Eye (1987) 1, 1-14 DOYNE LECTURE KERATOCONUS Y. POULIQUEN Paris For a physician specialising in the cornea, cor­ found is Campinchi and Haye,1 and more neal dystrophies pose several basic questions recently in Krachmer and et al.2 regarding clinical identification, anatomic 'Keratoconus or conical cornea is a disease characteristics, and aetiological diagnosis. defined as a non-inflammatory protrusion of Corneal dystrophies are most often accom­ the cornea in its axial region usually appearing panied by a distinctive distribution of in early adolescence and causing a serious opacities and of a localised deposition of decline in visual acuity due to a high degree of abnormal material (MPS, amylosis). irregular myopic astigmatism' (Duke Elder) Keratoconus presents between the ages of (Fig. 1). ten and twenty years as do many corneal dys­ If we add that the cornea thins in its centre, trophies but the corneal stroma remains trans­ that the complaint evolves slowly and that it is parent for a long time. Progression is marked usually bilateral and generally very disabling by a slow deformation of the cornea. It is we have summarised a little more completely histologically very different from other dys­ the clinical characteristics of the disease. trophies and a wide variety of questions arise Many important questions arise: concerning its aetiology. Over the twenty -relationship to heredity years that we have had the opportunity of -aetiology studying corneal pathology in both its clinical -relationship to certain local disorders and fundamental aspects, we have never (atopic disease, contact lens wearing) or stopped investigating Keratoconus and this general disorders occasion offers an opportunity to present our -characteristics which differentiate it from concepts concerning a subject particularly other ectatic disorders of the cornea dear to me. -treatment Keratoconus has interested a considerable number of ophthalmologists since it was I will try to answer these questions. recognised as a pathological entity in the mid­ dle of the Eighteenth Century. (Mauch art , Incidence 1748: Taylor, 1766). About a century later It is very difficultto estimate the frequency of keratoconus was differentiated from other keratoconus in an average population because corneal ectatic disorders. Nottingham (1854) it varies greatly from 4 per 100,000 defined its essential clinical features. (Amsler3,4,5) to 600 per 100,000 (Hofstetter6). Since then, a considerable amount of work The average is 50 to 230 per 100,000 by has been published on the subject, most Feder,2 who has summarised the known statis­ addressing either the clinical or the aetiologi­ tics. The variation in figures is done in varia­ cal aspects of the disorder. Their references tion of diagnostic criteria and for national and are listed in bibliographies of general reviews above all regional differences. All races are dedicated to keratoconus. The earliest to be implicated, but keratoconus appears to be Correspondence to: Dr Y. J. M. Pouliquen, Service d' Ophtalmologe, de L'Hotel-Dieu, 1 Place du Parvis, Notre­ Dame 75004, Paris, France. 2 Y. POULIQUEN (a) (b) (c) Fig, 1. Three clinical forms of corneal deformation on slit-lamp examination, (a) eccentric, (b) more or less pointed and (c) thinning of the deformed cornea. more widely spread in Mediterranean coun­ Keratoconus and Heredity tries rather than in northern Europe, and Keratoconus occurring in two members of the there is a higher incidence in French people of same family raises the question of heredity; predominantly Celtic ongm (western but, two people in the same family may have France), and in females compared with males. shared the same environmental factors. Keratoconus is generally a bilateral con­ Consequently assessing the precise role of dition. Amsler reported 14.3 per cent of cases heredity in keratoconus is difficult.However, to be unilateral. Bilaterality may only become several cases of identical twins suffering from apparent with time, the second eye usually keratoconus have been reported. We have being affected a few years after the first. performed surgery on male twins. In this case, The disorder most often appears in a it is difficultto disprove a genetic factor in the patient between ten and twenty years of age. pathogenesis of the disease. Numerous The exact beginning of the disease is often authors have attempted to define the fre­ missed by the clinician for the diagnosis is quency and manner of transmitting the often made a long time after the first signs of disease. trouble. It evolves slowly and it is difficult to (1) Waardenburg7 cites seven cases of ker­ be precise about the average interval between atoconus involving blood relatives and the early changes and the stage at which there