天津职业大学 文本 Anomalies binocular function in patients with longstanding asymmetric keratoconus_眼屈光学

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doi:10.1136/bjo.85.9.1057 Br. J. Ophthalmol. 2001;85;1057-1060 Sloper Hooman Sherafat, Joy E S White, Kenneth W Pullum, Gillian G W Adams and John J longstanding asymmetric keratoconus Anomalies of binocular function in patients with http://bjo.bmjjournals.com/cgi/content/full/85/9/1057 Updated information and services can be found at: These include: References http://bjo.bmjjournals.com/cgi/content/full/85/9/1057#otherarticles 1 online articles that cite this article can be accessed at: http://bjo.bmjjournals.com/cgi/content/full/85/9/1057#BIBL This article cites 12 articles, 3 of which can be accessed free at: Rapid responses http://bjo.bmjjournals.com/cgi/eletter-submit/85/9/1057 You can respond to this article at: service Email alerting top right corner of the article Receive free email alerts when new articles cite this article - sign up in the box at the Topic collections Vision Research (564 articles) Articles on similar topics can be found in the following collections Notes http://www.bmjjournals.com/cgi/reprintform To order reprints of this article go to: http://www.bmjjournals.com/subscriptions/ To subscribe to British Journal of Ophthalmology go to: Downloaded from bjo.bmjjournals.com on 2 December 2005

200 2001:107-10 Anomaies of inocular nction in patients with gs Hooman Sherafat,Joy E S White,Ken th W Pullum,Gillian G W Adams,John J Slp

Anomalies of binocular function in patients with longstanding asymmetric keratoconus Hooman Sherafat, Joy E S White, Kenneth W Pullum, Gillian G W Adams, John J Sloper Abstract Aims—To study binocular function in patients with longstanding asymmetric keratoconus. Methods—In 20 adult patients with long￾standing asymmetric keratoconus man￾aged with a scleral contact lens a full clinical and orthoptic assessment was performed with and without the scleral contact lens in the poorer eye. Results—All 20 patients had a corrected acuity of at least 6/9 in their better eye. With the scleral lens in situ the acuity of the poorer eye ranged from 6/6 to 6/60 and without the lens from 6/18 to hand move￾ments. Patients were aged from 18 to 68 years and had worn a scleral contact lens for between 3 and 106 months. Without the contact lens in their poorer eye all patients had a small exotropia and all showed sup￾pression, with the exception of one patient who had a right hypertropia with diplopia. With the scleral lens in situ 12 patients had an exophoria or esophoria, six a micro￾exotropia, and two a manifest exotropia with suppression. Conclusions—Binocular function breaks down in some adult patients with long￾standing asymmetric keratoconus. This is probably caused by longstanding unilat￾eral visual deprivation. There are simi￾larities to the breakdown of binocular function seen in some patients with a longstanding dense unilateral adult onset cataract who can develop intractable di￾plopia following cataract surgery. (Br J Ophthalmol 2001;85:1057–1060) This study was prompted by the clinical observation that some patients with long￾standing asymmetric keratoconus chose to wear a scleral contact lens in their poorer eye, even though the corrected vision of this eye was still substantially worse than that of their better eye. This suggested that their binocular function was improved by wearing the lens. A group of such patients was therefore investi￾gated using clinical tests of binocular function. These demonstrated striking abnormalities in their binocular function, which were reduced with the contact lens in situ. These changes are probably due to the longstanding, mainly unilateral, visual impairment resulting from their asymmetric keratoconus. There appear to be no previous reports of abnormalities of binocular function in patients with kerato￾conus. These data were presented at the 25th Annual Conference of the European Strabis￾mological Association, Jerusalem, September 1999.1 Methods From a database of approximately 350 patients with keratoconus being managed with a scleral contact lens, 35 were identified as having a corrected acuity with the scleral