −0.1980.076 (95% to 0.445) CI: −0.076 on 53 to observations. 0.445) on 53 observations. Despite the correlationsDespite the shown correlations in Figure shown4, eyes in with Figure smaller 4, eyes changes with smaller in BCVA changes than in BCVA than the median showedthe median more variability showed more in LLVA variability change in compared LLVA change to those compared who experienced to those who experienced higher gains in BCVA. For example, for repeat PRP eyes, the SD of LLVA letter change in

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higher gains in BCVA. For example, for repeat PRP eyes, the SD of LLVA letter change in eyes with less than -3 BCVA letter change (median or 50%) was 6.07; and the SD of LLVA change in eyes with more than or equal to −3 letter BCVA change was 13.43 (p < 0.001, test for equality of variances). For treatment naïve eyes that had PRP, the SD in eyes with less than −2 (median or 50%) letter BCVA change was 10.43, whereas eyes with greater than or equal to −2 letter BCVA change was 6.64 (p = 0.02, test for equality of variances). For treatment naïve eyes that had aﬂibercept, SD of LLVA letter change in eyes with less than 2 BCVA letter change was 6.11, and SD in eyes with greater than or equal to 2 letter BCVA change was 4.99 (p = 0.2960; test for equality of variances).

4. Discussion In this post-hoc analysis of the CLARITY trial, we found that LLVA in treatment naïve eyes is on average two lines lower than BCVA when all other variables are kept constant. Simplistically, these observations can be explained by the fact that both BCVA and LLVA are foveal cone mediated visual functions, thus the linear difference is due to the decrease in luminance. However, the mesopic pathway is more complex and we observed that, although these visual functions are highly correlated, the difference between BCVA and LLVA (LLD) is more marked in lower levels of BCVA and this is driven by a more variable LLVA at lower levels of BCVA. Stockman et al. showed that mesopic vision is governed by several factors such as rod-cone interactions, their retinal distributions, their integrated responses and the post-receptoral pathways governing the rod and cone signals [11]. This dissociation between BCVA and LLVA at lower levels of BCVA suggests that the post-receptoral pathway may be more vulnerable than BCVA to neuronal and/or ischaemic changes in PDR. A faster but less sensitive rod pathway is also active at mesopic levels. We also showed that although the change in BCVA was superior in the aflibercept arm compared to PRP, the changes in LLVA were not significant between these two treatment arms in treatment naïve eyes. These findings show that the mesopic pathway is likely to be slower to recover. We also showed that changes in BCVA did not correlate with changes in LLVA. Although the correlations were significant in the PRP arms, the change in LLVA in lower levels of change in BCVA are also more variable compared to those who had higher gains in BCVA. These substantiate the above findings that the vulnerable mesopic pathway seems to have a predictable response to either aflibercept or PRP. As our study duration was for only 52 weeks, these findings also suggest that the LLVA pathway is unlikely to show rapid responses if used as a clinical trial outcome. When we compare our observations to results of LLVA in studies on intermediate age related macular degeneration (AMD) and geographic atrophy, we can postulate a few points. Firstly, Sunness et al. found that LLD worsens with worsening BCVA [15]. They also showed that the LLD in eyes with geographic atrophy with good BCVA was about 4.6 lines, compared to those with drusen only which showed an average LLD of 2.2 lines. Therefore, in addition to BCVA, retinal atrophy may have affected the mesopic pathway (LLVA) more profoundly than BCVA. Other studies in AMD also substantiate these findings. Wu et al. classified AMD severity levels into six groups and reported that LLD was significantly different only in the non-foveal geographic atrophy (GA) group [16]. Furthermore, in a cross-sectional study, Cocce et al. showed that there are no differences in BCVA, LLVA and LLD between control, early and intermediate AMD, as the BCVA eligibility criteria of the study was Snellen 20/50 or better and the mean BCVA in each group was more than 80 letters [17]. Another study that evaluated the factors that determined LLD in AMD reported that LLD is affected by age, BCVA, AMD severity, presence of reticular pseudo-drusen and sub-foveal choroidal thinning in AMD patients [18]. Of these factors, only age and BCVA apply to this study but we found no age related change of LLD in our study cohort. In our study, only BCVA was related to LLVA. Our baseline inclusion criteria were limited to 54 ETDRS Letters (Snellen 20/80) or better. Similar dissociations between LLVA and BCVA have also been observed J. Clin. Med. 2021, 10, 358 9 of 10

in central serous chorioretinopathy and macular telangiectasia type 2 when compared to controls [9,19]. These observations suggest that LLVA and LLD may not be disease specific changes and the changes may be predominantly determined by the integrity of the mesopic pathway. Clinical trials on interventions in geographic atrophy have shown that the average LLD in geographic atrophy trials was >20 letters while for PDR it is about 12 letters [20–23]. In addition, an LLD of 20 or more letters is a risk factor of disease progression [22]. However, in PDR, our study shows that an LLD of 20 or more letters is a very rare event. Therefore, such a clinical trial outcome is not feasible in PDR. Moreover, our study shows that the mean LLVA and LLD changes post-PRP or aflibercept are minimal and may not be appropriate to be used as clinical outcome measures for future PDR trials. The strengths of our study are the large sample size, the fact that the BCVA and LLVA measurements were protocol driven assessments and the retention rate at 52 weeks was high. To our knowledge, this is the first study on the effects of PDR and its treatment on LLVA. The limitation of our study was that we did not incorporate Optical coherence tomography angiography (OCT-A) measurements, so the effect of diabetic macular ischaemia on BCVA and LLVA cannot be directly derived from this analysis. As the correlation of BCVA and size of foveal avascular zone is low to moderate, BCVA is not an ideal outcome measure for trials on diabetic macular ischaemia. We believe that studies on the effects of increasing macular ischaemia on LLVA need to be done to assess the rate of deterioration of LLVA when compared to BCVA in this condition. Our study cohort also did not include people with poor visual acuity as our BCVA cut-off was 54 letters to avoid eyes with no potential of BCVA improvement. Future research on LLVA in eyes with macular ischaemia confirmed by optical coherence tomography angiography is necessary to confirm or refute our postulation that the post-receptoral pathway may be more affected than the foveal cones in PDR and in diabetic macular ischaemia.

Author Contributions: Conceptualization, S.S.; methodology, E.K., P.S. and S.S.; formal analysis, S.G.; investigation, E.K., P.S.; resources, S.S.; data curation, E.K., P.S.; writing—original draft preparation, S.S., E.K., P.S.; writing—review and editing, S.S., E.K., P.S., S.G.; supervision, S.S. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: The study was granted approval by the National Research Ethics Committee Service London, South East (14/LO/0203). Clinical Trials Authorisation was given by the Medicines and Healthcare Products Regulatory Agency (11518/0013/001–0001) and the European Union Drug Regulating Authorities Clinical Trials (2013–003272–12). Trial steering and data monitoring committees provided independent oversight. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. Data Availability Statement: The authors are prepared to share their data with other researchers. Acknowledgments: The research was supported by the NIHR Biomedical Research Centre at Moor- fields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology and the NIHR Moorfields Clinical Research Facility. The views expressed are those of the author(s) and not neces- sarily those of the NHS, the NIHR or the Department of Health. Conflicts of Interest: S.S. has received research grants and attended advisory board meetings of Bayer, Allergan, Novartis, Roche, Boehringer Ingleheim, Optos. S.S. has attended advisory board meetings of Heidelberg Engineering, Oxurion, Apellis and Oculis. All other authors declare no conflict of interest. J. Clin. Med. 2021, 10, 358 10 of 10

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