Eye (1989) 3, 562-570

Glare and Contrast Sensitivity in Contact Lens Corrected Aphakia, Epikeratophakia and Pseudophakia

R. A. HARPER and B. L. HALLIDAY London

Summary The effects of glare on contrast sensitivity and high contrast Snellen acuity were investigated in a group of unilaterally aphakic patients with normal fellow eyes. In spite of relatively good visual acuity and apparently satisfactory surgical results, there was a marked reduction in contrast sensitivity in epikeratophakia and contact lens corrected aphakic eyes, relative to fellow normal eyes, especially in the presence of glare (Pintraocular lens implantation. The results also suggest that the measurement of visual acuity in the presence of glare fails to identify many patients with a functional visual impairment secondary to glare.

The standard methods of correcting aphakia methodological approaches. While some with either a contact lens or an intraocular investigators have found contrast sensitivity lens implant, can both result in subjectively losses in pseudophakic patients compared good vision and good Snellen acuity. 1-3 Recent with age matched controlsI5.17 others found no reports of aphakic patients corrected with epi­ such IOSS.16.18 keratophakia have also emphasised the There has been little emphasis on monitor­ potential for good visual acuity following this ing contrast sensitivity in aphakic patients cor­ procedure.4-7 However, the limitations of rected with epikeratophakia, although Justin Snellen acuity in the assessment of visual per­ et a[2u have reported depressed contrast sen­ formance are now widely recognised. Con­ sitivity three months post-operatively, especi­ trast sensitivity measurement provides an ally at intermediate spatial frequencies. additional means of evaluating visual per­ Repeat measurements at six to twelve months formance, with further information being post-operatively showed an improved per­ given if these tests are also performed in the formance, although contrast sensitivity still presence of glare. 8-12 remained depressed relative to the pre-opera­ There have been several reports on contrast tive results. sensitivity in aphakia and pseudophakia13-19 The aim of this study was to investigate the although the results have shown some vari­ effect of glare on contrast sensitivity and ability. This is probably partly related to Snellen acuity in patients who had aphakia patient selection criteria and to different corrected by one of three methods; contact

From: Moorfields Eye Hospital and Institute of Ophthalmology, University of London.

Correspondence: R. A. Harper BSc MBCO, Visual Science Unit, Radcliffe Infirmary, Woodstock Road, Oxford OX26HE. GLARE AND CONTRAST SENSITIVITY IN APHAKIA 563 lens, epikeratophakia or intraocular lens tested, with and without the glare source, with implant. a 0.5 second exposure of a stationary grating to which the patient responded by pressing a Materials and Methods 'yes' button (the grating was detected) or 'no' Twelve unilaterally aphakic patients were button (the grating was not detected) follow­ selected from the clinics at Moorfields Eye ing an auditory prompt. Testing was con­ Hospital. A paired eye design was used.21 tinued at each spatial frequency, using the These patients all had normal fellow eyes to method of constant stimuli, with a staircase act as a control, as it is known that the within procedure continued to four reversals. subject variance for contrast sensitivity measurements in such patients is typically less Results than the between subject variance. 17 An addi­ Table I provides clinical data on the patients. tional patient who was pseudophakic in one In the presence of glare, Snellen acuity only eye and had an epikeratophakia lens in the decreased in two out of the total of 26 eyes; in other was also included. one epikeratophakia eye (patient 13) and one All patients were tested at least three eye with early cataract (patient 12). In each of months post surgery and had a corrected these two cases the glare source reduced the visual acuity in each eye of 6/9 or better. acuity by one line on the Snellen chart. Pupil Patients with any additional ocular pathology diameters ranged from two to seven mm, but were excluded from the study except that the in no case did the interocular difference fellow eye of one patient had early cataract, exceed 1 mm. although visual acuity was still 6/6. Of the Figures 1-4 show contrast sensitivity and twelve unilateral aphakes, four patients were threshold elevation curves for all the patients. corrected with hard contact lenses, four with For each patient four contrast sensitivity epikeratophakia lenses and four patients were curves are shown; results for each eye are pseudophakic with posterior chamber lenses. shown with and without the glare source. (One patient with epikeratophakia sub­ Below the contrast sensitivity curves two sequently had the donor lenticule removed threshold elevation curves are shown for the due to high anisometropia and had a second­ conditions with and without glare. These ary intraocular lens implanted). curves plot the ratio of the operated eye's A Brightness Acuity Tester (Mentor Inc) contrast threshold to that of the normal fellow was used as a glare source. This consisted of eye at each spatial frequency. Ordinate values an illuminated hemispherical bowl, 60 mm in of zero (dashed lines) indicate equality of the diameter, with a central 12 mm circular aper­ operated eye with the patient's normal eye ture through which the patients viewed the and increasing positive values indicate reduc­ gratings or letter chart. The bowl luminance tion in contrast sensitivity in that eye relative was 300 cd/m2• Visual acuity was measured to the normal fellow eye. using an internally illuminated Snellen chart. Figure 1 illustrates the contrast sensitivity All patients had pupil diameters recorded results for the contact lens patients. There was with a pupil gauge in ambient room a relative depression in contrast sensitivity in illumination. the contact lens eyes at nearly all of the points Vertical sinewave gratings were computer plotted. Two patients (1 and 2) show accen­ generated on the screen of a Tektronix 608 tuation of this effect with increasing spatial monitor (P31 standard phosphor). The screen frequency, especially in the presence of glare. measured 9 cm by 11 cm at a viewing distance Figure 2 illustrates the contrast sensitivity of 1.5 m. The space averaged screen lumi­ results for the epikeratophakia patients. The nance was 14 cd/m2. All patients wore the threshold elevation curves show that there appropriate spectacle correction. Contrast was a marked relative depression in contrast thresholds were measured for seven different sensitivity in the epikeratophakia eyes at all spatial frequencies, 0.5, 1.0, 2.0, 4.0, 8.0, 16 spatial frequencies for all patients. This effect and 30 cycles per degree. After an initial tended to be greater at the higher spatial fre­ demonstration to each patient, each eye was quencies (patients 5,6 and 8) and more accen- 564 R. A. HARPER AND B. L. HALLIDAY