lens in their more aVected eye which was two or more Snel￾len lines worse than their fellow eye. Twenty of these 35 patients were recruited for this study. Visual correction was not possible with con￾ventional contact lenses in these patients with very marked keratoconus, as a stable fit could not be achieved. However, a stable fit had been achieved with a rigid gas permeable scleral lenses and these were well tolerated.2 Because of the irregularity of the cornea in advanced keratoconus and because scleral lenses use the fluid lens between the posterior lens surface and the corneal surface to produce em￾metropia, it is not possible to give meaningful refractive data for the patients. However, all were emmetropic with their lens in situ. Snellen visual acuities were measured with and without the contact lens. Binocular function was assessed with and without the scleral lens in their poorer eye using the cover test, prism cover test, Bagolini glasses, and prism fusion range at 6 metres and % metre. Stereopsis was initially tested using the TNO test; if a patient failed to demonstrate any ster￾eopsis with this method the Titmus test was used to look for the presence of gross stereop￾sis. The 4 dioptre base-out prism test was used to test for central suppression and aniseikonia was assessed using the Awaya Aniseikonia test and/or Rubens slides on the synoptophore. A microtropia was defined as a manifest squint of Table 1 Details of patients with keratoconus Patient Sex Age (years) Time from diagnosis (years) Fixing eye Fixing eye correction Duration scleral lens wear in aVected eye (months) 1 M 18 6 Right Corneal CL 30 2 M 18 3 Left Corneal CL 31 3 M 18 6 Left Corneal CL 40 4 M 26 8 Right Corneal CL 8 5 M 27 12 Left Corneal CL 92 6 F 28 10 Right Scleral CL+PK 27 7 M 29 10 Left Scleral CL 40 8 F 30 8 Right Corneal CL 7 9 M 32 18 Left Scleral CL+PK 41 10 M 35 12 Right Corneal CL 9 11 F 36 18 Left Corneal CL 27 12 M 36 17 Right Unaided 48 13 M 37 11 Right Corneal CL 106 14 F 40 14 Right Corneal CL 62 15 M 44 19 Right Spectacle 30 16 F 47 32 Right Corneal CL 60 17 F 51 28 Right Corneal CL 90 18 F 64 34 Left Spectacle 3 19 F 65 50 Left Corneal CL 48 20 F 68 51 Left Scleral CL 66 CL = contact lens; PK = penetrating keratoplasty. Br J Ophthalmol 2001;85:1057–1060 1057 Strabismus and Paediatric Service, Moorfields Eye Hospital, City Road, London EC1V 2PD, UK H Sherafat J E S White G G W Adams J J Sloper Contact Lens Service K W Pullum Correspondence to: Mr J Sloper john.sloper@dial.pipex.com Accepted for publication 4 April 2001 www.bjophthalmol.com Downloaded from bjo.bmjjournals.com on 2 December 2005

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10 prism dioptres or less, with evidence of anomalous binocular function. Results The 20 patients studied were from 18 to 68 years old. The diagnosis of keratoconus had been made between 3 and 51 years previously and the patients had worn a scleral lens for between 3 months and almost 9 years (Table 1, Fig 1). All patients had a corrected acuity of at least 6/9 in their better, fixing eye, in most cases by using a corneal contact lens (Tables 1 and 2). Acuities with the scleral lens in their poorer eye ranged from 6/6 to 6/60 and without the lens from 6/18 to hand movements (Table 2). Without the scleral lens all 20 patients had a manifest squint with absent binocular function (Table 2). Nineteen patients showed suppres￾sion of their poorer eye when tested with Bago￾lini glasses and one had diplopia and a small manifest vertical deviation. All except one were exotropic, although the angles were small and not cosmetically obvious. In most patients it was not possible accurately to measure the angle of the squint by cover test as fixation with the aVected eye was poor. An abnormal angle kappa was recorded in 15 cases. The corneal reflections were either temporally displaced giving rise to a pseudo-esotropia, inferiorly dis￾placed giving rise to a pseudohypertropia or a combination of both. With the scleral lens in their poorer eye, 16 of the 20 patients showed evidence of binocu￾lar single vision with Bagolini glasses and 14 had measurable stereoacuity. In four patients this was only gross stereopsis