Comparison of MTF through-focus curves from profilometer measurements

Most of techniques used to analyze optical quality of LIOs are based on optical bench by implementing the ISO standards[11, 12]. These studies provide the MTF through-focus curves by moving the detector through-focus. MTF through-focus curves obtained from profilometer measurements and from optical bench were compared using the profilometric measurements of a known IOL (Mini Well,) in a ISO eye model [12]. Dominguez et al. using a specific device (PMTF, Lambda-X, Belgium) obtained the MTF through-focus curves of these IOL using an aberration-free eye model of the instrument in accordance with the Standardization (ISO) 11,979–2 [33]. The MTF through-focus curves of the Mini Well from profilometric measurements for 3 mm and 4.5 pupil sizes are shown in Fig. 1. The shape of the MTF through-focus curves were almost identical to that obtained by Domínguez et al. In addition, similar results were showed by Belluci et al.[34] but using a different eye model configuration. Same comparisons were performed for the rest of the IOLs studied in this paper and the same results were concluded independent the eye model used [22, 25, 35,36,37].

Fig. 1

MTF through-focus curves of the Mini Well IOLs implementing the profilometer measurements in the eye model proposed in the (ISO) 11,979–2 standard [12] and for a pupil sizes of 3 mm (blue line) and 4.5 mm (red line) in IOL plane

Differences between the MTF through-object and MTF through-focus

As explained above, the MTF through-object curve was obtained by changing the vergence object instead the detector plane. The reference plane of MTF through-object is the corneal vertex while in MTF through-focus calculation is the exit pupil of the IOL. In any case, both curves will be related using power translation equations from one plane to the other. Figure 2 shown the MTF through-object and MTF through-focus curves for the Mini Well calculated using the model 2 (aberration-free cornea).

Fig. 2

Comparison of the MTF through-focus (blue line) and MTF through-object (red line) obtained for the Mini Well and for 3 mm pupil size (left) and 4.5 mm pupil size (right)

As seen in Fig. 2, significant differences were found. Although the shape of MTF through-focus and through-object were similar, the MTF through-object was narrowed compared to the MTF through-focus. For Mini Well and 3 mm pupil size, MTF through-focus curve provided a peak at -2.55 D and the MTF through-object at -1.6 D (0.95 D of difference). For 4.5 mm pupil size both peaks were located at far vision. An important consequence of this result is the fact that de zone of depth of focus was reduced when MTF through-object was considered. This conclusion was also observed around the far peak. These differences could be important when translating them into distances. The same conclusions were reached if other eye models were considered.

MTF through-object and its interpretation

Since the MTF through-object is representing the object space, the dioptric distances (and therefore the distances) are measured from corneal vertex without the use of any transformation. In order to be able to compare the possible quality of vision between different IOLs from MTF through-object curves, a qualitative criterion based on a minimum value of MTF for 50 cycles/mm of 0.1 was proposed. This value was established after several simulations with different IOL and finding that it provided a simulated optotype image with a recognizable visual acuity of at least 20/25 (see Fig. 3). This criterion does not mean that equal or better visual acuity can be obtained with lower MTF values, but, this limit will be valid to compare intermediate and near vision zones for different IOLs providing a good approximation of how different IOLs perform in these zones.

Fig. 3

Interpretation of the MTF through-object for the Tecnis Symfony (left) and the Mini Well (right) for 3 mm pupil size. Far, intermediate and near points when MTF (50 cycles/mm) value is 0.1 are shown with the corresponding simulated vision optotypes

As example, MTF through-object curves obtained from profilometric measurements for 3 mm pupil size of the Tecnis Symfony and the Mini Well IOLs are shown in Fig. 3. As seen, both IOLs provided good far vision as the optotypes were clearly recognizable. In addition, following the described criterion, a near point in 43.5 cm (-2.3 D) would be observed for Mini Well IOL and in 67.7 cm (-1.5 D) for the Tecnis Symfony, and an intermediate point in 83.3 cm (-1.2 D) for Mini Well and 100 cm (-1 D) for the Tecnis symphony.

With these criteria, the comparison between different IOLs can be better understood and conclusions such as that the Mini Well will provide a greater depth of focus and consequently a closer near point than the Tecnis Symfony can be affirmed.

MTF through-object curves depending on the eye model and pupil size

Figures 4, 5, 6, 7, and 8 showed the MTF though-Object curves for the five IOLs. As explained in methodology section, model 1 corresponded to an aberrated cornea of + 0.258 μm and it was represented with continuous lines, model 2 corresponded to an aberration-free cornea eye model and it was represented with dashed lines. Blue line corresponded to 3 mm pupil size and red line to 4.5 mm pupil size. In addition, a line indicated the minimum value of 0.1 for the MTF.

