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A patient exhibiting a congenital hypertrophy of the retinal pigment epithelium (CHRPE) was examined over a four-year period. The CHRPE significantly increased in size over this time. Optometrists should be aware that while this relatively common lesion reportedly rarely becomes malignant, such lesions should be monitored at regular intervals.
Introduction
Buettner first used the term 'congenital hypertrophy of the retinal pigment epithelium' to describe a specific type of pigmented ocular fundus lesions.1 Typical CHRPE consist of a single, flat, round lesion, with sharply demarcated smooth or scalloped margins, which may vary in colour from light brown or grey to black, and are unilateral in almost 100 per cent of cases.2,3,4 CHRPE may manifest atrophied window-like defects called lacunae. These lacunae are variable in size, shape and the percentage of the lesion which they cover. This appears to be mainly an inter-subject variable rather than a predictor of serious pathology, or may represent an involutional change. Coleman and Barnard reported a prevalence of 1.2 per cent for CHRPE in patients visiting a UK optometry practice.5
Other researchers state that on rare occasions CHRPE have been shown to enlarge over many years, but the growth is usually minimal.6,7,8 However, Shields et al9 in a study of 330 patients with CHRPE, reported that slow, flat enlargement of CHRPE was demonstrable in 83 per cent cases. In a small minority of cases, a raised nodule has been observed, which represents a primary malignant adenocarcinoma of the RPE.10 In all cases the nodule was present on initial examination, and although pre-existing nodules have been seen to increase in size with time, new nodules have not arisen.9,10
Case study
The Optomap retinal imaging device is used to image routinely the majority of patients attending the author's practice for an eye examination. This instrument has been discussed by Coleman and Barnard.5
The patient concerned was first examined with the Optomap system when she was 17 years old, in 2003. A small, round, regular shaped CHRPE with a distinct border and no lacunae was observed in the temporal periphery of the right eye (Figure 1). The patient was subsequently imaged again in 2004 and 2007, and the image of the latter is shown in Figure 2.
Assessment of the lesion showed an increase in size between the first and subsequent examinations. There was no evidence of a developing lacuna.
Real measurements from Optomap images cannot be made directly, but assessment of sizes may be made in terms of number of pixels. It is however important to ensure repeatability of pixel concentration for different images taken of the same eye. This is because, for any two image captures, any difference in head/eye position that is present at the moment of image capture will produce a different fundus size in terms of pixels between those two images.
To reduce error, measurements in pixels were taken for the vertical optic nerve head diameter as recorded in 2003 and 2007. Assuming that the optic nerve had not reduced in size and the optic nerve was equal in size in 2003 and 2007 - the optic nerve was actually represented by fewer pixels in the 2007 image than that of 2003, a correction factor was calculated to apply to the measurement of the CHRPE photographed in 2007. For the measurements of the optic nerve and CHRPE in 2003 and 2007, the mean of 10 measurements were calculated in each case.
It was thereby estimated that the CHRPE had increased in size from 92 pixels in 2003 to 138 pixels in 2007. At the eye examination in 2007 the vertical diameter of the right optic nerve was estimated to be 1.8mm using a Volk 66D BIO lens. Using this estimate it was calculated that the approximate vertical diameter of the CHRPE in 2003 was 1.6mm and that 48 months later it had increased to 2.3mm. Over this period of time the patient's ametropia had increased from -1.75DS to -2.50DS.
Discussion
Shields et al found that the most important factor associated with flat CHRPE lesion enlargement was the relative size of lacunae within the CHRPE.9 They postulate that one possible mechanism for enlargement of CHRPE is an increase in the atrophic portion of the lesion, which pushes the hyperpigmented part of the lesion outwards, thus increasing the lesion's size. They reported flat enlargement in 83 per cent of patients followed for three or more years.
The case presented here is of interest because there were no lacunae associated with the lesion either in 2003 or by 2007.
Shields et al report a median rate of enlargement of 10µ per month.9 This compares to an estimated 16µ average rate of change for the lesion presented in this case study. Optometrists should be aware that CHRPEs do commonly increase in size and, as with any pigmented lesion, should be monitored, preferably with photography, at regular intervals. Although rare, a raised nodule on a CHRPE should alert the optometrist to possible malignancy and referral for an ophthalmological opinion should be made. ?
References
1 Buettner H. Congenital Hypertrophy of the Retinal Pigment Epithelium. Am J Ophthalmol, 1975 79, 177-189.
2 Purcell JJ Jr and Shields JA. Hypertrophy with Hyperpigmentation of the Retinal Pigment Epithelium. Arch Ophthalmol, 1975 93, 1122-1126.
3 Lewis RA, Crowder WE, Eierman LA, Nussbaum RL, Ferrell RE. The Gardner Syndrome, Significance of Ocular Features, Ophthalmology, 1984 91, 916-925.
4 Cohen SY, Quentel G, Guiberteau B and Coscas GJ. Retinal Vascular Changes in Congenital Hypertrophy of the Retinal Pigment Epithelium, Ophthalmology, 1993 100, 471-474.
5 Coleman P & Barnard NAS. Congenital Hyperplasia of the Retinal Pigment Epithelium, Ophthalmic & Physiological Optics, 2007Nov 27(6):547-55.
6 Jones W. Peripheral Ocular Fundus, P. Chapter 3, Butterworth Heinemann Elsevier, St Louis, 2007.
7 Boldrey EE and Cleasby GW. An unusual case of congenital hypertrophy of the retinal pigment epithelium. Arch Ophthalmol, 1976 94, 1910-1911.
8 van der Torren K and Guyton GP. Progression of perimacular congenital hypertrophy of the retinal pigment epithelium with impaired visual function. Arch Ophthalmol, 1998 116, 256-257.
9 Shields CL, Mashayekhi A, Ho T, Cater J, Shields JA. Solitary Congenital Hypertrophy of the Retinal Pigment Epithelium, Clinical Features and Frequency of Enlargement in 330 Patients. Ophthalmology, 2003 110, 1968-1976.
10 Trichopoulos N, Augsburger JJ, Schneider S. Adenocarcinoma Arising From Congenital Hypertrophy of the Retinal Pigment Epithelium. Graefes Arch Clin Exp Ophthalmol, 2006 244, 125-128.
? Simon Barnard is in private optometric practice in North London and visiting associate professor at the Department of Optometry & Visual Science, School of Health Sciences, Hadassah, College, Jerusalem, Israel