and only one patient achieved a stereoacuity of 60 seconds of arc (Table 2). No patient overcame a 4 dioptre prism placed in front of the more aVected eye, indicating the presence of a central suppression area. On cover test 12 patients had a phoria, six a microexotropia, and two a manifest exotropia (Table 2). There was an associated vertical deviation on distance testing in 12 of the cases and for near in 10 cases (Table 3). Sixteen patients had a measurable motor fusion range at 6 metres and 17 at % metre (Table 3). Only one patient gave a history of any previous orthoptic treatment as a child and this patient had one of the best stereoacuities. No patient reported significant aniseikonia when tested using their scleral lens; this could not be tested without the contact lens because of suppression. Discussion This study describes 20 patients with long￾standing asymmetric keratoconus who all showed evidence of grossly abnormal binocu￾lar function by standard orthoptic tests. With a scleral contact lens in their poorer eye most achieved a degree of binocular single vision. Without the scleral lens no patient showed any evidence of binocular function and all except one suppressed the deviating eye. The patients thus gained a substantial functional advantage Figure 1 Age at diagnosis of keratoconus, duration of disease, and duration of scleral contact lens wear for 20 patients. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 80 Time (years) Time to diagnosis Diagnosis to scleral lens wear Duration of scleral lens wear Patient 0 20 40 60 Table 2 Visual acuity and binocular function with and without scleral lens in situ Patient Fixing eye acuity AVected eye with scleral lens in situ AVected eye without scleral lens Acuity Binocular function Bagolini glasses Stereopsis (seconds of arc) Acuity Binocular function Bagolini glasses 1 6/6 6/24 Exophoria Suppression 200 (w) 3/60 Exotropia + R/L Suppression 2 6/9 6/36 Microexotropia BSV NIL CF Exotropia Suppression 3 6/6 6/18 Microexotropia BSV NIL 1/60 Exotropia Suppression 4 6/9 6/36 Exophoria BSV 200 (w) CF Exotropia Suppression 5 6/9 6/60 Microexotropia BSV Gross (w) 1/120 Exotropia Suppression 6 6/6 6/24 Microexotropia BSV NIL CF Exotropia Suppression 7 6/6 6/36 Microexotropia BSV 480 1/120 Exotropia Suppression 8 6/9 6/24 Exophoria BSV NIL HM R/L Diplopia 9 6/5 6/18 Exophoria BSV 120 1/120 Exotropia Suppression 10 6/5 6/18 Exophoria BSV 60 1/60 Exotropia Suppression 11 6/6 6/18 Esophoria BSV 240 CF Exotropia Suppression 12 6/4 6/18 Exotropia Suppression NIL CF Exotropia Suppression 13 6/5 6/18 Esophoria BSV Gross (w) 1/60 Exotropia Suppression 14 6/9 6/12 Exophoria BSV 480 CF Exotropia Suppression 15 6/5 6/6 Exophoria BSV 480 6/18 Exotropia Suppression 16 6/6 6/36 Exotropia Suppression NIL CF Exotropia Suppression 17 6/6 6/12 Exophoria BSV 240 1/60 Exotropia Suppression 18 6/9 6/24 Exophoria BSV 200 (w) CF Exotropia Suppression 19 6/6 6/24 Exophoria Suppression Gross (w) 1/60 Exotropia Suppression 20 6/9 6/24 Microexotropia BSV Gross (w) HM Exotropia Suppression BSV = binocular single vision; (w) = Wirt stereotest, otherwise TNO; CF = counting fingers; HM = hand movements; R/L = right over left. 1058 Sherafat, White, Pullum, et al www.bjophthalmol.com Downloaded from bjo.bmjjournals.com on 2 December 2005

Downloaded frum bjo.bmjoums's.cum on 2 December 2006 1059 车.tnh中到 mn年wnwy mk vlra dus 0 PB0-4 PBI o-14 锅 10-1H1 4O-1H1 批 T 35-1011 T 21k D PKI-X FHI N PKIIh PHI P家 1XT IXT 19 PBO-8PBI 350-101 ct oncrou买 a ItVL T 见 21D0-2I 450-161 L限 N L 2K1 P0-14 2K 1L双 根 2B0-4电 NPBO-10PUI XT=adrviatin ET w euedeviarione PRC■riar hatea■riun hone ing P■mtraing biretgletry to SLra,L■t址Rw很Tltf frum wearring their sderal lens xmnd this xlmost iclueed amcenetnopi.By cumprisnn.xi af certainly explams their for doing the presant 20 keratoconic patients had nu 0. stereopsis with their contact lens in situ at To our knowkdge there are no ponvious acuities of between 618 and 636 (20160 to reports of onormal binocular function in 20V120)(Table 2].A xtseistieal compurisnn af patients with keratoconus.'The patients in the the sterenacuities of the 18 beratocunic sub- present stadly sill hod langstanding keratocnnus