Introduction
Understanding dysphotopsia is vital in achieving a high quality of life in all patients following multifocal intraocular lens (IOL) implantation. Dysphotopsia is a disturbance of vision and includes light phenomena such as haloes, the subjective perception of a bright ring around a light source; it occurs due to optical non-conformities in the optical path such as cataract or optical boundaries.1 The current literature shows that implantation of a multifocal rather than a monofocal IOL can lead to unwanted optical phenomenon termed dysphotopsia.1 2 However, the literature comparing IOLs is equivocal as to which design features minimise dysphotopsia, due principally to the lack of objective methods for assessing dysphotopsia. The majority of studies examining dysphotopsia use various subjective questioning in the form of verbal interviews,3 4 bespoke questionnaires,5 a validated questionnaire6 7 or through subject-initiated complaints.8 An alternative method is to use graphics depicting visual demonstrations of different types of dysphotopsia allowing the subject to indicate which is most representative of what they perceive.9 10
Instruments designed to measure the effects of disability glare have also been used in multifocal IOL studies. Disability glare is usually quantified as the reduction in vision from a glare source present within the visual field and is due to the spread of light (or straylight) across the retina.11 The majority of techniques used to assess disability glare are composed of a central optotype chart of varying spatial frequency or contrast surrounded by a glare source. The intensity of the ambient light is changed or a glare source is added to determine the effect this has on measures of visual acuity or contrast sensitivity. Examples of this approach can be found in the form of the Brightness Acuity Tester (BAT; Marco, Florida, USA), Mesoptometer II (Oculus Optikgera¨te GmbH, Wetzlar-Dutenhofen, Germany) or digital view-in visual testing units, such as the Optec 6500 (Stereo Optical Co, Chicago, Illinois). Several custom-built glare testing units have also been developed.12 13 However, these testing units do not quantify the extent of dysphotopsia and the literature shows variable results. Similar studies involving the C-Quant (Oculus Optikgera¨te GmbH, Wetzlar-Dutenhofen, Germany), an instrument for evaluating the quantity of ocular straylight, have shown similar variability with a marked difference in straylight identified in some studies,14–16 but not others,2 17–19 and higher straylight with diffractive designs than refractive and segmented designs.20 The difference in light scatter between a monofocal IOL and diffractive bifocal and trifocal IOLs has been recently reported with the light-distortion analyser (HLMP-CW47-RU000, Agilent Technologies) an experimental device consisting of a central white light–emitting diode (LED) surrounded by 240 small, white LEDs distributed in 24 meridians 15 degrees apart;21–23 a difference was found between them, but this was not correlated with visual acuity. The disparity between reported dysphotopsia and the results recorded with glare testing units may be due to the optical properties of multifocal IOLs. Pupil size does not seem to affect straylight measures, but this has only been assessed in spherical IOLs.24 Dysphotopsia due to multifocal IOLs may primarily be the result of a second out of focus image being present on the retina rather than diffuse straylight over the retinal surface (scatter affecting a much broader area) as induced by conditions such as cataract.13 17 To measure the qualitatively described light surrounding retinal blur circle or halo, several instruments often referred to as ‘halometers’ have been created.25–27 These devices measure the size of a photopic scotoma created by a central glare source.
The purpose of this study was to examine the phenomenon of dysphotopsia in patients implanted with two multifocal IOL designs (refractive and diffractive) and to compare subjective symptoms to the quantification of straylight and halo size. A standardised preoperative measure of halo size compared with subjectively reported symptoms due to cataract, might help to identify individuals who are more likely to better tolerate dysphotopsia effects potentially induced by multifocal IOLs.