Table I Clinical data for all patients

Time from Operated eye Fellow eye Age surgery Patient (years) (months) Status VA VA g Status VA VA g

1 39 24 CL 6/5 6/5 NORM 6/5 6/5 2 21 8 CL 6/5 6/5 NORM 6/5 6/5 3 15 8 CL 6/5 6/5 NORM 6/5 6/5 4 26 >24 CL 6/6 6/6 NORM 6/5 6/5 5 28 12 EPI 6/9 6/9 NORM 6/5 6/5 6 10 8 EPI 6/9 6/9 NORM 6/5 6/5 7 39 5 EPI 6/6 6/6 NORM 6/5 6/5 8 21 5 EPI 6/9 6/9 NORM 6/5 6/5 9 64 11 IOL 6/5 6/5 NORM 6/5 6/5 10 72 3 IOL 6/5 6/5 NORM 6/5 6/5 11 24 10 IOL 6/5 6/5 NORM 6/5 6/5 12 67 10 IOL 6/5 6/5 CAT 6/6 6/9 13 60 17 IOL 6/9 6/9 EPr 6/9 6/12

CL = contact lens correction, EPI = epikeratophakia, IOL = intraocular lens, NORM = normal phakic eye,

CAT = cataract, VAg = visual acuity measured with glare. For patient 7 the epikeratophakia lens was subsequently removed and a secondary IOL was implanted (where the visual acuity was 6/5 with and without glare. ) tuated in the presence of glare (patients S, 6 especially at the higher spatial frequencies. and 7). This was accentuated in the presence of glare. In the presence of glare, for the epi­ Figure 4a illustrates the contrast sensitivity keratophakia and contact lens patients com­ results for patient 13 who was pseudophakic in bined, there was significantly greater one eye and was corrected with an epi­ depression in mean contrast sensitivity (aver­ keratophakia lens in the other eye. There was aged over all spatial frequencies) in the a definite loss of contrast sensitivity in the operated eyes relative to the fellow eyes epikeratophakic eye, relative to the pseudo­ (WiJcoxan test for paired samples, p > :;: i ii ;100 ;100 fI) fI) .. .. • ...... � c c 0 10 0 10 u U

1 10 30 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree)

c c � �.. 1.5 .. 1.5 > > • is iii " � "0 .I:. 0 .I:. 0.5 • .5 • •.. f .I:. .I:. -0 l- -0 I- '" '" .3 -0.5 .3 -0.5

1 10 30 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree) Fig.13 Fig.lb 1000 1000 � � � � ii ii ; 100 ;100 fI) III .. .. iii .. � C C 0 10 0 10 U U

10 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree)

c c � .. 1.5 .g.. 1.5 > > • ... iii iii " " "0 "0 .I:. 0.5 .I:. 0.5 .. � • f ------f .I:. 0 .I:. 0 l- - I- - m '" oS -0.5 oS -0.5

1 10 30 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree) Fig. Ie Fig. Id Fig. 1 (3-d) Illustrate s the contrast se nsitivity functions (C SF) for patie nts 1-4 (contact le ns corre cte d aphake s) re spe ctive ly. (C ircle s re pre se nt normal eyesand square s re pre se nt ope rate d eye s.) Tw o curve s are show n for each eye.(C lose d symbols re pre se nt me asure me nts made without glare and ope n symbols re pre se nt me asure me nts made with glare .) The tw o log thre shold ele vation curve s show n be ne ath the CSFs plot the ratio of the ope rate d eye's contrast thre shold re lative to the normal eye at each spatial fre que ncy. (C lose d square s re pre se nt me asure me nts made without glare and ope n square s re pre se nt me asure me nts made with glare .) 566 R. A. HARPER AND B. L. HALLIDAY