ects who had acuties of between 6/12 and in which boch the uncornected and comcted 6/36 with the vales for the normal shjcets acuity of ooe eye was subetantially poorer than with the nearest equivalent acuities of between theit of the other.They were reeruited from a 20/10 and 20/100 in Goodwin and Rocano's pool of about 35 patients with keratoconus 裙udy,'hm台e kerancoerie su止ects to hawve a mangged with scleral contect lenses.All 20 sanibcnntly worse sterecacuity (kermrocoai median 3000 secoeds of are,normal 400 uraring a sdrral lens in their wone cyo and ernds af arc:p D(,Mamn-Whitney were found to have anomalous binocular func- tes).The mean stereoacuities of the normal tioo on tormal testing.The anomalies these xahjeets srudind hy Icvy and Glick'ur sh- patients were not readily apparent without for- stantialy better at cach Soellen acuity than the mal texting of hinunabr functien becauer the median values of Goodwin and Romano and squint angks were small and the corneal o山hek￥a1 ccomic su止ects were eve more distortion found in keratoconus or the pres abnormal compared to this group (Pig 2). ence of a coesct lens may give tise to Altozh su当comparzo幽ntbe在aled aboormaly algned comneal redexes.Most with coneidenhle cmtiom,it would :ppear tha pmtiemns suppressed由eea1 ing eye whe组 in the keratucomic is sub- strotialy worse than can be tcconted for by It is poesible that anomalous binocular fune- tion is noc uncommon in patients with More strikinz is the observation that six of longstanding keratocou the 20 keratoconic parients had a microexo Uroocular epeical blar akme retserx ster- coxcuity in nurmal subjocts.'+Thae studic used induced ansometropa to tause blur 正1000mr atich would als0pc山ace aniselkonin.日e cause of the advanced keratoconus and the way in which xcleral lensrx pruduce their cnrrcction 1000 by uing the fuid lerd herween the seleral lets and a vrry irreglar,it was nee pnssihk 0 to obeain meaningful refractive data for the present patlemss.However,all were emme ■Normal (Goodwin and Remanol tropic wirh their scleral lemrses in setu and were shmm nnt to he aniseibeeric.Nevertheless.foe ·Normal (Levy and Glickl an equivalent reduction in acuity of the poorer 010208040508 c%%ereoacu山wWsm0e【6 doced n the keratoconic patients than in Bormal subjects with redtced aruity in ane eye (Fig Fitvre 2 Copurie the madan servacnit or Svoler aasner gf the pearr oN bemrm 0/12 and t0 (W40 2).Of the 1+normal subpects studiod by av/Z0/A0)ie 20 penr Ei lamgtandere arwunctne Goodwin and Romano,'nome lost stereoocuity onocousu mind reo v4wa售4国6 ther unti th0ayo止wurse gye w A的I af (Tofiv4格s/asnd m物r9nbn桶dospin号 reduced to 20/200,even though they also bad aatty dymemee foer Lng md Cick' biphiialno.com

from wearing their scleral lens and this almost certainly explains their enthusiasm for doing so. To our knowledge there are no previous reports of abnormal binocular function in patients with keratoconus. The patients in the present study all had longstanding keratoconus in which both the uncorrected and corrected acuity of one eye was substantially poorer than that of the other. They were recruited from a pool of about 350 patients with keratoconus managed with scleral contact lenses. All 20 patients subjectively found an advantage in wearing a scleral lens in their worse eye and were found to have anomalous binocular func￾tion on formal testing. The anomalies in these patients were not readily apparent without for￾mal testing of binocular function because the squint angles were small and the corneal distortion found in keratoconus or the pres￾ence of a contact lens may give rise to abnormally aligned corneal reflexes. Most patients suppressed the deviating eye when manifest and so did not complain of diplopia. It is possible that anomalous binocular func￾tion is not uncommon in patients with longstanding keratoconus. Uniocular optical blur alone reduces ster￾eoacuity in normal subjects.3 4 These studies used induced anisometropia to cause blur, which would also produce aniseikonia. Be￾cause of the advanced keratoconus and the way in which scleral lenses produce their correction by using the fluid lens between the scleral lens and a very irregular