Fig. 4

MTF through-object curves of the Mini Well IOL for two eye models and two pupil sizes

Fig. 5

MTF through-object of the Tecnis Eyhance IOL for two eye models and two pupil sizes

Fig. 6

MTF through-object of the Tecnis Symfony IOL for two eye models and two pupil sizes

Fig. 7

MTF through-object of the Tecnis Synergy IOL for two eye models and two pupil sizes

Fig. 8

MTF through-object of the RayOne EMV IOL for two eye models and two pupil sizes

Mini WellModel 1

As seen in Fig. 4, aberrated cornea eye model for 3 mm pupil size provided a good far vision and a dioptric distance of 2 D up to near point. An extended DOF between -2 D (50 cm) and -0.75 D (1.33 m) was obtained. For 4.5 mm pupil size a -0.15 D myopic shift of the far focus was observed and the extended DOF converted to three different peaks at -1.85 D (54 cm), -1.35 D (74 cm) and -0.8 D (1.25 cm).

Model 2

When an aberration-free cornea eye model and 3 mm pupil size were considered, the MTF through-object curve was very similar to the model 1. The far focus shown a hypermetropic shift of + 0.4 D. The near point was at -1.95 D, therefore the dioptric distance between far and near vision increased to 2.35 D (instead 2 D in model 1). For 4.5 mm pupil size the Mini Well behaved as monofocal IOL with far focus centred in + 0.6 D (see Fig. 4).

Tecnis EyhanceModel 1

For model 1 and 3 mm pupil size, the Tecnis Eyhance IOL showed a far focus and some extend DOF around it up to -1.1 D (90.9 cm). When 4.5 mm pupil size was considered, the IOL behaved as a monofocal IOL (see Fig. 5).

Model 2

When aberration-free cornea eye model and 3 mm pupil size were considered, a general worsening effect and a far focus hypermetropic shift of + 0.35 D were observed. The dioptric distance between the far focus and the near point was slightly increased up to 1.2 D. For 4.5 mm pupil size the IOL only showed a peak at + 0.45 D with a decrease in optical quality (see Fig. 5).

Tecnis symfonyModel 1

As seen in Fig. 6, for both pupil sizes the Tecnis Symfony behaved as a bifocal IOL, with an intermediate point at -1.25 D (80 cm).

Model 2

There was a hypermetropic shift of + 0.3 D for both pupil size with a general worsening in optical quality. For 3 mm pupil size, the dioptric distance between the two peaks was the same than for model 1 (1.2 D). For a pupil size of 4.5 mm, the optical quality deteriorated considerably (see Fig. 6).

Tecnis SynergyModel 1

Tecnis synergy showed an extended DOF from -2.6 D (38.5 cm) to -1.3 D (76.9 cm), however, a worsening of the optical quality (MTF lower than 0.1) around 2 D (50 cm) was observed. For 4.5 mm pupil size, there was an overall worsening of the optical quality and only a peak centred at + 0.25 D was observed (see Fig. 7).

Model 2

For 3 mm pupil size, a hypermetropic shift of the curve of + 0.3 D was obtained. For 4.5 mm pupil size the MTF through-object decreased below 0.1 (see Fig. 7).

RayOne EMVModel 1

For 3 mm pupil size, RayOne EMV IOL showed an extended DOF around the far focus up to 1.5 D. When 4.5 mm pupil size was considered, decrease of the optical quality was observed (see.

Figure 8).

Model 2

At 3 mm pupil size the far focus is shifted + 0.3 D and a DOF of 0.8 D around the far focus was observed compared to model 1. At 4.5 mm pupil size, the optical quality decreased (see Fig. 8) and hyperopically shifted.

MTF through-object curves depending on the tilt and decentering

The effect of tilting and decentering in IOLs was studied for the Model 3 and 3 mm pupil size. Most IOL designs are thought to performance optimally when the cornea has positive spherical aberration and a photopic pupil size of 3 mm. Specifically, the effect of a 0.5 decentration in the y-direction and a five degree (5°) of tilt was analyzed. In following figures, the MTF through-object of the model 3 (blue line) is compared with the model 3 (orange line), with a decentering of 5 mm (green line) and a tilt of 5º (pink line).

Mini well

As can be seen in Fig. 9, decentration was the factor that modified the MTF through-object curve the most. Increasing the aberrations (Model 3) caused a general worsening effect but maintained the shape. Finally, the tilt was well tolerated by the IOL as the curve remained practically the same. Similar results (but with MTF through-focus) regarding the tilt were obtained by Belluci et al. [34].

Fig. 9

MTF through-object curves for a 3 mm pupil size of the Mini Well IOL. Model 1 (blue line) with a decentration of 5 mm (green line) and a tilt of 5º (pink line), and Model 3 (orange line)

Tecnis eyhance

Clearly, decentration was the factor that most affected IOL optical performance. Far vision was the most impaired although the curve remained above 0.1 for far and intermediate vision. Both Model 3 and the tilt showed very similar curves.

Tecnis symfony

Decentration was the factor that most influenced IOL behaviour. While the bifocality of the IOL was observed for Model 3 and tilt, decentration caused an EDOF effect but with a deterioration of the optical quality.

Tecnis synergy

Model 1, Model 3 and tilt showed the same results. Decentration caused a deterioration for distance vision, but for the EDOF zone all the curves remained similar. Our results were comparable tho those obtained by Can et al., except for the tilt, where we found a higher worsening [38].

RayOne EMV

The MTF through-object is hardly affected by decentration and tilt when a realistic eye model is used.