Chapter 21

LENS

Viktória Mester and Ferenc Kuhn

In the emmetropic human eye, the crystalline lens provides approximately one third of the refractive power necessary to project a focused image of the outside world on the retina. In younger individuals, the lens also changes its shape, maintaining a sharp view of the object even if it is close to the eye. To fulfill these requirements, the lens must maintain both clarity and position.

Although injury to the lens is rather common in serious eye trauma, it has received relatively little attention in the literature. Numerous publications discuss lens removal and IOL implantation in elective cases, but the number of reports dedicated to the same issues in the context of trauma is limited. Removing cataracts related to advanced age is the most commonly performed elective procedure in the human body, with very high rates of patient satisfaction once the eye’s lost refractive power is restored. Management of mechanical lens injury, however, may involve a less favorable outcome while representing a much greater challenge. Several clinical dilemmas (see Table 21–1) need to be solved, and the most appropriate treatment option often remains elusive.

Removal of the injured lens is often complicated by:

• decreased visibility (e.g., corneal wound, hyphema, fibrin);

• injuries to adjacent structures;

• weakness of the lens zonules;

• injury to, and weakness of, the lens capsules;

• the potential for or presence of vitreous prolapse; and

• the attending surgeon’s inexperience and lack of expertise in using vitrectomy instrumentation.

In this chapter we present a systematic approach to all of the important aspects of managing eyes with mechanical injury both to the lens and to IOLs (see Fig. 21–1).

FIGURE 21–1 Types of trauma involving the crystalline lens or IOL.

CRYSTALLINE LENS

Incidence: 23% (USEIRa) to 50%¹ among serious eye injuries;

• 39% in open globe injuries;

• 11% in closed globe injuries (USEIR);

• 432 to 75% (HEIR) of traumatic cataracts occur in eyes with open globe injury.

• Incidence of trauma-related cataract among all cataract cases in children: 13 to 57%.³–⁶

Age:

• range: 0–97 years (USEIR) [HEIR: 5–81 years];

• average: 28 years (USEIR) [HEIR: 36 years];

• 53% of patients between 7 and 30 years (USEIR).

Sex: 84% male (USEIR, HEIR).

Source:

• 28% various sharp objects;

• 22% various blunt objects;

• 18% hammering/nail;

• 7% gunshot/BB/pellet guns;

• 6% fireworks (USEIR).

Place:

• 46% home;

• 18% industrial premises;

• 10% sports/recreation;

• 8% street and highway (USEIR).

Bystanders: 17% (USEIR). Involved eye:

• 49% right;

• 3% bilateral (USEIR).

Injury type:

74% cataract (USEIR) [HEIR: 63%];

13% subluxation (USEIR) [HEIR: 23%];

13% dislocation (USEIR/HEIR); of these (HEIR):

61% complete loss (i.e., lens not found); 34% vitreous; 5% AC.

A study from Kenya found different numbers: only 8% of patients were older than 30 years and 59% of injuries involved the right eye.7

Pathophysiology

The two basic types of trauma-related lens abnormality are:

1. loss of transparency (cataract); and

2. loss of position (subluxation or dislocation [luxation]).

The two may be combined and complicated by lens fragmentation and/or swelling.

Cataract can be caused by

• nonmechanical factors such as:

drugs (e.g., corticosteroids);

diseases (e.g., diabetes);

electricity⁸;

laser⁹;

microwave;

thermal, and UV energy; or

lightning;^10,11 and

• mechanical factors

Surgical intervention (e.g., gas or silicone oil injection) may also result in temporary or permanent lens opacification.

In open globe injuries, the agent can breach the anterior (and posterior) capsules, although this may also occur in closed globe trauma.^12,13

In contusion injuries, coup and contrecoup forces may lead to cataract formation without (visible) violation of the capsules, although posterior capsule damage transmitted by movements of Wieger’s ligament has also been described.¹⁴

Opacification usually, but not necessarily,^16,17 occurs if the capsule is injured, and successful prevention of cataract formation using human fibrinogen tissue adhesive has been reported.¹⁸ The lens may remain at least partially clear even if an intralenticular IOFB causing siderosis is present,¹⁹ or the cataract progression may be very slow.²⁰

Following globe rupture, the surgeon may find no lens at all or one that is dislocated subconjunctivally.²¹

Such lens extrusions have been reported even after iatrogenic trauma (globe “explosion” after inadvertent intraocular injection of peribulbar anesthetic).²² In contused eyes, the lens may dislocate suprachoroidally (C. D. Witherspoon, personal communication), anteriorly,²³ and, most commonly, posteriorly.²⁴

Evaluation

The slit lamp is by far the most important tool in diagnosing a traumatic lens abnormality. The following must be determined.

• What associated injuries are present in the anterior segment?

• Is the anterior lens capsule breached?