cornea, it was not possible to obtain meaningful refractive data for the present patients. However, all were emme￾tropic with their scleral lenses in situ and were shown not to be aniseikonic. Nevertheless, for an equivalent reduction in acuity of the poorer eye, stereoacuity was more reduced in the keratoconic patients than in normal subjects with optically reduced acuity in one eye (Fig 2). Of the 14 normal subjects studied by Goodwin and Romano,4 none lost stereoacuity altogether until the acuity of the worse eye was reduced to 20/200, even though they also had induced anisometropia. By comparison, six of the present 20 keratoconic patients had no stereopsis with their contact lens in situ at acuities of between 6/18 and 6/36 (20/60 to 20/120) (Table 2). A statistical comparison of the stereoacuities of the 18 keratoconic sub￾jects who had acuities of between 6/12 and 6/36 with the values for the normal subjects with the nearest equivalent acuities of between 20/40 and 20/100 in Goodwin and Romano’s study,4 show the keratoconic subjects to have a significantly worse stereoacuity (keratoconic median 3000 seconds of arc, normal 400 seconds of arc; p <0.02, Mann-Whitney U test). The mean stereoacuities of the normal subjects studied by Levy and Glick3 were sub￾stantially better at each Snellen acuity than the median values of Goodwin and Romano and so the keratoconic subjects were even more abnormal compared to this group (Fig 2). Although such comparisons must be treated with considerable caution, it would appear that stereoacuity in the keratoconic subjects is sub￾stantially worse than can be accounted for by reduced acuity alone. More striking is the observation that six of the 20 keratoconic patients had a microexo￾tropia (with anomalous binocular function) Table 3 Details of orthoptic findings Patient Prism cover test with scleral lens Prism fusion range with scleral lens 4 Dioptre base-out prism Previous ophthalmic 6 metres (prism dioptres) % metre (prism dioptres) 6 metres (prism dioptres) % metre (prism dioptres) history 1 1XT 1R/L 4XT 1R/L 10 PBOX4 PBI 40 PBOX4 PBI Not overcome Patched 2 4XT 16XT 4 PBOX6 PBI 16 PBOX14 PBI Not overcome None 3 12XT 8XT NIL NIL Not overcome None 4 2XT 8XT 12 PBOX2 PBI 25 PBOX8 PBI Not overcome None 5 16XT 2L/R 16XT 2L/R 6 PBOX2 PBI 6 PBOX2 PBI Not overcome None 6 1XT 1L/R 4XT 1L/R NIL 18 PBOX8 PBI Not overcome PK 7 4XT 2R/L 10XT 6 PBOX1 PBI 6 PBOX1 PBI Not overcome None 8 4XT 2R/L 6XT 16 PBOX6 PBI 35 PBOX10 PBI Not overcome None 9 2XT 2L/R 8XT 2L/R 10 PBOX8 PBI 20 PBOX16 PBI Not overcome PK 10 1XT 4XT 16 PBOX8 PBI 35 PBOX10 PBI Not overcome None 11 2ET 1R/L 4XT 1R/L 20 PBOX2 PBI 45 PBOX16 PBI Not overcome None 12 6XT 16XT NIL NIL Not binocular None 13 1ET 2L/R 2XT 3L/R 16 PBOX4 PBI 30 PBOX14 PBI Not overcome None 14 1XT 1XT 20 PBOX8 PBI 40 PBOX16 PBI Not overcome None 15 0 4R/L 6XT 2R/L 16 PBOX6 PBI 30 PBOX14 PBI Not overcome None 16 6XT 4XT NIL NIL Not binocular None 17 2XT 1R/L 8XT 2R/L 6 PBOX6 PBI 25 PBOX14 PBI Not overcome None 18 20XT 6R/L 4XT 2R/L 20 PBOX10 PBI 20 PBOX12 PBI Not overcome None 19 0 1L/R 6XT 2L/R 12 PBOX4 PBI 30 PBOX10 PBI Not overcome None 20 1XT 10XT 2 PBOX4 PBI 4 PBOX4 PBI Not overcome None XT = exodeviation; ET = esodeviation; PBO = prism base out; PBI = prism base in; PK = penetrating keratoplasty to fellow eye; R/L = right over left; L/R = left over right. Figure 2 Comparing the median stereoacuity for Snellen acuities of the poorer eye between 6/12 and 6/60 (20/40 and 20/200) in 20 patients with longstanding asymmetric keratoconus with those for 14 normal subjects taken from table 1 of Goodwin and Romano4 and the mean stereoacuities for 10 normal subjects with a comparable acuity diVerence from Levy and Glick.3 10 000 1000 100 10 1 0.6 Decimalised Snellen acuity Keratoconus Normal (Goodwin and Romano) Normal (Levy and Glick) Stereoacuity (seconds of arc) 0 0.1 0.2 0.3 0.4 0.5 Binocular function in keratoconus 1059 www.bjophthalmol.com Downloaded from bjo.bmjjournals.com on 2 December 2005

