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on preoperative chamber depth and axial length. We wanted to study the efficacy of this 2-variable dependency on the accuracy of IOL power calculation. To do so, we recalculated the a0 to represent not the effective lens plane but, rather, the true anatomical position of the IOL and used this value in the Olsen ‘thick lens’ formula. I agree with Wolfgang Haigis that in theory the ACD of the IOL with the steepest anterior curvature is expected to be the smallest, other things being equal. However, if we had been able to improve our predictions by this small correction, all comparison groups would have been changed by an equal amount, which would not have altered our conclusions. We therefore still believe that our 5-variable method of predicting ACD is more accurate than the Haigis 2-variable method. As we demonstrated in Olsen (2006), lens thickness was ranked third after axial length and preoperative chamber depth in the statistical association of postoperative ACD with the IOL. Unfortunately, lens thickness is not measured with the current version of the Zeiss IOLMaster (Carl Zeiss Meditec AG, Jena, Germany) and therefore must continue to be measured with ultrasound.
References Haigis W (2004): The Haigis formula. In: Shammas HJ (ed). Intraocular Lens Power Calculations. Thorofare, NJ: Slack Inc. 5–57. Olsen T (2007): Improved accuracy of intraocular lens power calculation with the Zeiss IOLMaster. Acta Ophthalmol Scand 85: 84–87. Olsen T (2006): Prediction of the effective postoperative (intraocular lens) anterior chamber depth. J Cataract Refract Surg 32: 419–424.
True polycoria or pseudopolycoria? Niaz Islam,1 Jodbhir S. Mehta1 and Gordon T. Plant1,2 1
Moorfields Eye Hospital, London, UK National Hospital for Neurology and Neurosurgery, London, UK 2
doi: 10.1111/j.1600-0420.2007.00985.x
Editor, rue polycoria is extremely rare (Duke-Elder 1964; Loewenfeld 1993). An intact sphincter muscle is required in each of two or more pupils in a given iris. Patients with intensely miotic pupils, with or without polycoria, are at risk of amblyopia. To our knowledge this is the only reported and photographed case of polycoria and miosis, without profound amblyopia. A 55-year-old man with presbyopia was referred by his local optician. His visual acuity (VA) was 6 ⁄ 6 in the right eye and 6 ⁄ 9 in the left. He had had the observed iris abnormality all his life, and had no previous ocular inflammation, surgery or trauma. His right pupil was normal and measured 3 mm in diameter, whereas both left pupils presented within a 2-mm central zone (Fig. 1) and measured 1.3 mm and 0.5 mm in diameter, respectively. The subject had dimmer vision in his left eye, without
T
(A)
Correspondence: Thomas Olsen MD Associate Professor University Eye Clinic Aarhus Kommunehospital DK-8000 Aarhus C Denmark Tel: + 45 89 49 32 28 Fax: + 45 86 12 16 53 Email:
[email protected]
(C)
monocular diplopia. The photographs in Fig. 1 show that the left eye sphincter segments dilated to an equal degree around both pupils. Our patient declined all further imaging of the iris sphincter and pigment epithelium. Iris holes occur with considerable frequency, but in the great majority of cases they represent colobomata, iris dehiscence or iris diastasis. They are simple defects in the iris, have no pupillary sphincter and are not true pupils (Duke-Elder 1964). Pseudopolycoria is distinguished by the passive constriction of the accessory pupil when the true pupil is dilated. The mechanism of true polycoria remains uncertain. The most likely cause in our case (Fig. 2A) was the snaring off or segregation of a portion of the pupil margin (Mann 1957). Alternatively, the partial closure of a
Fig. 2. Possible formation of two pupils by (A) snaring off a portion of the pupillary margin, or (B) secondary closure of a coloboma.
(B)
(D)
Fig. 1. The patient’s left eye in (A) light and (B) dim light. (C, D) The pupillary margins are no longer puckered up following dilatation with guttae tropicamide 1% and phenylephrine 2.5%.
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Glare rays Glare source
E Target
Fig. 3. The second pupil allows for a contrast-lowering effect by enabling stray light at the retinal surface to obscure the macular image ‘E’.
coloboma (Fig. 2B) may be caused by a bridge containing ectoderm as well as mesoderm (Mann 1957). Thirdly, residual adherence of the lens to the cornea after the separation of the two tissues may lead to the formation of a bridge across this area when the anterior chamber forms, resulting in two pupillary apertures lined with muscular fibres (Jaffe & Knie 1952). Fourthly, the anomaly may date from an early stage when the cells of the neural ectoderm are pluripotential and differentiate into muscle fibres in abnormal situations. Duke-Elder (1964) noted three such cases published between 1899 and 1920, and stated that a sphincter surrounding a supernumerary pupil ‘has never been demonstrated to occur’. Additional pupils associated with iridoschisis tend to be elliptical rather
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than circular. Drawings of polycoria often show the extra pupils to be at some distance from the principal pupil (Loewenfeld 1993). In such instances it is clear that separate iris sphincters have developed independently. In our case, the two sphincters were adjacent on retro-illumination and iris transillumination. We can only hypothesize that the iris anomaly did not result from in utero exposure to a toxic agent, as there was no pertinent maternal obstetric history and no other systemic medical or ocular conditions, such as anterior capsular cataract or deep corneal opacities, were found. Visual acuity decreases linearly with pupil diameter below 1.5 mm (Miller & Judisch 1979); this may account for our patient’s VA of 6 ⁄ 9, which did not increase with pinhole or refraction. Glare can be defined as a contrast-lowering effect of stray light on a visual scene (Fig. 3). Our patient’s dimmer left eye vision or decreased retinal illumination can be explained by Airy disc effect or diffraction rings and interference fringes induced by the second pupil. Patients may not convey glare symptoms clearly and this complaint can often be ignored. We present and review this rare phenomenon in order to provide
further insight into the embryology of the pupil and to encourage others to investigate any known or future similar cases.
References Duke-Elder SS (1964): Congenital Deformities. System of Ophthalmology, Vol. III-2. St Louis: Mosby 592–593. Jaffe NS & Knie P (1952): True polycoria. Am J Ophthalmol 35: 253–255. Loewenfeld IE (1993): Iris Damage. The Pupil. Anatomy, Physiology and Clinical Applications, Vol. I. Detroit: Wayne State University Press 902–906. Mann I (1957): The Iris. Developmental Abnormalities of the Eye. London: British Medical Association 252–254. Miller SD & Judisch GF (1979): Persistent pupillary membrane: successful medical management. Arch Ophthalmol 97: 1911–1913.
Correspondence: Niaz Islam Queen’s Hospital Rom Valley Way Romford Essex UK Tel: + 44 1708 43500 ext. 3779 Fax: + 44 7092 061172 Email:
[email protected]