1000 1000 ?: ?: "> � :;:; OJ t: 100 � 100 • • UI UI .. .. � l! t: C 0 10 o 10 u U

10 30 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/ degree)

t: t:

�to 1.5 �to 1.5 > > • • iii iii " " "0 r. 0.5 � 0.5 .. .. • .. ! r. -0 r. -0 ...... 0> 0> .3-0.5 .3 -0.5

1 10 30 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree) Fig.2a Fig.2b 1000 1000 ?: ?: � � OJ OJ :Ii 100 i 100 UI UI - .. .. l! l! C o 10 � 10 u u

1 10 30 1 10 30 Spatial Frequency (cycles/ degree) Spatial Frequency (cycles/degree)

t: t: .2 1.5 1.5 m :8.. > > • iii itl " " "0 r. 0.5 � 0.5 .. • .. ! .E -0 r. -0 ...... 0> go .3 -0.5 .3 -0.5

1 10 30 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree) �k �M Fig. 2 (a-d) Illustrates the contrast sensitivity functions (CSF) for patients 5-8 (epikeratophakia) respectively. (C ircles represent normal eyes and squares represent operated eyes.) Tw o curves are show n for each eye. (C losed symbols represent measurements made without glare and open symbols represent measurements made with glare.) The tw o log threshold elevation curves show n beneath the CS Fs plot the ratio of the operated eye·s contrast threshold relative to the normal eye at each spatial frequency. (C losed squares represent measurements made without glare and open squares represent measurements made with glare.) GLARE AND CONTRAST SENSITIVITY IN APHAKIA 567 1000 1000 >-

�;: ii i 100 III .. • f C o 1 u 0

1 10 30 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree)

I: o :; 0.5 !• 0.5 > ... iii 0 W} -0 " - "0 � i-O.S �---- -0.5 i � • � -1 � -1 01 go .3-1.5 ..J -1.5

1 10 30 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree) Fig.3a Fig.3b 1000 1000 ?: ?: � � ii ii i100 ;100 UI III - ii co f f C C 0 10 0 u u 10

10 30 1 10 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree)

I: I: 0 o ;: .. 1.5 :; 0.5 > > • ... iii iii -0 " " "0 "0 z: co 0.5 i -0.5 � � z: � -0 � -1 00 01 .3-0.5 .3 -1.5

1 10 30 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree) �� �� Fig. 3 (a-d) Illustrates the contrast sensitivity functions (CSF) for patients 9-12 (pseudophakia) respectively. (C ircles represent normal eyes and squares represent operated eyes. ) Tw o curves are show n for each eye, except patient11 (w ithout glare test condition only) .(C losed symbols represent measurements made without glare and open symbols represent measurements made with glare.) The tw o log threshold elevation curves show n beneath theCSF s plot the ratio of the operated eye's contrast threshold relative to the normal eye at each spatial frequency. (C losed squares represent measurements made without glare and open squares represent measurements made with glare.) 568 R. A. HARPER AND B. L. HALLIDAY

1000 1000 !' !' � � 'i 'i i 100 c III : 100 ...... b .. c 'E � 10 � 10

1 10 30 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree)

c c .2 �.. 1.5 'lii 1.5 > > • II iii iii " " "0 "0 � 0.5 � 0.5 .. .. II II .. �------� -0 -0 l- � II» II» .3 -0.5 .3 -0.5

1 10 30 1 10 30 Spatial Frequency (cycles/degree) Spatial Frequency (cycles/degree) Fig.4a Fig.4b Fig. 4 (a-b) Illustrates the contrast sensitivity functions for patients 13 and 7 respectively. Patient 13 was epikeratophakic in one eye (squares) and pseudophakic in the fellow eye (circles). Patient 7 had the epi­ keratophakia lens (squares) removed and a secondary intraocular lens (circles) was implanted. (C losed symbols represent measurements made without glare and open symbols represent measurements made with glare. ) The tw o log threshold elevation curves plot the ratio of the epikeratophakia eye's contrast threshold relative to the pseudophakia eye at each spatial frequency.(C losed squares represent measurements made without glare and open squares represent measurements made with glare. )