Downloaded from bjo.bmjoumals.com on 2 December 2006 1040 Sn,ia八sdd putients with adult anset squints on)Wth由eir contact Len5鱼gu.5 oodwin from cranlal nerve peldes and throld eye dis odR心uno°spei6 cay looked for tropiss during testing of their narmal suhjectx :md d:momstrate the unket of a binocular anomaly found none and noce were Doted by Levy and in chkdhood.The abowe findings indicane that Glik.A fiurrther shady which examined th: relation betwoen the degree of mduced am- prolonpod visual depnvation and the present sometropia and biroculor function in normal patients wold appear to be another instance of subjects found anly occisiceal minor onot- this.It will be of considerable interest to see if malitiex such as hrief xmppressinn with an they have ooemanhle shnnrmaliticx in their induced difference of 2-3 dioptres,'but visual evoked to those found in the nothng ckre in the degree of hineeuls pitient with kmgtanding unilateral ctaracts. diruption fiund in the proent patientx It is prubahke that the patients destribed Although there is no direct evidence that the bere developed their anomalous binocular patients doeribed hene had rormal hinocular funetion hecate of prolongd redueed acmity in one eye fromn their keratoconus.In most keratoconus,only oce of the patents hod intances sclral lenses were introdaced loto their management at a fairly late atare in the vion in the aftected eye.Alrhough mcro dbease.It is possible that earller correction of trepia may go unrecognised in childhood.they their poorer eye woulld have preserved better hin- population with squnts,and it scems unhkely ocular function bas developed it is clar that ooos all had prevtously unrecogmised mocro- poorer cye from using a scleral lens can have a tropias.The abnermalites described bere absto四al impact o如也e overall visual fanc tion of a patient. suppcession ot也e deviaring eye,d如ction or of stereopsis with a mcrotropia when weiring their seeral lens,ad a manifext cxutropia with suppresoon when the poorer eye is uncorrected.It seems most likely that ome at least of these cham8程dus to n女 prolonged deprivution of torm vision in the poorer eye trom the asymmetric keratoconus. It has enerally been atumed that the semd- 22m tiwe period during which bnormal viual 5 x年een2 allecta viwu】develogmtrt i ha dan and Sailke 2a the adult visual system is not affeced by visual p单 our series ot patents was 12 years,and in most hond (Fir 1).Hoever,it hes heen shown that patients with Jongstanding,dense monocul vaal uked potentials recoded to stimula- tion of the deprived eye following cataract cxtractim."In most casas this resovved mer a 11 perod of mocths,but longstanding,monoca anset calaract eamn result in an irreversible loos following cataract surgery.Suppression is often cnsidered mn oc nnly in stintx nf cbildhood ooset,but we have observed it in e194301-3 eFirealu.oou

and two a manifest exotropia (with suppres￾sion) with their contact lens in situ. Goodwin and Romano4 specifically looked for tropias during testing of their normal subjects and found none and none were noted by Levy and Glick.3 A further study which examined the relation between the degree of induced ani￾sometropia and binocular function in normal subjects found only occasional minor abnor￾malities such as brief suppression with an induced diVerence of 2–3 dioptres,5 but nothing close to the degree of binocular disruption found in the present patients. Although there is no direct evidence that the patients described here had normal binocular function prior to the development of their keratoconus, only one of the patients had a known history of squint, amblyopia or poor vision in the aVected eye. Although micro￾tropias may go unrecognised in childhood, they are relatively uncommon within the overall population with squints, and it seems unlikely that at least 20 of the 350 patients with kerato￾conus all had previously unrecognised micro￾tropias. The abnormalities described here follow a consistent pattern, with central suppression of the deviating eye, reduction or loss of stereopsis with a microtropia when wearing their scleral lens, and a manifest exotropia with suppression when the poorer eye is uncorrected. It seems most likely that some at least of these changes are due to prolonged deprivation of form vision in the poorer eye from the asymmetric keratoconus. It has generally been assumed that