thus suspects a recessive genetic factor. is sufficient handicap to justify keratoplasty; (2) Hallerman8 and Wilson think that the fre­ an average of ten years (Pouliquen).40 There quency of hereditary factors is at least 7 are early cases of surgery on record of children per cent and that the mode of transmis­ younger than ten years and late cases of sion has multiple causes. patients over thirty. (3) Hammerstein9 in studying 52 families with DOYNE LECTURE 3 keratoconus determined that hereditary corneal stroma.lO•11 Generally oblique and influenceoccurs in the order of20 per cent very fine, they disappear with external pres­ of cases. sure on the globe (Fig. 2). They doubtless correspond to the reflection due to the dis­ Clinical Diagnosis of Keratoconus placement of posterior stromal lamellae with In most cases the clinical diagnosis of ker­ respect to the anterior stromal lamellae. atoconus is easy because it presents as (Katz,12 offers a theoretical explanation). advanced disease. An 'adolescent comes for These reversible striae are very differentfrom consultation because of a decline in visual the scarring of the subepithelial anterior acuity, intermittent misty vision and distor­ stroma at the cone apex; these are the real tion. These symptoms are particularly promi­ corneal opacities, resulting from ruptures of nant for distance vision and are frequently Bowman's membrane (Fig. 3). The lesions associated with ocular irritation. The examin­ which are of variable size, may contribute to ation reveals high and irregular myopic astig­ the visual loss in advanced keratoconus. Fol­ matism, and irregularity of the mires can be lowing rupture of Descemet's membrane in identified by keratometry. Observation of the acute hydrops, one observes other folds after pupil confirms the existence of a shadow clearing of the cornea. Several further bio­ thrown by the cornea on the major horizontal microscopic features can still be noted; the axis. In well developed cases a downward existence of Fleischer's ring. This is a more or glance causes angulation of the lower eyelid less complete rust-brown ring, encircling the (Munson's sign). base of the cone. It is composed of hemo­ On slit lamp examination, one notes the siderine deposited in the deep layers of the existance of corneal striae deeply seated in the corneal epithelium. Only its form is special (a) (b) ( c) Fig. 2. Three central abnormalities of the cornea, (a) folds of Elschnig or Vogl, (b) the fine white parallel striations are situated in the deep stromal cornea and (c) which disappear when pressed in the globe. 4 Y. POULIQUEN Fig. 3. Two forms of central sub-epithelial opacities seen in advanced keratoconus. because it does not differ in nature from the paracentric and inferior. Keratometry has lines of Hudson-Stahli, Stocker etc ... It is been carried out to document evolution of sometimes accompanied by fine white lines in corneal steepening and its slow development. concentric curves situated in the interior of Marechal-Courtoisl4 has emphasised that the ring.13 Hypertrophic nerves can some­ inferior steepening is a characteristic early times be seen in the cornea. Corneal sen­ change of keratoconus and pointed out the sitivity may be variable. need of a topographic keratometry. The mean at the disposal of an ophthal­ Clinical Forms of Keratoconus mologist to determine the changes on the cur­ Early stage vature of keratoconus is the Placido disk. It The above description can lead one to con­ provides qualitative topographical infor­ clude that it is easy to diagnose advanced mation, which Amsler subdivided into four keratoconus. This is not always so and it is stages. Although the hand held keratoscope often difficultto diagnose in the early stages of or Placido disk are subject to error, the photo­ development. In the first stage only the exis­ keratoscope (invented by Placido) provides tence of astigmatism which we are certain did an available method of measurement by not previously exist, leads to suspicion of the which the greater part of the corneal area can possibility of keratoconus and forsee its be photographed precisely. The alteration of development. All the other diagnostic reflectedring contours permits a fairly precise changes such as thinning, protrusion, striae, appraisal of corneal distortion. In this manner etc. are lacking. Keratometry is thus of major the keratoscope used by Rowsey allowed importance. There are always limitations with early detection of keratoconus which starts classic keratometers because measurements with steepening of the inferotemporal cornea, are difficult outside of the central cornea. The then peripheral steepening subsequently alterations of the curve in keratoconus are involving the inferonasal quadrant and then