Study Aim

This was a prospective study designed to assess the range of clear vision provided by numerous MIOL designs by measuring and analysing defocus curves in photopic conditions. Secondary aims were to assess the visual performance of these lenses in mesopic conditions and to examine the relationship between VA through defocus and VA at the corresponding distance.

2.2.1 Subjects

Seventy-five subjects (27 males, 48 females) of mean age 61.2 ± 8.9 years planning to undergo bilateral cataract surgery or electing for bilateral clear lens extraction were recruited from Solihull Hospital (Solihull, U.K.) and the Midland Eye Institute (Solihull U.K.). The principal investigator of the study (PB) recruited all participating subjects. The inclusion criteria for the study were as follows:

 Requiring bilateral cataract surgery or electing for bilateral clear lens extraction

 A likely postoperative best corrected distance visual acuity of at least 0.1 LogMAR

 The absence of any ocular pathology and previous surgery

 Corneal astigmatism less that 1.50 D

 Aged between 40 and 70 years

 Suitable for MIOL implantation

 Willing to have MIOL implantation

 Willing to participate in the study

 Able to achieve reliable partial coherence interferometry results

 Willing to attend an extra post-operative aftercare visit

 Absence of post-operative capsular opacification, corneal refractive surgery, and capsulotomy

The 75 recruited subjects were implanted with five combinations of IOLs. The subjects were strictly divided into one of five groups based on their operation date for their first eye. Each group was assigned a type of IOL:

 The first 15 subjects were bilaterally implanted using mix and match strategy; a ReZoom MIOL (Abbott Medical Optics, Inc.) was implanted in the right eye and a Tecnis ZM900 MIOL (Abbott Medical Optics, Inc.) was implanted in the left.

 The second 15 subjects were implanted bilaterally with the ReZoom MIOL.

 The third 15 subjects were implanted bilaterally with the Tecnis ZM900 MIOL.

 The fourth 15 subjects were implanted bilaterally with the Lentis Mplus MIOL (Topcon Europe).

 The remaining 15 subjects were implanted bilaterally with the Softec 1 monofocal IOL (Lenstec, St Petersburg, Fl, USA).

The implications of MIOL implantation were discussed with each subject by the principal investigator and consultant Ophthalmologist performing the surgery; the final decision to operate was made by the consultant Ophthalmologist.

Pre-operatively an IOLMaster (Carl Zeiss Meditec AG) running v5 analysis software and NIDEK OPD-Scan II (Optical Path Difference Scanning System II; NIDEK Co Ltd, Gamagori, Japan) Wavefront Aberrometer were used to determine axial length and corneal power. To determine IOL power, the Hoffer Q IOL formula was used for short axial lengths, (<22 mm; College of Ophthalmologists‘ Guidelines) and the SRK/T was used for all other axial lengths; emmetropia was the target in all cases.

All operations were performed by one of three surgeons using topical or local anaesthetic. A 2.85 mm clear corneal incision (widening to 3.2 mm before the insertion of the IOL) was placed on the steepest corneal axis to reduce residual levels of postoperative astigmatism. Phacoemulsification, aspiration, and irrigation were performed through a 5.5 mm capsulorhexis using the Millennium phacoemulsification system (Bausch and Lomb, Rochester, N.Y., USA.). All IOLs were implanted into the capsular bag.

Four subjects were later excluded from the study due to post operative complications:

two from the Lentis Mplus group (one developed cystoid macular oedema and one

required neodymium-doped yttrium aluminium garnet (Nd:YAG) Laser capsulotomy), one from the bilateral Tecnis ZM900 group (required post operative laser-assisted in situ keratomileusis) and one from the bilateral Mix and Match group (underwent post operative Nd:YAG capsulotomy). An additional four subjects were recruited to replace those who were excluded. The final patient demographics are detailed in Table 2.3.

Bilateral conducted in accordance with the tenets of the Declaration of Helsinki.

2.2.2

Methods

All subjects were examined 3-6 months post-operatively by the principal investigator.

