Why Multifocal IOL Patients Sometimes Have Poor Near Vision Despite Good Distance Vision

Patients with multifocal IOLs expect to be free from glasses for distance, intermediate, and near vision. However, refractive surprises can occur, leading some patients to still require glasses. In my earlier article, "The Mystery of the Near with Presbyopia Correction IOL" (link), I discussed how factors like corneal shape and axial length can affect near vision. In this article, I will explain how a refractive surprise or incorrect refraction can result in good distance vision but poor near vision problem.

Before diving into this topic, please read my article on "Understanding Defocus Curve of Multifocal IOLs" (link). In that piece, I explained that a patient with a bifocal diffractive IOL should have their distance focal point on the retina and the near focal point located anterior to the retina (see Fig 1). For trifocal IOLs, there is an additional focal point for intermediate vision, situated between the distance and near focal points.

Hyperopic Surprise Explained

Modern presbyopia-correcting intraocular lenses (IOLs)—including bifocal and trifocal designs—are intended to provide patients with functional vision across multiple distances. Many patients achieve excellent spectacle independence after cataract surgery with these lenses.

However, clinicians occasionally encounter a puzzling postoperative complaint:

“Doctor, I can see far away quite well, but I still cannot read comfortably.”

This situation can occur even when the patient reads 6/6 (20/20) on the distance chart.

One important cause of this paradox is what can be described as near-vision surprise, often related to a hyperopic refractive outcome.

Understanding the optical basis of this phenomenon helps clinicians interpret postoperative complaints more accurately and manage patient expectations effectively.

How Multifocal IOLs Create Multiple Focal Points

Multifocal IOLs use diffractive or refractive optical structures to split incoming light into multiple focal points.

Bifocal IOLs

Two primary focal points are produced:

• Distance focus – designed to fall on the retina

• Near focus – located anterior to the retina for reading tasks

Trifocal IOLs

Three focal points are generated:

• Distance

• Intermediate

• Near

Each focus corresponds to a specific working distance.

When surgery achieves the intended refractive target (emmetropia):

• Distance focus aligns with the retina

• Intermediate and near foci lie in front of the retina

• The brain selects the appropriate focus depending on the task.

This optical distribution is what allows patients to function across multiple distances.

What Happens in Hyperopic Refractive Surprise

A hyperopic refractive error shifts the focal system posteriorly relative to the retina.

This causes two key optical changes:

1. Distance focus moves behind the retina

2. Near focus shifts closer to the retinal plane

The degree of displacement depends on the magnitude of hyperopia.

This shift creates a misleading visual situation.

Why Distance Vision Can Still Be Good

Even when the intended distance focus is behind the retina, the patient may still read the distance chart well.

This occurs because the patient may unknowingly use the near or intermediate focal point to resolve distant objects.

In other words:

• The distance focus is misplaced

• Another focal point falls close enough to the retina to produce acceptable acuity.

As a result, the patient may demonstrate good Snellen acuity, masking the true refractive error.

Why Near Vision Becomes Poor

The problem becomes evident during reading or near work.

When the patient looks at a near object:

1. The eye's optical demand changes.

2. The near focal point—already displaced by the hyperopic error—moves further behind the retina.

3. The retinal image becomes blurred.

Clinically, the patient may present with:

Vision Type	Typical Finding
Distance vision	6/6 or 6/9
Near vision	N10–N14 or worse
Patient complaint	Difficulty reading

This paradox occurs because distance vision is being achieved through the wrong focal point of the multifocal optic.

Why This Matters in Postoperative Assessment

For surgeons, this highlights an important principle:

Good distance visual acuity does not always indicate an optimal refractive outcome in multifocal IOL patients.

When evaluating postoperative dissatisfaction, clinicians should assess:

• Thorough subjective refraction

• Near visual acuity

• Defocus curve performance

• Residual spherical error

• Corneal topography

Even a small hyperopic error (+0.25 to +0.50 D) may significantly affect near performance in multifocal IOL patients.

Practical Clinical Tip

How can clinicians determine if a patient is reading the distance chart using their near or intermediate focal point? Here are the steps to identify the correct focal point:

1. Assess Unaided Distance Vision: First, check what the patient can read unaided for distance.

   
   

2. Add Plus Glasses: If the patient reads 6/6, add a +2.5 diopter lens. For those reading 6/9, use a +2.0 or +1.5 diopter lens for patients reading 6/12.

   
   

3. Monitor Vision Drop: If the vision drops, it indicates that the patient used the distance focal point to read the distance chart. The drop in near acuity can also be due to other factors, such as decentration, pupil miosis post-surgery, or effective lens position. The expected drop in vision can be understood from the defocus curve of the specific IOL, but generally, it can be summarized as follows:

4. +2.5 diopter: less than .5 log mar

5. +2.0 diopter: less than .4 log mar

6. +1.5 diopter: less than .3 log mar

   
   

   Evaluate Near Focal Point: If the patient's vision does not drop significantly with the +2.5 diopter addition, it suggests they used the near or intermediate focal point to read the distance chart.

Key Takeaway

Hyperopic refractive surprise can create an optical illusion in multifocal IOL patients:

• Distance vision appears good

• Near vision becomes unexpectedly poor

This occurs because the patient may be using the near or intermediate focal point for distance vision, while the true near focus shifts behind the retina during reading.

Recognizing this pattern helps clinicians:

• Diagnose subtle refractive errors

• Avoid misinterpreting postoperative visual outcomes

• Improve patient satisfaction after presbyopia-correcting IOL implantation.

✔ Clinical pearl

Whenever a patient with a multifocal or trifocal IOL reports poor reading ability despite good distance acuity, always rule out hyperopic residual refractive error.

Multifactorial Causes of Near Vision Loss

As mentioned earlier, the causes of near vision loss can be multifactorial. I previously explained how steep corneas and longer axial lengths can affect near vision. In this article, I have highlighted how hyperopic outcomes can also lead to near vision loss, often masked by patients utilizing their intermediate or near focal points for distance vision.

A wrong refraction, where the clinician fails to locate the correct focal points, can also lead to a pseudo-near vision surprise. Therefore, it is crucial for surgeons and clinicians to take the time to perform a thorough refraction.

In conclusion, understanding the dynamics of multifocal IOLs and the potential for refractive surprises is essential for improving patient outcomes. By carefully assessing focal points and considering various factors affecting vision, we can enhance our approach to patient care in cataract surgery.

For more insights and resources, visit quickguide.org.