the sensi￾tive period during which abnormal visual experience aVects visual development in hu￾mans finishes at about 7 years of age and that the adult visual system is not aVected by visual deprivation in animals or humans.6–10 The ear￾liest age at which keratoconus was diagnosed in our series of patients was 12 years, and in most it was considerably later and well into adult￾hood (Fig 1). However, it has been shown that patients with longstanding, dense monocular cataracts of adult onset show a marked delay in visual evoked potentials recorded to stimula￾tion of the deprived eye following cataract extraction.11 In most cases this resolved over a period of months, but longstanding, monocu￾lar visual deprivation associated with adult onset cataracts can result in an irreversible loss of binocular function, with intractable diplopia following cataract surgery.12–14 Suppression is often considered to occur only in squints of childhood onset, but we have observed it in patients with longstanding adult onset squints from cranial nerve palsies and thyroid eye dis￾ease and so its presence does not necessarily demonstrate the onset of a binocular anomaly in childhood. The above findings indicate that the adult visual system is susceptible to prolonged visual deprivation and the present patients would appear to be another instance of this. It will be of considerable interest to see if they have comparable abnormalities in their visual evoked responses to those found in the patients with longstanding unilateral cataracts. It is probable that the patients described here developed their anomalous binocular function because of prolonged reduced acuity in one eye from their keratoconus. In most instances scleral lenses were introduced into their management at a fairly late stage in the disease. It is possible that earlier correction of their poorer eye would have preserved better binocular function. Even when anomalous bin￾ocular function has developed it is clear that even a limited improvement in acuity in the poorer eye from using a scleral lens can have a substantial impact on the overall visual func￾tion of a patient. Proprietary interests: KP manufactures and supplies scleral contact lenses. Grant support: None. 1 White JES, Adams GGW, Sherafat H, et al. Binocular func￾tions in patients with keratoconus managed with scleral contact lenses. Transactions of the 25th Meeting of the European Strabismological Association, 1999, Jerusalem. Lisse, Netherlands: Aeolus Press. 2 Pullum KW, Buckley, RJ. A study of 530 patients referred for rigid gas permeable scleral contact lens assessment. Cornea 1997;16:612–22. 3 Levy NS, Glick EB. Stereoscopic perception and Snellen visual acuity. Am J Ophthalmol 1974;78:722–4. 4 Goodwin RT, Romano PE. Stereoacuity degradation by experimental and real monocular and binocular amblyopia. Invest Ophthalmol Vis Sci 1985;26:917–23. 5 Brooks SE, Johnson D, Fischer N. Anisometropia and binocularity. Ophthalmology 1996;103:1139–43. 6 Boothe RG, Dobson V, Teller DY. Postnatal development of vision in human and non–human primates. Ann Rev Neurosci 1985;8:485–545. 7 Von Noorden GK. Amblyopia: a multidisciplinary ap￾proach. Invest Ophthalmol Vis Sci 1985;26:1704–16. 8 Wiesel TN. Postnatal development of the visual cortex and the influence of environment. Nature 1982;299:583–91. 9 Sloper JJ. Competition and co-operation in visual develop￾ment. Eye 1993;7:319–31. 10 Vaegan, Taylor D. Critical period for deprivation amblyopia in children. Trans Ophthal Soc UK 1979;99:432–9. 11 Sloper JJ, Collins AD. Delayed visual evoked potentials in adults after monocular visual deprivation by a dense cataract. Invest Ophthalmol Vis Sci 1995;36:2663–71. 12 Hamed LM, Helveston EM, Ellis FD. Persistent binocular diplopia after cataract surgery. Am J Ophthalmol 1977;103: 741–4. 13 Pratt-Johnson JA, Tillson G. Intractable diplopia after vision restoration in unilateral cataract. Am J Ophthalmol 1989;107:23–6. 14 Sharkey JA, Sellars PW. Acquired central fusion disruption following cataract extraction. J Paediatr Ophthalmol Strabis￾mus 1994;391–3. 1060 Sherafat, White, Pullum, et al www.bjophthalmol.com Downloaded from bjo.bmjjournals.com on 2 December 2005