During this visit the following tests were performed:

2.2.2.1 Full Refraction

A combination of several techniques were used to establish the full refraction:

Retinoscopy using the Keeler Professional Retinoscope (Keeler Ltd, Windsor, UK) and autorefraction using the Shin-Nippon NVision-K 5001 (Ajinomoto Trading, Inc., Tokyo, Japan) were performed followed by a full subjective refraction at 6 m using the Thomson Test Chart 2000 (Thomson Software Solutions, Hatfield, Herts., UK.). The Shin-Nippon NVision-K 5001 autorefractor (Ajinomoto Trading, Inc., Tokyo, Japan) provides valid and repeatable measures of pseudophakic eye refraction in monofocal and accommodating IOLs (Wolffsohn et al., 2010b). Autorefraction is also a valid starting point with diffractive MIOLs (Bissen-Miyajma et al., 2010); however, with refractive concentric MIOLs, autorefraction results overestimate the levels of spherical myopia present in the eye (Muñoz et al., 2007). The distance focal point was the target with all subjects.

2.2.3 Monocular and Binocular Intermediate (80 cm) and Near (40 cm) Visual Acuity

The Early Treatment of Diabetic Retinopathy Study (ETDRS) Near LogMAR Chart 2000 (Precision VisionTM, La Salle, IL., USA) was used to measure VA for intermediate and near. The ETDRS chart is a LogMAR chart and therefore uses the standard logarithmic progression of letter sizes; a factor of 1.259. It is designed for use at 40 cm but can also be used at a distance of 79.8 cm (40*1.259³). Near and intermediate LogMAR VA was calculated using the M notation for letter size and working distance (Holladay 1997; Equation 2.2). As several measurements of near and intermediate vision were required for the study, 4 EDTRS charts were cycled to prevent memorisation of letters.

Equation 2.2

VA = Visual Acuity D = working distance M = letter size (M notation)

2.2.4 Monocular Defocus Curves in Photopic Conditions and Binocular Defocus Curves in Photopic and Mesopic Conditions

In total 4 best distance corrected defocus curves were measured per subject. The Thomson test chart 2000 (Thomson Software Solutions, Hatfield, Herts., UK.), positioned at 6 m, was used to measure the VA with each defocus lens. These were placed in a random order over the range of +1.50 to –5.00 D in 0.50 D steps and the letters on the Thomson test chart 2000 were randomised between measures. An Oculus Universal Trial Frame (Keeler Ltd, Windsor, UK) was used to house the manifest refraction and each additional defocus lens; it was adjusted to ensure a 12 mm Back Vertex Distance. For each measurement of VA subjects were prompted once using the phrase ―can you read any more letters on the line below?‖ according to the methodology described by Gupta and colleagues (2008).

In photopic conditions the defocus curves were measured monocularly and binocularly and in mesopic conditions the defocus curves were measured binocularly. Light levels were strictly controlled to a constant luminance of 120 cdm² and illuminance of 100 lux for photopic conditions, for mesopic conditions the luminance was a constant 3 cdm²



VA(LogMAR) log D M

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 



and illuminance 10 lux; the Minolta LS-110 luminance meter (Konica Minolta Photo Imaging Inc., Mahwah, NJ, USA) was used to measure luminance. Illumination was measured using a light meter at the position of the subjects‘ eyes. To achieve 3 cdm² the room lights were lowered, the screen brightness was reduced and a neutral density screen filter was placed over the computer monitor. Neutral density filters have been used previously to reduce the brightness of a screen to mesopic levels (Walkey et al., 2006). Each subject was allowed five minutes to adapt to the transition between photopic and mesopic conditions prior to the resumption of measurements.

2.2.5 Subjective Assessment of Near and Intermediate Vision

Each subject was requested to rate their intermediate and near vision on a scale of 0 (completely satisfied) to 5 (completely unsatisfied) by completing a short questionnaire of two questions:

 How satisfied are you with the near visual ability that you have?

 How satisfied are you with the intermediate visual ability that you have?

2.2.6 Measurement of Pupil Size

Monocular pupil size were measured in both photopic and mesopic conditions using a validated portable infrared pupillography device (Murray et al., 1991; Scheffel et al., 2010); the Pupilscan II infrared pupillometer (Keeler Ltd, Windsor, UK).