sensitivity results in the pseudophakic group three of the four epikeratophakia patients as were more variable. Whereas most operated having reduced visual performance (i.e. the eyes corrected with contact lens or epi­ visual acuity of the epikeratophakia eye was keratophakia showed a reduction in contrast 6/9 only) it failed to identify any difference sensitivity when compared to the fellow eye, between normal and operated eyes in the con­ in the pseudophakic group one patient tact lens group. However, contrast sensitivity showed a superiority of the operated eye over testing showed marked deficits in all epi­ the fellow eye (patient 12) and two patients keratophakia patients and also indicated rela­ showed approximate equivalence between tively reduced visual function in three out of their operated and fellow eyes (patients 9 and the four contact lens corrected eyes compared 10). It is likely that the relatively good per­ to their fellows. Even in the presence of glare, formance of the operated eye in these three visual acuity measurements on the Snellen cases was due to the relatively poorer per­ chart showed no deficitin 24 out of the 26 eyes formance of the fellow eye secondary to senile tested, reducing acuity by one line only in one lens changes. The single pseudophakic patient epikeratophakia eye and one eye with early who did show a definite contrast sensitivity cataract. However, while Snellen acuity test­ reduction in the operated eye (patient 11) was ing identified only two eyes with reduced 24 years old. In contrast, patients 9,10 and 12 visual performance secondary to glare, con­ were over 64 years old and one of these trast sensitivity measurements showed deficits (patient 12) had clinically apparent cataract. in all operated eyes and in most normal eyes. Although Snellen acuity testing identified These results highlight the inadequacy of the GLARE AND CONTRAST SENSITIVITY IN APHAKIA 569 assessment of visual performance and glare suggest that epikeratophakia provides disability by the measurement of visual acuity inferior visual function to that obtained from alone. The poor discriminatory potential of contact lens correction. In this study evalua­ the Snellen chart may be partially due to its tion of pseudophakia is complicated by the design. The chart was truncated beyond '6/5 possibility of early catar.cataract surgery does not necessarily mum sized target that can be resolved or indicate normal visual function. Reduced recognised), whereas contrast sensitivity contrast sensitivity may have important impli­ measures an intensity threshold (the mini­ cations for everyday visual tasks and job per­ mum luminance difference that can be formance. Therefore where alternative means detected). Thus the two tests do not measure of visual correction are available, consider­ the same underlying ability. As glare is due to ation should not only be given to the relative the contrast lowering effect of intraocular safety and convenience of such corrections, light scatter, creating a veiling luminance but also to their visual quality. superimposed on the retinal image, it has a marked effect on contrast thresholds, although high contrast Snellen letters may still References be detected and recognised, e.ven in the pres­ 1 Clayman HM, Jaffe NS, Jaffe MS, Luscombe SM: ence of reduced contrast. Bilateral intraocular lens implantation. Ophthal­ Our results suggest that the measurement molog y 1983,90: 321-3 . 2 Kraff MC, Sanders DR, Lieberman HL, Kraff J: of visual acuity in the presence of glare using a Secondary intraocular lens implantation. Oph­ standard Snellen chart, as has been sug­ thalmolog y1983,90: 324-6. gested26.27 will not necessarily identify many 3 Stark WJ, Leske MC, Worthan DM, Murray GC: patients with a functional visual impairment Trends in cataract surgery and intraocular lens implantation in the United States. Am J secondary to glare. Thus, although the Bright­ Ophthalmol1983, 96: 304-10. ness Acuity Tester may well be able to predict 4 Morgan KS, McDonald MB, Hiles DA et al: The outdoor visual acuity26.2R it is unlikely to detect nationwide study of epikeratophakia for aphakia all patients with visual loss secondary to glare. in children. AmJ Ophthalmol1987, 103: 366-74. 5 These relative threshold contrast sensitivity Durrie DS, Habrich DL, Dietze TR: Secondary intraocular lens implantation vs epikeratophakia losses, which often exceeded 1 log unit, are for the treatment of aphakia. Am J Ophthalmol likely to be practically important, as any loss 1987, 103: 384-91. of contrast sensitivity at threshold will 6 Lass JH, Stocker EG, Fritz ME, Collie DM: The similarly effect supra threshold perform­ surgical correction of aphakia, myopia and ker­ atoconnus. Ophthalmolog y1987,94: 912-25. ancel5.29 and reduced contrast sensitivity at 7 Kelly CG, Keates RH, Lembach RG: Epi­ low spatial frequencies may have important keratophakia for pediatric aphakia. Arch visual significance.30.31 Additionally, recent Ophthalmol1986, 104: 680-2. evidence suggests that reduced monocular S Paulsson LE and Sjostrand J: Contrast sensitivity in the presence of a glare light. Inve st Ophthalmol contrast sensitivity may reduce binocular per­ Vis Sci 1980, 19: 401-6. formance due to binocular inhibition.32 The 9 Atkin A, Asbell P, Justin N, Smith H, Wayne R, results from the unilaterally aphakic patients Winterkorn J: Radial keratotomy and glare 570 R. A. HARPER AND B. L. HALLIDAY

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