• Is there a lens opacity?

• Is the lens opacity likely to progress and, if yes, how rapidly?

• Is the lens subluxated or dislocated (luxated) and, if yes, where and to what extent?

• Are there lens fragments/particles in the AC?

• Is vitreous present in the AC?

• Is the posterior lens capsule breached?

• Has the vitreous prolapsed into the lens, or, conversely, are there lens particles in the vitreous (is lens-vitreous admixture present)?

• Is there an IOFB in the eye/lens?

• What associated injuries are present in the posterior segment?

Especially in eyes with a corneal wound, edema, and/or fibrin and blood in the AC, it may be difficult to determine the following characteristics of the lens:

• clarity;

• position;

• stability;

• anteroposterior diameter (i.e., swelling); and

• capsule(s) integrity.

Retroillumination (see Chapter 14) may be helpful to reveal lens opacity and position, but the pupil may not dilate and false-positive findings may result because of material in front of the lens; vitreous hemorrhage may also interfere. In addition, even if the presence of a lens injury is confirmed, its visual significance may be difficult to assess.1 Slit-lamp findings in case of subluxation are listed later in this chapter.

Additional helpful diagnostic modalities include:

• IBO;

• ultrasound/biomicroscopy²⁵ (although it may be ineffective in detecting posterior capsule damage^26,27);^b

• CT, showing lens damage in 38% of eyes that were diagnosed as clinically having an intact lens.28

The question of whether the posterior lens capsule is intact is of crucial importance. The preoperative evaluation, even if carefully performed, may give a false-negative answer. In the HEIR, posterior capsule injury was found in:

• 23% preoperatively (another 10% was questionable);

• 45% postoperatively (another 8% was still questionable).

* Usually better tolerated in children than in adults.

Cataract

Strategy

There are two basic questions to answer:

1. whether primary or secondary cataract removal should be performed; and

2. if intervention is decided, what the most proper technique is.

Primary versus Secondary Cataract Removal The advantages and disadvantages of primary extraction of a cataractous lens are listed in Table 21–2. The benefits and risks of primary removal must be carefully considered.

• The greatest benefit of primary removal is the surgeon’s ability to inspect the posterior segment otherwise blocked by lens opacity. Involvement of the posterior segment is rarely mentioned in published series; the reported rate is 13³⁰ to 36%.³¹

• In addition, the lens-induced inflammatory reaction can be reduced/prevented.

In general, primary cataract removal is recommended if the lens is:

• fragmentized;

• swollen; or

• causing pupillary block.

The results with primary lens removal are encouraging.^7,32,33

Techniques of Cataract Removal The instrumentation of lens removal is primarily determined by:

• the condition of the posterior lens capsule; and

• the presence of vitreous prolapse.

In open globe injuries, a breach can be expected:

• in the anterior capsule in 71% of the eyes (HEIR);

• in the posterior capsule in 387 to 45%(HEIR) of eyes.

* In the HEIR, 308 out of 705 eyes had lens injury of any type; in the USEIR, 2447 out of 10,450 eyes.

^† Indicates information from the HEIR, all other data are from the USEIR.

In the HEIR, vitreous prolapse was found to be present in 34% of eyes.

To restore the eye’s lost refractive power (see later in this chapter), preserving posterior capsular support for (simultaneous or subsequent) IOL implantation, while generally preferred, is only one of several options. The eye’s overall condition and long-term prosperity should be taken into account.

An additional factor to consider when the surgeon is contemplating instrument selection is whether vitreoretinal surgery is also needed: vitrectomy has been performed in 18% (HEIR) to 24% (USEIR) of eyes; one study³¹ reported a 57% rate.

* Watch for lens capsule lesion’s enlargement.

The incision site for cataract extraction may be clear corneal,³⁴ limbal,³⁵ scleral,³⁶ or pars plana.³⁷ The selection is determined by several factors, including:

• site of the original wound (usually less traumatic if a new incision away from the wound is created);

• additional anterior segment injuries (e.g., avoid further compromising the cornea);

• the extraction technique applied and the need for vitrectomy equipment; and

• the surgeon’s experience.

If the vitrectomy probe is used, the surgeon can choose between various (original wound, limbal, and pars plana) approaches; Table 21–5 provides an overview of their advantages and disadvantages. Certain authors³⁸ prefer the pars plana approach, whereas others³⁹ found no difference. In the HEIR, the pars plana was used in 76% of eyes and the limbal route in 23%; only in 1% of the cases was the original wound utilized. The vitrectomy probe can be used in most patients up to 45–50 years old; beyond this age the nucleus usually proves to be too hard. In such eyes, careful combination of the vitrectomy probe to remove all prolapsed vitreous and pars plana phacofragmentation or vectis removal of the nucleus is recommended.

In children,^d a unique problem is the high rate (39–92%^6,30

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