Morphological and histological changes in eye lens: Possible application for estimating postmortem interval

Highlights

• We study changes in eye lens and its possible application for estimating PMI.

• Sphericity and absorbance has a tendency to decrease as the PMI increase.

• Gradual loss of lens histological structure is a function of the hours postmortem.

• Lens modifications to be useful for determining the PMI between 24 and 96 h.

Abstract

Establishing the postmortem interval is a very complex problem in Forensic Science despite the existence of several macro- and microscopic methods. In the case of ocular methods, most are based on an evaluation of the biochemical components of the vitreous humour 24–36 h after death, but, to our knowledge, there are no studies on the relationship between lens and the postmortem interval. Since the lens is protected between the vitreous humour and the aqueous humour inside the eyeball, postmortem changes are assumed to start later in the lens. To evaluate the usefulness of using the lens to establish the postmortem interval, we examined 80 rabbit lens enucleated 24, 48, 72 and 96 h after death, assessing changes in sphericity and absorbance at different wavelengths and any histological alterations. Both sphericity and absorbance were seen to decrease to a statistically significant extent, and there was a gradual loss of structure and organisation of the lens components as a function of the postmortem interval. Modifications in the lens were seen to be useful for determining the postmortem interval between 24 and 96 h.

Introduction

Establishing the postmortem interval continues to be one of the most complex problems in Forensic Science. Studies based on ocular data to establish PMI are few and tend to be based on an evaluation of the biochemical components of the vitreous humour, such as sodium, potassium, chloride, lactate and hypoxanthine 24–36 h after death [1], [2], [3], [4].

The lens is positioned in the eye behind the iris. The anterior lens surface is bathed by aqueous humor, while the posterior lens surface is in contact with the vitreous body [5]. Contains 1000–3000 layers of fiber cells [6]. The adult lens contains two kinds of fiber cells: (i) those located in the cortex (the outermost layers of the lens), which are not yet mature and still contain organelles (including mitochondria), all of which are degraded through protease- and nuclease-regulated processes, leaving behind membrane-enclosed bags of crystallines, and (ii) those located in the nucleus (the core of the lens), which are mature and do not contain organelles [6]. Into subcellular organelle evacuation during maturation is necessary to ensure the transparency of the lens, as organelles scatter light, whereas ordered proteins (crystallins) do not. Protein synthesis and protein degradation are minimal or non-existent, and crystallins and perhaps other proteins that were synthesized at the birth of the cell persist throughout the life of the organism [7].

The transparency of the eye lens thus depends on the regular alignment of elongated fiber cells, which perform the difficult task of stacking together neatly to fill a spheroidal volume, filled with cytoplasmic crystallins and cytoskeletal intermediate filaments encased in membranes made from a few integral membrane proteins. The lens proteins belong to common protein families, but the lens tends to have its own unusual version [8].

Crystallines, which are expressed as three different isoforms (α-crystallin, β-crystallin and γ-crystallin), are major cytoplasmic components of the vertebrate eye lens that constitute >90% of the total protein content in eye lens fiber cells and >35% of their wet weight [7]. The chaperone action of α-crystallin is vital for maintaining eye lens transparency.

The reasons for using rabbit as an experimental model to study the lens are the following: First, both the rabbit and human lens have branched sutures, although the former is of the “line” type and the latter of the “star” type. For this reason, the rabbit lens can be considered as a simplification of the more complex organisation of the fibers of the human eye [9], [10], [11], [12], [13]. Secondly, the rabbit lens is closer in size and sphericity to the human lens than other lens commonly used in experiments, such as mouse or rat. The first study to use rabbit eye as an experimental model measured the thickness of the cornea by ultrasounds [2]. Lastly, in this study what we have achieved of the functional parameters of rabbit lens provides a basis for comparison with the human lens [10], [14], [15], [16].

While there are many studies on the morphological and histological changes related to certain pathologies, we have found no reference to the use of the lens to establish the PMI. Determining the changes in lens transparency postmortem would be a useful starting point for testing the possibility of determining visual impairment conditions’ in a cadaver [17]. The postmortem evaluation of the lens would provide the added benefit of associating different forms and stages of cataracts with accidents, thus affording new information relevant to the development of preventive measures [18].

Apart from estimating the PMI, the age of the subject could be ascertained between 24 and 48 h after death by applying radiocarbon techniques to the lens [17]. In conclusion, the postmortem determination of lens opacity would provide helpful information that could be used during legal proceedings and it would be also a good complement to clinical data, and fundamental in cases where there is no medical documentation.

The aim of the present study was to assess whether the postmortem morphological and histological modifications that take place in the lens may be related to the postmortem interval itself.